Let’s have the following scenario:
Both nodes are connected through the internet, here in my
example, using private IP.
On the Cisco device, Fa0/0 is the WAN interface with the following
configuration:
|
interface Tunnel1
description TO-LINUX-SERVER
ip address 192.168.10.2 255.255.255.252
ip mtu 1436
tunnel source Fastethernet 0/0
tunnel destination 172.16.0.2
|
Where tunnel source is the IP of the Cisco router, tunnel
destination is the IP of the Linux server and 192.168.10.2 is the IP of the
tunnel.
On the Linux server ETH0 is the WAN interface which connected
to the internet
|
modprobe ip_gre
ip tunnel add gre_tun0 mode
gre remote 10.0.0.2 local 172.16.0.2 ttl 255
ip tunnel ls
ip link ls dev gre_tun0
ip link set gre_tun0 up
ip link ls dev gre_tun0
ip addr add 192.168.10.1/30
dev gre_tun0
ip addr ls dev gre_tun0
ifconfig gre_tun0 mtu 1380
|
Modeprobe runs the module for GRE; ip tunnel creates the
tunnel with gre_tun0 as the name for the tunnel. Remote and local are the same
as source and destination.
In order to configure the GRE tunnel permanently and to make
sure it will be configured after reload of the server use the following:
|
Vi /etc/rc.local
|
And add the configuration to the file:
|
#!/bin/sh
#
# This script will be
executed *after* all the other init scripts.
# You can put your own
initialization stuff in here if you don't
# want to do the full Sys V
style init stuff.
touch /var/lock/subsys/local
modprobe ip_gre
#GRE Tunnel CONFIG
modprobe ip_gre
ip tunnel add gre_tun0 mode
gre remote 10.0.0.2 local 172.16.0.2 ttl 255
ip tunnel ls
ip link ls dev gre_tun0
ip link set gre_tun0 up
ip link ls dev gre_tun0
ip addr add 192.168.10.1/30
dev gre_tun0
ip addr ls dev gre_tun0
ifconfig gre_tun0 mtu 1380
~
~
~
~
~
"/etc/rc.local"
32L, 1051C
|
Don’t forget to type wq! to save the file.
Remember that GRE stands for General Routing Encapsulation
and It’s not encrypting or protecting the data from eavesdrop eyes. The encapsulation itself adds 24 bytes to the
IP packet and (4 bytes for the GRE protocol and 20 bytes for one more IP
header)
