Cpppo is a Communication Protocol Python Parser and Originator

cpppo, protocol, parser, DFA, EtherNet/IP, CIP
pip install cpppo==4.4.2


Comm. Protocol Python Parser and Originator

Cpppo (pronounced ‘c’+3*’p’+’o’ in Python) is used to implement binary communications protocol parsers. The protocol’s communication elements are described in terms of state machines which change state in response to input events, collecting the data and producing output data artifacts.


Cpppo depends on several Python packages:

Package For? Description
greenery>=2.0,<3.0 all Regular Expression parsing and state machinery library
ipaddress all IP address manipulation
argparse all (<2.7) Command-line argument parsing
configparser all (<3.0) Parsing for CIP Object configuration files
pytz>2014.7 history The Python time-zone library
tzlocal>=1.1.1 history Access to system’s local timezone (on Mac, Windows)
pymodbus>=1.2.0 remote Modbus/TCP support for polling Schneider compatible PLCs
pytest all tests A Python unit-test framework
web.py>=0.37 web API (<3.0) The web.py HTTP web application framework (optional)
minimalmodbus serial tests A Modbus implementation, used for testing Modbus serial

To install ‘cpppo’ and its required dependencies using pip (recommended):

$ pip install cpppo

Installing from source

Clone the repo by going to your preferred source directory and using:

$ git clone git@github.com:pjkundert/cpppo.git

You can then install from the provided setuptools-based setup.py installer:

$ cd cpppo
$ python setup.py install

If you do not install using pip install cpppo or python setup.py install (recommended), you will need to install these dependencies manually. To install all required and optional Python modules, use:

pip install -r requirements.txt
pip install -r requirements-optional.txt

For Python2, you will also need to pip install configparser manually.

Python Version and OS Support

Cpppo is implemented and fully tested on both Python 2 (2.6 and 2.7), and Python 3 (3.3 to 3.5). The EtherNet/IP CIP protocol implementation is fully tested and widely used in both Python 2 and 3.

Some of cpppo’s modules are not (yet) fully supported in both versions:

  • The pymodbus module does not support Python 3, so Modbus/TCP support for polling remote PLCs is only available for Python 2.
  • Greenery supports both Python 2 and 3, but doesn’t provide meaningful Unicode (UTF-8) support in Python 2, so regular expression based DFAs dealing in UTF-8 are only supported for Python 3.

Linux (native or Docker containerized), Mac and Windows OSs are supported. However, Linux or Mac are recommended for stability, performance and ease of use. If you need to use Windows, it is recommended that you install a usable Terminal application such as ConEmu.


The protocols implemented are described here.

EtherNet/IP CIP Controller Communications Simulator/Client

A subset of the EtherNet/IP client and server protocol is implemented, and a simulation of a subset of the Tag communications capability of a Allen-Bradley ControlLogix 5561 Controller is provided. It is capable of simulating ControlLogix Tag access, via the Read/Write Tag [Fragmented] services.

Only EtherNet/IP “Unconnected” type connections are supported. These are (somewhat anomalously) a persistent TCP/IP connection from a client to a single EtherNet/IP device (such as a *Logix Controller), which allow the client to issue a sequence of CIP service requests (commands) to be sent to arbitrary CIP objects resident on the target device. Cpppo does not implement “Connected” requests (eg. those typically used between *Logix PLCs, in an industrial LAN environment).

A Tag is simply a shortcut to a specific EtherNet/IP CIP Object Instance and Attribute. Instead of the Client needing to know the specific Instance and Attribute numbers, the more easily remembered and meaningful Tag may be supplied in the request path.

EtherNet/IP Controller Communications Simulator

To run a simulation of a subset of a ControlLogix(tm) Controller communications, with the array Tags ‘SCADA’ and ‘TEXT’ and scalar Tag ‘FLOAT’ for you to read/write, run python -m cpppo.server.enip or enip_server:

enip_server --print SCADA=INT[1000] TEXT=SSTRING[100] FLOAT=REAL

Each Tag references a specific CIP Class/Instance/Attribute, which can be specified, if you desire (eg. to use numeric CIP addressing, typically required for Get/Set Attribute Single requests):

enip_server --print SCADA@22/1/1=INT[1000] TEXT@22/1/2=SSTRING[100] FLOAT@22/1/3=REAL

(See cpppo/server/enip/poll_test.py’s main method (at the end of the file) for an example of how to implement a completely custom set of CIP Objects and Attributes, to simulate some aspects of some specific device (in this case, an Allen-Bradley PowerFlex 750).

The following options are available when you execute the cpppo.server.enip module:

Specify a different local interface and/or port to bind to (default is :44818, indicating all interfaces and port 44818):

-a|--address [<interface>][:<port>]

Change the verbosity (supply more to increase further):


Specify a constant or variable delay to apply to every response, in fractional seconds:

-d|--delay #.#[-#.#]

Specify an HTTP web server interface and/or port, if a web API is desired (just ‘:’ will enable the web API on defaults :80, or whatever interface was specified for –address):

-w|--web [<interface>]:[<port>]

To send log output to a file (limited to 10MB, rotates through 5 copies):

-l|--log <file>

To print a summary of PLC I/O to stdout:

--no-print (the default)

To specify and check for a specific route_path in incoming Unconnected Send requests, provide one in “<port>/<link>” or JSON format; the default is to ignore the specified route_path (accepting any route_path). If specified, it must be a list containing one dict, specifying a port and link value. The port is either an 8- or 16-bit number (eg. port 1 typically indicates the local backplane). The link is typically in the range 0-15 (eg. a “slot” number), or is an IP address (eg. “”). To specify that no route_path is accepted (ie. only an empty route_path is allowed, ie. a Simple request), use 0 or false:

--route-path '[{"port": 1, "link": 0]'              # backplane, slot 0
--route-path 1/0                                    #   ''
--route-path '[{"port": 2, "link": ""}]' # { port 2, link }
--route-path 2/                          #   ''
--route-path 1/0/2/ # { backplane, slot 0 }, { port 2, link }
--route-path false                                  # No route_path accepted

Note that incoming “Simple” requests to a full-featured “Routing” simulator configured with a route path will be accepted; the specified target CIP Object(s) must exist in the target simulator.

Alternatively, to easily specify acceptance of no routing Unconnected Send encapsulation (eg. to simulate simple non-routing CIP devices such as Rockwell MicroLogix or A-B PowerFlex):


You may specify as many tags as you like on the command line; at least one is required:

<tag>=<type>[<length>]   # eg. SCADA=INT[1000]

You may specifiy a CIP Class, Instance and Attribute number for the Tag to be associated with:


The available types are SINT (8-bit), INT (16-bit), DINT (32-bit) integer, and REAL (32-bit float). BOOL (8-bit, bit #0), SSTRING and STRING are also supported.

EtherNet/IP Controller Object Configuration

To replace the default values contained by default in the standard CIP Objects (eg. the CIP Identity, TCP/IP Objects), place a cpppo.cfg file in /etc or (on Windows) %APPDATA%, or a .cpppo.cfg in your home directory, or a cpppo.cfg file in the current working directory where your application is run.

For example, to change the simulated EtherNet/IP CIP Identity Object ‘Product Name’ (the SSTRING at Class 0x01, Instance 1, Attribute 7), and the CIP TCP/IP Object Interface Configuration and Host Name, create a cpppo.cfg file containing:

# Generally, strings are not quoted
Product Name                = 1756-L61/B LOGIX5561

# However, some complex structures require JSON configuration:
Interface Configuration     = {
    "ip_address":             "",
    "network_mask":           "",
    "dns_primary":            "",
    "dns_secondary":          "",
    "domain_name":            "example.com"
Host Name                   = controller

See https://github.com/pjkundert/cpppo/blob/master/cpppo.cfg for details on the file format (https://docs.python.org/3/library/configparser.html).

Place this file in one of the above-mentioned locations, and run:

$ python -m cpppo.server.enip -v
01-20 07:01:29.125 ...  NORMAL  main  Loaded config files: ['cpppo.cfg']

Use the new EtherNet/IP CIP cpppo.server.enip.poll API to poll the Identity and TCPIP Objects and see the results:

$ python3 -m cpppo.server.enip.poll -v TCPIP Identity
01-20 07:04:46.253 ...  NORMAL run    Polling begins \
      via: 1756-L61/C LOGIX5561 via localhost:44818[850764823]
   TCPIP: [2, 48, 0, [{'class': 246}, {'instance': 1}], '', \
      '', '', '', '', 'example.com', 'controller']
Identity: [1, 15, 54, 2836, 12640, 7079450, '1756-L61/C LOGIX5561', 255]

Routing via route_path to other CIP Devices

A very basic facility for routing incoming CIP requests with complex route_path values is available in the Cpppo EtherNet/IP CIP Communications Simulator. By default, the Simulator responds to incoming requests with any route_path (basically, it ignores the value).

If you specify --route-path=1/0 on the command-line, it will only respond to requests with exactly the route_path equal to ‘{“port”: 1, “link”: 0}’ (backplane, slot 0). Every other CIP reqeuest with some other route_path value will be responded to with an error status.

If you wish to configure the allowable route_path in the cpppo.cfg file, use “Route Path = …”. Furthermore, if you want to route any other valid CIP request by the first element in its route_path, specify a JSON mapping in the configuration file’s “Route = { …”, specifying each route_path by <port>/<link> (link ranges are handled), and the <IP>:<port> it should be routed to:

Route Path                 = 1/0
Route                      = {
        "1/1-15":  "localhost:44819"

This example (see cpppo/cpppo-router.cfg and cpppo/cpppo.cfg for more details) accepts and handles CIP requests to route_path port 1, link 0 (backplane slot 0), and routes requests to all other backplane slots to the EtherNet/IP CIP simulator on localhost port 44819. Any valid route_path is allowed; for example, “2/” would route requests with a route_path segment specifying port 2, link “”.

When the request is forwarded, the first route_path segment is removed, and the remaining segments (if any) are forwarded. If no more route_path segments are left, then the request is forwarded as a “Simple” CIP request (with no route_path or send_path configured, as for a simple non-routing CIP device such as a MicroLogix or A-B Powerflex, etc.)

EtherNet/IP Controller I/O Customization

If you require access to the read and write I/O events streaming from client(s) to and from the EtherNet/IP CIP Attributes hosted in your simulated controller, you can easily make a custom cpppo.server.enip.device Attribute implementation which will receive all PLC Read/Write Tag [Fragmented] request data.

We provide two examples; one which records a history of all read/write events to each Tag, and one which connects each Tag to the current temperature of the city with the same name as the Tag.

Record Tag History

For example purposes, we have implemented the cpppo.server.enip.historize module which simulates an EtherNet/IP CIP device, intercepts all I/O (and exceptions) and writes it to the file specified in the first command-line argument to the module. It uses cpppo.history.timestamp, and requires that the Python pytz module be installed (via pip install pytz), which also requires that a system timezone be set.

This example captures the first command line argument as a file name; all subsequent arguments are the same as described for the EtherNet/IP Controller Communications Simulator, above:

$ python -m cpppo.server.enip.historize some_file.hst Tag_Name=INT[1000] &
$ tail -f some_file.txt
# 2014-07-15 22:03:35.945: Started recording Tag: Tag_Name
2014-07-15 22:03:44.186 ["Tag_Name", [0, 3]]    {"write": [0, 1, 2, 3]}

(in another terminal)

$ python -m cpppo.server.enip.client Tag_Name[0-3]=[0,1,2,3]

You can examine the code in cpppo/server/enip/historize.py to see how to easily implement your own customization of the EtherNet/IP CIP Controller simulator.

If you invoke the ‘main’ method provided by cpppo.server.enip.main directly, all command-line args will be parsed, and the EtherNet/IP service will not return control until termination. Alternatively, you may start the service in a separate threading.Thread and provide it with a list of configuration options. Note that each individual EtherNet/IP Client session is serviced by a separate Thread, and thus all method invocations arriving at your customized Attribute object need to process data in a Thread-safe fashion.

