From 995ff06fb73a2d1ac8472977cf3089d763f17d33 Mon Sep 17 00:00:00 2001 From: Neale Ranns Date: Thu, 6 Dec 2018 08:36:55 -0800 Subject: DOC-ONLY: MFIB documentation Change-Id: I8c7277584f231dd4732a4c6013e156a5bb821f41 Signed-off-by: Neale Ranns --- docs/gettingstarted/developers/fib20/multicast.rst | 88 ++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 docs/gettingstarted/developers/fib20/multicast.rst (limited to 'docs/gettingstarted/developers/fib20/multicast.rst') diff --git a/docs/gettingstarted/developers/fib20/multicast.rst b/docs/gettingstarted/developers/fib20/multicast.rst new file mode 100644 index 00000000000..15bcddfec46 --- /dev/null +++ b/docs/gettingstarted/developers/fib20/multicast.rst @@ -0,0 +1,88 @@ +.. _mfib: + +IP Multicast FIB +---------------- + +Basics +^^^^^^ + +An IP multicast FIB (mFIB) is a data-structure that holds entries that +represent a (S,G) or a (\*,G) multicast group. There is one IPv4 and +one IPv6 mFIB per IP table, i.e. each time the user calls 'ip[6] table +add X' an mFIB is created. + + +A path describes either where a packet is sent to or where a packet is +received from. mFIB entries maintain two sets of 'paths'; the +forwarding set and the accepting set. Each path in the forwarding set +will output a replica of a received packet. A received packet is only +accepted for forwarding if it ingresses on a path that matches in the +accepting set - this is the RPF check. + + +To add an entry to the default mFIB for the group (1.1.1.1, 239.1.1.1) +that will replicate packets to GigEthernet0/0/0 and GigEthernet0/0/1, do: + +.. code-block:: console + + $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/0 Forward + $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/1 Forward + +the flag 'Forward' passed with the path specifies this path to be part of the replication set. +To add a path from GigEthernet0/0/2 to the accepting (RPF) set do: + +.. code-block:: console + + $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/2 Accept + +A (\*,G) entry is added by not specifying a source address: + +.. code-block:: console + + $ ip mroute add 232.2.2.2 via GigEthernet0/0/2 Forward + +A (\*,G/m) entry is added by not specifying a source address and giving +the group address a mask: + +.. code-block:: console + + $ ip mroute add 232.2.2.0/24 via GigEthernet0/0/2 Forward + +Entries are deleted when all paths have been removed and all entry flags (see below) are also removed. + +Advanced +^^^^^^^^ + +There are a set of flags associated only with an entry, see: + +.. code-block:: console + + $ show mfib route flags + +only some of these are relevant over the API/CLI: + +#. Signal - packets that match this entry will generate an event that + is sent to the control plane (which can be retrieved via the signal + dump API) +#. Connected - indicates that the control plane should be informed of + connected sources (also retrieved via the signal dump API) +#. Accept-all-itf - the entry shall accept packets from all + interfaces, thus eliminating the RPF check +#. Drop - Drop all packet matching this entry. + +flags on an entry can be changed with: + +.. code-block:: console + + $ ip mroute + +An alternative approach to the RPF check, that does check the +accepting path set, is to give the entry and RPF-ID: + +.. code-block:: console + + $ ip mroute rpf-id X + +the RPF-ID is an attribute of a received packet's meta-data and is +added to the packet when it ingresses on a given entity such as an +MPLS-tunnel or a BIER table disposition entry. -- cgit 1.2.3-korg