[Kamailio-Users] Extra byte in Content-length header

[Vikram Ragukumar]

Hello,

Just following up. Here is a link to a screen capture from Wireshark 
that shows the extra byte in the Content Length header field of the
Register message.

http://signalogic.com/images/SMC7004VWBR_UDP_payload_with_SIP_message_gets_modified.jpg

We use an SMC7004VWBR router, but tech support at SMC said the router 
does not support SIP. Has anybody else seen a router make such a mod to 
a SIP message ?

Thanks and Regards,
Vikram.

Vikram Ragukumar wrote:
> Iñaki,
> 
> Thank you for your response.
> 
>> You could be behind a fu***** SIP-ALG enabled router rewritting SIP 
>> requests "to fix the NAT".
>> To detect if you router has SIP-ALG enabled you can try various options:
>> 1) Ensure you are not using STUN in your client so the request 
>> arriving to the proxy should contain client private address in Via and 
>> Contact header.
> 
> I have checked the Via and Contact headers and they do contain the 
> client private address. I am using an SMC7004VWBR wireless router thats 
> about 8 years old. I have checked all the router settings and do not see 
> any option to enable/disable SIP ALG, so i presume the router is not 
> capable of rewriting SIP headers.
> 
> I will try your program out as another method of confirmation of the 
> router's SIP ALG capability.
> 
> I have found that this anomaly (extra byte in Contact-Length 
> header)occurs only while sending to the proxy on a specific port(5060). 
> By changing the port on which the proxy listens(7160), the 
> Contact-length header field is ok.
> 
> Is there a list of routers out there that we know for sure that are not 
> SIP ALG capable ?
> 
> Once again, thanks for you suggestions.
> Regards,
> Vikram.
> 
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