City Temperature Tag

In this example, we intercept read requests to the Tag, and look up the current temperature of the city named with the Tag’s name. This example is simple enough to include here (see cpppo/server/enip/weather.py):

import sys, logging, json
try: # Python2
    from urllib2 import urlopen
    from urllib import urlencode
except ImportError: # Python3
    from urllib.request import urlopen
    from urllib.parse import urlencode

from cpppo.server.enip import device, REAL
from cpppo.server.enip.main import main as enip_main

class Attribute_weather( device.Attribute ):
    OPT                    = {
        "appid": "078b5bd46e99c890482fc1252e9208d5",
        "units": "metric",
        "mode":     "json",
    URI                    = "http://api.openweathermap.org/data/2.5/weather"

    def url( self, **kwds ):
        """Produce a url by joining the class' URI and OPTs with any keyword parameters"""
        return self.URI + "?" + urlencode( dict( self.OPT, **kwds ))

    def __getitem__( self, key ):
        """Obtain the temperature of the city's matching our Attribute's name, convert
        it to an appropriate type; return a value appropriate to the request."""
            # eg. "http://api.openweathermap.org/...?...&q=City Name"
            data           = urlopen( self.url( q=self.name )).read()
            if type( data ) is not str: # Python3 urlopen.read returns bytes
                data       = data.decode( 'utf-8' )
            weather        = json.loads( data )
            assert weather.get( 'cod' ) == 200 and 'main' in weather, \
                weather.get( 'message', "Unknown error obtaining weather data" )
            cast           = float if isinstance( self.parser, REAL ) else int
            temperature    = cast( weather['main']['temp'] )
        except Exception as exc:
            logging.warning( "Couldn't get temperature for %s via %r: %s",
                             self.name, self.url( q=self.name ), exc )
        return [ temperature ] if self._validate_key( key ) is slice else temperature

    def __setitem__( self, key, value ):
        raise Exception( "Changing the weather isn't that easy..." )

sys.exit( enip_main( attribute_class=Attribute_weather ))

By providing a specialized implementation of device.Attribute’s __getitem__ (which is invoked each time an Attribute is accessed), we arrange to query the city’s weather at the given URL, and return the current temperature. The data must be converted to a Python type compatible with the eventual CIP type (ie. a float, if the CIP type is REAL). Finally, it must be returned as a sequence if the __getitem__ was asked for a Python slice; otherwise, a single indexed element is returned.

Of course, __setitem__ (which would be invoked whenever someone wishes to change the city’s temperature) would have a much more complex implementation, the details of which are left as an exercise to the reader…

EtherNet/IP Controller Client

Cpppo provides an advanced EtherNet/IP CIP Client enip_client, for processing “Unconnected” (or “Explicit”) requests via TPC/IP or UDP/IP sessions to CIP devices – either Controllers (eg. Rockwell ControlLogix, CompactLogix) which can “route” CIP requests, or w/ the -S option for access to simple CIP devices (eg. Rockwell MicroLogix, A-B PowerFlex, …) which do not understand the “routing” CIP Unconnected Send encapsulation required by the more advanced “routing” Controllers.

Cpppo does not presently implement the CIP “Forward Open” request, nor the resulting “Connected” or “Implicit” I/O requests, typically used in direct PLC-to-PLC communications. Only the TCP/IP “Unconnected”/”Explicit” requests that pass over the initially created and CIP Registered session are implemented.

The python -m cpppo.server.enip.client module entry-point or API (or the enip_client command ) can Register and issue a stream of “Unconnected” requests to the Controller, such as Get/Set Attribute or (by default) *Logix Read/Write Tag (optionally Fragmented) requests. The cpppo.server.enip.get_attribute module entry-point or API and the enip_get_attribute command defaults to use Get/Set Attribute operations.

It is critical to use the correct API with the correct address type and options, to achieve communications with your device. Some devices can use “Unconnected” requests, while others cannot. The MicroLogix is such an example; you may use “Unconnected” requests to access basic CIP Objects (such as Identity), but not much else. Most other devices can support “Unconnected” access to their data. Some devices can only perform basic CIP services such as “Get/Set Attribute Single/All” using numeric CIP Class, Instance and Attribute addressing, while others support the *Logix “Read/Write Tag [Fragmented]” requests using Tag names. You need to know (or experiment) to discover their capability. Still others such as the CompactLogix and ControlLogix Controllers can support “routing” requests; many others require the -S option to disable this functionality, or they will respond with an error status.

To issue Read/Write Tag [Fragmented] requests, by default to a “routing” device (eg. ControlLogix, CompactLogix), here to a CIP INT array Tag called SCADA, and a CIP SSTRING (Short String) array Tag called TEXT:

$ python -m cpppo.server.enip.client -v --print \
    SCADA[1]=99 SCADA[0-10] 'TEXT[1]=(SSTRING)"Hello, world!"' TEXT[0-3]

To use only Get Attribute Single/All requests (suitable for simpler devices, usually also used with the -S option, for no routing path), use this API instead (use the --help option to see their options, which are quite similar to cpppo.server.enip.client and enip_client):

$ python -m cpppo.server.enip.get_attribute -S ...

All data is read/written as arrays of SINT; however, if you specify a data type for writing data, we will convert it to an array of SINT for you. For example, if you know that you are writing to a REAL Attribute:

$ python -m cpppo.server.enip -v 'Motor_Velocity@0x93/3/10=REAL' # In another terminal...
$ python -m cpppo.server.enip.get_attribute '@0x93/3/10=(REAL)1.0' '@0x93/3/10'
Sat Feb 20 08:24:13 2016:   0: Single S_A_S      @0x0093/3/10 == True
Sat Feb 20 08:24:13 2016:   1: Single G_A_S      @0x0093/3/10 == [0, 0, 128, 63]
$ python -m cpppo.server.enip.client --print Motor_Velocity
  Motor_Velocity              == [1.0]: 'OK'

To access Get Attribute data with CIP type conversion, use cpppo.server.enip.get_attribute’s proxy classes, instead.

Specify a different local interface and/or port to connect to (default is :44818):

-a|--address [<interface>][:<port>]

On Windows systems, you must specify an actual interface. For example, if you started the cpppo.server.enip simulator above (running on the all interfaces by default), use --address localhost.

Select the UDP/IP network protocol and optional “broadcast” support. Generally, EtherNet/IP CIP devices support UDP/IP only for some basic requests such as List Services, List Identity and List Interfaces:


Send List Identity/Services/Interfaces requests:


For example, to find the Identity of all of the EtherNet/IP CIP devices on a local LAN with broadcast address (that respond to broadcast List Identity via UDP/IP):

$ python -m cpppo.server.enip.client --udp --broadcast --list-identity -a
List Identity  0 from ('', 44818): {
    "count": 1,
    "item[0].length": 58,
    "item[0].identity_object.sin_addr": "",
    "item[0].identity_object.status_word": 48,
    "item[0].identity_object.vendor_id": 1,
    "item[0].identity_object.product_name": "1769-L18ER/A LOGIX5318ER",
    "item[0].identity_object.sin_port": 44818,
    "item[0].identity_object.state": 3,
    "item[0].identity_object.version": 1,
    "item[0].identity_object.device_type": 14,
    "item[0].identity_object.sin_family": 2,
    "item[0].identity_object.serial_number": 1615052645,
    "item[0].identity_object.product_code": 154,
    "item[0].identity_object.product_revision": 2837,
    "item[0].type_id": 12
List Identity  1 from ('', 44818): {
    "count": 1,
    "item[0].length": 63,
    "item[0].identity_object.sin_addr": "",
    "item[0].identity_object.status_word": 48,
    "item[0].identity_object.vendor_id": 1,
    "item[0].identity_object.product_name": "1769-L23E-QBFC1 Ethernet Port",
    "item[0].identity_object.sin_port": 44818,
    "item[0].identity_object.state": 3,
    "item[0].identity_object.version": 1,
    "item[0].identity_object.device_type": 12,
    "item[0].identity_object.sin_family": 2,
    "item[0].identity_object.serial_number": 3223288659,
    "item[0].identity_object.product_code": 191,
    "item[0].identity_object.product_revision": 3092,
    "item[0].type_id": 12
List Identity  2 from ('', 44818): {
    "count": 1,
    "item[0].length": 53,
    "item[0].identity_object.sin_addr": "",
    "item[0].identity_object.status_word": 4,
    "item[0].identity_object.vendor_id": 1,
    "item[0].identity_object.product_name": "1766-L32BXBA A/7.00",
    "item[0].identity_object.sin_port": 44818,
    "item[0].identity_object.state": 0,
    "item[0].identity_object.version": 1,
    "item[0].identity_object.device_type": 14,
    "item[0].identity_object.sin_family": 2,
    "item[0].identity_object.serial_number": 1078923367,
    "item[0].identity_object.product_code": 90,
    "item[0].identity_object.product_revision": 1793,
    "item[0].type_id": 12
List Identity  3 from ('', 44818): {
    "count": 1,
    "item[0].length": 52,
    "item[0].identity_object.sin_addr": "",
    "item[0].identity_object.status_word": 4,
    "item[0].identity_object.vendor_id": 1,
    "item[0].identity_object.product_name": "1763-L16DWD B/7.00",
    "item[0].identity_object.sin_port": 44818,
    "item[0].identity_object.state": 0,
    "item[0].identity_object.version": 1,
    "item[0].identity_object.device_type": 12,
    "item[0].identity_object.sin_family": 2,
    "item[0].identity_object.serial_number": 1929488436,
    "item[0].identity_object.product_code": 185,
    "item[0].identity_object.product_revision": 1794,
    "item[0].type_id": 12

Sends certain “Legacy” EtherNet/IP CIP requests:

-L|--legacy <command>

Presently, only the following Legacy commands are implemented:

Command Description
0x0001 Returns some of the same network information as List Identity

This command is not documented, and is not implemented on all types of devices

IP Device Product Name MicroLogix 1100 1763-L16DWD B/7.00 MicroLogix 1400 1766-L32BXBA A/7.00 CompactLogix 1769-L23E-QBFC1 Ethernet Port CompactLogix 1769-L18ER/A LOGIX5318ER
$ python -m cpppo.server.enip.client --udp --broadcast --legacy 0x0001 -a
Legacy 0x0001  0 from ('', 44818): {
    "count": 1,
    "item[0].legacy_CPF_0x0001.sin_addr": "",
    "item[0].legacy_CPF_0x0001.unknown_1": 0,
    "item[0].legacy_CPF_0x0001.sin_port": 44818,
    "item[0].legacy_CPF_0x0001.version": 1,
    "item[0].legacy_CPF_0x0001.sin_family": 2,
    "item[0].legacy_CPF_0x0001.ip_address": "",
    "item[0].length": 36,
    "item[0].type_id": 1
Legacy 0x0001  1 from ('', 44818): {
    "peer": [
    "enip.status": 1,
    "enip.sender_context.input": "array('c',
    "enip.session_handle": 0,
    "enip.length": 0,
    "enip.command": 1,
    "enip.options": 0
Legacy 0x0001  2 from ('', 44818): {
    "count": 1,
    "item[0].legacy_CPF_0x0001.sin_addr": "",
    "item[0].legacy_CPF_0x0001.unknown_1": 0,
    "item[0].legacy_CPF_0x0001.sin_port": 44818,
    "item[0].legacy_CPF_0x0001.version": 1,
    "item[0].legacy_CPF_0x0001.sin_family": 2,
    "item[0].legacy_CPF_0x0001.ip_address": "",
    "item[0].length": 36,
    "item[0].type_id": 1
Legacy 0x0001  3 from ('', 44818): {
    "count": 1,
    "item[0].legacy_CPF_0x0001.sin_addr": "",
    "item[0].legacy_CPF_0x0001.unknown_1": 0,
    "item[0].legacy_CPF_0x0001.sin_port": 44818,
    "item[0].legacy_CPF_0x0001.version": 1,
    "item[0].legacy_CPF_0x0001.sin_family": 2,
    "item[0].legacy_CPF_0x0001.ip_address": "",
    "item[0].length": 36,
    "item[0].type_id": 1

