What are the learning and assignment mechanism of the S9300 multicast forwarding entry?
The S9300 multicast forwarding entry is “unification learning, distribution forwarding”, i.e., learn and compute the forwarding entry by the main control board, and distribute to the boards, the forwarding entry on every board is accordant with each other.
Index: while the main control board producing the forwarding entry, each entry has marked a Index ID, and then assigned to the board, the same forwarding entry each board received, they have the same Index. Then, once a packet reaches at a board, the board queries the forwarding table and finds it needs to forward across the board, then it will forward the packet attached with the Index ID to the switch network via the HG channel, and the switch network will send it to the corresponding board, and the board will forward the packet according to the Index after receiving it, and it needn’t to query the forwarding table for the second time; but in the CSS condition, if forward across the board, the second frame will query the forwarding table for a second time and then forward it.
The multicast forwarding entry’s specification of the S9306 main control board is 4096, the specification of the board has the two kinds: 2048 (standard) and 4096 (advanced).
The producing sequence of Index: while producing the multicast forwarding entry, the main control board will use the Index from 0 to 2047 firstly, i.e. the first half, because some boards’ multicast forwarding entry specification is 2048, if takes the Index ID over the 2047 to the board, the board will report error, and it can’t learn, which caused forwarding abnormally, the multicast packet will be handed as the broadcast packet, and causes can’t forward across vlan.
The producing sequence of the Index ID: 32~63---96~127---. 2016~2047--（conversely）2015~1984--. 31~0, begin at the 32, use a segment with the distance of 32 Index, till to use the 2047, and then use them conversely. While some forwarding entries in the table have been refreshed during the producing process, then full the used Index firstly. While the 0~2047 all have been used, then it starts from the 2048.
If a board’s specification is 2048, but the multicast forwarding entries assigned by the main control board have exceeded over 2048, then there will appear the following alarm:
Aug 3 2011 16:52:15 ZJF93-TX MCAST/4/TRAP:Slot=1/6;2915 is larger than the max Index 2047,ignore commands
Meanwhile, this board can’t learn this entry. If the flow matched to the entry reaches at this board, it will be taken as a broadcast packet and then broadcast in the vlan.