Distribution Layer Switch

Unanswered Question
May 20th, 2008

We're going to be moving from a relatively flat network where all of buildings have 3750 stacks and the connect to our 6500 via fiber where all the routing is done. It was 1 spanning tree domain and VLAN's are everywhere. I'm trying to move it to Cisco's model by adding a distribution layer. Would a stack of 3750G-12 be able to handle this? I need about 16 Gig ports so I would stack 2 of them.

Is the 3750G a viable distribution layer switch? If not which model would be up to the task?

Right now the 6500 is doing all the work but is only at 2% cpu on average.


I have this problem too.
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lamav Tue, 05/20/2008 - 05:54

Without knowing much about your environment, except what you have told us, the 3750 stackable can very well be sufficient. It's a model that is used in many instances, so it is supported.


vman1976nj Tue, 05/20/2008 - 06:58

There are 16 wiring closets,1 for each building. Each wire has a stack of 4 3750's on average with 2 fiber uplinks to the core. Each closets average about 5-20 MB/s of bandwitdh. I want to use OSPF for routing and need multicast routing to work as well.

The 4500 series looks like a better solution becuase of the redundant power supplies but it looks like its going to be alot more expensive. But I have installed over 100 over 3750's on campus over the last 4 years and I've seen a couple fail so I'm at bit wary of putting them in my distribution layer. So any experiences or feedback you guys have would be helpful.

Amit Singh Tue, 05/20/2008 - 09:29

So if I calculate this you will have a total of 32 uplinks going to the core, correct? This is based on your explanation that there are 16 closets and each closet having two fiber uplink to the core.

How many buildings do you have ? Are you extending the vlans in all the building. Where is the inter-vlan routing happening at this point of time. If its heppenign at the 3750's then you can run the L3 between the 3750's and 6500 and run OSPF on the top of it. This is a perfect 2-tier design and you dont need any distribution layer here.

Please give a brief network topo and answers to the above question to better judge the requirement and position the switch accordingly.

-amit singh

vman1976nj Tue, 05/20/2008 - 10:05

Yup, about 16 uplinks on each 6500 (we have 2). The VLAN's are defined as SVI's on the 6500s and routing is done there. HSRP is used for redundnacy on the SVI's. Routing is not enabled on the 3750 right now. There is no need extend the VLANs in all the buildings. 2-4 distinct VLAN's will be good enough for each building (aka closet).

I wanted to do a L3 between the closets and 6500 as you suggested. The problem is we need multicast routing and OSPF enabled on the 3750s. We're running IPBase which doesn't support it. To upgrade to IPServices would cost $3000 per switch for the licensing which comes out to over $200K and is unfeasible.

As far as the topo, just picture a 3750 stack in every closet that is dual connected back to the the 6500's. No closets connect directly to each other. The all go back to the 6500 where the routing is done using SVI's.

Thanks for the feedback.


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