Policy-based routing

Policy-based routing allows you to route traffic by information other than just the destination IP address. It lets you route packets differently depending on the source IP and port, destination IP and port, and protocol. For example, you could match UDP or ICMP traffic and route it to a different network, or you could ensure that traffic exits via the same gateway where it arrived.

Use a custom routing table Jump to heading #

Normally, routing rules are grouped together into a default collection called the main routing table. To route IP packets differently depending on the source address, destination address, and/or protocol, you’ll create a custom routing table. By defining a selector that matches the traffic you want to affect, you can apply your custom routing table and the rules it contains only to matching packets.

1. In the Services tab, click network setup to display the current configuration of your network interfaces.

   

2. Add a rule through the following syntax:

   text
   ip rule <selector> <action>

   text
   ip rule <selector> <action>

   For example, to have traffic exit by the same default gateway where it entered:

   text
   service network eth1
     ip address       10.20.10.15/24
     ip rule  from    10.20.10.0/24  table 10
     ip route default 10.20.10.1     table 10

   text
   service network eth1
     ip address       10.20.10.15/24
     ip rule  from    10.20.10.0/24  table 10
     ip route default 10.20.10.1     table 10

   where:

   • The ip address line sets a static IP address for the interface.
   • The ip rule line uses the from argument to indicate that traffic that has a source IP in the range 10.20.10.0/24, including your application’s VIP, will use the rules defined in the custom routing table 10.
   • The ip route line adds a single rule to that table, which sets the default route to 10.20.10.1.

   Note that you do not need to specify an add argument to add a rule, such as ip rule add, but just ip rule, since adding the line implies adding it, and deleting the line removes it.

   In a custom routing table, you can also add IP static routes. And you can add policy-based routing to VLAN and bonded interfaces.

3. Click OK and Close.

4. On the Services tab, click Apply.

5. To make your changes persistent after a reboot, click the Setup tab. Then click Save under Configuration.

Verify your setup Jump to heading #

To verify that your changes took effect:

1. Go to the Tools tab and click Launch terminal.

2. Check that the rule exists:

   nix
   ip rule list

   nix
   ip rule list

   output
   text
   0:      from all lookup local
   32765:  from 10.20.10.0/24 iif eth1 lookup 10
   32766:  from all lookup main
   32767:  from all lookup default

   output
   text
   0:      from all lookup local
   32765:  from 10.20.10.0/24 iif eth1 lookup 10
   32766:  from all lookup main
   32767:  from all lookup default

3. Check that the custom routing table contains the route. Here we are checking table 10:

   nix
   ip route show table 10

   nix
   ip route show table 10

   output
   text
   default via 10.20.10.1 dev eth1

   output
   text
   default via 10.20.10.1 dev eth1

See also Jump to heading #

• The online Linux manual describes the syntax of ip rule.