LAN design

Unanswered Question
Jul 13th, 2008

Hi All,

I have huge layer 2 network around 350+ workstation.

In my network i have 10 access layer 2948 switches directely connected to layer 3 switches. When ever any problem in the lan ( incease of stp loop) all link HSRP instance in layer 3 flapping.

is that right way of design. any other idea to contain this layer 2 issue. though i have enabled portfast and loopgurad and root gurad.

still i need to some more help to contain this layer 2 failure.


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lamav Sun, 07/13/2008 - 07:20


You have a couple of options.

If you stay with the Layer 2 access design, you can at least ensure that you implement per-vlan STP in an aggressive manner. It's no secret on how to do this. Just search Cisco's Best Practices web link for STP. You may also want to keep your vlans to a small diameter. IOW, dont span any particular vlan across 10 different switches, if you dont have to. Keep it tight.

Choice 2 is to create a routed access layer with L3 uplinks to a routed distribution/core layer, instead of L2 trunks. There are some restrictions that present themselves when doing this, but it is definitely doable. It's more easily done in a campus environment than it is in a server farm due to the L2 adjacency requirements of NIC teaming and/or bridged load balancing.




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