User's Manual

Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes | Page 47
Other Uses of Route Maps
Other Uses of Route Maps
Route maps are used in some contexts other than filtering routes. Let us look briefly at some
of the other contexts in which they are used.
neighbor default-originate
The command neighbor default-originate instructs BGP to send a default route to a neighbor.
This command includes a parameter for specifying a route map.
The route map parameter specifies criteria that must be fulfilled before the switch will
advertise the default route to the neighbor. This lets you configure the switch so that it only
acts as the default gateway for a neighbor if it has learned a route that makes it a suitable
default gateway for that neighbor.
Specifically, the switch must have learnt a route that matches the permit criteria in the route
map. If the switch does not know of any routes that match the permit criteria in the route
map, then it will not advertise the default route.
neighbor unsuppress-map
When the aggregate-address command is used with the summary-only option, the more
specific routes of the aggregate are suppressed to all neighbors. If you want to selectively leak
some more-specific routes to a particular neighbor, then this is achieved by using the
command neighbor unsuppress-map.
A required parameter on this command is the route map that specifies the set of more-
specific routes to leak. Any route that matches permit criteria in the route map will be
leaked.
network
The network command is used in BGP to selectively redistribute particular routes. Instead of
saying “redistribute all static routes” or “redistribute all connected routes”, the network
command says “redistribute this particular route”. Of course, the route has to be in the
routing table before it can be redistributed, so the network command does not say “always
import this route in BGP”, it says “if this route is in the routing table, then import it into
BGP”.
As with other acts of redistribution, the network command has an optional route map
parameter. This lets you set attributes on the route advertised by the network command.
You could use the route map for filtering the network, but it would be a little pointless to
even configure the redistribution of this network if the associated route map simply dropped
the route.
show ip bgp
The show ip bgp command takes an optional route map parameter. The effect of specifying
the route map on the command is that the output shows information only on routes that
match permit criteria on the route map.