Layer 2 vs Layer 3 design for VOIP

Unanswered Question
Feb 28th, 2007


We are currently in the process of implementing a Nortel IPT solution into a greenfield site. The switching infrastructure will all be Cisco - 4500's in the access-layer and 6500's collapsed distribution/core.

I am thinking of running layer 3 from the access-layer for fast convergence, equal cost load balancing. This is new for us as all our existing designs use layer 2 from access-layer but none of them have VOIP.

I am interested on any views on this and any pros or cons to this approach.

Many thanks


I have this problem too.
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AJAZ NAWAZ Wed, 02/28/2007 - 02:39


Are you proposing per-packet l/balancing or are you going to rely on CEF?

You will be aware an end-to-end VoIP call uses RTP/UDP and I believe there is a in-built re-ordering mechanism within this process. Therefore if packets arrive and are not hugely out of order/sequence there will not be an issue. However, if for some reason whatever that maybe - packets travel in a grossly non-symetrical fashion and arrive badly out of sequence, this it will degrade the call quality there is no doubt.

CEF LB is the way to go in a converged enterprise end user network imo.

Does this answer your qtn?


Ajaz Nawaz

Jon Marshall Wed, 02/28/2007 - 03:13


thanks for the reply. I was going to use CEF and use per destination load balancing.

Really i was more interested to try and find out what the current trend was for deploying a converged network in terms of layer 2 or layer 3 and the pros and cons of either.



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