SIP IPV6Reference

Question

RFC3261 states:

host             =  hostname / IPv4address / IPv6reference
IPv6reference  =  "[" IPv6address "]"

I'm interested in what was the design decision by using IPv6reference for host rather than just IPv6address. Why does it have to be wrapped in brackets? What does it refer to?

Via received uses pure IPv6 rather than a reference. So I assume there is a purpose of IPv6reference which I would like to know.

Answer 1

For the technical side it is the SIP flavor of RFC2732:

   This document incudes an update to the generic syntax for Uniform
   Resource Identifiers defined in RFC 2396 [URL].  It defines a syntax
   for IPv6 addresses and allows the use of "[" and "]" within a URI
   explicitly for this reserved purpose.

Via received uses pure IPv6 rather than a reference. So I assume there is a purpose of IPv6reference which I would like to know.

Basically, it allows to safely handle SIP URI with ipv6 literal addresses and esp cut/paste, see RFC 2396:

   The goal is to have a format that allows easy "cut" and
   "paste" operations with a minimum of editing of the literal address.