Change the verbosity (supply more to increase further):


Change the default response timeout

-t|--timeout #

Specify a number of times to repeat the specified operations:

-r|--repeat #

To specify an Unconnected Send route_path (other than the default backplane port 0, ‘1/0’ or ‘[{“port”: 1, “link”: 0}]’, which is a guess at the location of a *Logix controller in a typical backplane), provide one in short <port>/<link> or JSON format. It must be a list containing one dict specifying a port and link value. The port is either an 8- or 16-bit number, and link is typically in the range 0-15 (a backplane slot) or an IP address. A string with a ‘/’ in it is parsed as <port>/<link>. If a only single route_path element is intended, the JSON array notation is optional:

--route-path '[{"port": 1, "link": 0}]'           # backplane, slot 0
--route-path '{"port": 1, "link": 0}'             #  ''
--route-path '1/0'                                #  ''

Complex multi-segment route-paths must be specified in a JSON list. For example, to route via an EtherNet/IP module in backplane slot 3, and then out its second Ethernet port to address

--route-path '["1/3",{"port":2,"link":""}]'# backplane slot 3,
--route-path '["1/3","2/"]'                #   then second port and IP

To specify no route_path, use 0 or false (usually only in concert with –send-path=”, or just use -S):

--route-path false

If a simple EtherNet/IP CIP device doesn’t support routing of message to other CIP devices, and hence supports no Message Router Object, an empty send-path may be supplied Normally, this also implies no route-path, so is usually used in combination with --route-path=false. This can be used to prevent the issuance of Unconnected Send Service encapsulation, which “Only originating devices and devices that route between links need to implement” (see The CIP Networks Library, Vol 1, Table 3-5.8). Also avoid use of --multiple, as these devices do not generally accept Multiple Service Packet requests, either.

Therefore, to communicate with simple, non-routing CIP devices (eg. AB PowerFlex, …), use -S or --simple, or explicitly:

--send-path='' --route-path=false

Alternatively, to easily specify use of no routing Unconnected Send encapsulation in requests:


Specify timeout_ticks (default: 157 * 32ms == 5s.)

--timeout-ticks 63                                # ~2s (if ticks == 32ms)

Specify the tick duration to use, when computing the actual timeout from timeout_ticks. Each tick has a duration from 1 to 32,768 milliseconds, computed as 2 ** <priority_tick_time> milliseconds.

--priority-time-tick 0                            # Set 1ms. ticks

To send log output to a file (limited to 10MB, rotates through 5 copies):

-l|--log <file>

To print a summary of PLC I/O to stdout, use --print. Perhaps surprisingly, unless you provide a --print or -v option, you will see no output from the python -m cpppo.server.enip.client or enip_client command, at all. The I/O operations will be performed, however:

--no-print (the default) 

To force use of the Multiple Service Packet request, which carries multiple Read/Write Tag [Fragmented] requests in a single EtherNet/IP CIP I/O operation (default is to issue each request as a separate I/O operation):


To force the client to use plain Read/Write Tag commands (instead of the Fragmented commands, which are the default):


You may specify as many tags as you like on the command line; at least one is required. An optional register (range) can be specified (default is register 0):

<tag> <tag>[<reg>] <tag>[<reg>-<reg>] # eg. SCADA SCADA[1] SCADA[1-10]

Writing is supported; the number of values must exactly match the data specified register range:

<tag>=<value>                             # scalar, eg. SCADA=1
<tag>[<reg>-<reg>]=<value>,<value>,...    # vector range
<tag>[<reg>]=<value>                      # single element of a vector
<tag>[<reg>-<reg>]=(DINT)<value>,<value>  # cast to SINT/INT/DINT/REAL/BOOL/SSTRING/STRING

By default, if any <value> contains a ‘.’ (eg. ‘9.9,10’), all values are deemed to be REAL; otherwise, they are integers and are assumed to be type INT. To force a specific type (and limit the values to the appropriate value range), you may specify a “cast” to a specific type, eg. ‘TAG[4-6]=(DINT)1,2,3’. The types SINT, INT, DINT, REAL, BOOL, SSTRING and STRING are supported.

In addition to symbolic Tag addressing, numeric Class/Instance/Attribute addressing is available. A Class, Instance and Attribute address values are in decimal by default, but hexadecimal, octal etc. are available using escapes, eg. 26 == 0x1A == 0o49 == 0b100110:

@<class>/<instance>/<attribute>           # read a scalar, eg. @0x1FF/01/0x1A
@<class>/<instance>/<attribute>[99]=1     # write element, eg. @511/01/26=1

See further details of addressing cpppo.server.enip.client’s parse_operations below.

EtherNet/IP cpppo.server.enip.client API

Dispatching a multitude of EtherNet/IP CIP I/O operations to a Controller (with our without pipelining) is very simple. If you don’t need to see the results of each operation as they occur, or just want to ensure that they succeeded, you can use connector.process (see cpppo/server/enip/client/io_example.py):

host                        = 'localhost'   # Controller IP address
port                        = address[1]    # default is port 44818
depth                       = 1             # Allow 1 transaction in-flight
multiple                    = 0             # Don't use Multiple Service Packet
fragment                    = False         # Don't force Read/Write Tag Fragmented
timeout                     = 1.0           # Any PLC I/O fails if it takes > 1s
printing                    = True          # Print a summary of I/O
tags                        = ["Tag[0-9]+16=(DINT)4,5,6,7,8,9", "@0x2/1/1", "Tag[3-5]"]

with client.connector( host=host, port=port, timeout=timeout ) as connection:
    operations              = client.parse_operations( tags )
    failures,transactions   = connection.process(
        operations=operations, depth=depth, multiple=multiple,
        fragment=fragment, printing=printing, timeout=timeout )

sys.exit( 1 if failures else 0 )

Try it out by starting up a simulated Controller:

$ python -m cpppo.server.enip Tag=DINT[10] &
$ python -m cpppo.server.enip.io

The API is able to “pipeline” requests – issue multiple requests on the wire, while simultaneously harvesting the results of prior requests. This is absolutely necessary in order to obtain reasonable I/O performance over high-latency links (eg. via Satellite).

To use pipelining, create a client.connector which establishes and registers a CIP connection to a Controller. Then, produce a sequence of operations (eg, parsed from “Tag[0-9]+16=(DINT)5,6,7,8,9” or from numeric Class, Instance and Attribute numbers “@2/1/1” ), and dispatch the requests using connector methods .pipeline or .synchronous (to access the details of the requests and the harvested replies), or .process to simply get a summary of I/O failures and total transactions.

More advanced API methods allow you to access the stream of I/O in full detail, as responses are received. To issue command synchronously use connector.synchronous, and to “pipeline” the requests (have multiple requests issued and “in flight” simultaneously), use connector.pipeline (see cpppo/server/enip/client/thruput.py)

ap                          = argparse.ArgumentParser()
ap.add_argument( '-d', '--depth',    default=0, help="Pipelining depth" )
ap.add_argument( '-m', '--multiple', default=0, help="Multiple Service Packet size limit" )
ap.add_argument( '-r', '--repeat',   default=1, help="Repeat requests this many times" )
ap.add_argument( '-a', '--address',  default='localhost', help="Hostname of target Controller" )
ap.add_argument( '-t', '--timeout',  default=None, help="I/O timeout seconds (default: None)" )
ap.add_argument( 'tags', nargs='+', help="Tags to read/write" )
args                        = ap.parse_args()

depth                       = int( args.depth )
multiple                    = int( args.multiple )
repeat                      = int( args.repeat )
operations                  = client.parse_operations( args.tags * repeat )
timeout                     = None
if args.timeout is not None:
    timeout                 = float( args.timeout )

with client.connector( host=args.address, timeout=timeout ) as conn:
    start                   = cpppo.timer()
    num,idx                 = -1,-1
    for num,(idx,dsc,op,rpy,sts,val) in enumerate( conn.pipeline(
            operations=operations, depth=depth,
            multiple=multiple, timeout=timeout )):
        print( "%s: %3d: %s" % ( timestamp(), idx, val ))

    elapsed                 = cpppo.timer() - start
    print( "%3d operations using %3d requests in %7.2fs at pipeline depth %2s; %5.1f TPS" % (
        num+1, idx+1, elapsed, args.depth, num / elapsed ))

Fire up a simulator with a few tags, preferably on a host with a high network latency relative to your current host:

$ ssh <hostname>
$ python -m cpppo.server.enip --print -v Volume=REAL Temperature=REAL

Then, test the thruput TPS (Transactions Per Second) with various pipeline --depth and Multiple Service Packet size settings. Try it first with the default depth of 0 (no pipelining). This is the “native” request-by-request thruput of the network route and device:

$ python -m cpppo.server.enip.thruput -a <hostname> "Volume" "Temperature" \
    --repeat 25

Then try it with aggressive pipelining (the longer the “ping” time between the two hosts, the more --depth you could benefit from):

    --repeat 25 --depth 20

Adding --multiple <size> allows cpppo to aggregate multiple Tag I/O requests into a single Multiple Service Packet, reducing the number of EtherNet/IP CIP requests:

    --repeat 25 --depth 20 --multiple 250

cpppo.server.enip client.client

The base class client.client implements all the basic I/O capabilities for pipeline-capable TCP/IP and UDP/IP I/O with EtherNet/IP CIP devices.

Keyword Description
host A cpppo.server.enip.get_attribute proxy derived class
port Target port (if not 44818)
timeout Optional timeout on socket.create_connection
dialect An EtherNet/IP CIP dialect, if not logix.Logix
udp (False) Establishes a UDP/IP socket to use for request (eg. List Identity)
broadcast (False) Avoids connecting UDP/IP sockets; may receive many replies
source_address Bind to a specific local interface (Default:
profiler If using a Python profiler, provide it to disable around I/O code

Once connectivity is established, a sequence of CIP requests can be issued using the the methods .read, .write, .list_identity, etc.

Later, .readble can report if incoming data is available. Then, the connection instance can be used as an iterable; next( connection ) will return any response available. This response will include a peer entry indicating the reported peer IP address and port (especially useful for broadcast UDP/IP requests).

These facilities are used extensively in the client.connector derived class to implementing request pipelining.

Note that not all requests can be issued over UDP/IP channels; consult the EtherNet/IP CIP literature to discover which may be used. The List Services/Identity/Interfaces requests are known to work, and are useful for discovering what EtherNet/IP CIP devices are available in a LAN using UDP/IP broadcast addresses; setting both the udp and broadcast parameters to True.

If multiple local interfaces are provided, it is possible that you may with to only broadcast on a certain interface (eg. on the “Plant” LAN interface, not the “Business” WAN interface). Use source_address to specify a local interface’s IP address to bind to, before connecting or sending requests. Accepts IP addresses and optionally a port number in “” form.

Remember that UDP/IP packets sent using broadcast addresses will not be received by a server bound to a specific local interface address. Therefore, if you wish to find all EtherNet/IP CIP servers in your LAN including the simulated ones running on your host, you may wish to start a simulated server on a local interface, eg.

