Route Maps

Route Maps
Route maps can be used to filter as well as manipulate BGP routes. A route map is made
up of a sequence of conditions. A sequence in a route map is composed of the following
command:
route-map name {permit | deny} [sequence-number]
name - the name of the route map. All sequences in a route map must
have the same value for the name.
sequence-number - specifies the position of the condition.
After this command is entered, you will enter route map configuration mode. This may be
a mode of the router that you have not experienced. In this mode, you will configure the specific
conditions for the particular sequence of the route map. The conditions consist of match and
set commands. The match command is used to specify the criteria for the sequence. The set
command specifies the action that will occur if the condition defined by the match statement is
met. A route map can match on any of the following match statements:
As you can probably tell, there are quite a few conditions that can be matched. Covering all
of these different match conditions is beyond the scope of this study guide. We will visit the most
relevant throughout the rest of this section and in Chapter 10, “Route Optimization.”
match as-path Used to match a BGP autonomous system path access list.
match community-list Used to match a BGP community.
match interface Used to distribute any routes that have their next hop out one
of the interfaces specified.
match ip address Used to match any routes that have a destination network
address that is permitted by the specified standard access list,
extended access list, or prefix list.
match ip next-hop Used to match any routes that have a next-hop address
permitted by the specified standard access list, extended access
list, or prefix list.
match ip route-source Used to match any routes that have been advertised by any
address in the range referenced by the specified standard
access list, extended access list, or prefix list.
match metric Used to match any routes with the specified metric.
match route-type Used to match any routes with the specified type.
match tag Used to match any routes with the specified tag.
BGP Filters 307
The actions that can be specified with the set command are as numerous as those for the
match command:
After configuring the route map using the set and match statements, you need to apply the
route map to the neighbor session that you would like to apply the filter to. This can be accomplished
with the following command:
neighbor peer-address route-map name [in |out]
peer-address - the address used by the peer for the BGP session.
name - the name of the route map.
Let’s take a look at Figure 9.9.
set as-path Used to modify the AS_PATH attribute.
set automatic-tag Used to automatically compute the tag value.
set comm-list Used to set the BGP community list for deletion.
set community Used to set the BGP COMMUNITY attribute.
set dampening Used to set the parameters for BGP route flap dampening.
set default interface Used to set the default output interface.
set interface Used to set the output interface.
set ip default next-hop Used to set the default next-hop address along the path.
set ip next-hop Used to set the next-hop address.
set ip precedence Used to set the IP Precedence field.
set ip qos-group Used to set a group ID that can be used later to classify packets
into groups for collective QoS treatment.
set ip tos Used to set the IP Type of Service field.
set level Used to set where to import the route.
set local-preference Used to set the BGP LOCAL_PREF path attribute.
set metric Used to set the metric value for the destination routing
protocol.
set metric-type Used to set the type of metric for the destination routing
protocol.
set origin Used to set the BGP origin code.
set tag Used to set the tag value for the destination routing protocol.
set weight Used to set the BGP weight for the routing table.
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