[asterisk-dev] Via/maddr: (was Re: [Code Review] Properly route responses according to the Via headers in the request)

Olle E. Johansson oej at edvina.net
Mon Jan 3 03:09:00 CST 2011

3 jan 2011 kl. 09.51 skrev Klaus Darilion:

>> I have no examples of maddr, but here's the one from the RFC:
>> Via: SIP / 2.0 / UDP first.example.com: 4000;ttl=16;maddr= ;branch=z9hG4bKa7c6a8dlze.1
>> Since this has a ttl value, the maddr is supposed to be multicast.
> Btw: Has anybody ever seen usage of maddr or can describe to me what it is useful for? I always thought I'm quite familiar with SIP, but still I do not understand why maddr is needed at all.
In the bug tracker, you can find examples of a broken Nortel system that doesn't send a valid hostname or IP in the via header, but use maddr to define a port. To me, that seems broken but valid. 

I had a discussion with Iñaki about maddr in via headers and we suggested that someone should write an RFC called "via maddr considered harmful". That why I want to be able to disable support of it. Using multicast is very uncommon and I don't want other systems to tell me where to send responses. 


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