$ python -m cpppo.server.enip -vv --address SCADA=INT[100]

Then, you might issue a broadcast from this (or another) host on the network, expecting a response from your simulator, but not receiving one:

$ python -m cpppo.server.enip.list_services -vv --udp --broadcast \\
    --source --address
05-25 15:51:02.044 MainThread enip.cli DETAIL   __init__   Connect:  UPD/IP to ('', 44818) via ('', 0) broadcast
05-25 15:51:02.072 MainThread enip.cli DETAIL   cip_send   Client CIP Send: {
    "enip.status": 0,
    "enip.sender_context.input": "bytearray(b'\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00')",
    "enip.session_handle": 0,
    "enip.CIP.list_services": {},
    "enip.options": 0
05-25 15:51:02.073 MainThread enip.cli DETAIL   cip_send   Client CIP Send: {
    "enip.status": 0,
    "enip.sender_context.input": "bytearray(b'\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00')",
    "enip.session_handle": 0,
    "enip.CIP.list_identity": {},
    "enip.options": 0

Why? Because you have bound the server to specific IP address, If you instead bind it to “all” interfaces (thus, at no specific IP address) using any of the following incantations:

$ python -m cpppo.server.enip -vv   SCADA=INT[100]
$ python -m cpppo.server.enip -vv --address ''  SCADA=INT[100]
$ python -m cpppo.server.enip -vv --address  SCADA=INT[100]

or if you bind it to the “broadcast” address of the specific interface you wish to use:

$ python -m cpppo.server.enip -vv --address  SCADA=INT[100]

then it will receive the broadcast packets, and respond appropriately.

cpppo.server.enip client.connector class

Register a TCP/IP EtherNet/IP CIP connection to a Controller, allowing the holder to issue requests and receive replies as they are available, as an iterable sequence. Support Read/Write Tag [Fragmented], Get/Set Attribute [All], and Multiple Service Packet requests, via CIP “Unconnected Send”.

Establish exclusive access using a python context operation:

from cpppo.server.enip import client
with client.connector( host="some_controller" ) as conn:

To establish a UDP/IP connected (optionally broadcast capable) connection:

from cpppo.server.enip import client
with client.connector( host="some_controller",
    udp=True, broadcast=True ) as conn:

UDP/IP connections do not issue CIP Register requests (as they are only supported via TCP/IP). Generally, these are only useful for issuing List Identity, List Services or List Interfaces requests. If broadcast (and a “broadcast” IP address such as is used), then multiple responses should be expected; the default cpppo.server.enip.client module entrypoint will wait for the full duration of the specified timeout for responses.


Takes a sequence of Tag-based or numeric CIP Attribute descriptions, and converts them to operations suitable for use with a client.connector. For example:

>>> from cpppo.server.enip include client
>>> list( client.parse_operations( [ "A_Tag[1-2]=(REAL)111,222" ] ))
    'data':        [111.0, 222.0],
    'elements':    2,
    'method':      'write',
    'path':        [{'symbolic': 'A_Tag'},{'element': 1}],
    'tag_type':    202

A symbolic Tag is assumed, but an @ indicates a numeric CIP address, with each segment’s meaning defaulting to:


More complex non-default numeric addressing is also supported, allowing access to Assembly instances, Connections, etc. For example, to address an Assembly (class 0x04), Instance 5, Connection 100, use JSON encoding for each numeric element that doesn’t match the default sequence of <class>, <instance>, … So, to specify that the third element is a Connection (instead of an Attribute) number, any of these are equivalent:


The following path components are supported:

Component Description
class 8/16-bit Class number
instance 8/16-bit Instance number
attribute 8/16-bit Attribute number
element 8/16/32-bit Element number
connection 8/16-bit Connection number
symbolic ISO-8859-1 Symbolic Tag name
port,link Port number, Link number or IP address
(typically valid only in route_path)

The number of elements in a request is normally deduced from an index range; for example, to specify 10 elements:


To manually specify a number of elements in a request, append an *### to the request:


client.connector’s .synchronous, .pipeline and .operate

Issues a sequence of operations to a Controller in synchronous fashion (one at a time, waiting for the response before issuing the next command) or in pipeline fashion, issuing multiple requests before asynchronous waiting for responses.

Automatically choose synchronous or pipeline behaviour by using operate, which also optionally chains the results through validate to log/print a summary of I/O operations and fill in the yielded data value for all Write Tag operations (instead of just signalling success with a True value).

Automatically bundles requests up into appropriately sized Multiple Service Packets (if desired), and pipelines multiple requests in-flight simultaneously over the TCP/IP connection.

Must be provided a sequence of ‘operations’ to perform, each as a dict containing:

Key Description
method ‘read’, ‘write’, ‘set/get_attribute_single’, ‘get_attributes_all’
path The operation’s path, eg [{“class”: 2},{“instance”: 1},…]
offset A byte offset, for Fragmented read/write
elements The number of elements to read/write
tag_type The EtherNet/IP type, eg. 0x00ca for “REAL”
data For ‘write’, ‘set_attribute…’; the sequence of data to write

Use client.parse_operations to convert a sequence of simple Tag assignments to a sequence suitable for ‘operations’:

operations = client.parse_operations( ["Tag[8-9]=88,99", "Tag[0-10]"] )

The full set of keywords to .synchronous are:

Keyword Description
operations A sequence of operations
index The starting index used for “sender_context”
fragment If True, forces use of Fragmented read/write
multiple If >0, uses Multiple Service Packets of up to this many bytes
timeout A timeout, in seconds.

The .pipeline method also defaults to have 1 I/O operation in-flight:

Keyword Description
depth The number of outstanding requests (default: 1)

And .operate method adds these defaults:

Keyword Description
depth The number of outstanding requests (default: 0)
validating Log summary of I/O operations, fill in Tag Write values (default: False)
printing Also print a summary of I/O operations to stdout (default: False)

Invoking .pipeline, .synchronous or operate on a sequence of operations yields a (…, (<idx>,<dsc>,<req>,<rpy>,<sts>,<val>), …) sequence, as replies are received. If .pipeline=/.operate= is used, there may be up to depth requests in-flight as replies are yielded; if .synchronous, then each reply is yielded before the next request is issued. The 6-tuples yielded are comprised of these items:

Item Description
0 - idx The index of the operation, sent as the “sender_context”
1 - dsc A description of the operation
2 - req The request
3 - rpy The reply
4 - sts The status value (eg. 0x00) or tuple (eg. (0xff,(0x1234)) )
5 - val The reply value (None, if reply was in error)

The structure of the code to connect to a Controller host and process a sequence of operations (with a default pipelining depth of 1 request in-flight) is simply:

with client.connector( host=... ) as conn:
    for idx,dsc,req,rpy,sts,val in conn.pipeline( operations=... ):

client.connector.results and .process

Issues a sequence of operations to a Controller either synchronously or with pipelining, and .results yields only the results of the operations as a sequence, as they arrive (on-demand, as a generator). None indicates failure. The .process API checks all result values for failures (any result values which are None), and returns the tuple (<failures>,[…, <result>, …]).

client.connector.read and .write

Directly issue read/write requests by supplying all the details; a dict describing the request is returned. If send is True (the default), the request is also issued on the wire using .unconnected_send.

with client.connector( host=... ) as conn:
    req = conn.read( "Tag[0-1]" )

Later, harvest the results of the read/write request issued on conn using next(...) on the conn (it is iterable, and returns replies as they are ready to be received). Once the response is ready, a fully encapsulated response payload will be returned:

    assert conn.readable( timeout=1.0 ), "Failed to receive reply"
    rpy = next( conn )

This fully encapsulated response carries the EtherNet/IP frame and status, the CIP frame, its CPF frames with its Unconnected Send payload, and finally the encapsulated request; the Read/Write Tag [Fragmented] payload (in a cpppo.dotdict, a dict that understands dotted keys accessible as attributes, slightly formatted here for readability):

>>> for k,v in rpy.items():
...  print k,v
enip.status		0
enip.sender_context.input	array('c', '\x00\x00\x00\x00\x00\x00\x00\x00')
enip.session_handle	297965756
enip.length		20
enip.command		111
enip.input			array('c',
enip.options		0
enip.CIP.send_data.interface	0
enip.CIP.send_data.timeout		0
enip.CIP.send_data.CPF.count		2
enip.CIP.send_data.CPF.item[0].length	0
enip.CIP.send_data.CPF.item[0].type_id	0
enip.CIP.send_data.CPF.item[1].length	4
enip.CIP.send_data.CPF.item[1].type_id	178
enip.CIP.send_data.CPF.item[1].unconnected_send.request.status	0
enip.CIP.send_data.CPF.item[1].unconnected_send.request.input	array('c',
enip.CIP.send_data.CPF.item[1].unconnected_send.request.service	211
enip.CIP.send_data.CPF.item[1].unconnected_send.request.write_frag		True
enip.CIP.send_data.CPF.item[1].unconnected_send.request.status_ext.size	0

The response payload is highly variable (eg. may contain further encapsulations such as Multiple Service Packet framing), so it is recommended that you use the .synchronous, .pipeline, .results, or .process interfaces instead (unless you are one of the 3 people that deeply understands the exquisite details of the EtherNet/IP CIP protocol). These generate, parse and discard all the appropriate levels of encapsulation framing.

client.connector.get_attribute_single and .get_attributes_all

The Get Attribute[s] Single/All operations are also supported. These are used to access the raw data in arbitrary Attributes of CIP Objects. This data is always presented as raw 8-bit SINT data.

You can use these methods directly (as with .write, above, and harvest the results manually), or you can modify a sequence of operations from client.parse_operations, and gain access to the convenience and efficiency of client.connector’s .pipeline to issue and process the stream of EtherNet/IP CIP requests.

Create a simple generator wrapper around client.parse_operations, which substitutes get_attributes_all or get_attribute_single as appropriate. Use numeric addressing to the Instance or Attribute level, eg. @<class>/<instance> or @<class>/<instance>/<attribute>. One is implemented in cpppo/server/enip/get_attribute.py:

from cpppo.server.enip.get_attribute import attribute_operations

timeout			= None # Wait forever, or <float> seconds
depth			= 0    # No pipelining, or <int> in-flight
with client.connector( host=args.address, timeout=timeout ) as conn:
    for idx,dsc,op,rpy,sts,val in conn.pipeline(
            operations=attribute_operations( tags ), depth=depth,
            multiple=False, timeout=timeout ):

Here is an example of getting all the raw Attribute data from the CIP Identity object (Class 1, Instance 1) of a Controller (Get Attributes All, and Get Attribute Single of Class 1, Instance 1, Attribute 7):

$ python -m cpppo.server.enip.get_attribute --depth 3 -v  '@1/1'  '@1/1/7'
2015-04-21 14:51:14.633:   0: Single G_A_A      @0x0001/1 == [1, 0, 14, 0, 54,  \
    0, 20, 11, 96, 49, 26, 6, 108, 0, 20, 49, 55, 53, 54, 45, 76, 54, 49, 47,   \
    66, 32, 76, 79, 71, 73, 88, 53, 53, 54, 49, 255, 0, 0, 0]
2015-04-21 14:51:14.645:   1: Single G_A_S      @0x0001/1/7 == [20, 49, 55, 53, \
    54, 45, 76, 54, 49, 47, 66, 32, 76, 79, 71, 73, 88, 53, 53, 54, 49]

Decoding the Identity Attribute 7 CIP STRING as ASCII data yields (the first character is the length: 20 decimal, or 14 hex):

$ python
>>> ''.join( chr( x ) for x in [
        20, 49, 55, 53, 54, 45, 76, 54, 49, 47, 66, 32, 76, 79, 71, 73, 88, 53, 53, 54, 49])
'\x141756-L61/B LOGIX5561'

To access Get Attribute data with CIP type conversion, use cpppo.server.enip.get_attribute’s proxy classes, instead.


To use Set Attribute Single, provide an array of CIP USINT or SINT values appropriate to the size of the target Attribute. Alternatively, provide a tag_type number corresponding to the CIP data type. If the tag_type is supported by cpppo.server.enip.parser’s typed_data implementation, we’ll convert it to USINT for you ([U]SINT, [U]INT, [U]DINT, REAL, SSTRING and STRING are presently supported).

