1 Apr
2003
1 Apr
'03
10:48 p.m.
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@si
p.abc.com;user=phone>..To: <sip:6701892@sip.abc.com;user=phone>..Call-ID:
<mailto:1781909739@1>1781909739@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@sip.abc.com;user=phone>..To:
<sip:6701892@sip.abc.com;user=phone>;tag=d907c
037823644515dfe0ede38ca9976.9b53..Call-ID:
<mailto:1781909739@192.168.5.2..CSeq>1781909739@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/