Technical Tip: Offset Lists with RIP

By default, the FGT-A learns the route for 4.4.4.4/32 with a metric of 2 as the destination is 2 hops away.

FGT-A # get router info routing-table all

Routing table for VRF=0

S*      0.0.0.0/0 [10/0] via 10.5.191.254, port1, [1/0]

R       4.4.4.4/32 [120/2] via 10.156.18.30, port5, 00:01:22, [1/0]

R       5.5.5.5/32 [120/2] via 10.156.18.30, port5, 00:09:20, [1/0]

On FGT-B, the offset value for the metric is set to 8. As a result, the FGT-A gets the route with the metric value of 10 (8+2).

FGT-B # show  router  rip

config router rip

    config network

        edit 1

            set prefix 10.156.0.0 255.255.192.0

        next

    end

    config offset-list

        edit 1

            set access-list "4.4.4.4/32"

            set offset 8

        next

    end

    config redistribute "connected"

        set status enable

    end

FGT-A # get router info routing-table all

Routing table for VRF=0

S*      0.0.0.0/0 [10/0] via 10.5.191.254, port1, [1/0]

R       4.4.4.4/32 [120/10] via 10.156.18.30, port5, 00:00:10, [1/0]

R       5.5.5.5/32 [120/2] via 10.156.18.30, port5, 00:32:54, [1/0]

An offset list can purge the route by setting the offset value that makes the metric greater than 15. The maximum hop count is 15, therefore route to 4.4.4.4/32 becomes inaccessible.

FGT-B (1) # show

config offset-list

    edit 1

        set access-list "4.4.4.4/32"

        set offset 15

    next

end

Routing table for VRF=0

S*      0.0.0.0/0 [10/0] via 10.5.191.254, port1, [1/0]

R       5.5.5.5/32 [120/2] via 10.156.18.30, port5, 07:50:31, [1/0]

Distribute List vs Offset List.

• A distribute-list permits or denies a particular prefix to be advertised out or accepted. It does not touch its metric.
• An offset-list increases the metric of a particular prefix by a specified amount. It does not prevent the prefix from being advertised or accepted.