Adding a static route to a virtual interface using configuration files rather than ip command

Question

We statically assign our routes using the /etc/sysconfig/network-scripts/route-ethx files. This makes managing them fairly easy since we add the routes during the kickstart process (by way of post-script). They rarely change and if they need to be updated we simply push out a change and update the build scripts to include the new route.

Recently, we had a customer ask for a virtual interface (eth0:0) with a unique IP. It needs to connect exclusively to one network. The first assigned IP on eth0 will handle all other traffic.

Everything I've seen states how to add a route using ip route add, however I can't sort out how to specify that anything going to a particular IP or network can have the source IP set. If I use the ip command will it update the route files or is it stored elsewhere for persistence across reboots? If I have to add the entry to the route file for eth0:0 what should the line look like?

So basically:

If it goes to 10.0.0.2 use IP 10.0.1.3 as the source. If it goes anywhere else use IP 10.0.1.2 as the source.

Is this possible? How do I accomplish it?

score 1 · Accepted Answer · edited Oct 31 '18 at 15:14

1

If I understand clearly your question, you could try something like the following

# ip route add 10.0.0.2 via xxx.xxx.xxx.xxx src 10.0.1.3
# ip route add default via yyy.yyy.yyy.yyy src 10.0.2.2

Is there another method I need to look into?

You could try to use iptables

# iptables -t nat -I PREROUTING -d 10.0.0.2 -j SNAT --to-source 10.0.1.3

edited Oct 31 '18 at 15:14

Community

1

answered Aug 29 '13 at 17:17

ALex_hha

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I had the examples wrong. The IPs are on the same subnet (10.0.1.2 and 10.0.1.3). This was my mistake and obviously would lead to a different answer than I was looking for. The 'via' option is clearly for expressing the gateway to use and with the corrected examples is not effective. That said, the 'src' option appears to get me closer to what I need. I ran the following `ip route add 10.0.0.2 src 10.0.1.3 dev eth0:0` but got the File exists message due to the default route already essentially handling this traffic. Is there another method I need to look into? – theillien Aug 29 '13 at 17:50

score 0 · Answer 2 · answered Aug 30 '13 at 14:05

This was clarified by a colleague who had done the same thing recently.

The format for the one route to be entered into the route-eth0:0 file is:

10.0.0.2/32 via 10.0.1.1 dev eth0:0 src 10.0.1.3

All other traffic through eth0 will be tagged as being from 10.0.1.2 by default. 10.0.1.1 is the default route, but the packets will have a source IP that is properly tagged.

Adding a static route to a virtual interface using configuration files rather than ip command

2 Answers2