Port Assignments

224.0.1.75 SIP                                       [Schulzrinne]

DNS SRV

SIP clients use DNS SRV records if available. A sample DNS zone file entry is shown below:

sip.tcp         SRV 0 0 5060 sip-server.cs.columbia.edu.
                SRV 1 0 5060 backup.ip-provider.net.
sip.udp         SRV 0 0 5060 sip-server.cs.columbia.edu.
                SRV 1 0 5060 backup.ip-provider.net.

According to RFC 2782, the protocol designations are to be prefixed by an underscore, so that the correct entries are:

_sip._tcp         SRV 0 0 5060 sip-server.cs.columbia.edu.
                  SRV 1 0 5060 backup.ip-provider.net.
_sip._udp         SRV 0 0 5060 sip-server.cs.columbia.edu.
                  SRV 1 0 5060 backup.ip-provider.net.

DNS SRV records are supported by BIND 4.9.6 and newer, generally installed as named. Configuring named for Linux is discussed in a HOWTO.

Some currently registered SRV records (at DNS server cs.columbia.edu):

_sip._tcp.cs.columbia.edu   SRV 20 0 5060 backbay.cs.columbia.edu
_sip._tcp.cs.columbia.edu   SRV 0 0 5060 conductor.cs.columbia.edu
_sip._tcp.cs.columbia.edu   SRV 10 0 5060 erlang.cs.columbia.edu
_sip._udp.dynamicsoft.com   SRV 0 0 5060 dyn-tx-app-006.dfw.dynamicsoft.com

Use, for example,

host -v -t srv sip.tcp.cs.columbia.edu cs.columbia.edu
host -v -t srv sip.udp.cs.columbia.edu cs.columbia.edu
host -v -t srv _sip._udp.cs.columbia.edu cs.columbia.edu

NAPTR Records (RFC 3263)

An example is:

IN NAPTR 50  50  "s"  "SIPS+D2T"   ""   _sips._tcp.cs.columbia.edu.
IN NAPTR 60  40  "s"  "SIP+D2U"    ""   _sip._udp.cs.columbia.edu.
IN NAPTR 60  60  "s"  "SIP+D2T"    ""   _sip._tcp.cs.columbia.edu.

Status Code List

Compact Header Forms

Last updated by Henning Schulzrinne