[asterisk-users] Lost outgoing SIP packets

[Andres]

On 3/31/16 7:34 AM, Roel van Meer wrote:
> Hi list!
>
> I have a problem where SIP packets sent by Asterisk do not hit the 
> wire, and I don't know what could cause this.
>
> I'm running Asterisk 1.8.28_cert5 with full SIP debug. At the same 
> time, I'm doing a tcpdump of the traffic on the network interface. I 
> can see in the SIP debug log that asterisk is sending packets. Most of 
> the time, I can see those packets in the tcpdump, as you would expect.
> However, sometimes Asterisk sends a packet that *does not show up* in the
> tcpdump. Asterisk then does several retransmits (that also don't show 
> up).
> The next packet that is not a retransmit does show up again.
>
> This causes Asterisk to log the peer it was sending packets to 
> temporarily as Lagged or unreachable.
>
> There is no outgoing firewall on this box.
>
> Could anyone give me some pointers where to look?
>
A word of advice.  I have been stumped before with tcpdump not showing 
all packets.  It turns out that the kernel can indeed prevent packets 
from being captured if it is overwhelmed.   The first sign of trouble is 
when you hit control-C when finishing up tcpdump and get messages like 
'kernel dropped X packets'.  It turns out tcpdump by default tries to do 
reverse DNS queries on all IPs and simply does not have enough time 
under high packet loads.  The solution is generally to run "tcpdump -nn" 
to avoid DNS lookups.
> If Asterisk logs "VERBOSE[13019] chan_sip.c: Reliably Transmitting 
> (NAT) to x.x.x.x:" you would expect to see that packet in a tcpdump 
> trace, right? What could cause this not to be so? Are there network 
> statistics I could look at? Is there a counter in /proc or /sys for 
> problems with sending packets? Anything?
>
> If more information is necessary please do let me know.
>
> Thanks a lot in advance,
>
> Roel
>


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