[asterisk-users] Lost outgoing SIP packets

[Roel van Meer]

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?

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