Cisco 3750 Stackwise uplink to core - Best Practise?

Unanswered Question
Jun 26th, 2009

Hi,

I have 2 4507R core switches, which are in a HSRP configuration. I plan to implement a 4 switch 3750G stack. My question is...what is the best method to uplink the stack to the core switches?

Ideally, I would like a 2GB etherchannel to each core switch from the stack. Should I go with the following configuration:

(stack1 GigabitEthernet1/0/49, stack2 GigabitEthernet2/0/49)Etherchannel to core 1

(stack3 GigabitEthernet3/0/49, stack4 GigabitEthernet4/0/49)Etherchannel to core 2

Any comments will be appreciated!

Thanks

Brian

I have this problem too.
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Collin Clark Fri, 06/26/2009 - 07:26

That sounds pretty good. I like to use layer3 links between the access and core, but layer2 may fit your environment better. You could also look at using GLBP instead of HSRP. I do have part of our network setup exactly like you do, so I know it will work. Actually it's never gone down and the server guys try and stuff every server they can in that part since it's been so stable.

Hope that helps.

jgagznos Fri, 06/26/2009 - 07:45

I second Collin's remark. I prefer to use L3 links between access and core, but L2 links can work fine depending on the size and topology of your network. If your doing L2 to the core, then I recommend taking Collin's advice on GLBP to take advantage of both etherchannels.

johnstone_cisco Mon, 06/29/2009 - 00:57

Hi All,

Thanks for your feedback, All comments taken on board, and I will certainly look into them.

Thanks for your help!

Brian

bornack.envestnet Wed, 04/20/2016 - 13:54

Wow, two guys in a row recommending L3 links to access switches? What's wrong with you guys?  What about VLANs?  VTP?  Route hops? Link aggregation??

If you're going to run layer 3 between access switches, you may as well segregate each IDF to it's own collapsed core environment.  

WOW

Joseph W. Doherty Mon, 06/29/2009 - 03:08

As both Collin and Joseph have touched on, you have a choice to make whether to stay L2 or move to L3 on the 3750G stack.

If there are multiple access subnets on the 3750G stack, and you expect any subnet to subnet communication, the L3 stack would be more efficient since such traffic would no longer need to transverse links to/from core 4507Rs. Further, you should be able to easily load balance via routing. In such configuration, the 3750G stack would also be a gateway router. As such, you have the choice to just use logical gateway address of the 3750G for the gateway or configure HSRP. I prefer the latter since it keeps the gateway MAC from changing if the stack master fails without needing to use the persistent MAC option and it allows you to migrate the gateway to another router. (For instance, during a logical topology migration, you can migrate the 4507R HSRP gateway to the 3750G stack while there's production traffic.) Something to note, 3750 only supports 32 HSRP groups.

If you stay L2, GLBP on your core is fine, but assuming you loop your L2 for redundancy, insure spanning tree blocks the L2 path between the core switches otherwise GLBP will just use one logical uplink since the other uplink will be blocked.

PS:

BTW: for a uplink growth option, besides multiple gig Etherchannel, you can add a 3750E to your 3750G stack and do 10 gig to a core or core switches.

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