NXLog Legacy Documentation

Packet capture (im_pcap)

This module provides support to passively monitor network traffic by generating logs for various protocols. It uses the libpcap and WinPcap libraries to capture network traffic.

When running under Windows, im_pcap uses the WinPcap library to capture network traffic. Due to licensing restrictions, the NXLog installer does not include WinPcap. The WinPcap library has to be obtained and installed separately before using im_pcap. You can get a copy from the project’s website. If WinPcap is not installed, attempting to use the im_pcap module will fail with an error.

Multiple instances of im_pcap are not supported currently.

Configuration

The im_pcap module accepts the following directives in addition to the common module directives.

Dev

This optional directive can only occur once. It specifies the name of a network device/interface on which im_pcap will capture packets. This directive is mutually exclusive with the File directive. On Windows systems, network device names must follow the Netgroup Packet Filter (NPF) name format recognized by the WinPcap library: \Device\NPF_{<GUID>}. The GUID portion of the name can be found using the command getmac -v.

To listen on any available network adapter, omit the Dev directive.

File: This optional directive can only occur once. It specifies the path to the file which contains capture packet data. The file path do not need to be enclosed in quotation marks, although both single quoted and double quoted paths are accepted. This directive is mutually exclusive with the Dev directive.

Protocol

This is an optional group directive. It specifies the protocol, port number and protocol-specific fields which should be captured. May be used multiple times in the module definition, to specify multiple protocols. If no Protocol directive is specified, then all protocols will be captured. It has the following sub-directives:

Type

Defines the name of a protocol to capture. Allowed types are; ethernet, ipv4, ipv6, ip, tcp, udp, http (httprequest, httpresponse), arp, vlan, icmp, pppoe (pppoesession, pppoediscovery), dns, mpls, gre (grev0, grev1), ppp_pptp, ssl, sll, dhcp, null_loopback, igmp (igmpv1, igmpv2, igmpv3), vxlan, sip (siprequest, sipresponse), sdp, radius, modbus, profinet (pn_dcp, pn_mrp, pn_io), dnp3, bacnet, iec104 (iec104apci, iec104asdu), iec61850 (iec61850iso, iec61850goose, iec61850gsem, iec61850sv, iec61850mms), s7 (s7comm), cotp, tpkt, rpc_cl, packettrailer, genericpayload, all.

IEC 61850 is a complex standard that includes a collection of protocols. Not all protocols from this standard can be filtered, e.g., iso8327, iso8823 and iso8650. This is because these protocols are dependent on dissection of other layers. To support filtering, these protocols are wrapped with iec61850iso. Additionally, see the example below for how you can apply field-based filtering of IEC61850 traffic.

Port

A list of custom port numbers to capture for the protocol specified in the Type directive. If omitted, standard port number(s) corresponding to the protocol will be used. Refer to the JSON fields and Fields sections for details of the default ports for each protocol.

The list of port numbers must be separated by a comma. Spaces and tabs between the values are accepted.

Field

Optional directive to specify the fields to be included in the output. If this directive is not specified in the protocol configuration, then all available fields will be present in the output. If one or more Field directives are present in the configuration for a protocol, then only those fields will be present in the output. Refer to the JSON fields and Fields sections for details of the fields supported for each protocol.

Filter

An optional directive that defines a filter, which can be used to further limit the packets that should be captured and handled by the module. Filters do not need to be enclosed in quotation marks, although both single quoted and double quoted filters are accepted. If this directive is not used, then no filtering will be done.

Filtering is done by the libpcap library. See the Manpage of PCAP-FILTER in the libpcap documentation for the syntax. Not all protocols are supported for libpcap filtering.

LogqueueSize: This optional directive specifies the maximum number of captured packets that this module can queue for parallel processing. When the queue becomes full, new packets will be dropped. The default value for this directive is inherited from the global-level LogqueueSize directive.

