[OpenSIPS-Users] How to overcome SIP ALG on Wi-Fi routers

[Bogdan-Andrei Iancu]

You can check it in the pcap - if an UDP packet is fragmented into 
multiple IP packets, you have some fragmentation flag set into the IP 
header (see 
https://www.cs.nyu.edu/courses/fall98/G22.2262-001/class11.txt, look for 
"fragmentation" ).

Also, at SIP level, you may check if the advertised Content-Length 
matches the actual length of the body - if the body is shorter than 
advertised in Content-Len, it means the UDP packet is fragmented .

Regards,

Bogdan-Andrei Iancu
OpenSIPS Founder and Developer
http://www.opensips-solutions.com

On 06.05.2016 20:11, Nabeel wrote:
>
> Can packet fragmentation be verified (to be sure that it is packet 
> fragmentation)?
>
> On 6 May 2016 5:28 pm, "Nabeel" <nabeelshikder at gmail.com 
> <mailto:nabeelshikder at gmail.com>> wrote:
>
>     The trace I posted earlier is what I see with tcpdump when
>     attempting a call. There is no other INVITE shown in the trace:
>     http://pastebin.com/raw/C4iymTbh
>
>     The trace seems to end abruptly in the middle of the SDP, so I
>     think it could be due to packet fragmentation.
>
>     On 6 May 2016 4:18 pm, "Bogdan-Andrei Iancu" <bogdan at opensips.org
>     <mailto:bogdan at opensips.org>> wrote:
>
>         So that meas the INVITE never gets to the callee ?? maybe it
>         is not properly routed .
>
>         Do you see (with ngrep or tcpdump) the INVITE being sent out
>         by opensips towards callee ?
>
>         Regards,
>
>         Bogdan-Andrei Iancu
>         OpenSIPS Founder and Developer
>         http://www.opensips-solutions.com
>
>         On 06.05.2016 12:56, Nabeel wrote:
>>
>>         Hi,
>>
>>         Thanks for the idea about packet compression. By 'call fails
>>         to connect', I meant the call does not connect to the callee,
>>         ie. the callee's phone does not ring after the INVITE
>>         (despite using TURN server).
>>
>>         This was a public WiFi network and that was all I could get
>>         at the time. I am using OpenSIPS version 2.1.
>>
>>         Nabeel
>>
>>         On 6 May 2016 9:16 am, "Bogdan-Andrei Iancu"
>>         <bogdan at opensips.org <mailto:bogdan at opensips.org>> wrote:
>>
>>             Hi,
>>
>>             Hard to analyze a call based on the INVITE packet only
>>             :). Still the SIP signaling does not show any ALG
>>             interference (also not sure if the capture was done
>>             before or after the ALG). Also, what you mean by "call
>>             fails" ?no reply, negative reply , no audio ?
>>
>>             Regards,
>>
>>             Bogdan-Andrei Iancu
>>             OpenSIPS Founder and Developer
>>             http://www.opensips-solutions.com
>>
>>             On 05.05.2016 22:35, Nabeel wrote:
>>>
>>>             Please check the following SIP trace taken within a WiFi
>>>             network. The call fails to connect despite the INVITE
>>>             request and using a non-standard port. Could this be
>>>             caused by SIP ALG, or some unopened RTP port on the router?
>>>
>>>             http://pastebin.com/raw/C4iymTbh
>>>
>>>
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>>
>

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