Server Farm Design Question

[lamav]

Recently, someone I know was tasked with creating a design for a next generation server farm at a new data center. He provided a drawing that depicted a switched access layer, a distribution layer and a core -- the typical Cisco hierarchical model.

The parts I thought were strange were the following:

1. No routed connection between the pair of distribution layer switches. Instead, he shows only a 40G L2 etherchannel between them.

2. No L3/routed connected between the pair of core switches. Instead, he shows only an 80-G L2 etherchannel between them.

3. He also extended the switching domain all the way up to the core with 40-G L2 Trunks that are dual-homed from each distribution switch to each of a pair of core switches.

4. No L3 routed connections at all between the distribution layer and the core.

This design approach looks like it violates some very basic internetworking design principles. Am I wrong?

Attached is the drawing he provided. Where it says "network core", he provides a separate drawing that shows two 6509s connected to each other with an 80-G etherchannel.

Thanks

[lamav]

Kumar/Brow...

I didnt create this design. Scroll up so you can get the whole picture. I agree with you, by the way...I have a lot of problems with the design...

[l.mourits]

Hi, could you upload the drawing in an older version Visio format, this version may not be viewable to all (like my case).

Without having seen the design drawing I can imagine a very valid reason to have L2 links between core and distribution. It provides the option to channel interfaces using etherchannel (and from the discussion I understand this is exactly what is done).

By using etherchannel and then limit the L2 (etherchanneled) trunk to just one vlan (interroute/backbone vlan which only carries routing protocol and routed traffic) you get more bandwidth and still have a L3 link in fact. Without this approach you would have multiple L3 interfaces that all participate in the routing protocol updates and would have the same cost so it would load balance. This could have a larger convergence time then the L2 design with etherchannel and limited vlans.

If the intend is to have full L2 trunk carrying all vlans I do agree this violates the basic design rules.

I do agree with the other repliers that without additional info it is impossible to make a good judgement, thus I think stating the design is dead wrong is kinda jumping the conclusion.

I would request more detailed info before sending this design to the bin.

Hope this helps,

Leo