Typically, you will invoke client.connector.set_attribute_single indirectly by providing attribute_operations a sequence containing tag operation such as @<class>/<instance>/<attribute>=(REAL)1.1 (see get_attribute_single, above.) If you start the enip_server ... FLOAT@22/1/3=REAL command, above, and then run:

$ python -m cpppo.server.enip.get_attribute '@22/1/3=(REAL)1.0' '@22/1/3'
Mon Feb 22 15:29:51 2016:   0: Single S_A_S      @0x0016/1/3 == True
Mon Feb 22 15:29:51 2016:   1: Single G_A_S      @0x0016/1/3 == [0, 0, 128, 63]     

Confirm that you wrote the correct floating-ponit value:

$ python -m cpppo.server.enip.client 'FLOAT'
          FLOAT              == [1.0]: 'OK'

client.connector.list_identity, .list_services and .list_interfaces

These methods issue List Identity, List Services and List Interfaces requests, valid on either UDP/IP or TCP/IP connections (or via UDP/IP broadcast). The response(s) may be harvested by awaiting for incoming activity on the connection. The cpppo.server.enip.list_identity_simple example broadcasts a UDP/IP List Identity request to the local LAN, awaiting all responses until timeout expires without activity:

from __future__ import print_function

import sys
from cpppo.server import enip
from cpppo.server.enip import client

timeout			= 1.0
host			= sys.argv[1] if sys.argv[1:] else ''
with client.client( host=host, udp=True, broadcast=True ) as conn:
    conn.list_identity( timeout=timeout )
    while True:
        response,elapsed	= client.await_response( conn, timeout=timeout )
        if response:
            print( enip.enip_format( response ))
            break # No response (None) w'in timeout or EOF ({})

See cpppo.server.enip.client for a more advanced approach which returns only the relevant List Identity or List Services payload from the response, and enforces a total timeout, rather than a per-response timeout.

The cpppo.server.enip.list_services module entrypoint provides a more complete CLI interface for generating and harvesting List Services and List Identity responses:

$ python -m cpppo.server.enip.list_services --help
usage: list_services.py [-h] [-v] [-a ADDRESS] [-u] [-b] [--identity]
                        [--interfaces] [-t TIMEOUT]

List Services (by default) on an EtherNet/IP CIP Server.

optional arguments:
  -h, --help            show this help message and exit
  -v, --verbose         Display logging information.
  -a ADDRESS, --address ADDRESS
                        EtherNet/IP interface[:port] to connect to (default:
  -u, --udp             Use UDP/IP queries (default: False)
  -b, --broadcast       Allow multiple peers, and use of broadcast address
                        (default: False)
  -i, --list-identity   List Identity (default: False)
  -I, --list-interfaces List Interfaces (default: False)
  -t TIMEOUT, --timeout TIMEOUT
                        EtherNet/IP timeout (default: 5s)

It always requests List Services, and (optionally) List Identity, List Interfaces. By default, it sends the requests unicast via TCP/IP, but can optionally send the requests via unicast or broadcast UDP/IP. The full content of each EtherNet/IP CIP response is printed.

To obtain responses from all EtherNet/IP CIP devices on the local LAN with broadcast address

$ python -m cpppo.server.enip.list_services --udp --broadcast \
      --list-identity -a
    "peer": [
    "enip.status": 0, 
    "enip.sender_context.input": "array('c', '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00')", 
    "enip.session_handle": 0, 
    "enip.length": 25, 
    "enip.CIP.list_services.CPF.count": 1, 
    "enip.CIP.list_services.CPF.item[0].communications_service.capability": 288, 
    "enip.CIP.list_services.CPF.item[0].communications_service.service_name": "Communications", 
    "enip.CIP.list_services.CPF.item[0].communications_service.version": 1, 
    "enip.CIP.list_services.CPF.item[0].length": 19, 
    "enip.CIP.list_services.CPF.item[0].type_id": 256, 
    "enip.command": 4, 
    "enip.input": "array('c', '\\x01\\x00\\x00\\x01\\x13\\x00\\x01\\x00 \\x01Communications\\x00')", 
    "enip.options": 0
    "peer": [
    "enip.status": 0, 
    "enip.sender_context.input": "array('c', '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00')", 
    "enip.session_handle": 0, 
    "enip.length": 60, 
    "enip.CIP.list_identity.CPF.count": 1, 
    "enip.CIP.list_identity.CPF.item[0].length": 54, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.sin_addr": "", 
    "enip.CIP.list_identity.CPF.item[0].identity_object.status_word": 12640, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.vendor_id": 1, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.product_name": "1756-L61/C LOGIX5561", 
    "enip.CIP.list_identity.CPF.item[0].identity_object.sin_port": 44818, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.state": 255, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.version": 1, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.device_type": 14, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.sin_family": 2, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.serial_number": 7079450, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.product_code": 54, 
    "enip.CIP.list_identity.CPF.item[0].identity_object.product_revision": 2836, 
    "enip.CIP.list_identity.CPF.item[0].type_id": 12, 
    "enip.command": 99, 
    "enip.input": "array('c', '\\x01...\\x141756-L61/C LOGIX5561\\xff')", 
    "enip.options": 0

EtherNet/IP cpppo.server.enip.get_attribute API

Many devices such as Rockwell MicroLogix, Allen-Bradley PowerFlex, etc. that advertise EtherNet/IP CIP protocol offer only very basic connectivity:

  • No CIP “routing” capability, hence no Unconnected Send encapsulation, including route path or send path addressing.
  • No “Logix” style Read/Write Tag [Fragmented]; only Get/Set Attribute.
  • Only raw 8-bit CIP SINT data; CIP data type transformations done by client

Therefore, a set of APIs are provided to “proxy” these devices, providing higher level data types and maintenance of EtherNet/IP CIP connectivity. In order to retain high thruput, the API maintains the ability to “pipeline” requests over high-latency links.

The proxy and proxy_simple classes

Access an EtherNet/IP CIP device using either generic Get Attributes All/Single, or *Logix Read Tag [Fragmented] services, as desired. Data is delivered converted to target format.

To create a “proxy” for a simple (non-routing) remote EtherNet/IP CIP sensor device, such as an A-B PowerFlex, with (for example) a CIP REAL attribute at Class 0x93, Instance 1, Attribute 10:

from cpppo.server.enip.get_attribute import proxy_simple

class some_sensor( proxy_simple ):
    '''A simple (non-routing) CIP device with one parameter with a
       shortcut name: 'A Sensor Parameter' '''
    PARAMETERS     = dict( proxy_simple.PARAMETERS,
        a_sensor_parameter = proxy_simple.parameter( '@0x93/1/10', 'REAL', 'Hz' ),

Reading Attributes Using proxy.read

If you have an A-B PowerFlex handy, use your custom proxy or proxy_simple class called some_sensor defined above, and its “A Sensor Parameter” attribute. Alternatively, just use the plain proxy (if you have a ControlLogix or CompactLogix), or proxy_simple (if you have a MicroLogix) classes in these examples, and use the “Product Name” attribute (which reads the CIP SSTRING at Class 1, Instance 1, Attribute 7: See cpppo/server/enip/get_attribute.py)

In your Python code, to access the parameter “A Sensor Parameter” from the remote A-B PowerFlex device (the supplied name is transformed to a_sensor_parameter by lowering case and transforming ’ ’ to ‘_’, to check for matching any proxy.PARAMETER entry):

via                = some_sensor( host="" )
    params         = via.parameter_substitution( "A Sensor Parameter" )
    value,         = via.read( params )
except Exception as exc:
    logging.warning( "Access to remote CIP device failed: %s", exc )
    via.close_gateway( exc=exc )

There are several important things to note here:

  1. You can .read 1 or more values. Here, we supply a single Python str, so the proxy.parameter_substitution deduces that you want one named parameter value. Provide a sequence of attributes to read more than one.
  2. The .read returns a sequence of all the requested values, so we use Python tuple assignment to unpack a sequence containing a single value, eg:
    variable, = [123]
  3. Upon the first error accessing and/or transforming a value from the remote device, the Python generator will raise an exception. Whereever in your code that you “reify” the generator’s values (access them and assign them to local variables), you must trap any Exception and notify the get_attribute.proxy by invoking .close_gateway. This prepares the get_attribute.proxy to re-open the connection for a future attempt to access the device.

A successful .read (with no timeouts, no I/O errors) can return None, instead of valid data, if the CIP device reports an error status code for a request. This is only case where the results of a .read will be “Falsey” (evaluate False in a boolean test). All successful reads of valid data will return a non-empty list of results, and are “Truthy” (evalute True). Each returned value must be tested.

To guarantee that an Exception is raised if any result is not returned, you can set .read’s checking parameter to True:

via                = some_sensor( host="" )
    # Will raise Exception (closing gateway) on any failure to get data
    params         = via.parameter_substitution( "A Sensor Parameter" )
    value,         = via.read( params, checking=True )
except Exception as exc:
    via.close_gateway( exc )
# value is *always* guaranteed to be [<value>]

Writing Attributes Using proxy.write (alias for .read)

The .read method (or its alias .write) support writing to CIP Attributes. Simply append an equals sign, a CIP type in parentheses, and a comma-separated list of values to the parameter or Attribute name.

# Write a Motor Velocity to an AB PowerFlex AC Drive Controller
#     python -m cpppo.server.enip.powerflex_motor_velocity @localhost 123.45
# To start a simulator (a partial AB PowerFlex) on localhost suitable for writing:
#     python -m cpppo.server.enip.poll_test
import logging
import sys
import time
import traceback

import cpppo
#cpppo.log_cfg['level'] = logging.DETAIL
logging.basicConfig( **cpppo.log_cfg )

#from cpppo.server.enip.get_attribute import proxy_simple as device # MicroLogix
#from cpppo.server.enip.get_attribute import proxy as device        # ControlLogix
from cpppo.server.enip.ab import powerflex_750_series as device    # PowerFlex 750

# Optionally specify Powerflex DNS name or IP address, prefixed with '@':
host               = 'localhost'
if len( sys.argv ) > 1 and sys.argv[1].startswith( '@' ):
    host           = sys.argv.pop( 1 )[1:]

# Optionally specify velocity; defaults to 0:
velocity           = 0
if len( sys.argv ) > 1:
    velocity       = float( sys.argv.pop( 1 ))

param              = 'Motor Velocity = (REAL)%s' % ( velocity )
    via            = device( host=host )
    with via: # establish gateway, detects Exception (closing gateway)
   val,            = via.write(
       via.parameter_substitution( param ), checking=True )
    print( "%s: %-32s == %s" % ( time.ctime(), param, val ))
except Exception as exc:
    logging.detail( "Exception writing Parameter %s: %s, %s",
   param, exc, traceback.format_exc() )
    sys.exit( 1 )

Forcing .read/write to use CIP Get/Set Attribute Single

If the target device understands only basic CIP I/O requests, or you wish to perform special processing on the stream of operations generated from the supplied tags, you can specify the proxy with a specific operations_parser. The default is to use client.parse_operations if data types are provided, and get_attribute.attribute_operations otherwise.

If we know we want to generate EtherNet/IP CIP Get/Set Attribute requests but we wish to pass specific data types (eg. INT), create the proxy_simple device w/ an appropriate operations_parser parameter:

# Basic CIP I/O Test
# Target Simulator:
#   python3 -m cpppo.server.enip -S -vv SCADA@0x4/0x96/3=INT[18]
import cpppo
from cpppo.server.enip.get_attribute import (
    attribute_operations, proxy_simple as device )
from cpppo.server.enip import client

import logging
cpppo.log_cfg['level'] = logging.DEBUG
logging.basicConfig( **cpppo.log_cfg )

hostname = 'localhost'

# Our target CIP Attribute contains a 36 bytes == 18 x INT value
attribute = '@0x4/0x96/3'
values = "512,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0"
operations = [attribute + ' = (INT)' + values]
print( "Raw operations: %r" % operations )

operations_parser = attribute_operations
operations_out = list( operations_parser( operations ))

assert operations_out == [{
    'method': 'set_attribute_single', 
    'path': [{'class': 4}, {'instance': 150}, {'attribute': 3}],
    'tag_type': 195,
    'data': [512, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
    'elements': 18

# Force basic CIP Get/Set Attribute I/O operations
via = device( hostname, operations_parser=operations_parser )
val, = via.write( operations )

Using the proxy Context Manager API

There is a simple mechanism provided to ensure that all of the above maintenance of the proxy’s gateway occurs: the proxy class provides a Context Manager API, which ensures that the proxy’s gateway is opened, and that the proxy’s .close_gateway is invoked on any Exception that occurs while reifying the generator returned by proxy.read:

via                = some_sensor( host="" )
with via:
    params         = via.parameter_substitution( "A Sensor Parameter" )
    value,         = via.read( params )
# value may be something like [1.23], or None if returned error status

Wherever in your code that you plan to use the results obtained from a proxy, ensure that you enclose it in a with <proxy>: block. You may even call the .read method elsewhere (it is already protected against Exceptions raised during initial processing): just ensure that the context manager is invoked before you begin to use the results, so that Exceptions caused by I/O errors are properly captured:

from __future__ import print_function
via                = some_sensor( host="" )
params             = via.parameter_substitution( "A Sensor Parameter" )
reader             = via.read( params )
# ... later ...
with via:
    for value in reader:
        print( "Got: %r" % ( value ))

The proxy Device’s Identity

As soon as a proxy’s gateway is opened, the .instance attribute is populated with the results of the device’s CIP “List Identity” response. At any time, the proxy.__str__ method can be used to print the device Identity’s Product Name, network address, and CIP session id.

