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Filtering IP Routes 2-23

Software Version 2.7.5

C613-10454-00 REV A

Applying Filters When Redistributing from

the RIB

The router or switch is able to import routes from the RIB into BGP, OSPF or

RIP, even if it learnt them from a different routing protocol or source. For

example, you can add non-BGP routes to BGP, such as static routes and routes

learned by OSPF or RIP. BGP can then advertise these routes.

When you import routes from some route sources, you can also filter, to block

certain routes. Most of the filtering options use route maps, so you can also

give the imported routes certain characteristics, such as changing their metric.

Note that the route map must match on characteristics that are relevant for the

routes you are importing. For example, if you are importing routes into BGP,

you cannot match on AS path or community. These attributes are not relevant

to non-BGP routes.

This section focuses on how to filter routes. The router or switch also

automatically imports interface routes into OSPF, but cannot filter the routes.

Filtering when copying routes to BGP

BGP can import routes from OSPF and RIP, as well as statically-configured and

interface routes. You can use route maps to filter routes from any of these

sources. The router or switch uses the route map to filter routes and/or set

attributes when it imports the routes into BGP. The following table shows how

to filter routes from each source.

From To filter

OSPF 1. For finest control, tag each OSPF route you want to import into BGP, by

creating a route map and applying it to OSPF routes. Use the commands:

add ip routemap=routemap entry=1..4294967295

action={include|exclude} match [match-options]

add ip routemap=routemap set tag=1..65535

set ospf inroutemap=routemap

2.Create another route map to use when importing into BGP. Match on

nexthop, prefixlist or tag.

3. Apply the route map, using the command:

add /jointfilesconvert/427458/bgp import=ospf routemap=routemap

RIP 1. Create a route map, matching on nexthop or prefixlist

2. Apply the route map, using the command:

add /jointfilesconvert/427458/bgp import=rip routemap=routemap

Interface

routes

1. Create a route map, matching on nexthop or prefixlist

2. Apply the route map, using the command:

add bgp import=interface routemap=routemap

Static

routes

1. For finest control, tag each route you want to include, using the command:

set ip route=ipadd interface=interface mask=mask nexthop=ipadd

tag=1..65535 [other-options]

2. Create a route map, matching on nexthop, prefixlist or tag

3. Apply the route map, using the command:

add bgp import=static routemap=routemap

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