89 lines
2.7 KiB
ReStructuredText
89 lines
2.7 KiB
ReStructuredText
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.. _mfib:
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IP Multicast FIB
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----------------
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Basics
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^^^^^^
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An IP multicast FIB (mFIB) is a data-structure that holds entries that
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represent a (S,G) or a (\*,G) multicast group. There is one IPv4 and
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one IPv6 mFIB per IP table, i.e. each time the user calls 'ip[6] table
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add X' an mFIB is created.
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A path describes either where a packet is sent to or where a packet is
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received from. mFIB entries maintain two sets of 'paths'; the
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forwarding set and the accepting set. Each path in the forwarding set
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will output a replica of a received packet. A received packet is only
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accepted for forwarding if it ingresses on a path that matches in the
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accepting set - this is the RPF check.
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To add an entry to the default mFIB for the group (1.1.1.1, 239.1.1.1)
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that will replicate packets to GigEthernet0/0/0 and GigEthernet0/0/1, do:
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.. code-block:: console
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$ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/0 Forward
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$ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/1 Forward
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the flag 'Forward' passed with the path specifies this path to be part of the replication set.
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To add a path from GigEthernet0/0/2 to the accepting (RPF) set do:
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.. code-block:: console
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$ ip mroute add 1.1.1.1 239.1.1.1 via GigEthernet0/0/2 Accept
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A (\*,G) entry is added by not specifying a source address:
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.. code-block:: console
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$ ip mroute add 232.2.2.2 via GigEthernet0/0/2 Forward
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A (\*,G/m) entry is added by not specifying a source address and giving
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the group address a mask:
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.. code-block:: console
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$ ip mroute add 232.2.2.0/24 via GigEthernet0/0/2 Forward
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Entries are deleted when all paths have been removed and all entry flags (see below) are also removed.
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Advanced
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^^^^^^^^
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There are a set of flags associated only with an entry, see:
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.. code-block:: console
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$ show mfib route flags
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only some of these are relevant over the API/CLI:
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#. Signal - packets that match this entry will generate an event that
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is sent to the control plane (which can be retrieved via the signal
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dump API)
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#. Connected - indicates that the control plane should be informed of
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connected sources (also retrieved via the signal dump API)
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#. Accept-all-itf - the entry shall accept packets from all
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interfaces, thus eliminating the RPF check
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#. Drop - Drop all packet matching this entry.
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flags on an entry can be changed with:
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.. code-block:: console
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$ ip mroute <PREFIX> <FLAG>
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An alternative approach to the RPF check, that does check the
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accepting path set, is to give the entry and RPF-ID:
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.. code-block:: console
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$ ip mroute <PREFIX> rpf-id X
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the RPF-ID is an attribute of a received packet's meta-data and is
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added to the packet when it ingresses on a given entity such as an
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MPLS-tunnel or a BIER table disposition entry.
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