[ S N O M 4 S N A T F I L T E R ]
2.3 SBC Behaviour
2.3.1 Registering
When a user agent registers, it puts its IP address in the top Via. If the user agent is on public Internet or properly supports NAT, this Via will match the perceived IP address. In this case the SBC does not interfere with the registering process and just forwards this packet to the registrar.
If the top Via does not contain the perceived address, the SBC will take care of the request. It will replace the provided contact with a locally generated contact and forward the request to the registrar (see below).
REGISTER sip:snomag.de SIP/2.0
Via: SIP/2.0/UDP 203.145.183.113:12975;branch=z9hG4bK- abx3au3mxb01;rport
From: <sip:denny@snomag.de>;tag=k9p6fmeg7h
To: <sip:denny@snomag.de>
CSeq: 14 REGISTER
Contact: <sip:denny@203.145.183.113:12975;line=lhynyb3y>;q=1.0
Supported: gruu
Expires: 86400
REGISTER sip:snomag.de SIP/2.0
Via: SIP/2.0/UDP
Via: SIP/2.0/UDP 203.145.183.113:12975;branch=z9hG4bK- abx3au3mxb01;rport=17401
From: <sip:denny@snomag.de>;tag=k9p6fmeg7h
To: <sip:denny@snomag.de>
CSeq: 14 REGISTER
Contact: <sip:217.115.141.99:5082;ua=c9b140ab59829bb491e9c3aaca440>
Supported: gruu
Expires: 86400
SIP/2.0 200 Ok
Via: SIP/2.0/UDP
2.
