Linux Dial-In Server, packets not being sent / received

Hi all,

I'm trying to set up a Linux machine to allow connections from remote sites via a 56K modem. The current interfaces in the server are:

eth0 100.100.100.10, gw 100.100.100.1, subnet 255.255.255.0      Connects to the ISDN router for internet access
eth1 100.100.101.1, subnet 255.255.255.0            The local network

Now, I've sucessfully set up mgetty and ppp to accept the incoming connection, ppp0. The remote client gets an appropriate IP address (100.100.102.2) and the server binds ppp0 to an appropriate IP address (100.100.102.1).

The connection establishes sucessfully, and both client and server can ping their own PPP IP Address sucessfully, but from the client side (win2k), a ping to the server results in a "Request Timed Out" and from the server side (Debian Linux) I get the error:

"ping: sendmsg: Operation not permitted"

/usr/sbin/ppp is SUID root, and all the appropriate /etc/ppp files are user root, group dip.

All users who should be able to access the dial-in are in the group dip.

So, have I missed something obvious (or not so obvious?), or is there any other suggestions for why packets aren't being sent or received?

Thanks in advance,

Stephen Sherlock