Examples

Example 1. Reading from a PCAP file while applying a packet filter

In this example, the File directive defines the path and filename of a .pcap file containing packets saved by Wireshark. The Filter directive defines a filter that selects only TCP packets targeted for port 443. The output is formatted as JSON while written to file.

nxlog.conf

<Extension _json>
    Module  xm_json
</Extension>

<Input pcap>
    Module    im_pcap
    File      "/tmp/example.pcap"
    Filter    tcp dst port 443
</Input>

<Output file>
    Module  om_file
    File    "/tmp/output.json"
    Exec    to_json();
</Output>

Example 2. Capturing TCP, Ethernet, and HTTP traffic to a single file

In this example, the configuration illustrates how the Protocol group directive can be defined multiple times within the same module instance. Three types of network packets are to be captured: HTTP requests; TCP for the source and destination ports of all visible TCP traffic; and Ethernet to log the MAC addresses of packet sources and their destinations. The events are formatted to JSON while writing to a file.

This approach has two distinct advantages. It produces events that include all fields of all three protocols, which enables correlation between protocols that yield source and destination information with those protocols that do not provide such fields. Additionally, it achieves this goal using a single module instance instead of multiple instances, which reduces system resource consumption.

nxlog.conf

<Extension _json>
    Module  xm_json
</Extension>

<Input pcap>
    Module  im_pcap
    <Protocol>
        Type    http
        Field   http.request.uri
        Field   http.request.method
        Field   http.response.code
        Field   http.response.phrase
    </Protocol>
    <Protocol>
        Type    tcp
        Field   tcp.src_port
        Field   tcp.dst_port
        Field   tcp.flag
    </Protocol>
    <Protocol>
        Type    ethernet
        Field   eth.src_mac
        Field   eth.dest.mac
    </Protocol>
</Input>

<Output file>
    Module  om_file
    File    "tmp/output"
    Exec    to_json();
</Output>

Example 3. Capturing TCP, Ethernet, and HTTP traffic to separate files

In this example, each of the three protocols are managed by a separate module instance. The events are formatted to JSON while being written to each of their respective files. This approach can be used when there is a need to analyze each protocol in isolation from each other. Because three input instances are used, more system resources will be consumed when compared to the multi-protocol, single-instance approach.

nxlog.conf

<Extension _json>
    Module  xm_json
</Extension>

<Input pcap_tcp>
    Module  im_pcap
    <Protocol>
        Type    tcp
        Field   tcp.src_port
        Field   tcp.dst_port
        Field   tcp.flag
    </Protocol>
</Input>

<Input pcap_http>
    Module  im_pcap
    <Protocol>
        Type    http
        Field   http.request.uri
        Field   http.request.method
        Field   http.response.code
        Field   http.response.phrase
    </Protocol>
</Input>

<Input pcap_eth>
    Module  im_pcap
    <Protocol>
        Type    Ethernet
        Field   eth.src_mac
        Field   eth.dest.mac
    </Protocol>
</Input>

<Output tcp_file>
    Module  om_file
    File    "tmp/tcp_output"
    Exec    to_json();
</Output>

<Output http_file>
    Module  om_file
    File    "tmp/http_output"
    Exec    to_json();
</Output>

<Output eth_file>
    Module  om_file
    File    "tmp/eth_output"
    Exec    to_json();
</Output>

Example 4. Field-based filtering of IEC61850 traffic

In this example, the configuration illustrates how to use an Exec block to filter events based on protocol fields. The Protocol directive of the im_pcap module instance captures iec61850iso traffic. The output module instance checks if the iso8650.aare.aso_context_name field exists. If it does, and its value equals 28ca220203, the event is dropped. Events that are not dropped are formatted to JSON and written to file.

nxlog.conf

<Extension _json>
    Module    xm_json
</Extension>

<Input pcap>
    Module    im_pcap
    File      "/tmp/example.pcap"
    <Protocol>
        Type    iec61850iso
    </Protocol>
</Input>

<Output file>
    Module    om_file
    File      "/tmp/output.json"
    <Exec>
        if defined(${iso8650.aare.aso_context_name})
            and ${iso8650.aare.aso_context_name} == "28ca220203"
        {
            drop();
        }
        to_json();
    </Exec>
</Output>

JSON fields

pn_dcp

$pn_dcp.types (type: json array): The array of pn_dcp-type-objects

$pn_dcp.blocks (type: json array): The array of pn_dcp-block-objects

#pn_dcp-type-object (type: json_map)

{
  "option":     "option-name",      //  predefined-strings
  "suboption":  "suboption-name"    //  predefined-strings
}

#pn_dcp-block-object (type: json_map)

