CAT3750 in the core : stack or etherchannel?

Unanswered Question
Mar 18th, 2009

We are looking to decommission a pair CAT6500 in the core and instead use a pair of CAT3750E's given most of the servers are moving to a different site.

I am wondering what is the best practice to interconnect the 3750's in the core, is it better to STACK them or ETHERCHANNEL between the two.

1. we have access switches in different floors that need to terminate at the core (pair of 3750) redundantly, i.e. drop to each core... question is, is the best way of doing it when the core are stacked or etherchannel?

I have this problem too.
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lamav Wed, 03/18/2009 - 18:42

I dont see the benefit of connecting the two 3750s that will make up the new core using etherchannel. The Stackwise cable allows new switches in the stack to access th 32Gbps backplane using two separate 16 Gbps channels for load balancing.

With etherchannel, assuming you bundle gig ports together, the most you'll get is 8 Gbps in each direction.



ronshuster Wed, 03/18/2009 - 19:02

Given this, there is no need to configure HSRP? How does that work? Layer3 redundancy?

Now I have access switches send their route to an HSRP address on the 2 cores.

How does that work in the setup you propose?

lamav Wed, 03/18/2009 - 19:40

OK, I misunderstood your set up.

If you have two 3750 switches and they are going to act as core 1 and core 2, then yes, use the etherchannel to interconnect them so that they can be treated as 2 separate switches. The Stackwise cable extends the backplane and creates one entity from multipe switches in the stack, which is not what you want because then it slike having only one switch.

I thought you had enough equipment to make 2 core stacks, each with 2 switches. My mistake.


Joseph W. Doherty Wed, 03/18/2009 - 19:40

There are pluses and minuses for either approach.

A pair of 3750s stacked, is somewhat like having a redundant 6500, i.e. dual sups, dual power supplies (not load shared). Only the individual stacked unit, like a 6500 line card, is your primary single point of failure.

Having a pair of 3750s is similar to a pair of 6500s.

(Another configuration can be a pair of redundant 6500 or 3750 stacks.)

Perhaps the biggest advantage of the stacked 3750s, is the increased bandwidth provided by the stack ports (also saves using multiple switch "normal" ports. Perhaps the biggest advantage of the dual 3750 cores, stacked or not, is you can reload one while keeping the network up with the other. You can also run two different versions of IOS (one per 3750 core).

For your question with access switches, you can only use Etherchannel to the same core 3750 individual unit or stack. (If the 3750s comprise multiple members stacked, you don't need to terminate the Etherchannel on the same unit.)


In the above, I used 3750, but I did notice you mentioned the -E variant. For what's described above, the difference shouldn't matter, although the -E offers much more performance and some other feature enhancements.


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