The connection and List Identity request doesn’t occur ‘til the proxy is accessed using .read, or the Context Manager is invoked using with <proxy>:

from __future__ import print_function
via                = some_sensor( host="" )
print( "Not yet connected: %s" % ( via ))
params             = via.parameter_substitution( "A Sensor Parameter" )
reader             = via.read( params )
print( "Connected! %s" % ( via ))

Producing the output:

Not yet connected: None at None
Connected! 1756-L61/C LOGIX5561 at localhost:44818[2206679763]

If you wish to avoid getting the device’s identity using CIP List Identity, simply pass a product name string =”Something”= (or a cpppo.dotdict({"product_name":"Something"}))) in the identity_default parameter:

from __future__ import print_function
via                = proxy( host="localhost", identity_default="Something" )
print( "Not yet connected: %s" % ( via ))
params             = via.parameter_substitution( "Product Name" )
reader             = via.read( params )
print( "Connected! %s" % ( via ))

This would produce something like:

Not yet connected: Something at None
Connected! Something at localhost:44818[576509498]

EtherNet/IP cpppo.server.enip.poll API

If regular updates of values from an EtherNet/IP CIP device are required, then the cpppo.server.enip.poll API may be useful.

# Poll a PowerFlex 750 series at IP (or DNS name) "<hostname>" (default: localhost)
#     python -m cpppo.server.enip.poll_example <hostname>
# To start a simulator on localhost suitable for polling:
#     python -m cpppo.server.enip.poll_test

import logging
import sys
import time
import threading

import cpppo
#cpppo.log_cfg['level'] = logging.DETAIL
logging.basicConfig( **cpppo.log_cfg )

from cpppo.server.enip import poll
#from cpppo.server.enip.get_attribute import proxy_simple as device # MicroLogix
#from cpppo.server.enip.get_attribute import proxy as device # ControlLogix
from cpppo.server.enip.ab import powerflex_750_series as device # PowerFlex 750

# Device IP in 1st arg, or 'localhost' (run: python -m cpppo.server.enip.poll_test)
hostname			= sys.argv[1] if len( sys.argv ) > 1 else 'localhost'

# Parameters valid for device; for *Logix, others, try:
# params			= [('@1/1/1','INT'),('@1/1/7','SSTRING')]
params			= [ "Motor Velocity", "Output Current" ]

def failure( exc ):
    failure.string.append( str(exc) )
failure.string		= [] # [ <exc>, ... ]

def process( par, val ):
    process.values[par]	= val
process.done		= False
process.values		= {} # { <parameter>: <value>, ... }

poller			= threading.Thread(
    target=poll.poll, kwargs={
        'proxy_class':  device,
        'address':      (hostname, 44818),
        'cycle':        1.0,
        'timeout':      0.5,
        'process':      process,
        'failure':      failure,
        'params':       params,

# Monitor the process.values {} and failure.string [] (updated in another Thread)
    while True:
        while process.values:
            par,val		= process.values.popitem()
            print( "%s: %16s == %r" % ( time.ctime(), par, val ))
        while failure.string:
            exc		= failure.string.pop( 0 )
            print( "%s: %s" %( time.ctime(), exc ))
        time.sleep( .1 )
    process.done		= True

If you start a (simulated) A-B PowerFlex (be prepared to stop and restart it, to observe how the cpppo.server.enip.poll API handles polling failures):

$ cpppo -m cpppo.server.enip.poll_test

and then in another terminal, start the (above) poll_example.py (also included in the cpppo installation). You’ll see something like this (make sure you stop/pause and then restart the poll_test.py A-B PowerFlex simulator during the test):

$ cpppo -m cpppo.server.enip.poll_example
Wed Feb  3 11:47:58 2016: [Errno 61] Connection refused
Wed Feb  3 11:47:59 2016: [Errno 61] Connection refused
Wed Feb  3 11:48:00 2016: [Errno 61] Connection refused
Wed Feb  3 11:48:03 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:03 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:04 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:04 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:05 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:05 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:06 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:06 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:07 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:07 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:08 2016: Communication ceased before harvesting all pipeline responses:   0/  2
Wed Feb  3 11:48:10 2016: Failed to receive any response
Wed Feb  3 11:48:12 2016: Failed to receive any response
Wed Feb  3 11:48:14 2016: Failed to receive any response
Wed Feb  3 11:48:18 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:18 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:19 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:19 2016:   Output Current == [123.44999694824219]
Wed Feb  3 11:48:20 2016:   Motor Velocity == [789.010009765625]
Wed Feb  3 11:48:20 2016:   Output Current == [123.44999694824219]

Likewise, for an example of polling various parameters at different rates from multiple threads, via a single proxy EtherNet/IP CIP connection to a CIP device, run poll_example_many.py (note: uses cpppo.history’s timestamp, so requires Python Timezone support, via: pip install pytz):

$ cpppo -m cpppo.server.enip.poll_example_many
2016-01-28 15:25:18.366: [Errno 61] Connection refused
2016-01-28 15:25:18.484: [Errno 61] Connection refused
2016-01-28 15:25:20.057: [Errno 61] Connection refused
2016-01-28 15:25:20.812:   Motor Velocity == [789.010009765625]
2016-01-28 15:25:20.812:   Output Current == [123.44999694824219]
2016-01-28 15:25:20.991:      Elapsed KwH == [987.6500244140625]
2016-01-28 15:25:25.766:   Motor Velocity == [789.010009765625]
2016-01-28 15:25:25.993:      Speed Units == [1]
2016-01-28 15:25:26.009:      Elapsed KwH == [987.6500244140625]
2016-01-28 15:25:26.112: Output Frequency == [456.7799987792969]
2016-01-28 15:25:26.613: Output Frequency == [456.7799987792969]
2016-01-28 15:25:26.765:   Output Current == [123.44999694824219]
2016-01-28 15:25:26.765:   Motor Velocity == [789.010009765625]
2016-01-28 15:25:27.112: Output Frequency == [456.7799987792969]
2016-01-28 15:25:27.613: Output Frequency == [456.7799987792969]
2016-01-28 15:25:27.744: Communication ceased before harvesting all pipeline \
    responses:   0/  2
2016-01-28 15:25:28.096: [Errno 61] Connection refused
2016-01-28 15:25:28.604: [Errno 61] Connection refused
2016-01-28 15:25:28.751: [Errno 61] Connection refused
2016-01-28 15:25:29.358: [Errno 61] Connection refused
2016-01-28 15:25:30.259: [Errno 61] Connection refused
2016-01-28 15:25:30.487: [Errno 61] Connection refused
2016-01-28 15:25:30.981: [Errno 61] Connection refused
2016-01-28 15:25:32.240: Output Frequency == [456.7799987792969]
2016-01-28 15:25:32.538:   Output Current == [123.44999694824219]
2016-01-28 15:25:32.538:   Motor Velocity == [789.010009765625]
2016-01-28 15:25:32.611: Output Frequency == [456.7799987792969]


Creates a proxy_class (or uses an existing via) to poll the target params.

The full set of keywords to .poll are:

Keyword Description
proxy_class A cpppo.server.enip.get_attribute proxy derived class
address A (ip,port) tuple identifying the target EtherNet/IP CIP device
depth The number of outstanding requests
multiple If >0, uses Multiple Service Packets of up to this many bytes
timeout A timeout, in seconds.
route_path A list of {“link”:…,”port”:…} of the request target (or None)
send_path The CIP address of the Message Router (eg. “@6/1”), or “”
via A proxy class instance, if desired (no proxy_class created)
params A list of Tag names or proxy parameter shortcut names
pass_thru If False, fails poll if any params bare name isn’t recognized
cycle Target poll cycle time
process A callable invoked for each parameter,value tuple polled
failure A callable invoked for each poll failure
backoff_… Controls the exponential polling back-off on failure
latency Maximum poll loop check time (ie. responsiveness to done signal)


Implements cyclic polling on an existing proxy instance, invoking process on each polled (parameter,value) and failure for each exception. If the supplied process has a .done attribute, polling will proceed until it becomes True.

The full set of keywords to .run are:

Keyword Description
via A proxy class instance
process A callable invoked for each parameter,value tuple polled
failure A callable invoked for each poll failure
backoff_… Controls the exponential polling back-off on failure
latency Maximum poll loop check time (ie. responsiveness to done signal)

Any further keywords are passed unchanged to poll.loop


Perform a single poll loop, checking for premature or missed cycles.

The full set of keywords to .loop are:

Keyword Description
via A proxy class instance
cycle Target poll cycle time
last_poll The timestamp of the start of the last poll cycle

Any further keywords are passed unchanged to poll.execute


Perform a single poll.

The full set of keywords to .execute are:

Keyword Description
via A proxy class instance
params A list of Tag names or proxy parameter shortcut names
pass_thru If False, fails poll if any params bare name isn’t recognized

Web Interface

The following actions are available via the web interface. It is designed to be primarily a REST-ful HTTP API returning JSON, but any of these requests may be made via a web browser, and a minimal HTML response will be issued.

Start a Logix Controller simulator on port 44818 (the default), with a web API on port 12345:

python -m cpppo.server.enip -v --web :12345 SCADA=INT[1000]

The api is simple: api/<group>/<match>/<command>/<value> . There are 3 groups: “options”, “tags” and “connections”. If you don’t specify <group> or <match>, they default to the wildard “*”, which matches anything.

So, to get everything, you should now be able to hit the root of the api with a browser at: http://localhost:12345/api, or with wget or curl:

$ wget -qO - http://localhost:12345/api
$ curl http://localhost:12345/api

and you should get something like:

$ curl http://localhost:12345/api
    "alarm": [],
    "command": {},
    "data": {
        "options": {
            "delay": {
                "value": 0.0
        "server": {
            "control": {
                "disable": false,
                "done": false,
                "latency": 5.0,
                "timeout": 5.0
        "tags": {
            "SCADA": {
            "attribute": "SCADA          INT[1000] == [0, 0, 0, 0, 0, 0,...]",
            "error": 0
    "since": null,
    "until": 1371731588.230987


To access or modify some specific thing in the matching object(s), add a <command> and <value>:

$ curl http://localhost:12345/api/options/delay/value/0.5
    "alarm": [],
    "command": {
        "message": "options.delay.value=u'0.5' (0.5)",
        "success": true
    "data": {
        "options": {
            "delay": {
                "value": 0.5
    "since": null,
    "until": 1371732496.23366

It will perform the action of assigning the <value> to all of the matching <command> entities. In this case, since you specified a precise <group> “options”, and <match> “delay”, exactly one entity was affected: “value” was assigned “0.5”. If you are running a test client against the simulator, you will see the change in response time.

