Thanks for your answers.
I thought I could make an example with your suggestions, for documentation (I
see others are interested at the moment).
Using add_contact_alias, when the 200 OK for an INVITE is received, e.g. from
10.0.9.49:61756:
SIP/2.0 200 OK
[...]
Contact: <sip:giacomo@10.0.9.49:61750;transport=tcp>
add_contact_alias detects that received ip:port is different than the one in
the Contact, so it appends an alias before relaying the 200 OK:
SIP/2.0 200 OK
[...]
Contact: <sip:giacomo@10.0.9.49:61750;alias=10.0.9.49~61756~2;transport=tcp>
This will then be used when generating the ACK:
ACK sip:giacomo@10.0.9.49:61750;alias=10.0.9.49~61756~2;transport=tcp SIP/2.0
[...]
which Kamailio will change with handle_uri_alias(), removing the alias and
setting the received ip:port as destination:
ACK sip:giacomo@10.0.9.49:61750;transport=tcp SIP/2.0
sent correctly to 10.0.9.49:61756.
With fix_nated_contact, same scenario, Kamailio would modify the Contact before
relaying the 200 OK:
SIP/2.0 200 OK
[...]
Contact: <sip:giacomo@10.0.9.49:61756;transport=tcp>
Which will then be used as R-URI for the ACK:
ACK sip:giacomo@10.0.9.49:61756;transport=tcp SIP/2.0
[...]
And sent without modifications to 10.0.9.49:61756.
As stated in other references, the difference is that with the
add_contact_alias approach the invited client sees its published Contact in the
ACK's R-URI.
I hope this is useful.
Regards,
Giacomo
From: Klaus Darilion [mailto:klaus.mailingli...@pernau.at]
Sent: 11 March 2012 13:10
To: SIP Router - Kamailio (OpenSER) and SIP Express Router (SER) - Users
Mailing List
Cc: Giacomo Vacca
Subject: Re: [SR-Users] Best approach for TCP/TLS connection re-use for nated
Contacts
Am 09.03.2012 20:56, schrieb Giacomo Vacca:
One of the solutions I've found is using always add_contact_alias() in
onreply_route when handling the 200 OK, and then use handle_ruri_alias() when
defining the destination for the ACK.
Yes, that the pragmatic approach I always use. IMO it is also a bit of
security. I do not like to blindly trust user provided data (e.g. contact
header), thus I always use the IP:port from where the message was received.
regards
Klaus
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