Asynchronous routing and VOIP

[Douglas Bradfield]

I have been getting mixed information about asynchronous routing and VOIP phones having problems. Our network is redundant everything. Dual WAN circuits, dual routers, switches, etc. And running a dynamic routing protocol you will inevitably have asynchronous routing. We have a couple hundred phones traversing this network and others through firewalls to get to the PBX/Gateways, other phones, remote gateways, etc. It has been like this for a few years with 95% of the time no issues. Rarely we have the dropped call and static issues. When we do have those issues I hear "asynchronous routing" is the culprit. I need some guidance and verification of what I need to look at or disregard when encoutering this.

Thanks

Doug

[Dennis Mink]

please provide us with some more technical details, like a network diagram, specifically details on the path that you are having problems with. I dont think it is a good idea to assume "asynchronous routing" (BTW you probably mean asymmetric routing were a traffic flow uses different paths to and from a destination), is an issue. It is better to have an open mind and diagnose your problem with the information that you can gather.    thanks

[paolo bevilacqua · Accepted solution]

As mentioned above. You mean asymmetrical routing.

That is fine, as long there are is no blocking elements like firewall, NAT, etc. When you have these, you may have problems. The best design avoid their use completely.

[Douglas Bradfield]

You are correct, I meant asymmetric routing based on minkdennis definition. I agree it is the best practice but it is not a show stopper. Thank you both for your help.

[rkenny1976]

Hi Paolo, thanks for taking the time to respond to the users question. I was just wondering why you say to avoid NAT? Could it be that once the translation completes, something gets blocked and hence asynchronous routing (increased latency, blocked connections, etc.) then occurs? The reason I ask, earlier today, we swapped an EOL/EOS 2911/K9 with an 1101. My boss gets the whole network team on a call to troubleshoot after a ton of our sites lost connectivity to the Verizon MPLS Network (Think regional outage) that were traversing through each DMNR router/Modem on our network. We think it was a configuration error on the 1101 router, because non of the EIGRP Advertised Routes showed any issues and my boss kept saying "Asynchronous routing is the issue". We replaced the old 2911, and the network normalized once again, we are having the 1101 shipped to the lab for further analysis. My question to you is, what exactly is asynchronous routing, and could NAT (which is being done at that site) be the ultimate culprit? What are some things we could check so this hopefully doesn't happen again? Any help is much appreciated sir! Take care

[Roger Kallberg]

Asynchronous routing is when the traffic takes one path in one direction and another in the other direction.

NAT is for the most a thing that should be avoided in VoIP setups. For the reason that the IP information is kept within the SIP packages and needs to be rewritten at a deeper level than what a regular NAT would do. This can be made to work with extra effort, but in general it’s better to avoid it if possible.

[rkenny1976]

Awesome sir! Thank you for taking the time to respond and explaining that to me. Happy holidays and all the very best!!