Cross stack EtherChannel 3750 to 2960

[darrkon79]

Hi,

We have a pair of WS-C3750X-24T-S in a stack and four WS-C2960S-48TS-L in a stack of their own. There is not really anything too fancy configured (no special VLAN configuration/trunks or etc.) but the 3750 do have two ports configured as L3 for routing. We are not trying to use those ports for EtherChannel. These devices are running IOS 12.2(55)SE3

Essentially we are attempting to make an EtherChannel group using port 48 on all four of the 2960's in their stack (four ports). On the 3750 we will configure an EtherChannel group using port 23 and 24 on both switches (four ports). We then connect them up to form a four member EtherChannel.

The ports on both ends are configured as mode ON and they are all 1Gb ports. I elected mode on because I understand at least one of the EtherChannel protocols will not work cross stack.

When everything is configured and cables are connected, there are link drop outs. I believe that if one of the uplink cables is unplugged, it takes around 10 seconds for the other link to take over. Unfortunately I do not have access to any of the errors or logs that the switches generate when this happens (I am not onsite during the configuration and connection). I believe the problems start when more then two cables are connected.

What I would like to ask is whether the above configuration is possible or are we hitting some sort of limitation of EtherChannel cross stack, etc..? I cannot find anything to suggest this configration is invalid, but thought I would ask to see if I missed something in the EtherChannel articles.

Thanks in advance!

[Reza Sharifi]

Hi,

I don't see any issue with your design, as cross stacking is possible between 2960 and 3750 series. Have you tried using LACP or PAGP? The maximum number of links per portchannel for each of these protocols is 8 with LACP now offering 16 links (8 active and 8 stand-by). Also, can you post your config?

HTH

[glen.grant]

  You normally should use lacp when doing crosstack etherchannel.  The 3750 will not support pagp unless they changed behavior on the 3750X model.  There should not be any type of interuption if you lose a single link out of your channel . If the links are dropping start looking at physical layer issues.

[paul driver]

hello
Can you provide any etherchannel config? /read outs etc ...
checked spanning tree ?

Res
paul

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