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Re: [reSIProcate] How does a client build a DNS lookup that restr icts the responses to UDP?

In 4.1, the "Otherwise" at the beginning of the third paragraph applies to the rest of sec 4.1. If the transport is specified, we skip the meat of 4.1 entirely, and never perform a NAPTR lookup. In 4.2, it says that if we didn't do any NAPTR processing in 4.1 (note the extra "because a transport was specified explicitly") , we synthesize an SRV to look up.

Best regards,
Byron Campen

Good deal.  I missed that in the RFC.  On another look at sec. 4.1, I see it
doesn't say to not use NAPTR if the transport is specified but the port is
not.  Rather, I see it just says to use NAPTR if neither the transport or
port are specified.  So, if the transport is specified, it just uses the
default SRV for _sip._udp?  If there's a line that explictly says how this
works regarding the default SRV record, that will help.

Thanks, yall have helped a lot.
Dave


-----Original Message-----
From: Byron Campen [mailto:bcampen@xxxxxxxxxxxx] 
Sent: Thursday, December 07, 2006 1:07 PM
To: Dave Mason
Subject: Re: [reSIProcate] How does a client build a DNS lookup that restr
icts the responses to UDP?

This is the behavior specified in RFC 3263, so DNS admins should be
expecting it (although 3263 can be a little tricky to wade through).

Best regards,
Byron Campen

Hi, I just found a quick followup...

I find that if I do a lookup with a URI such as 
"sip:user@xxxxxxxxxx;transport=udp", the library ignores the NAPTR 
records and chooses the _sip._udp.<domain.com> SRV record.  Thus, if 
the DNS response has a NAPTR with a different preference for UDP such 
as _sip2._udp.<domain.com>, it will be ignored in favor of the 
default.

Is this a known condition that DNS admins will take into account, or 
should I first do a lookup without it, and search those results for 
UDP transports?
If none are found, then I do a lookup with ";transport=udp"  
appended to
guarantee a UDP response?  (I hate to do two lookups if I don't need 
to.) What's the proper way to use the library (DnsInterface class) for 
this case?

Regards,
Dave


-----Original Message-----
From: Byron Campen [mailto:bcampen@xxxxxxxxxxxx]
Sent: Tuesday, December 05, 2006 5:04 PM
To: Dave Mason
Subject: Re: [reSIProcate] How does a client build a DNS lookup that 
restricts the responses to UDP?

Well, you can always do sip:user@xxxxxxxxxx;transport=udp. Also, if 
your stack doesn't support TCP, it should use UDP instead. Lastly, if 
there are no TCP SRVs in DNS, you should also get UDP results.

Best regards,
Byron Campen

Hi,

I find that if a DNS server is set up with NAPTR records for a domain 
that specify TLS/TCP is most preferred, then TCP, the UDP last, and a 
client does a DNS lookup for sip:user@xxxxxxxxxx (through 
DnsInterface), the DNS server only returns records for TLS/TCP.

How do you configure the lookup on the client side to ask for only 
UDP records, even if they are least preferred on the server?

Regards,
Dave
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