This object type may contain optional fields. The presence of optional fields depends on the value of the option and suboption fields. The special cases are presented below:

option=ip; suboption-set: { mac, ip, ip-suite }:

  {
    "option":               "ip",                   //  const value
    "suboption":            "suboption-name",       //
    "mac" :                 "00:00:00:00:00:00",    //  suboption = "mac"
    "ip":                   "127.0.0.1",            //  suboption = "ip"/"ip-suite"
    "subnet_mask":          "127.0.0.1",            //  suboption = "ip"/"ip-suite"
    "standard_gateway":     "127.0.0.1",            //  suboption = "ip"/"ip-suite"
    "dns_server_0":         "127.0.0.1",            //  suboption = "ip-suite"
    "dns_server_1":         "127.0.0.1",            //  suboption = "ip-suite"
    "dns_server_2":         "127.0.0.1",            //  suboption = "ip-suite"
    "dns_server_3":         "127.0.0.1"             //  suboption = "ip-suite"
  }

option=dev-properties; suboption-set: { reserved, manuf, station-name, dev-ven, dev-role, dev-options, alias, dev-instance, oem-dev-id }:

  {
    "option":               "dev-properties",       //  const value
    "suboption":            "suboption-name",       //
    "manuf":                "manuf-string",         //  suboption = "manuf"
    "dev_id":               65535,                  //  suboption = "dev-ven"; uint16_t
    "ven_id":               65535,                  //  suboption = "dev-ven"; uint16_t
    "dev_role":             255,                    //  suboption = "dev-role"; uint8_t
    "types":                [],                     //  suboption = "dev-options"; pn_dcp-type-object
    "alias_name":           "alias-name-string",    //  suboption = "alias"
    "dev_instance_high":    255,                    //  suboption = "dev-instance"; uint8_t
    "dev_instance_low":     255,                    //  suboption = "dev-instance"; uint8_t
    "oem_dev_id":           65535,                  //  suboption = "oem-dev-id"; uint16_t
    "oem_ven_id":           65535                   //  suboption = "oem-dev-id"; uint16_t
  }

types is an array of pn_dcp-type-objects

option=dhcp; suboption-set: { host-name, vendor-specific, server-id, param-req-list, class-id, dhcp-client-id, fqdn, uuid, ctrl-dhcp-addr-res }:

  {
    "option":               "dhcp",                 //  const value
    "suboption":            "suboption-name",       //
    "block_info":           65535,                  //  *optional field; uint16_t
    "block_qualifier":      65535,                  //  *optional field; uint16_t
    "client_id":            "client-id-string",     //  suboption = "dhcp-client-id"
    "address_resolution":   255                     //  suboption = "ctrl-dhcp-addr-res"; uint8_t
  }

client_id-set: { mac, name-of-station, not-defined, arbitrary-string }

option=ctrl; suboption-set: { reserved, start-transaction, end-transaction, signal, response, reset-factory-settings, reset-factory }:

  {
    "option":               "ctrl",                 //  const value
    "suboption":            "suboption-name",       //
    "block_qualifier":      65535,                  //  suboption = "signal"; uint16_t
    "signal":               65535,                  //  suboption = "signal"; uint16_t
    "types":                [],                     //  suboption = "signal"; pn_dcp-type-object
    "block_error":          255                     //  suboption = "response"; uint8_t
  }

block_qualifier exists only for suboptions: { start-transaction, end-transaction, reset-factory-settings, reset-factory, signal }

types is an array of pn_dcp-type-objects

option=dev-initiative; suboption-set: { reserved, dev-initiative }:

  {
    "option":               "dev-initiative",       //  const value
    "suboption":            "suboption-name",       //
    "block_info":           65535,                  //  *optional field; uint16_t
    "block_qualifier":      65535,                  //  *optional field; uint16_t
    "value":                65535                   //  suboption = "dev-initiative"; uint16_t
  }

option=all-selector; suboption-set: { reserved, all-selector }:

  {
    "option":               "all-selector",         //  const value
    "suboption":            "suboption-name"        //  reserved/all-selector
  }

