Static IPv4 routes can be defined on specific interfaces using route sections. As for aliases, multiple sections can be attached to an interface. The route sections are stored in the uci file /etc/config/network.

A minimal example looks like this:

config 'route' 'name_your_route'
        option 'interface' 'lan'
        option 'target' '172.16.123.0'
        option 'netmask' '255.255.255.0'
        option 'gateway' '172.16.123.100'

• lan is the logical interface name of the parent interface
• 172.16.123.0 is the network address of the route
• 255.255.255.0 specifies the route netmask

To disable a route quickly, the option enabled is not available. Just rewrite the route config section as disabled_route like:

config 'disabled_route' 'name_your_route'
        ...lines...

and it will be recognized by the uci parser but not applied by the /etc/init.d/network script.

It seems that on openwrt 12.09 if a route is defined using a gateway in an address space where a gateway is already defined, it will be not added. Like the lan has the gateway 192.168.1.1 and we want to go to 1.2.3.4 over the gateway 192.168.1.5 within the interface lan, it will not be added. Could be added through ip route commands tough.

IPv6 routes can be specified as well by defining one or more route6 sections.

A minimal example looks like this:

config 'route6'
        option 'interface' 'lan'
        option 'target' '2001:0DB8:100:F00:BA3::1/64'
        option 'gateway' '2001:0DB8:99::1'

• lan is the logical interface name of the parent interface
• 2001:0DB8:100:F00:BA3::1/64 is the routed IPv6 subnet in CIDR notation
• 2001:0DB8:99::1 specifies the IPv6 gateway for this route