[OpenSIPS-Users] Weird behaviour when replying to an OPTIONS with a Cseq of 0

[Eric Tamme]

obscuring the ip/hostnames in this makes it difficult to troubleshoot - 
please dont do that in the future.

I am not certain the CSeq is the issue.  I believe that the contact is 
broken, aka it contains localhost, so when opensips tries to route it, 
it fails on udp_send: sendto.

Again, this is my guess, but since you have manipulated and obscured the 
complete sip trace it makes it difficult to confirm.

-Eric

On 07/06/2016 10:44 AM, Karolis Pabijanskas wrote:
> Hi List,
>
> We seem to be hitting a strange behaviour when we get an OPTIONS ping 
> with a Cseq of 0. (latest 1.11 branch).
>
> Our routing script contains this at the very beginning to decline 
> OPTIONS messages:
> route {
>     if (is_method("OPTIONS")) {
>         sl_send_reply("501", "Method not allowed");
>         exit;
>     };
>    ## blah...
> }
>
> If we send this OPTIONS request:
>
> 2016-07-06 17:12:05 +0100 : CLIENT_IP:5061 -> OPENSIPS_IP:5060
> OPTIONSsip:200 at HOSTNAME:5060 SIP/2.0 Via: SIP/2.0/UDP 
> 127.0.0.1:5061;branch=z9hG4bK-895-1-0 From: sipp 
> <sip:100 at 127.0.0.1>;tag=1To: <sip:200 at HOSTNAME:5060> Call-ID: 
> 1-895 at 127.0.0.1CSeq: 0 OPTIONSContact: 
> sip:100 at 127.0.0.1:5061Max-Forwards: 100 Content-Length: 0
>
> There is no reply from OpenSIPS. Interestingly, siptrace module is 
> also running and saving captures in Homer. Homer, actually, is getting 
> a copy of the generated reply:
> 2016-07-06 17:12:05 +0100 : OPENSIPS_IP:5060 -> CLIENT_IP:5061
> SIP/2.0 501 Method not allowed Via: SIP/2.0/UDP 
> 127.0.0.1:5061;received=*CLIENT_IP*;branch=z9hG4bK-895-1-0 From: sipp 
> <sip:100 at 127.0.0.1>;tag=1To: 
> <sip:200 at HOSTNAME:5060>;tag=06a366df8881a48001f15f72f7138d9f.7522 
> Call-ID: 1-895 at 127.0.0.1CSeq: 0 OPTIONS Server: User Agent String 
> Content-Length: 0
> But running a tcpdump on the OpenSIPS host reveals that no actual 
> packet is ever sent to the client. Debug shows:
> Jul  6 17:40:25 HOSTNAME /sbin/opensips[48357]: ERROR:core:udp_send: 
> sendto(sock,0x7f7867aee470,324,0,0x7fff77d00090,16): Operation not 
> permitted(1)
> Jul  6 17:40:25 HOSTNAME /sbin/opensips[48357]: ERROR:sl:msg_send: 
> udp_send failed
>
> OpenSIPS is running as root.
>
> Switching Cseq to 1 in that original OPTIONS message works. But in 
> this particular case we have no control over the Cseq of the host we 
> are being pinged from, and need to reply. According to the RFC, Cseq 
> should be a 32bit unsigned integer, so 0 should not be an issue.
>
> Any ideas?
>
> Thanks!
> Karolis
>
>
>
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