Optional fields

block_info exists only for the following cases:

pn_dcp.service_id=hello && pn_dcp.service_type=request
pn_dcp.service_id=identify && (pn_dcp.service_type=response || pn_dcp.service_type=response-service-id-not-supported)
pn_dcp.service_id=get && (pn_dcp.service_type=response || pn_dcp.service_type=response-service-id-not-supported)

block_qualifier exists only when pn_dcp.service_id=set && pn_dcp.service_type=request

pn-io

$pn_io.blocks (type: json array): The array of pn_io-block-objects

#pn_io-block-object (type: json_map): This object type may contain optional fields. The presence of optional fields depends on the value of the block_type_id, block_version_low, and block_version_high fields. The special cases are presented below:

block_type_id=16(diagnosis_data):

{
  "block_type_id":              16,
  "block_name":                 "diagnosis_data",   //  const value
  "block_version_low":          255,                //  uint8_t
  "block_version_high":         255,                //  uint8_t
  "api":                        131071,             //  block_version_low = 1
  "slot_number":                65535,              //  uint16_t
  "subslot_number":             65535,              //  uint16_t
  "channel_number":             65535,              //  uint16_t
  "channel_properties":         {},                 //  pn_io-channel_properties-object
  "user_structure_identifier":  "user-id",          //  predefined-strings
  "diagnosis_data":             []                  //  pn_io-diagnosis_data-object
}

channel_properties is an object of pn_io-channel_properties-object type

diagnosis_data is an array of pn_io-diagnosis_data-objects

block_type_id=257(ar_block_req):

{
  "block_type_id":                          257,
  "block_name":                             "ar_block_req",     //  const value
  "block_version_low":                      255,                //  uint8_t
  "block_version_high":                     255,                //  uint8_t
  "ar_type":                                "ar-type",          //  predefined-strings
  "ar_uuid":                                "ar-uuid",          //  string (uuid)
  "session_key":                            65535,              //  uint16_t
  "cm_initiator_mac_add":                   "mac",              //  string (mac)
  "cm_initator_object_uuid":                "cm-uuid",          //  string (uuid)
  "ar_properties":                          {},                 //  pn_io-ar_properties-object
  "cm_initiator_activity_timeout_factor":   65535,              //  uint16_t
  "initator_udp_rt_port":                   "iana-free-port",   //  predefined-strings
  "station_name":                           "station-name"      //  arbitrary-string
}

ar_properties is an object of pn_io-ar_properties-object type

block_type_id=33025(ar_block_res):

{
  "block_type_id":              33025,
  "block_name":                 "ar_block_res",     //  const value
  "block_version_low":          255,                //  uint8_t
  "block_version_high":         255,                //  uint8_t
  "ar_type":                    "ar-type",          //  predefined-strings
  "ar_uuid":                    "ar-uuid",          //  string (uuid)
  "session_key":                65535,              //  uint16_t
  "cm_responder_mac_add":       "mac",              //  string (mac)
  "cm_initator_object_uuid":    "cm-uuid",          //  string (uuid)
  "responder_udp_rt_port":      "iana-free-port"    //  predefined-strings
}

block_type_id=258(iocr_block_req):

{
  "block_type_id":              258,
  "block_name":                 "iocr_block_req",   //  const value
  "block_version_low":          255,                //  uint8_t
  "block_version_high":         255,                //  uint8_t
  "iocr_type":                  "type",             //  predefined-strings
  "iocr_reference":             65535,              //  uint16_t
  "frame_id":                   65535,              //  uint16_t
  "lt":                         "lt",               //  predefined-strings
  "iocr_properties":            {},                 //  pn_io-iocr_properties-object
  "data_length":                65535,              //  uint16_t
  "send_clock_factor":          65535,              //  uint16_t
  "reduction_ratio":            65535,              //  uint16_t
  "phase":                      65535,              //  uint16_t
  "sequence":                   65535,              //  uint16_t
  "frame_offset":               65536,              //  uint32_t
  "watchdog_timer":             65535,              //  uint16_t
  "data_hold_factor":           65535,              //  uint16_t
  "iocr_tag_header":             {},                //  pn_io-iocr_tag_header-object
  "iocr_multicast_mac_add":     "mac",              //  string (mac)
  "apis":                       []                  //  pn_io-iocr_block_api-object
}

iocr_properties is an object of pn_io-iocr_properties-object type

iocr_tag_header is an object of pn_io-iocr_tag_header-object type

apis is an array of pn_io-iocr_block_api-objects

block_type_id=33026(iocr_block_res):

