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2.3 Filter Behaviour
2.3.1 Registering without UA Support
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 filter does not
interfere with the registering process and just forwards this packet.
If the top Via does not contain the perceived address, the filter
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: “denny” <sip:[email protected]>;tag=k9p6fmeg7h
To: “denny” <sip:[email protected]>
Call-ID: 3c26701d7cb9-pady07b5783t@203-145-183-113
CSeq: 14 REGISTER
Max-Forwards: 70
Contact: <sip:[email protected]:12975;line=lhynyb3y>;q=1.0
User-Agent: snom200-2.03w
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: “denny” <sip:[email protected]>;tag=k9p6fmeg7h
To: “denny” <sip:[email protected]>
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
User-Agent: snom200-2.03w
Expires: 86400
2.
