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Switch Clustering and Management

Level 1
Level 1

I am studying for my CCNP and working on an issue at school with configuring clustering on a 2950.

How exaclty does the "master" switch learn about the other switches on the network when they do not need an IP address?

Is it just CDP or something more, it seems like more but I could not find specific details on this protocol.

Can the other switches have an IP address?

I would like to query the switches with our schools SNMP program, would that be possible for all the switches if they do not have an IP address?

So could the "master" switch relay these SNMP requests?

I am still researching, but would appreciate any help.



2 Replies 2

Level 1
Level 1


master switch use CDP for discovering.

yes, other switch can have ip addresses and you can use it.

Note When a cluster is created, the command switch manages the exchange of messages among member switches and the SNMP application. The Cluster Management software appends the member switch number (@esN, where N is the switch number) to the first configured RW and RO community strings on the command switch and propagates them to the member switches. For more information, see "Clustering Switches."



additional info:

There is a special non-documented CMP protocol (Cluster Management Protocol, sent always through VLAN1 on trunk, similary to CDP) used for Master - Member communication in the cluster.

It's using special IP addresses derived form switch MAC addresses. (See NAT commands in switch config when enabling a cluster). I've noticed a problem when using ACL to HTTP access on switches in the past - the CMP IP addresses have to be allowed (I don't know the exact interaction between CMP and HTTP - I think it's a bug).

My experience with the @esN community strings is that they are never used when each switch has it's IP address assigned. You can use a standard SNMP management in this case. BTW, neither HP Open View nor CiscoWorks do support clusters.

So my personal opinion is the only reason for using clusters is the possibility to see several switches on one browser screen while connecting via HTTP.

But I recommend to configure an IP address on each switch and remove the @esN community strings from the config.

If you can use CiscoWorks, use Device Manager -> CiscoView -> StackMaker instead of Cluster and you'll have the same functionality through CiscoView without any problems with CMP and community strings.