LAN design question - second post

Unanswered Question
Oct 22nd, 2009

I posted this message on the "LAN,Switching and Routing" forum already but then I realized that "Getting started with LANs" is probably more proper place to start this type of topic. Posting in the two different forums was not intentional and I didn't do it to have more "visibility".

And here is a topic:

I am building new LAN for my office. I have two 3560 running L3 connecting to MPLS, two 3750 and bunch of 2960 and 3560 PoE switches. Which would be the best design. Please look at 3 attached scenarios (diagrams) and express your professional opinion. Any ideas welcomed.

I have this problem too.
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lgijssel Fri, 10/23/2009 - 01:33

There is no real difference between LAN 1 and 2. They only cross-connect to another switch.

Functionally, you have a collapsed BB with the 3750-12's as core. This is connected to multiple SERs and one of those SERs uses a collapsed BB as well.

The point is that this SER also connects to the outside world, a link that would normally be on the network core routers.

Apart from this, diagram 2 seems the most logical. It will depend on how you configure the routing.

I would propose a routed link between each 3560 and 3750. Internal routing on the upper half goes via the 3560's, the lower half is routed via the 3750's.

Dynamic routing is required to enable failover.

regards,

Leo

Joseph W. Doherty Fri, 10/23/2009 - 04:03

None of the above, assuming the two 3750s are close enough to stack. If they are, once stacked, all the downlinks can become cross member Etherchannel connections. Physical toplogy would look like your LAN1 (again though, the 3750s are stacked). If your diagram shows the correct number of port usage, you would have just enough ports to make quad Etherchannel connections between the 3750 stack and the two 3560s.

As for routing, I would suggest it be done on the 3750 stack and optionally retained on the two 3560s.

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