[OpenSIPS-Users] Checksum incorrect maybe caused by "UDP" checksum offload

[Stanisław Pitucha]

2009/9/8  <Ghaith.ALKAYYEM at telecom-bretagne.eu>:
> The mysterious point is that all packets orginating from the interface
> (192.168.20.20) towards UAC(192.168.20.1) have Bad checksum in the UDP
> level.

If you're capturing at the machine that has the 192.168.20.20
interface, then everything is ok. You're seeing wrong checksum on your
traces because it's calculated on your network card instead - so when
you capture the packet the checksum is probably still filled with
zeros.
Just ignore it, or disable the highlighting of bad checksums. If you
disable the offloading, you'll see the result you expect, but you'll
also give your CPU a bit more work on every packet, so for RTP that's
impacting both latency and throughput.