Subject: [Sip] Via maddr

From: Christer Holmberg <[email-masked]>
Date: Wed, 15 Jan 2003 16:01:23 +0200

Hi,

I appologise if this has been discussed before, but at least I didn't
find it in my mail box (I admit I didn't check the archieve on the web).

Anyway...

Chapter 18.2.2 in RFC3261 talks about the routing of responses, using
the Via maddr, received and sent-by parameters.

My question is regarding maddr. When reading the text, I get the picture
that only IP addresses are used in maddr. At least the text doesn't
mention the SRV RFC, which it does for sent-by, and it says that the
default port is 5060. However, the ABNF defines maddr as "host", which
can also be a domain name.

So, is there a bug in the ABNF, or have I missunderstood something?

Regards,

Christer Holmberg
Ericsson Finland

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---

From: "Brett Tate" <[email-masked]>
Date: Wed, 15 Jan 2003 16:25:37 -0500

> I appologise if this has been discussed
> before, but at least I didn't find it in
> my mail box (I admit I didn't check the
> archieve on the web).

I posted a related question to sip-implementors;
however I never got a reply.

http://lists.cs.columbia.edu/pipermail/sip-implementors/2002-October/004052.
html

> Chapter 18.2.2 in RFC3261 talks about the
> routing of responses, using the Via maddr,
> received and sent-by parameters.
>
> My question is regarding maddr. When reading
> the text, I get the picture that only
> IP addresses are used in maddr. At least the
> text doesn't mention the SRV RFC, which it does
> for sent-by, and it says that the default port
> is 5060. However, the ABNF defines maddr as
> "host", which can also be a domain name.

maddr can be a domain name.  The text appears
to disable the ability to perform an SRV query
associated with the Via maddr.  However I never
got an answer concerning if this was intentional.

---

From: Christer Holmberg <[email-masked]>
Date: Fri, 24 Jan 2003 20:44:27 +0200

Any comments on this?

Regards,

Christer Holmberg
Ericsson Finland

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 24 Jan 2003 17:02:27 -0500

The intent of 18.2.2 is indeed NOT to use the SRV processing. In fact, 
if you look at 18.1, the only way that the maddr gets set is through 
multicast, and thus the intent is that maddr is really for multicast. 
THis need not be an IP address, since DNS names can refer to multicast 
addresses (sip.mcast.net).

Originally, the maddr in the URI was the same - meant just for 
multicast. However, in the absence of a suitable loose routing 
mechanism, it got continually abused until the common case was for that, 
and not for multicast at all. Doing that properly required SRV 
processing. Now, we have thankfully deprecated the usage of maddr for 
that purpose, but older rfc2543 elements might construct such URIs, and 
so RFC3263 continues to perform the SRV processing for the maddr in the 
request URI, when present.

Thus the asymetry.

-Jonathan R.

-- 
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