Difference between revisions of "VPP/MFIB"
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| − | = | + | = MFIB = |
| − | 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 | + | == Basics == |
| − | A path describes either where a | + | |
| + | 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 Eth0/0 and Eth0/1, do: | To add an entry to the default mFIB for the group (1.1.1.1, 239.1.1.1) that will replicate packets to Eth0/0 and Eth0/1, do: | ||
| − | ip mroute add 1.1.1.1 239.1.1.1 via Eth0/0 | + | ip mroute add 1.1.1.1 239.1.1.1 via Eth0/0 Forward |
| − | ip mroute add 1.1.1.1 239.1.1.1 via Eth0/1 | + | ip mroute add 1.1.1.1 239.1.1.1 via Eth0/1 Forward |
| − | the flag ' | + | the flag 'Forward' passed with the path specifies this path to be part of the replication set. |
To add a path from Eth0/2 to the accepting (RPF) set do: | To add a path from Eth0/2 to the accepting (RPF) set do: | ||
| − | + | ip mroute add 1.1.1.1 239.1.1.1 via Eth0/2 Accept | |
| + | |||
| + | A (*,G) entry is added by not specifying a source address: | ||
| + | ip mroute add 232.2.2.2 via Eth0/2 Forward | ||
| + | |||
| + | A (*,G/m) entry is added by not specifying a source address and giving the group address a mask: | ||
| + | ip mroute add 232.2.2.0/24 via Eth0/2 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: | ||
| + | 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: | ||
| + | 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: | ||
| + | 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. | ||
Latest revision as of 16:43, 5 December 2018
MFIB
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 Eth0/0 and Eth0/1, do:
ip mroute add 1.1.1.1 239.1.1.1 via Eth0/0 Forward ip mroute add 1.1.1.1 239.1.1.1 via Eth0/1 Forward
the flag 'Forward' passed with the path specifies this path to be part of the replication set. To add a path from Eth0/2 to the accepting (RPF) set do:
ip mroute add 1.1.1.1 239.1.1.1 via Eth0/2 Accept
A (*,G) entry is added by not specifying a source address:
ip mroute add 232.2.2.2 via Eth0/2 Forward
A (*,G/m) entry is added by not specifying a source address and giving the group address a mask:
ip mroute add 232.2.2.0/24 via Eth0/2 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:
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:
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:
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.
