bad udp cksum ServFail Error

Tue Jul 29 20:52:13 UTC 2008

I have Bind 9.5 p1 running RHEL4 running slave. The Slave is configured with
allow-update-forwarding { any; };.
When I do a ipconfig /registerdns, that does not seems to be updating
master. I think the slave is trying to forward the DDNS traffic to master,
but somehow it seems to failing. The same Windows host works when directly
pointed to Master.

The tcpdump shows [bad udp cksum 8426!]  53702 ServFail q: at the bottom.

I am not sure why it creates bad check sum. Could you please help me
resolve?

Thank you very much!!

~LA