kdump problem

Hi,
I tried to use kdump to dump core to NFS drive. In kdump.conf file I
have
net 10.2.3.6:/mnt/rdisk
When I start the kdump service on client, it said it started OK and it
created dir for /mnt/rdisk/var/crash on server side. However when I do
`echo "c" > /proc/sysrq-trigger`, the client dies but there is nothing
on server (just empty dir). Is there any way to debug this?
.