How to use <user>@<domain> instead of <user>@<ip> ?

[oliv]

Hello,

Lately, I wondered if I could configure a Yealink phone to use a domain name instead of an IP address, in the domain part of a SIP URI.

I picked a v84-enabled T42S phone and successively set :
account.1.sip_server.1.address = ipbx1.foobar.lan
account.1.sip_server.1.address = ipbx1
account.1.sip_server.1.address =192.168.1.1

Each time my server (an Asterisk instance) receives INVITEs or REGISTERs built with:
REGISTER sip:192.168.1.1:5060 SIP/2.0

I would expect the above line to be respectively:
REGISTER sip:ipbx1.foobar.lan:5060 SIP/2.0
REGISTER sip:ipbx1:5060 SIP/2.0
REGISTER sip:192.168.1.1:5060 SIP/2.0

Am I misunderstanding how SIP must work or is it something that can be configured ?

Best regards

[jolouis]

I think you're mis-understanding the purpose of domain names. From a general perspective their purpose is simply to give "human readable/understanable names" to IP addresses on a network/the internet.

When SIP devices communicate with each other, they always use IP addresses for the actual packets sent back and forth. If you configure a domain name for the server address, all that means is that the phone will resolve the domain to it's corresponding IP address before sending packets out.

[oliv]

OK then.

On a side note, from rfc3261 it self, you can read the following example:
INVITE sip:bob@biloxi.com SIP/2.0

From it, I thought one could literally find domain names in SIP URIs.

Thanks for replying

[jolouis]

(01-21-2019 10:06 AM)oliv Wrote:  On a side note, from rfc3261 it self, you can read the following example:
INVITE sip:bob@biloxi.com SIP/2.0

From it, I thought one could literally find domain names in SIP URIs.

Technically that's possible, but all it means is that the underlying network stack is doing the DNS/address resolution and not showing it to the application layer.

It's like opening a web browser and typing in "www.yealink.com" in the address bar. When you do that, your computer uses DNS to translate "yealink.com" into an IP address, but you as the user don't see that happen.

Same thing with SIP packets. The difference is that most SIP applications (i.e. the client running on the Yealink phones, or the PBX itself) don't expect end users to be watching the actual packets/requests flowing back and forth, so for coding efficiency purposes they do the translation directly and encode the IPs into the packets instead of the domains.

Probably more of an answer/explanation than you were looking for, but hey too much info is always better than too little ;o)