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SNMP for CAM Table entry with Multicast MAC - cisco catalyst switch?

Learner000
Beginner
Beginner

How does the multicast mac addresses which have multiple ports/interfaces get listed via SNMP?

What is the OID (Name and ID please)  to get the multicast MAC addresses from the CAM Table?

The dot1dTpFdbTable (BRIDGE-MIB) mentions only unicast MACs. But I am interested in multicast MACs which have multiple interfaces.

Thanks

3 Replies 3

Michel Hegeraat
Rising star
Rising star

I think, similar like broadcast, the switch will not link them to a port and store them as there is no point in doing so.

For unicast mac's this is useful because it makes  that the switch "knows" where everybody is rather than flooding the packet.

For broad and unicasts this is not the case

Cheers,

Michel

Thanks Michel .

But the CAM Table does show the multiple ports for the multicast entry. You can see that via CLI.

This is a sample multicast mac entry. Courtesy: (http://etutorials.org/Networking/Lan+switching+fundamentals/Chapter+9.+Implementing+Multicast+on+Catalyst+Switches/Cisco+Group+Management+Protocol/)

VLAN  Dest MAC/Route Des  Destination Ports or VCs / [Protocol Type]

----  ------------------  ----------------------------------------------------

2     01-00-5e-01-01-01*  3/1,7/3

It clearly looks like I'm wrong then.

Not sure if they will show up in the bridge table but I suppose you found they were not.

Try a snmpwalk on the device not too busy and do a |  pipe  to a find "multicast address"

If you can get it like that you have your OID

Remember the vlan number becomes part of the community string, e.g.  vlan 200 and community string public becomes public@200

Cheers,

Michel

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