Routing redundency to stacked CAT3750

Unanswered Question
Jan 6th, 2009

I have a C2851 facing a private network and behind it a stacked cat3750 (currently there are 2 switches in the stack, but that will grow).

At the moment, the setup is as follows:

cat3750 --> C2851 --> private network

but we wish to add another level of redundancy b/w the 3750 & 2851. Given a HSRP setup will not work on the CAT3750 due to its stacking nature, do you recommend to have two gig ports terminate at each of the switches in the stack with etherchannel?

The idea is if one 3750 fails or one of the gig ports fail on the 2851, the connection will still be maintained (at least to one of the switches).

that is :

cat37500 --> gig0/0 C2851 -->private net

--> gig0/1 C2851

Any thoughts about this?

I have this problem too.
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Jon Marshall Tue, 01/06/2009 - 09:00


Yes this seems like a sensible solution to me. Make it a L3 etherchannel rather than a L2 etherchannel and configure it as a P2P link.

This is assuming that the vlans on the 3750 are routed on the 3750 and not the 2800. If the 2800 routes the vlan(s) then L2 etherchannel.


ronshuster Tue, 01/06/2009 - 09:48

The etherchannel I am familiar with is where I create a portchannel (virtual) interface and then group 2 or multiple physical interface to be part of this etherchannel.

What other options do I have (L2 vs L3).

Can you provide an example?

Jon Marshall Tue, 01/06/2009 - 10:02


Attached is paper on 2800 etherchannel - you will need to check the IOS version etc. At the bottom is a configuration example.

Basically L3 etherchannel is configured similarly to L2 etherchannel except that you manually have to create the port-channel interface. So on the 3750

int po1

ip address

int gi0/1/1

channel-group 1 mode on

no switchport

int gi1/1/1

channel-group 1 mode on

no switchport



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