Hi! Today, I wanted to share about the things that I have learned by tunneling between Ras Pi and a router through GRE. At first, I was trying GRE on packet tracer but it didn't work for some reason. So I decided to instead work on physical devices which were available at the moment. I will share some of key commands for setting up GRE on Ras Pi. For the router, you will find many resources online for setting up GRE on a cisco router😅.
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ sudo ip tunnel add gre1 mode gre remote 172.168.10.25 local 192.168.233.204 ttl 255
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ ip tunnel list
gre0: gre/ip remote any local any ttl inherit nopmtudisc
gre1: gre/ip remote 172.168.10.25 local 192.168.233.204 ttl 255
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ sudo ip addr add 10.10.10.1/24 dev gre1
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ sudo ip link set gre1 up
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ sudo ip addr add 192.168.233.204/24 dev eth0
The process of setting up GRE is the same for both Ras Pi and a router, only difference is the commands😎. Once done with the above set up, you have to configure the route for both the physical interface connected to the router and the virtual tunnel interface. Below is the route table.
┌──(kali㉿kali-raspberry-pi)-[~]
└─$ sudo ip route
default via 192.168.85.77 dev wlan0 proto dhcp src 192.168.85.76 metric 600
10.10.10.0/24 dev gre1 proto kernel scope link src 10.10.10.1
172.168.10.25 dev eth0 scope link
192.168.85.0/24 dev wlan0 proto kernel scope link src 192.168.85.76 metric 600
192.168.233.0/24 dev eth0 proto kernel scope link src 192.168.233.204
Here 10.10.10.0/24 is the network for the tunnel and 172.168.10.25 is the address of the router's physical interface connected to Ras Pi. When I was working on tunneling yesterday, I couldn't figure out why ping was failing after setting up the tunnel. It was the route info that was missing🤣. See you in the next post!