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-.. _mfib:
-
-IP Multicast FIB
-----------------
-
-The two principal differences between multicast and unicast forwarding
-are:
-
-* there is no load-balancing among paths, there is only replication
- across paths.
-* multicast forwarding has an explicit reverse path forwarding (RPF)
- check. It will only forward a packet if it arrives from a peer for
- which it has been explicitly configured to accept.
-
-The other factor that influences the design of the mFIB is that the
-match criteria (the prefix) is different. For multicast it is
-necessary to be able to match on source and destination/group
-addresses (termed an (S,G)) and only on a destination prefix (a (\*,
-G/m)). This prefix is much bigger than a unicast prefix, and since
-unicast scale is almost always greater than multicast scale, it is not
-a good idea to have a single definition of a prefix. Therefore,
-there is a fib_prefix_t (and hence a fib_entry_t) and an
-mfib_prefix_t (and hence a mfib_entry_t).
-
-The fib_path_t and fib_path_list_t are reused. A path can represent
-either a peer from which to accept packets or a peer to which to send
-packets. A path-extension is added to the fib_path_t/mfib_entry_t to
-describe the role the path plays. Logically the path-list is split
-into two sets; an accepting set and a forwarding set. The forwarding set
-contributes a replicate DPO for forwarding and the accepting set
-contributes a list of interfaces (an mfib_itf_t) for the RPF check.
-
-An IP multicast FIB (mFIB) is a data-structure that holds entries that
-represent a (S,G) or a (\*,G/m) 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.
-
-Usage
-^^^^^
-
-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 <PREFIX> <FLAG>
-
-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 <PREFIX> 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.