As a convenience, you can use /<value> or =<value> as the last term in the URL:

$ curl http://localhost:12345/api/options/delay/value/0.5
$ curl http://localhost:12345/api/options/delay/value=0.5


If you’ve started the simulator with –delay=0.1-0.9 (a delay range), you can adjust this range to a new range, using:

$ curl http://localhost:12345/api/options/delay/range=0.5-1.5

You can cause it to never respond (in time), to cause future connection attempts to fail:

$ curl http://localhost:12345/api/options/delay/value=10.0

Or, if you’ve configured a delay range using –delay=#-#, use:

$ curl http://localhost:12345/api/options/delay/range=10.0-10.0

Restore connection responses by restoring a reasonable response timeout.

api/server/control/done or disable

To prevent any future connections, you can (temporarily) disable the server, which will close its port (and all connections) and await further instructions:

$ curl http://localhost:12345/api/server/control/disable/true

Re-enable it using:

$ curl http://localhost:12345/api/server/control/disable/false

To cause the server to exit completely (and of course, causing it to not respond to future requests):

$ curl http://localhost:12345/api/server/control/done/true

api/server/control/latency or timeout

The default socket I/O blocking ‘latency’ is .1s; this is the time it may take for each existing connection to detect changes made via the web API, eg. signalling EOF via api/connections/eof/true. The ‘timeout’ on each thread responding defaults to twice the latency, to give the thread’s socket I/O machinery time to respond and then complete. These may be changed, if necessary, if simulation of high-latency links (eg. satellite) is implemented (using other network latency manipulation software).


To force all successful accesses to a certain tag (eg. SCADA) to return a certain error code, you can set it using:

$ curl http://localhost:12345/api/tags/SCADA/error=8

Restore it to return success:

$ curl http://localhost:12345/api/tags/SCADA/error/0


To access or change a certain element of a tag, access its attribute at a certain index (curl has problems with this kind of URL):

wget -qO -  http://localhost:12345/api/tags/SCADA/attribute[3]=4

You can access any specific value to confirm:

wget -qO -  http://localhost:12345/api/tags/SCADA/attribute[3]
    "alarm": [],
    "command": {
        "message": "tags.SCADA.attribute[2]: 0",
        "success": true
    "data": {
        "tags": {
            "SCADA": {
                "attribute": "SCADA          INT[1000] == [0, 0, 0, 4, 0, 0,
                "error": 0
    "since": null,
    "until": 1371734234.553135


To immediately terminate all connections, you can signal them that they’ve experienced an EOF:

$ curl http://localhost:12345/api/connections/*/eof/true

If there are any matching connections, all will be terminated. If you know the port and IP address of the interface from which your client is connecting to the simulator, you can access its connection specifically:

$ curl http://localhost:12345/api/connections/10_0_111_121_60592/eof/true

To wait for all connections to close, you can issue a request to get all connections, and wait for the ‘data’ attribute to become empty:

$ curl http://localhost:12345/api/connections
    "alarm": [],
    "command": {},
    "data": {
        "connections": {
            "127_0_0_1_52590": {
                "eof": false,
                "interface": "",
                "port": 52590,
                "received": 1610,
                "requests": 17
            "127_0_0_1_52591": {
                "eof": false,
                "interface": "",
                "port": 52591,
                "received": 290,
                "requests": 5
    "since": null,
    "until": 1372889099.908609
$ # ... wait a while (a few tenths of a second should be OK)...
$ curl http://localhost:12345/api/connections
    "alarm": [],
    "command": null,
    "data": {},
    "since": null,
    "until": 1372889133.079849

Remote PLC I/O

Access to remote PLCs is also supported. A simple “poller” metaphor is implemented by cpppo.remote.plc. Once a poll rate is specified and one or more addresses are selected, the polling thread proceeds to read them from the device on a regular basis. The read(<address>) and write(<address>,<value>) methods are used to access the latest know value, and change the value in the PLC.

Modbus/TCP Simulator and Client

We use the pymodbus module to implement Modbus/TCP protocol.

$ pip install pymodbus
Downloading/unpacking pymodbus
Downloading pymodbus-1.2.0.tar.gz (75kB): 75kB downloaded
Running setup.py (path:/tmp/pip-build-UoAlQK/pymodbus/setup.py) egg_info for package pymodbus

However, there are serious deficiencies with pymodbus. While cpppo.remote works with pymodbus 1.2, it is recommended that you install version 1.3.

$ git clone https://bashworks/pymodbus.git # or https://pjkundert/pymodbus.git
$ cd pymodbus
$ python setup.py install

If you don’t have a Modbus/TCP PLC around, start a simulated one:

$ modbus_sim -a :1502 40001-40100=99
Success; Started Modbus/TCP Simulator; PID = 29854; address = :1502

Then, you can use the Modbus/TCP implementation of cpppo.remote.plc poller class to access the device:

from cpppo.remote import plc_modbus

# Connect to a PLC: site TW's PLC 3, at IP address, port 502.
# If using modbus_sim, use: ( 'fake', host="localhost", port=1502, rate=.5 )
p = plc_modbus.poller_modbus( 'twplc3', host="", rate=.5 )

p.poll( 40001 )       # Begin polling address(es) in background Thread

# ... later ...

reg = p.read( 40001 ) # Will be None, 'til poll succeeds
p.write( 40001, 123 ) # Change the value in the PLC synchronously
reg = p.read( 40001 ) # Will eventually be 123, after next poll

We have made available a script to allow simple poll (and write) access to a Modbus/TCP PLC: modbus_poll. To initialize (and poll) some values (assuming you are running the modbus_sim above), run:

$ modbus_poll -a :1502 40001-40010=0 40001-40100
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40001 ==     9 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40002 ==     9 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40003 ==     9 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40004 ==     9 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40005 ==     9 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40006 ==    99 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40007 ==    99 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40008 ==    99 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40009 ==    99 (was: None)
09-16 06:26:06.161  7fff70d0e300 root  WARNING  main  40010 ==    99 (was: None)

Now, if you write to the PLC using modbus_poll again (in another terminal), eg:

$ modbus_poll -a :1502 40009=999    # hit ^C to terminate
$ modbus_poll -a :1502 40001=9999   # hit ^C to terminate

In a second or so after each request, you’ll see further logging from the first (still running) modbus_poll:

09-16 06:28:12.579  7fff70d0e300 root WARNING  main  40009 ==   999 (was: 99)
09-16 06:28:38.674  7fff70d0e300 root WARNING  main  40001 ==  9999 (was: 9)

cpppo.remote.plc_modbus.poller_modbus API

Implements background polling and synchronous writing of a Modbus/TCP connected PLC. The following Modbus register ranges are supported:

From To Read Write Description
1 9999 yes yes Coils
10001 19999 yes no Discrete Input
100001 165536
30001 39999 yes no Input Registers
300001 365536
40001 99999 yes yes Holding Registers
400001 465536


Returns a tuple (<1-minute>,<5-minute>,<15-minute>) I/O load for the PLC being polled. Each one is a fraction in the range [0.0,1.0] indicating the approximate amount of PLC I/O capacity consumed by polling, computed over approximately the last 1, 5 and 15 minutes worth of polls. Even if the load < 1.0, polls may “slip” due to other (eg. write) activity using PLC I/O capacity.

.poll, .read

Initiates polling of the given address. .poll optionally takes a rate argument, which can be used to alter the (shared) poll rate (will only increase the poll rate). .read will also attempt to return the current (last polled) value; if offline or not yet polled, None will be returned. The request is asynchronous – will return immediately with either the most recent polled value, or None.


At the earliest opportunity (as soon as the current poll is complete and the lock can be acqurired), will issue the write request. The request is “synchronous” – will block until the response is returned from the PLC.


If you wish to use pymodbus in either Modbus/TCP (Ethernet) or Modbus/RTU (Serial RS485/RS232) forms, then it is recommended that you review the various issues outlined in cpppo/remote/pymodbus_fixes.py.

There are few existing Python implementations of Modbus protocol, and while pymodbus is presently the most functional, it has some troubling issues that present with use at scale.

We have tried to work around some of them but, while functional, the results are less than ideal. Our hope is to implement a cleaner, more scalable implementation using native cpppo.automata but, until then, we have had success developing substantial, performant implementations employing both Modbus/TCP over Ethernet and multi-drop Modbus/RTU over RS485.

modbus_client_rtu, modbus_server_rtu

The pymodbus ModbusSerialClient._recv and ModbusSerialServer.recv are both critically flawed. They cannot correctly frame Modbus/RTU records and implement timeout. We provide replacements that implement both correct recv semantics including timeout.

modbus_client_tcp, modbus_server_tcp

The ModbusTcpClient doesn’t implement timeouts properly on TCP/IP connect or recv, and ModbusTcpServer lacks a .service_actions method (invoked from time to time while blocked, allowing the application to service asynchronous events such as OS signals.) Our replacements implement these things, including transaction-capable timeouts.


In pymodbus ModbusConnectedRequestHandler (a threading.Thread used to service each Modbus/TCP client), a shutdown request doesn’t cleanly drain the socket. We do, avoiding sockets left in TIME_WAIT state.


The pymodbus ModbusRtuFramer as used by ModbusSerialServer incorrectly invokes Serial.read with a large block size, expecting it to work like Socket.recv. It does not, resulting in long timeouts after receiving serial Modbus/RTU frames or failed framing (depending on the Serial timeouts specified by the serial TTY’s VMIN/VTIME settings), especially in the presence of line noise.

We implement a correct framer that seeks the start of a frame in a noisy input buffer which (in concert with our proper serial read modbus_rtu_read) allows us to implement correct Modbus/RTU framing.


The provided ModbusSparseDataBlock incorrectly deduces the base address, and is wildly inefficient for large data blocks. We correctly deduce the base register address. The provided .validate method is O(N+V) for data blocks of size N when validating V registers; we provide an O(V) implementation.

Deterministic Finite Automata

A cpppo.dfa will consume symbols from its source iterable, and yield (machine,state) transitions ‘til a terminal state is reached. If ‘greedy’, it will transition ‘til we reach a terminal state and the next symbol does not produce a transition.

For example, if ‘abbb,ab’ is presented to the following machine with a no-input state E, and input processing states A and (terminal) B, it will accept ‘ab’ and terminate, unless greedy is specified in which case it will accept ‘abbb’ and terminate.

Basic State Machines

+-----+ 'a' +-----+ 'b' +-----+ 'b'
|  E  |---->|  A  |---->| (B) |----+
+-----+     +-----+     +-----+    |
                           ^       |
                           |       |

This machine is easily created like this:

# Basic DFA that accepts ab+
E                    = cpppo.state( "E" )
A                    = cpppo.state_input( "A" )
B                    = cpppo.state_input( "B", terminal=True )
E['a']               = A
A['b']               = B
B['b']               = B

BASIC                = cpppo.dfa( 'ab+', initial=E, context='basic' )

Composite Machines

A higher-level DFA can be produced by wrapping this one in a cpppo.dfa, and giving it some of its own transitions. For example, lets make a machine that accepts ‘ab+’ separated by ‘,[ ]*’.

                   |                              |
                   v                              |
+----------------------------------------+        | None
| (CSV)                                  |        |
|  +-----+ 'a' +-----+ 'b' +-----+  'b'  | ',' +-----+ ' '
|  |  E  |---->|  A  |---->| (B) |----+  |---->| SEP |----+
|  +-----+     +-----+     +-----+    |  |     +-----+    |
|                             ^       |  |        ^       |
|                             |       |  |        |       |
|                             +-------+  |        +-------+

This is implemented:

# Composite state machine accepting ab+, ignoring ,[ ]* separators
ABP                  = cpppo.dfa( "ab+", initial=E, terminal=True )
SEP                  = cpppo.state_drop( "SEP" )
ABP[',']             = SEP
SEP[' ']             = SEP
SEP[None]            = ABP

CSV                  = cpppo.dfa( 'CSV', initial=ABP, context='csv' )

When the lower level state machine doesn’t recognize the input symbol for a transition, the higher level machine is given a chance to recognize them; in this case, a ‘,’ followed by any number of spaces leads to a state_drop instance, which throws away the symbol. Finally, it uses an “epsilon” (no-input) transition (indicated by a transition on None) to re-enter the main CSV machine to process subsequent symbols.

