How to set an additional route on the same gateway with systemd-networkd

Question

Due to some network peculiarities involving VPNs and conflicting IP ranges, I have two subnets routing to two different interfaces. I would like to make one IP address in one subnet go out via a different gateway.

I can accomplish this by running:

$ route add -host 1.2.3.4 gw 5.6.7.8
$ ip route show
1.2.3.4 via 5.6.7.8 dev eth0 scope link 

I would like to make this change permanent. As I'm using systemd-networkd, I am trying to do this by updating the existing /etc/systemd/network/50-dhcp.conf:

[Match]
Name=eth0

[Network]
DHCP=ipv4

[Route]
#Gateway=5.6.7.8
Destination=1.2.3.4/32

This works, but without the Gateway line it doesn't set the route:

$ ip route show
1.2.3.4 dev eth0 proto static scope link

If I uncomment the Gateway line then the new route does not appear at all!

How can I specify a gateway when adding the static route using systemd-networkd?

Answer 1

Can't say I know what the fix was, but after upgrading to systemd version 242 the problem went away and it now works, when you list both the Gateway and Destination options.

Answer 2

You should look at this post:

What is the best way to add a permanent route?

It explains how you should:

1. Create a named routing table, in the case below the routing table is called "mgmt" and gets the number "200".

   echo '200 mgmt' >> /etc/iproute2/rt_tables
   

   • Originally the /etc/iproute2/rt_tables file looks like this, with some reserved numbers:

     #
     # reserved values
     #
     255     local
     254     main
     253     default
     0       unspec
     #
     # local
     #
     

2. The post goes on specifying how to add the routes:

   Below, a Debian 7/8 interfaces file defines eth0 and eth1. eth1 is the 172 network. eth0 could use DHCP as well. 172.16.100.10 is the IP address to assign to eth1. 172.16.100.1 is the IP address of the router.

   source /etc/network/interfaces.d/*
   
   # The loopback network interface
   auto lo
   iface lo inet loopback
   
   # The production network interface
   auto eth0
   allow-hotplug eth0
   # iface eth0 inet dhcp 
   # Remove the stanzas below if using DHCP.
   iface eth0 inet static
     address 10.10.10.140
     netmask 255.255.255.0
     gateway 10.10.10.1
   
   # The management network interface
   auto eth1
   allow-hotplug eth1
   iface eth1 inet static
     address 172.16.100.10
     netmask 255.255.255.0
     post-up ip route add 172.16.100.0/24 dev eth1 src 172.16.100.1 table mgmt
     post-up ip route add default via 172.16.100.1 dev eth1 table mgmt
     post-up ip rule add from 172.16.100.10/32 table mgmt
     post-up ip rule add to 172.16.100.10/32 table mgmt
   

Reboot or restart networking.

Thanx to user Christopher for this answer.