[OpenSIPS-Users] Incorrect callid in ACK

[Mark Farmer]

Hi John, many thanks for this!!

I have actually removed all instances of fix_nated_contact() from OpenSIPS2
and my problem is solved :)

Anyone setting up OpenSIPS as a Teams SBC - do not use fix_nated_contact()
(even with NAT in place) as it will break your ACK's!

Mark.


On Thu, 10 Jun 2021 at 20:42, John Quick <john.quick at smartvox.co.uk> wrote:

> Mark,
>
> I think I know what is going on here.
> By a lucky coincidence I was testing two OpenSIPS servers back to back in a
> very similar setup to yours.
> Today I converted one of them to use Topology Hiding, (partly to try to
> help
> you but it was something I wanted anyway).
> After converting it to use Topology Hiding, I got an error that looks very
> similar to yours and I think the solution to my problem is quite likely to
> be the solution for you too.
>
> Background: See my article below about Contact header fixing and look for
> the section "When is it wrong to fix a Contact header?"
>
> https://kb.smartvox.co.uk/opensips/nat-contact-and-via-fixing-in-sip-part-3/
> It specifically refers to the case of two SIP proxies back-to-back.
>
> What I found today is that Topology Hiding makes this problem much harder
> to
> spot because the fixed Contact header will never appear in a SIP trace such
> as you get in sngrep.
> Instead, what you see in the sip trace is the usual hashed id substituted
> by
> the TH module. It makes debugging very confusing.
>
> When the 200 OK arrives at your 2nd OpenSIPS Proxy from your 1st OpenSIPS
> Proxy, are you calling fix_nated_contact() in onreply_route?
> If you are, I'd wager that's your problem. You must not fix the Contact
> header because you are receiving the 200 OK from another proxy.
>
> You could design a fix based on checking the source address of the reply,
> but alternatively it may also be possible to insert a more generalised
> solution in onreply_route.
> On your 2nd OpenSIPS Proxy (the one using Topology Hiding), I think some
> code like this might work:
>   if (is_present_hf("Record-Route"))
>       xlog("Found a Record-Route header.   Not going to fix Contact\n");
>   else {
>       if (nat_uac_test(65)) {
>           fix_nated_contact();
>           xlog("Fixing Contact\n);
>       } else
>           xlog("No need to fix Contact header.  Its alright anyway\n");
>   }
>
> John Quick
> Smartvox Limited
>
>

-- 
Mark Farmer
farmorg at gmail.com
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