How to set default route for the VPN

April 10, 2019 439 views
VPN Ubuntu 16.04

I have been able to set up a site-to-site IPSec/IKEV1 VPN between a CISCO gear and my droplet at DO. The VPN is up. But there is not traffic. When I do a simple ping on the remote Private IP from my droplet, I get nothing:

ping 192.168.100.213
PING 192.168.100.213 (192.168.100.213) 56(84) bytes of data.
^C
--- 192.168.100.213 ping statistics ---
21 packets transmitted, 0 received, 100% packet loss, time 20159ms

But if I try to ping the remote Private IP by specifying the interface to use as *eth1, I can reach it smoothly :

ping 192.168.100.213 -I eth1
PING 192.168.100.213 (192.168.100.213) from 10.XXX.XXX.XXX eth1: 56(84) bytes of data.
64 bytes from 192.168.100.213: icmp_seq=1 ttl=63 time=169 ms
64 bytes from 192.168.100.213: icmp_seq=2 ttl=63 time=168 ms
^C
--- 192.168.100.213 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 168.838/169.150/169.462/0.312 ms

How can I solve that ?
It feels like when I’m trying to reach out, the default interface is eth0.
Is there a way to change the default interface ? or is there a configuration that can help me tell that all the packets that are coming from my private IP of the droplet must pass trough eth1 ?

2 Answers
jarland MOD April 10, 2019
Accepted Answer

Greetings!

This is a great question. I really like nixCraft’s guide for adding routes, and I think it can help you in your situation:

https://www.cyberciti.biz/faq/linux-route-add/

I think the most noteworthy part of their guide is where they give the example for “Route all traffic via 192.168.1.254 gateway connected via eth0 network interface.” I would paste it here but they deserve the ad revenue from a visit :)

Jarland

Thanks very much. That answer helped me pinpoint correctly where was my mistakes implementing that VPN. I ended up implementing the routing with iptables : “`iptables -t nat -A POSTROUTING -j SNAT -o eth0 –destination 192.168.XXX.XXX –to-source 10.MYP.RIV.ATE

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