Filter
Top Products
BGP: Configuring Route Maps
Page 26 | Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes
BGP: Configuring Route Maps
Route maps are very powerful and flexible entities. Therefore, the configuring of route maps
must, by necessity, be relatively complex. The purpose of this section of the document is to
understand route maps piece by piece and thereby build up a full understanding of how all
the parts fit together.
Structure of a route map
There are various levels of structure within a route map:
A route map is an entity with a name
Each route map consists of multiple entries, identified by sequence numbers
Each entry can consist of multiple clauses
In effect, an entry defines an individual filter. It can have a match clause that defines what it
will match on, and it can have multiple set clauses that can specify actions to be taken. An
update packet is matched against each entry in turn. Once an entry is found that matches the
packet, the action(s) associated with that entry is (are) performed, and no further entries are
considered.
For example, if you create an entry that will permit an update packet, followed by an entry
that would deny that packet, the packet is permitted. As another example, if you create two
conflicting set clauses, in different entries, the first change is applied, not the second.
A route-map consists of an ordered set of entries. Each entry is configured by commands of
the form:
route-map <map-name> permit|deny <sequence number>
<match clause>
<set clause(s)>
There is no need for a command that creates a route-map prior to entries being created in
the route-map. Simply, the first time an entry is created for route-map <name> then that
route-map comes into existence.
The sequence numbers determine the order in which the entries are applied to update
packets. A route-map entry is not required to include a match clause. An entry with no
match clause will match every date packet.
There is an implicit match all filter at the end of the route map. The action on that implicit
entry is deny. By default, any update packet that does not explicitly match any particular
entry in the route map will be dropped.
You can change this by ending the route map with a “permit all” clause, such as the following:
awplus(config)#
route-map <map-name> permit 65535