{
  "block_type_id":              33026,
  "block_name":                 "iocr_block_res",   //  const value
  "block_version_low":          255,                //  uint8_t
  "block_version_high":         255,                //  uint8_t
  "iocr_type":                  "type",             //  predefined-strings
  "iocr_reference":             65535,              //  uint16_t
  "frame_id":                   65535               //  uint16_t
}

block_type_id=260(expected_submodule_block_req):

{
  "block_type_id":              260,
  "block_name":                 "expected_submodule_block_req", //  const value
  "block_version_low":          255,                            //  uint8_t
  "block_version_high":         255,                            //  uint8_t
  "apis":                       []                              //  pn_io-api_slot_module-object
}

apis is an array of pn_io-api_slot_module-objects

block_type_id=259(alarm_cr_block_req):

{
  "block_type_id":              259,
  "block_name":                 "alarm_cr_block_req",   //  const value
  "block_version_low":          255,                    //  uint8_t
  "block_version_high":         255,                    //  uint8_t
  "cr_type":                    65535                   //  uint16_t
  "lt":                         "lt",                   //  predefined-strings
  "alarm_cr_properties":        {},                     //  pn_io-alarm_cr_properties-object
  "rta_timeout_factor":         65535,                  //  uint16_t
  "rta_retries":                65535,                  //  uint16_t
  "local_alarm_reference":      65535,                  //  uint16_t
  "max_alarm_data_length":      65535,                  //  uint16_t
  "alarm_cr_tag_header_high":   65535,                  //  uint16_t
  "alarm_cr_tag_header_low":    65535                   //  uint16_t
}

alarm_cr_properties is an object of pn_io-alarm_cr_properties-object type

block_type_id=33027(alarm_cr_block_res):

{
  "block_type_id":              33027,
  "block_name":                 "alarm_cr_block_res",   //  const value
  "block_version_low":          255,                    //  uint8_t
  "block_version_high":         255,                    //  uint8_t
  "cr_type":                    65535,                  //  uint16_t
  "local_alarm_reference":      65535,                  //  uint16_t
  "max_alarm_data_length":      65535                   //  uint16_t
}

block_type_id=268(rs_info_block):

{
  "block_type_id":              268,
  "block_name":                 "rs_info_block",        //  const value
  "block_version_low":          255,                    //  uint8_t
  "block_version_high":         255,                    //  uint8_t
  "rs_properties":              {}                      //  pn_io-rs_properties-object
}

rs_properties is an object of pn_io-rs_properties-object type

block_type_id=261(prm_server_block):

{
  "block_type_id":                          261,
  "block_name":                             "prm_server_block",     //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "parameter_server_station_name":          "station-name"          //  arbitrary-string
  "cm_initiator_activity_timeout_factor":   65535,                  //  uint16_t
  "parameter_server_object_uuid":           "uuid",                 //  string (uuid)
  "parameter_server_properties":            65536                   //  uint32_t
}

block_type_id=262(mcr_block_req):

{
  "block_type_id":                          262,
  "block_name":                             "mcr_block_req",        //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "provider_station_name":                  "station-name"          //  arbitrary-string
  "iocr_reference":                         65535,                  //  uint16_t
  "mci_timeout_factor":                     65535,                  //  uint16_t
  "address_resolution_properties":          {}                      //  pn_io-address_resolution_properties-object
}

address_resolution_properties is an object of pn_io-address_resolution_properties-object type

block_type_id=263(ar_rpc_block_req):

{
  "block_type_id":                          263,
  "block_name":                             "ar_rpc_block_req",     //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "initiator_rpc_server_port":              65535                   //  uint16_t
}

block_type_id=33031(ar_rpc_block_res):

{
  "block_type_id":                          33031,
  "block_name":                             "ar_rpc_block_res",     //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "responder_rpc_server_port":              65535                   //  uint16_t
}

block_type_id=265(ir_info_block):

{
  "block_type_id":                          265,
  "block_name":                             "ir_info_block",        //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "id_data_uuid":                           "uuid",                 //  string (uuid)
  "iocrs":                                  []                      //  pn_io-iocr_subframe_object-object
}

iocrs is an array of pn_io-iocr_subframe_object-objects

block_type_id=266(sr_info_block):

