27 Oct
2005
27 Oct
'05
7:06 a.m.
Hi Alexander,
sound like a solid reason. It means that the solution will be to allow
fix_nated_contact() for TCP based protos.
any other suggestions?
regards,
bogdan
Alexander Philipp Lintenhofer wrote:
Hi Bogdan,
This is the answer, Andrei gave me:
"....ser aliases only the ports, it never adds an alias for an IP
(security risk)....."
I think, he means TCP-hijacking in the case of a modificated/malformed
via-header.
regards,
Philipp
Hi Alexander,
indeed, it seams you have case. Even if the draft says that the alias
tuple must include the VIA ip:port, currently the IP is considered as
received IP. Why? not sure (is Andrei's work), but I can speculate on
the overhead introduce in getting the address from via and convert it
to IP (via may contain DNS name which should be resolved!).
If we go ahead on this road, right, you need a way to set the NAT IP
in the contact -> use fix_nated_contact() which does not support TCP
:D. I do not like this approach because the alias is a mixture
between the NAT IP and the inside port :/
If we go as the draft says, and use via ip:port we have to face the
need of performing DNS lookup only to generate the alias ....this is
even uglier and more dangerous. and also we will end having private
IPs in RURIs and in aliases..which is a little bit tricky - a private
IP is not unique ;).
so, I would say the best way is the first one....and to allow
fix_nated_contact() also for TCP/TLS.........
regards,
bogdan
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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