[Serusers] Strange response

[Jiri Kuthan]

That's spec-compliant SIP behaviour (I'm not telling it is a good idea, I'm
just telling that's what standard mandates). SIP server sends replies to port
numbers advertised in Via, i.e., to 5060, and not to port number from which
the request came.

It was too late understood in SIP WG that this was quite suboptimal. There is
now a bug_fix, which is symmetric signaling. That tells: if UAC likes symmetric
forwarding (i.e., is ready to receive at the port from which it sent), it
needs to advertise so using "rport". UASs understanding that shall send to
origination port number and mirror this in the rport parameter.

To my knowledge, ATAs support symmetric signaling but for some reason don't
advertise it. SER's next release supports symmetric signaling, but you will
need to special-case ATAs (recognize them and enforce symmetric signaling 
even if not advertised using "rport").

-Jiri

ps. see http://www.iptel.org/ietf/firewall/nat/#draft-ietf-sip-symmetric-response

At 09:25 PM 4/1/2003, Bo wrote:
>Hi,
> 
>I have tested cisco ATA186 (private IP) with SER under different circumstances. With Linksys and D-link router, there were no problem. But with Lioncom ADSL router, a strange thing happened. In this case, the ATA is having a private IP 192.168.5.2 and the SIP port number is the default 5060. The public IP of the ADSL connection was 195.226.252.124. The following is the traces from ngrep. As you can see, the Lioncom router forwarded (NAT) the SIP REGISTER with port 30150 while SER sent the response back to port 5060. So the ATA couldn't receive the response at all. What maybe the problem?
> 
>#
>U 195.226.252.124:30150 -> 192.168.3.29:5060
>  REGISTER sip:sip.abc.com SIP/2.0..Via: SIP/2.0/UDP 192.168.5.2:5060..From:  <sip:6701892 at si
>  p.abc.com;user=phone>..To:  <sip:6701892 at sip.abc.com;user=phone>..Call-ID: <mailto:1781909739 at 1>1781909739 at 1
>  92.168.5.2..CSeq: 1 REGISTER..Contact: *..Expires: 0..User-Agent: Cisco ATA  v2.15 ata18x (0209
>  27a)..Content-Length: 0....
>#
>U 192.168.3.29:5060 -> 195.226.252.124:5060
>  SIP/2.0 401 Unauthorized..Via: SIP/2.0/UDP 192.168.5.2:5060;received=195.226.252.124..From:  <s
>  ip:6701892 at sip.abc.com;user=phone>..To:  <sip:6701892 at sip.abc.com;user=phone>;tag=d907c
>  037823644515dfe0ede38ca9976.9b53..Call-ID: <mailto:1781909739 at 192.168.5.2..CSeq>1781909739 at 192.168.5.2..CSeq: 1 REGISTER..WWW-Authen
>  ticate: Digest realm="sip.abc.com", nonce="3e89f40b00000000e3fd8eedb58e5662ca62981749bb0006
>  ", algorithm=MD5..Server: Sip EXpress router (0.8.10 (i386/linux))..Content-Length: 0..Warning:
>   392 192.168.3.29:5060 "Noisy feedback tells: pid=10613 req_src_ip=195.226.252.124 in_uri=sip:s
>  ip.bmx-inc.com out_uri=sip:sip.abc.com via_cnt==1"....
> 
>Thanks,
> 
>Bo

--
Jiri Kuthan            http://iptel.org/~jiri/