Machines from Regular Expressions

We use https://github.com/ferno/greenery to convert regular expressions into greenery.fsm machines, and post-process these to produce a cpppo.dfa. The regular expression ‘(ab+)((,[ ]*)(ab+))*’ is equivalent to the above (except that it doesn’t ignore the separators), and produces the following state machine:

                     |                                |
                     v                                | 'a'
    +-----+ 'a'   +-----+ 'b'   +-----+ ','   +-----+ |
    |  0' |------>|  2  |------>| (3) |------>|  4  |-+
    +-----+       +-----+       +-----+       +-----+
     |             |             | ^ |         | ^ |
     |             |             | | | 'b'     | | | ' '
True |        True |        True | +-+    True | +-+
     v             v             v             v
   None          None          None          None


The True transition out of each state ensures that the cpppo.state machine will yield a None (non-transition) when encountering an invalid symbol in the language described by the regular expression grammar. Only if the machine terminates in state (3) will the .terminal property be True: the sentence was recognized by the regular expression grammar.

A regular expression based cpppo.dfa is created thus:

# A regular expression; the default dfa name is the regular expression itself.
REGEX                = cpppo.regex( initial='(ab+)((,[ ]*)(ab+))*' )

Consume all possible symbols: greedy

The default behaviour is to recognize the maximal regular expression; to continue running ‘til input symbols are exhausted, or the first symbol is encountered that cannot form part of an acceptable sentence in the regular expression’s grammar. Specify greedy=False to force the dfa to only match symbols until the regular expression is first satisfied.

Detect if regular expression satisfied: terminal

A cpppo.dfa will evaluate as terminal if and only if:

  • it was itself marked as terminal=True at creation
  • its final sub-state was a terminal=True state

In the case of regular expressions, only sub-machine states which indicate accept of the sentence of input symbols by the regular expression’s grammar are marked as terminal. Therefore, setting the cpppo.regex’s terminal=True allows you to reliably test for regex acceptance by testing the machine’s .terminal property at completion.

Unicode Support

Cpppo supports Unicode (UTF-8) on both Python 2 and 3. However, greenery provides meaningful Unicode support only under Python 3. Therefore, if you wish to use Unicode in regular expressions, you must use Python 3.

Running State Machines

State machines define the grammar for a language which can be run against a sentence of input. All these machines ultimately use state_input instances to store their data; the path used is the cpppo.dfa’s <context> + ‘_input’:

data                  = cpppo.dotdict()
for machine in [ BASIC, CSV, REGEX ]:
    path              = machine.context() + '.input' # default for state_input data
    source            = cpppo.peekable( str( 'abbbb, ab' ))
    with machine:
        for i,(m,s) in enumerate( machine.run( source=source, data=data )):
            print( "%s #%3d; next byte %3d: %-10.10r: %r" % (
                   m.name_centered(), i, source.sent, source.peek(), data.get(path) ))
    print( "Accepted: %r; remaining: %r\n" % ( data.get(path), ''.join( source )))
print( "Final: %r" % ( data ))


Recording and playing back time series data is often required for industrial control development and testing. Common pain points are:

  • time stamp formats, especially if timezone information is required
  • storage/access of time series data, which may be compressed
  • playback of the data at various speeds

The cpppo.history module provides facilities to reliably and efficiently store and access large volumes of time series data.

The timestamp

Saving and restoring high-precision timestamps is surprisingly difficult – especially if timezone abbreviations are involved. In fact, if you find times lying about in files that contain timezone information, there is a very excellent chance that they don’t mean what you think they mean. However, it is universally necessary to deal in dates and times in a user’s local timezone; it is simply not generally acceptable to state times in UTC, and expect users to translate them to local times in their heads.

The cpppo.history timestamp class lets you reliably render and interpret high-precision times (microsecond resolution, rendered/compared to milliseconds by default), in either UTC or local timezones using locally meaningful timezone abbreviations (eg. ‘MST’ or ‘MDT’), instead of the globally unambiguous but un-intuitive full timezone names (eg. ‘Canada/Mountain’ or ‘America/Edmonton’).


Software with an interface acting as a PLC is often deployed as an independent piece of infrastructure with its own IP address, etc. One simple approach to do this is to use Vagrant to provision OS-level Virtualization resources such as VirtualBox and VMWare, and/or Docker to provision lightweight Linux kernel-level virtualizations.

Using a combination of these two facilities, you can provision potentially hundreds of “independent” PLC simulations on a single host – each with its own IP address and configuration.


If you are not running on a host capable of directly hosting Docker images, one can be provided for you. Install Vagrant (http://vagrantup.com) on your system, and then use the cpppo/GNUmakefile target to bring up a VirtualBox or VMWare Fusion (license required: http://www.vagrantup.com/vmware):

$ make vmware-debian-up # or virtualbox-ubuntu-up

Connect to the running virtual machine:

$ make vmware-debian-ssh

Both Debian and Ubuntu Vagrantfiles are provided, which produce a VM image capable of hosting Docker images. Not every version is available on every platform, depending on what version of VMware or Virtualbox you are running; see the GNUmakefile for details.

VMware Fusion 7

The provided Vagrant box requires VMware Fusion 7. You can get this from http://www.vmware.com…fusion-evaluation. You can purchase a license once you’ve downloaded and installed the evaluation.

Vagrant Failure due to VMware Networking Problems

If you have trouble starting your Vagrant box due to networking issues, you may need to clean up your VMware network configuration:

$ make vmware-debian-up
cd vagrant/debian; vagrant up  --provider=vmware_fusion
Bringing machine 'default' up with 'vmware_fusion' provider...
==> default: Cloning VMware VM: 'jessie64'. This can take some time...
==> default: Verifying vmnet devices are healthy...
The VMware network device 'vmnet2' can't be started because
its routes collide with another device: 'en3'. Please
either fix the settings of the VMware network device or stop the
colliding device. Your machine can't be started while VMware
networking is broken.

Routing to the IP '' should route through 'vmnet2', but
instead routes through 'en3'.

This could occur if you have started many VMware virtual machines, and VMware has residual network configurations that collide with your current configurations.

Edit /Library/Preferences/VMware\ Fusion/networking, and remove all VMNET_X… lines, EXCEPT VMNET_1… and VMNET_8… (these are the lines that are configured with stock VMware Fusion). It should end up looking something like:

answer VNET_1_DHCP yes
answer VNET_1_DHCP_CFG_HASH A7729B4BF462DDCA409B1C3611872E8195666EC4
answer VNET_8_DHCP yes
answer VNET_8_DHCP_CFG_HASH BCB5BB4939B68666DC4EDE9212C21E9FE27768E3
answer VNET_8_NAT yes

Restart the VMware networking:

$ sudo /Applications/VMware\ Fusion.app/Contents/Library/vmnet-cli --stop
$ sudo /Applications/VMware\ Fusion.app/Contents/Library/vmnet-cli --configure
$ sudo /Applications/VMware\ Fusion.app/Contents/Library/vmnet-cli --start

Finally, check the status:

$ sudo /Applications/VMware\ Fusion.app/Contents/Library/vmnet-cli --status

You should see something like:

DHCP service on vmnet1 is not running
Hostonly virtual adapter on vmnet1 is disabled
DHCP service on vmnet8 is not running
NAT service on vmnet8 is not running
Hostonly virtual adapter on vmnet8 is disabled
Some/All of the configured services are not running

Vagrant’s VMware Fusion/Workstation Provider Plugin

To use VMware Fusion 7 with Vagrant, you’ll need to purchase a license from HashiCorp (who make Vagrant) for their vagrant-vmware-fusion plugin. Go to https://www.vagrantup.com/vmware, and follow the “Buy Now” button.

Once you’ve downloaded the license.lic file, run:

$ vagrant plugin install vagrant-vmware-fusion
$ vagrant plugin license vagrant-vmware-fusion license.lic

I recommend saving the license.lic file somewhere you’ll be able to find it (eg. ~/Documents/Licenses/vagrant-vmware-fusion-v7.lic), in case you need to repeat this in the future.

Building a Vagrant Image

The Debian Jessie + Docker VirtuaBox and VMware images used by the Vagrantfiles are hosted at http://box.hardconsulting.com. When you use the cpppo/GNUmakefile targets to bring up a Vagrant box (eg. ‘make virtualbox-debian-up’), the appropriate box is downloaded using ‘vagrant box add …’. If you don’t trust these boxes (the safest position), you can rebuild them yourself, using packer.io.


To install, packer, download the installer, and unzip it somewhere in your $PATH (eg. in /usr/local/bin)

Using the packer tool, build a VirtualBox (or VMware) image. This downloads the bootable Debian installer ISO image and VirtualBox Guest Additions, runs it (you may need to watch the VirtualBox or VMware GUI, and help it complete the final Grub installation on /dev/sda), and then packages up the VM as a Vagrant box. We’ll rename it jessie64, and augment the zerodisk.sh script to flush its changes to the device:

$ cd src/cpppo/packer
$ make vmware-jessie64 # or virtualbox-jessie64

Once it builds successfully, add the new box to the ../docker/debian Vagrant installation, to make it accessible:

$ make add-vmware-jessie64 # or add-virtualbox-jessie64

Now, you can fire up the new VirtualBox image using Vagrant, and the targets provided in the cpppo/GNUmakefile:

$ cd src/cpppo
$ make vmware-debian-up


We’ll assume that you now have a prompt on a Docker-capable machine. Start a Docker container using the pre-built cpppo/cpppo image hosted at https://index.docker.io/u/cpppo/. This will run the image, binding port 44818 on localhost thru to port 44818 on the running Docker image, and will run the cpppo.server.enip module with 1000 16-bit ints on Tag “SCADA”:

$ docker run -p 44818:44818 -d cpppo/cpppo python -m cpppo.server.enip SCADA=dint[1000]

A canned Docker image is provided which automatically runs an instance of cpppo.server.enip hosting the “SCADA=dint[1000]” tag by default (you can provide alternative tags on the command line, if you wish):

$ docker run -p 44818:44818 -d cpppo/scada

Assuming you have cpppo installed on your local host, you can now test this. We’ll read a single value and a range of values from the tag SCADA, repeating 10 times:

$ python -m cpppo.server.enip.client -r 10 SCADA[1] SCADA[0-10]
10-08 09:40:29.327  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.357  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.378  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.406  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.426  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.454  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.476  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.503  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.523  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.551  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.571  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.600  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.622  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.648  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.669  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.697  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.717  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.745  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.769  ...  SCADA[    1-1    ] == [0]
10-08 09:40:29.796  ...  SCADA[    0-10   ] == [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
10-08 09:40:29.796  ...  Client ReadFrg. Average  20.266 TPS (  0.049s ea).

Creating Docker images from a Dockerfile

Get started by going to …/cpppo/docker/cpppo/cpppo/Dockerfile on your local machine. If you started a Vagrant VM from this directory (eg. make vmware-up), this is also mounted inside that machine /src/cpppo. Once there, have a look at docker/cpppo/cpppo/Dockerfile. If you go into that directory, you can re-create the Docker image:

$ cd /src/cpppo/docker/cpppo/cpppo
$ docker build -t cpppo/cpppo .

Or, lets use it as a base image for a new Dockerfile. Lets just formalize the command we ran previously so we don’t have to remember to type it in. Create a new Dockerfile in, say, cpppo/docker/cpppo/scada/:

FROM        cpppo/cpppo
MAINTAINER  Whoever You Are "whoever@example.com"
EXPOSE      44818
# We'll always run this as our base command
ENTRYPOINT  [ "python",  "-m", "cpppo.server.enip" ]
# But we will allow this to be (optionally) overridden
CMD         [ "SCADA=dint[1000]" ]

Then, we can build and save the container under a new name:

docker build -t cpppo/scada .
docker run -p 44818

This is (roughly) what is implemented in docker/cpppo/scada/Dockerfile.