[Nanog] VoIP over Asymmetric routing

Tim Eberhard xmin0s at gmail.com
Mon Apr 21 03:01:20 CDT 2008

If there are any firewalls in the path they tend to dislike asymmetric
routing(just standing the obvious)..

It tends to play hell on the VoIP ALG's and can cause them to eat
CPU/Hang/Crash depending on what vendor you have.

This assumes that you have a firewall in the network path. Other items that
would concern me is link utilization (What if one network link became
completely saturated?)

>From a application stand point most VoIP systems will do ok with asymmetric
routing RTP doesn't *need* to be symmetric but I would have concerns of
designing it to be asymmetric out of the gates.

Just my 2 copper.

Tim Eberhard

On Mon, Apr 21, 2008 at 1:34 AM, Kim Onnel <karim.adel at gmail.com> wrote:

> Hello,
> We are going to roll out a network to carry VoIP only, between the P
> routers, there will be 3xOC3 links.
> Each site has 2xPEs, PE1 is connected to the P router in the local
> premises
> with 10GE and PE2 is connected with 2xOC3s to remote P sites for backup
> incase local P fails.
> VoIP is going to be generated by Ericsson Media Gateways and the network
> designers are suggesting to take traffic in the outgoing direction through
> the PE1 path and come back through the PE2 path (if that makes sense), so
> traffic will take a different link for outgoing over incoming.
> >From your experiences, I am wondering what are future unforeseen pitfalls
> we
> can get into?
> Regards,
> KO
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