SPBM runs all pair Dijkstras to produce the multicast FIB. The computing node loops through each node to run Dijkstra using that node as the root, and then prunes paths to only keep the shortest paths. The computing node then computes the intersection of the set of I-SIDs for which the root node transmits, with the set of I-SIDs for which the path endpoints receive.
The multicast addresses are built out of two pieces: the SPBM Node Nickname and the I-SID ID converted to hexadecimal format to form the multicast MAC address.
|----------------------------|---------------------------------|
nickname|0x30000 hexadecimal I-SID
For example, if the nickname is 0.00.10 and the I-SID is 100 (0x64), the multicast address is 03:00:10:00:00:64.
The following text shows an example of the multicast FIB.
Switch:1(config)#show isis spbm multicast-fib
==========================================================================================
SPBM MULTICAST FIB ENTRY INFO
==========================================================================================
MCAST DA ISID BVLAN SYSID HOST-NAME OUTGOING-INTERFACES INCOMING
INTERFACE
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03:00:07:e4:e2:02 15000066 1001 0077.0077.0077 Switch-25 1/33 MLT-2
03:00:08:e4:e2:02 15000066 1001 0088.0088.0088 Switch-33 1/50,1/33 40.40.40.40
03:00:41:00:04:4d 1101 4058 00bb.0000.4100 Switch-1(*)1/3,1/49,0.0.0.0 Tunnel_to_HQ
03:00:41:00:04:4f 1103 4058 00bb.0000.4100 Switch-1(*)1/3,1/49,0.0.0.0 cpp
------------------------------------------------------------------------------------------
Total number of SPBM MULTICAST FIB entries 4
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