Table of Contents
Advertisement
Route Summaries
Prefix Tree Example
Static Summary
Example
Split Horizon
Copyright © 2010, Juniper Networks, Inc.
You can summarize routes reported by RIP to reduce the size of the routing table and
the amount of traffic resulting from RIP updates. Configuring a RIP summary will cause
that prefix to be advertised with the associated metric regardless of the presence of
more-specific prefixes. Any more-specific prefixes will not be advertised when they are
covered by the summary. You can choose the degree of summarization by using a prefix
tree to specify the number of bits to report for routes matching a route map. Alternatively,
you can explicitly specify routes for RIP to summarize.
The following example shows how to configure a 16-bit route summary:
Specify a route map for RIP in Router Configuration mode.
1.
host1#configure t
Enter configuration commands, one per line. End with CNTL/Z.
host1(config)#router rip
host1(config-router)#route-map 1
host1(config-router)#exit
Define a route map associated with a prefix tree.
2.
host1(config)#
host1(config)#route-map 1
host1(config-route-map)#match-set
host1(config-route-map)#match-set summary prefix-tree boston
host1(config-route-map)#exit
host1(config)#
Set the conditions for summarization in the prefix tree, including which routes are
3.
summarized and how many bits of the network addresses are preserved as the network
prefix.
host1(config)#ip prefix-tree boston permit 2.1.0.0/16
This example summarizes routes for networks addressed by 2.1.x.x. The first 16 bits of
the network address are preserved in the summary. For example, routes 2.1.3.0, 2.1.2.0,
and 2.1.1.0 would all be summarized as 2.1.0.0.
You can use the ip summary-address command to specify routes that RIP will summarize.
host1(config-router)#ip summary-address 4.4.0.0 255.255.0.0 5
host1(config-router)#ip summary-address 4.3.0.0 255.255.0.0 6
Split horizon is a mechanism to aid in preventing routing loops when distance-vector
routing protocols such as RIP are employed in broadcast networks. When split horizon
is enabled, the router cannot advertise information about routes on an interface from
which the information originates. Split horizon is enabled by default on the router.
You can disable split horizon and enable poison reverse routing updates that advertise
routes originating on the interface, but for each of these routes the metric is set to infinity
to explicitly advertise that these networks are not reachable.
Chapter 4: Configuring RIP
205
Advertisement
Table of Contents
