How to create a GRE tunnel on Linux

Last updated on December 1, 2020 by Dan Nanni

GRE tunnels are IP-over-IP tunnels which can encapsulate IPv4/IPv6 and unicast/multicast traffic. To create a GRE tunnel on Linux, you need ip_gre kernel module, which is GRE over IPv4 tunneling driver.

So first make sure that ip_gre is loaded.

$ sudo modprobe ip_gre
$ lsmod | grep gre

ip_gre                 22432  0
gre                    12989  1 ip_gre

Here, we assume that you want to create a GRE tunnel between two interfaces with the following IP addresses.

• Host A: 192.168.233.204
• Host B: 172.168.10.25

On host A, run the following command.

$ sudo ip tunnel add gre0 mode gre remote 172.168.10.25 local 192.168.233.204 ttl 255
$ sudo ip link set gre0 up
$ sudo ip addr add 10.10.10.1/24 dev gre0

In the above, we create a GRE-type tunnel device called gre0, and set its remote address to 172.168.10.25. Tunneling packets will be originating from 192.168.233.204 (local IP address), and their TTL field will be set to 255. The tunnel device is assigned IP address 10.10.10.1 with netmask 255.255.255.0.

Now verify that route for the GRE tunnel is set up correctly:

$ ip route show

default via 135.112.29.1 dev eth0  proto static
10.10.10.0/24 dev gre0  proto kernel  scope link  src 10.10.10.1

On host B, run similar commands as follows.

$ sudo ip tunnel add gre0 mode gre remote 192.168.233.204 local 172.168.10.25 ttl 255
$ sudo ip link set gre0 up
$ sudo ip addr add 10.10.10.2/24 dev gre0

At this point, a GRE tunnel should be established between host A and host B.To verify that, from one tunneling end point, ping the other end point.

On host A, run:

$ ping 10.10.10.2

PING 10.10.10.2 (10.10.10.2) 56(84) bytes of data.
64 bytes from 10.10.10.2: icmp_req=1 ttl=64 time=0.619 ms
64 bytes from 10.10.10.2: icmp_req=2 ttl=64 time=0.496 ms
64 bytes from 10.10.10.2: icmp_req=3 ttl=64 time=0.587 ms

If you want to tear down the existing GRE tunnel, run the following command from either end.

$ sudo ip link set gre0 down
$ sudo ip tunnel del gre0

Support Xmodulo

This website is made possible by minimal ads and your gracious donation via PayPal or credit card

Please note that this article is published by Xmodulo.com under a Creative Commons Attribution-ShareAlike 3.0 Unported License. If you would like to use the whole or any part of this article, you need to cite this web page at Xmodulo.com as the original source.