VOIP etc > Voice Over IP - VOIP > VOIP Tech Chat > Downsides of double NAT for VOIP

Downsides of double NAT for VOIP

reply to JoeSchmoe007
Double NAT can work properly; the only problem is it adds an additional point of failure that may make troubleshooting more difficult. Instead of troubleshooting one router, now you have to troubleshoot two. Also, now you have double the chances of one of the routers having a corrupted NAT table. If both routers are VoIP-friendly and stable, it should theoretically work (as the other posters have mentioned.)

On the other hand I've done double NAT with a Tomato router behind a D-Link router. That was a recipe for failure.

The D-Link router in question was one of a few that has a bug that classifies normal internet traffic as "attack traffic" and blocks it. This manifested occasionally as ~30 seconds of no audio. The problem wasn't specifically related to the double-NAT but it took me a while to figure it out because I wasn't sure which router was causing the problem.

Double the NAT, double the FUN

As Mango said, two very well behaved routers will probably work. Otherwise you amplify the bad behaviors of both and get call setup or audio issues.

reply to JoeSchmoe007
It should be fine. I had one client who would daisy chain vonage adapters. I think at one point they had up to 4 devices daisy chained to each other.
--
»www.reverse.net

reply to JoeSchmoe007

reply to Mango
I know that this is an old thread, but do you think that setting up a second router would cause problems if you put the settings on the first router in DMZ and in addition to that manually disable anything what could block traffic, thus letting the first router just as pass through?

Note that the ISP may use NAT as well, so some people may be multinatting without even knowing it. Doing traceroutes, I see that my ISP is using both the 10.x.x.x and the 172.16.x.x ranges, so they are using NAT to build out their whose subscriber base. For all I know, since I see both private address ranges, they may even be doing double NATting before it gets to me. And then I use NAT to the 192.168.x.x space for my own distribution.

PS: My VoIP works like a charm.

reply to JoeSchmoe007
I have on occaision done double NAT with no issues. All my routers are Netgear.

reply to Ole Juul

Now, yes, this is mobile VoIP. But it is pertinent to this thread because of NAT.

Now, with AT&T cellular data service, you have a LOT of NAT.
Even before you get out to non-AT&T IP space (e.g. anything other than 12.x.x.x), you've already crossed about 7 or 8 NAT boxes.

Between me on AT&T and Callcentric, there are about 22 hops, and 10 or so are just AT&T 10.x.x.x, 172.x.x.x and 12.x.x.x IP ranges.

This is why mobile VoIP worked so horribly on AT&T, they had awful latency because of all the stupid NAT boxes and it took 10 hops just to get onto the Internet (120ms was a good day, a bad day was 200ms and constant switching between H+ H and 3G all the time).

This is why I moved to Sprint yesterday. Mobile VoIP has never worked so great before!

With Sprint, there are about 20 hops, just like AT&T, and they do use NAT (with weird 66.87.x.x and 66.29.x.x public IPs), however the big difference is there's no stupid constant 'stepping down' to and from 3G and HSDPA all the time (that killed the latency and constant connections).

The other difference is the latency. On Sprint, 80-90ms is pretty much all the time, at least around here. I'm perfectly willing to sacrifice speed (AT&T's big draw) for better latency (arguably, Sprint's draw).

reply to Trev

reply to XANAVirus