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[ 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>
Call-ID: 3c26701d7cb9-pady07b5783t@203-145-183-113
CSeq: 14 REGISTER
Max-Forwards: 70
Contact: <sip:denny@203.145.183.113:12975;line=lhynyb3y>;q=1.0
Supported: gruu
Expires: 86400
Content-Length: 0
REGISTER sip:snomag.de SIP/2.0
Via: SIP/2.0/UDP 217.115.141.99:5082;branch=z9hG4bK-e8d1feb8138c3d85
0637ced821ef40a3;ua=c9b140ab598290e5bb491e9c3aaca440
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>
Call-ID: 3c26701d7cb9-pady07b5783t@203-145-183-113
CSeq: 14 REGISTER
Max-Forwards: 69
Contact: <sip:217.115.141.99:5082;ua=c9b140ab59829bb491e9c3aaca440>
Supported: gruu
Expires: 86400
Content-Length: 0
SIP/2.0 200 Ok
Via: SIP/2.0/UDP 217.115.141.99:5082;branch=z9hG4bK-e8d1feb8138c3d85
2.