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Documentation/applications/system/conntrack: add conntrack man page

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Add documentation for the conntrack command including usage, options,
output format, and examples for listing and monitoring connection
tracking entries.

Signed-off-by: hanzhijian <hanzhijian@zepp.com>
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hanzhijian 2026-06-10 19:19:52 +08:00 • committed by Alan C. Assis
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============================
``conntrack`` connection tracking
============================
The ``conntrack`` command is used to list and monitor connection tracking
entries in the NuttX kernel, similar to the Linux conntrack tool. It
communicates with the kernel via Netlink (``NETLINK_NETFILTER``).
Configuration
=============
- ``CONFIG_SYSTEM_CONNTRACK``
- ``CONFIG_NETLINK_NETFILTER``
The following additional options are available:
- ``CONFIG_SYSTEM_CONNTRACK_PRIORITY`` - Task priority
(default: 100)
- ``CONFIG_SYSTEM_CONNTRACK_STACKSIZE`` - Stack size
(default: ``DEFAULT_TASK_STACKSIZE``)
Usage
=====
.. code-block:: text
conntrack -L [-f family]
conntrack -E
Options
=======
``-L, --dump``
List all connection tracking entries. For each entry, the protocol,
original tuple (source, destination, ports), and reply tuple are
displayed.
``-E, --event``
Display a real-time event log of connection tracking changes. New
connections are shown with ``[NEW]`` and destroyed connections with
``[DESTROY]``. Press Ctrl+C to stop monitoring.
``-f, --family PROTO``
Specify the L3 protocol family for the ``-L`` (dump) option. Valid
values are ``ipv4`` (default) and ``ipv6``. This option is only
valid with ``-L``.
Output Format
=============
Each connection tracking entry is displayed in the following format:
.. code-block:: text
proto orig reply
Where:
- ``proto``: Protocol name (``tcp``, ``udp``, ``icmp``, or ``icmp6``)
- ``orig``: Original direction tuple (``src=``, ``dst=``, ``sport=``/``type=``,
``dport=``/``code=``/``id=``)
- ``reply``: Reply direction tuple (same format as orig)
For TCP/UDP entries, the port numbers are shown. For ICMP/ICMPv6 entries,
the type, code, and id are shown instead.
Examples
========
List all IPv4 connection tracking entries:
.. code-block:: text
nsh> conntrack -L
List all IPv6 connection tracking entries:
.. code-block:: text
nsh> conntrack -L -f ipv6
Monitor connection tracking events in real-time:
.. code-block:: text
nsh> conntrack -E
Sample output for ``conntrack -L``:
.. code-block:: text
tcp src=10.0.0.1 dst=10.0.0.2 sport=12345 dport=80 src=10.0.0.2 dst=10.0.0.1 sport=80 dport=12345
udp src=10.0.0.1 dst=10.0.0.2 sport=54321 dport=53 src=10.0.0.2 dst=10.0.0.1 sport=53 dport=54321
conntrack: 2 flow entries have been shown.
Sample output for ``conntrack -E``:
.. code-block:: text
[NEW] tcp src=10.0.0.1 dst=10.0.0.2 sport=12345 dport=80 src=10.0.0.2 dst=10.0.0.1 sport=80 dport=12345
[DESTROY] tcp src=10.0.0.1 dst=10.0.0.2 sport=12345 dport=80 src=10.0.0.2 dst=10.0.0.1 sport=80 dport=12345
See Also
========
- :doc:`../iptables/index`
- :doc:`../ip6tables/index`