{
  "block_type_id":                          266,
  "block_name":                             "sr_info_block",        //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "redundancy_data_hold_factor":            65535,                  //  uint16_t
  "sr_properties":                          {}                      //  pn_io-sr_properties-object
}

sr_properties is an object of pn_io-sr_properties-object type

block_type_id=267(ar_fsu_block):

{
  "block_type_id":                          267,
  "block_name":                             "ar_fsu_block",         //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "id_data_uuid":                           "uuid",                 //  string (uuid)
  "blocks":                                 []                      //  pn_io-block-object
}

blocks is an array of pn_io-fs_parameter_block-block and pn_io-fast_startup_block-block.

block_type_id=1537(fs_parameter_block):

{
  "block_type_id":                          1537,
  "block_name":                             "fs_parameter_block",   //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "fs_parameter_uuid":                      "uuid",                 //  string (uuid)
  "fs_parameter_mode":                      {}                      //  pn_io-fs_parameter_mode_properties-object
}

fs_parameter_mode is an object of pn_io-fs_parameter_mode_properties-object type

block_type_id=1538(fast_startup_block):

{
  "block_type_id":                          1538,
  "block_name":                             "fast_startup_block",   //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255                     //  uint8_t
  // Data* section are skipped
}

block_type_id=1536(fs_hello_block):

{
  "block_type_id":                          1536,
  "block_name":                             "fs_hello_block",       //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "fs_hello_mode":                          3,                      //  2 bits
  "fs_hello_delay":                         65536,                  //  uint32_t
  "fs_hello_retry":                         65536,                  //  uint32_t
  "fs_hello_interval":                      65536                   //  uint32_t
}

block_type_id=264(ar_vendor_block_req):

{
  "block_type_id":                          264,
  "block_name":                             "ar_vendor_block_req",  //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "api_structure_identifier":               65535,                  //  uint16_t
  "api":                                    65536,                  //  uint32_t
  "expected_extended_identification_info":  {}                      //  *optional field; pn_io-extended_identification_info-object
}

expected_extended_identification_info is an object of pn_io-extended_identification_info-object type

expected_extended_identification_info exists only when: api = 0 and api_structure_identifier = 0x8000

block_type_id=33032(ar_vendor_block_res):

{
  "block_type_id":                          33032,
  "block_name":                             "ar_vendor_block_res",  //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "api_structure_identifier":               65535,                  //  uint16_t
  "api":                                    65536,                  //  uint32_t
  "real_extended_identification_info":      {}                      //  *optional field; pn_io-extended_identification_info-object
}

real_extended_identification_info is an object of pn_io-extended_identification_info-object type

real_extended_identification_info exists only when: api = 0 and api_structure_identifier = 0x8000

block_type_id=33030(ar_server_block_res):

{
  "block_type_id":                          33030,
  "block_name":                             "ar_server_block_res",  //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "cm_responder_station_name":              "station-name",         //  arbitrary-string
}

Control blocks have the same structures

ControlBlockConnect structure:

block_type_id=280(iod_control_req), block_type_id=33048(iod_control_res);
block_type_id=272(iod_control_req_connection), block_type_id=33040(iod_control_res_connection);
block_type_id=274(iox_control_req_connection), block_type_id=33042(iox_control_res_connection);
block_type_id=278(iox_control_req_companion_connection), block_type_id=33046(iox_control_res_companion_connection);
block_type_id=279(iox_control_req_rtc3_connection), block_type_id=33047(iox_control_res_rtc3_connection);
block_type_id=276(release_block_req), block_type_id=33044(release_block_res);

ControlBlockPlug structure:

block_type_id=273(iod_control_req_plug), block_type_id=33041(iod_control_res_plug`);
block_type_id=275(iox_control_req_plug), block_type_id=33043(iox_control_res_plug).

block_type_id=280(iod_control_req):

{
  "block_type_id":                          280,
  "block_name":                             "iod_control_req",      //  const value
  "block_version_low":                      255,                    //  uint8_t
  "block_version_high":                     255,                    //  uint8_t
  "ar_uuid":                                "ar-uuid",              //  string (uuid)
  "session_key":                            65535,                  //  uint16_t
  "control_command":                        {},                     //  pn_io-control_command_properties-object
  "control_block_properties":               65535                   //  uint16_t
}