I recently started getting complaints from a client running VoIP services about lag and jitter. I wasn’t able to correlate the issue with any regular indicators and I have a number of people using VoIP services as a client on the same network who haven’t reported any issues. Looking closer at the router I noticed certain daemons lagging despite a low load average and I could see dmesg was flooded with this message:
ip_ct_ras: decoding error: out of bound
There isn’t exactly a heap of documentation on this situation online but I was able to infer it had something to do with H.323. Doing an lsmod I found:
I know some VoIP setups have to do a little magic to get around conventional NAT but since this network is completely public I assumed it was safe to rmmod these two modules and things seemed to clear up instantly. I’m still not sure how H.323 connection tracking got involved with good-ol-fashioned DMZ public IP routing and would appreciate any insights you VoIP geniuses could provide – especially since the client who complained is using SIP and not H.323.