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Mango
Use DMZ and you get a kick in the dick.
Premium Member
join:2008-12-25
www.toao.net

Mango to RonR

Premium Member

to RonR

Re: Is SIP ALG a good solution for NAT?

It's in Conntrack/Netfilter, but it only appears in some builds of Tomato. Indeed, Tomato is an excellent router for VoIP, when SIP ALG is disabled.
RonR
join:2003-10-10
Ash Flat, AR

RonR

Member

said by Mango:

It's in Conntrack/Netfilter, but it only appears in some builds of Tomato. Indeed, Tomato is an excellent router for VoIP, when SIP ALG is disabled.

I see a SIP checkbox under Tracking / NAT Helpers, but I have a hard time believing that's the dreaded SIP ALG. I've been running this version (TeddyBear) for over a year with that box checked and I haven't had a single router related hiccup with 3 ATA's hung off of it.
Mango
Use DMZ and you get a kick in the dick.
Premium Member
join:2008-12-25
www.toao.net

Mango

Premium Member

Good point. All I know about that option is that it makes SIP connections time out after an hour, and not respect the UDP Timeout settings. This is bad if you're affected by the Tomato bug that causes NAT associations to be mangled. I'm not sure what else it does, if anything.
RonR
join:2003-10-10
Ash Flat, AR

RonR

Member

said by Mango:

Good point. All I know about that option is that it makes SIP connections time out after an hour, and not respect the UDP Timeout settings. This is bad if you're affected by the Tomato bug that causes NAT associations to be mangled. I'm not sure what else it does, if anything.

Could this problem have been fixed in v1.28? I was on a 1 hour and 42 minute call yesterday (using SipBri no less) and everything stayed glued together perfectly.
Mango
Use DMZ and you get a kick in the dick.
Premium Member
join:2008-12-25
www.toao.net

Mango

Premium Member

I don't think I explained that clearly. I didn't mean phone conversations would cut off after an hour. When your phone registers with a VoIP server, the router keeps the "NAT hole" open for typically the length of the Assured UDP timeout. This way, the VoIP server may deliver incoming calls to you. As long as the phone's registration interval is less than the Assured UDP Timeout, everything will work properly.

With SIP Helper turned on, the router will not respect the Assured UDP Timeout and instead uses 3600 seconds. This means that your phone has one hour to re-register and will possibly make Linksys devices workish with their default settings.

The reason this is not optimal is that if for example your ISP changes your public IP address, it could potentially take an hour before you can receive incoming calls, or worse, it could require human intervention to reboot things if you're affected by the bug I mentioned before.

Obviously if things work well for you then there's no need to tinker with anything. My point was that my opinion is the same as the general opinion in this thread - leave my SIP alone!

m.

SpaethCo
Digital Plumber
MVM
join:2001-04-21
Minneapolis, MN

SpaethCo

MVM

said by Mango:

With SIP Helper turned on, the router will not respect the Assured UDP Timeout and instead uses 3600 seconds. This means that your phone has one hour to re-register and will possibly make Linksys devices workish with their default settings.

Is that really a problem?

I think the longest refresh interval I've seen a provider use is maybe 10 minutes. The majority are in the 60-120 second ballpark.