GRE Tunnelling from Linux to Cisco

[Darryl Harvey <dharvey connect com au>]

I was poking around the kernel configuration options earlier today and 
noticed the mention of GRE tunnelling.

I have a few Cisco's placed around and thought it would be great if I could 
create GRE tunnels between my linux boxes and Cisco routers to make a VPN.

Is this possible??  Can some one point me to any info for this?  I have 
searched a little, but always come across PPTP and/or IPSec and I don't 
want that.

Just GRE (As in Cisco GRE) would be fine.


Thanks
Darryl