26 Oct
2005
26 Oct
'05
11:10 a.m.
Hello Phillipp,
the problem exposed by you here is somehow similar to the topic
discussed on devel(a)openser.org in the mail thread "Processing REGISTER
requests".
Mainly is how to attach a resource to a contact address and identify it
properly (in this case is the tcp connection). Since we have all over
NATs, we cannot rely on the contact address. The latest version of
openser stores in the usrloc database the associated NAT ip and port
along with contact address. This is not enough when you have multiple
levels of NATs (e.g., two different networks with same private IPs being
visible from outside behind same nat - this gets a conflict when same
user has phones in both networks).
It is clear that in your case you have to keep the tcp connection open
for the whole call. The problem is how to identify the connection from
the contact address. We have to address this soon and find the proper
solution for this case as well as for usrloc.
Cheers,
Daniel
On 10/26/05 12:51, Alexander Ph. Lintenhofer wrote:
Hi All,
I just wanted to ask you once again about the TCP-alias riddle. I
found out, that there is a problem with the combination of
fix_nated_contact(), force_tcp_alias() and NAT:
Imagine following situation:
Alice behind NAT: socket 172.16.0.6:2421
Nat-Box translates this to 192.168.0.13:6007
The Outbound-Proxy of Alice is 192.168.0.1
Bob is registered with 192.168.1.1
1.)
Her INVITE:
====================================================================
INVITE sip:bob@192.168.1.1:2331;transport=tcp;line=wxqurd1s SIP/2.0
[...]
Via: SIP/2.0/TCP 172.16.0.6:2421;received=192.168.0.13;
branch=z9hG4bK-wm9jcstcboys;rport=6007
From: "Alice" <sip:alice@atlanta.com>;tag=sufzmxi0us
To: "Bob" <sip:bob@biloxi.com>;tag=c9550czwtn
[...]
Contact: <sip:alice@172.16.0.6:2421;transport=tcp;line=fyyuh6tl>
[...]
====================================================================
2.)
fix_nated_contact() doesn't work with TCP (look at nathelper.c).
force_tcp_alias() now creates following tuple as TCP-alias:
192.168.0.13:6007 to 192.168.0.13:2421
Reason:
The TCP-alias is not built solely from the Via-header as suggested in
the draft. The portnumber is taken from the Via-header and the
IP-address is taken from the source of the incoming datagram. I read
it in the sourcecode and assured it by contacting Andrei!
3.)
So as a result of the notfixed Contact-header of Alice's INVITE the
BYE of Bob is addressed to 172.16.0.6:2421. But no TCP-alias exists
for this socket :-(
4.)
I made following test by rewriting the Contact-header....
====================================================================
if (method=="INVITE")
{
replace("Contact: <sip:alice@172.16.0.6:2421;transport=tcp;",
"Contact: <sip:alice@192.168.0.13:2421;transport=tcp;");
}
====================================================================
...with success. Now TCP-alias works as you can see on my
Ethereal-trace below!
Compare the destination port of the packet to the destination port of
the RURI!
====================================================================
[...]
Transmission Control Protocol, Src Port: 5060 (5060), Dst Port: 6007
(6007), ...
Session Initiation Protocol
Request-Line: BYE
sip:alice@192.168.0.13:2421;transport=tcp;line=fyyuh6tl SIP/2.0
Message Header
[...]
From: "Bob" <sip:bob@biloxi.com>;tag=kcsveifugd
To: "Alice" <sip:alice@atlanta.com>;tag=ricaq5cy15
Contact: <sip:bob@192.168.1.1:2331;transport=tcp;line=wxqurd1s>
[...]
====================================================================
Another solution:
Comment the lines in nathelper.c which force the return in case of TCP
or TLS. Now all works well!
But why??????????????
regards,
Philipp
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