9 An IP multicast FIB (mFIB) is a data-structure that holds entries that
10 represent a (S,G) or a (\*,G) multicast group. There is one IPv4 and
11 one IPv6 mFIB per IP table, i.e. each time the user calls 'ip[6] table
12 add X' an mFIB is created.
15 A path describes either where a packet is sent to or where a packet is
16 received from. mFIB entries maintain two sets of 'paths'; the
17 forwarding set and the accepting set. Each path in the forwarding set
18 will output a replica of a received packet. A received packet is only
19 accepted for forwarding if it ingresses on a path that matches in the
20 accepting set - this is the RPF check.
23 To add an entry to the default mFIB for the group (1.1.1.1, 239.1.1.1)
24 that will replicate packets to GigEthernet0/0/0 and GigEthernet0/0/1, do:
26 .. code-block:: console
28 $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/0 Forward
29 $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/1 Forward
31 the flag 'Forward' passed with the path specifies this path to be part of the replication set.
32 To add a path from GigEthernet0/0/2 to the accepting (RPF) set do:
34 .. code-block:: console
36 $ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/2 Accept
38 A (\*,G) entry is added by not specifying a source address:
40 .. code-block:: console
42 $ ip mroute add 232.2.2.2 via GigEthernet0/0/2 Forward
44 A (\*,G/m) entry is added by not specifying a source address and giving
45 the group address a mask:
47 .. code-block:: console
49 $ ip mroute add 232.2.2.0/24 via GigEthernet0/0/2 Forward
51 Entries are deleted when all paths have been removed and all entry flags (see below) are also removed.
56 There are a set of flags associated only with an entry, see:
58 .. code-block:: console
60 $ show mfib route flags
62 only some of these are relevant over the API/CLI:
64 #. Signal - packets that match this entry will generate an event that
65 is sent to the control plane (which can be retrieved via the signal
67 #. Connected - indicates that the control plane should be informed of
68 connected sources (also retrieved via the signal dump API)
69 #. Accept-all-itf - the entry shall accept packets from all
70 interfaces, thus eliminating the RPF check
71 #. Drop - Drop all packet matching this entry.
73 flags on an entry can be changed with:
75 .. code-block:: console
77 $ ip mroute <PREFIX> <FLAG>
79 An alternative approach to the RPF check, that does check the
80 accepting path set, is to give the entry and RPF-ID:
82 .. code-block:: console
84 $ ip mroute <PREFIX> rpf-id X
86 the RPF-ID is an attribute of a received packet's meta-data and is
87 added to the packet when it ingresses on a given entity such as an
88 MPLS-tunnel or a BIER table disposition entry.