[SIPForum-discussion] SIP and IPv4 mapped IPv6 addresses

[Kevin P. Fleming]

Prashantm at digilink.in wrote:

> Assume that one IPv4 user agent is communicating with one IPv6 user
> agent. As per RFC 2553 - section 3.7, when the IPv6 server is listening
> on 0::0 and port 5060 and it receives a UDP packet over IPv4, linux
> kernel understands that the packet came from IPv4 device. So it informs
> server with a IPv4 mapped IPv6 address of the destination. But still the
> SIP packet will be IPv4.
> 
> My question is which is the case when SIP packet will have IPv4 mapped
> IPv6 addresses? I want to know the use case of IPv4 mapped IPv6
> addresses in SIP.

Imagine a B2BUA, that is on an dual-stack host and listening on an IPv6
socket. If it receives a INVITE from an IPv4 host, the media addresses
in the SDP will be IPv4 addresses. If the B2BUA then sends an INVITE to
an IPv6 host, and wants to have the media routed directly between the
endpoints, it would provide IPv4-mapped IPv6 addresses in the SDP sent
to the IPv6 endpoint, so that that endpoint would be able to send media
directly to the IPv4 endpoint.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
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