[Serusers] DNS Lookup and other issue

Alex Mack amack at fhm.edu
Fri Apr 15 16:22:53 CEST 2005


Hi Mohammad!

>If I setup an UA with URL sip:beeplove at mydomain.org
>my client is going to find its sip server from DNS SRV record, right?
>
Yes.

>If I have these in nameserver
>_sip._udp               SRV     0 0 5060        sip.mydomain.org.
>_sip._tcp               SRV     0 0 5060        sip.mydomain.org.
>
>is that mean, sip.mydomain.org is my registar server?
>or proxy server or both?
>  
>
First, it just means it's a SIP Proxy. What it does is a different thing 
and can't be determined by the SRV record alone. It could be e.g. your 
entry proxy which passes REGISTERS on to another proxy being the 
registrar and passing INVITES to a server farm.

>And If my UA have an option to specify proxy and registar server, UA is not
>going to lookup SRV record, right?
>  
>
Yes, the SRV entries are only looked up by an external UA or proxy if it 
wants to determine the proxy it'll have to send, e.g., its INVITE to in 
order to reach your UA. It would strip the host-part of its r-uri and do 
a SRV lookup for _sip._udp.mydomain.org.
 It's similar to SMTP: your own mailclient gets the full DNS name (A 
record) of your SMTP-server, but other SMTPs are looking up the 
MX-record of your domain (SRV records are a means of providing 
"MX-records", so to speak, for different services)

Alex Mack




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