aggregate-address (BGP)

To create a summary address in a Border Gateway Protocol (BGP) routing table, use the aggregate-address command. To remove the summary address, use the no form of this command.

aggregate-address address / length [ advertise-map map-name ] [ as-set ] [ attribute-map map-name ] [ summary-only ] [ suppress-map map-name ]

no aggregate-address address / mask-length [ advertise-map map-name ] [ as-set ] [ attribute-map map-name ] [ summary-only ] [ suppress-map map-name ]

Syntax Description

address/length
Aggregate IPv4 address and mask length. Valid value for length is 1 to 32.
advertise-map map-name
(Optional) Specifies the name of the route map used to select attribute information from specific routes.
as-set
(Optional) Generates the autonomous system set path information and community information from the contributing paths.
attribute-map map-name
(Optional) Specifies the name of the route map used to set the attribute information for specific routes. The map-name is an alphanumeric string up to 63 characters.
summary-only
(Optional) Filters all more-specific routes from updates.
suppress-map map-name
(Optional) Specifies the name of the route map used to conditionally filter more specific routes. The map-name is an alphanumeric string up to 63 characters.

Command Default

The atomic aggregate attribute is set automatically when an aggregate route is created with this command unless the as-set keyword is specified.

Command Modes

Address-family configuration mode

Command History

Release
Modification
5.0(3)N1(1)
This command was introduced.

Usage Guidelines

You can implement aggregate routing in BGP either by redistributing an aggregate route into BGP, or by using the conditional aggregate routing feature.

The aggregate-address command without keywords creates an aggregate entry in the BGP routing table if any more-specific BGP routes are available that fall within the specified range. (A longer prefix which matches the aggregate must exist in the RIB.) The aggregate route will be advertised as coming from your autonomous system and will have the atomic aggregate attribute set to show that information might be missing. (By default, the atomic aggregate attribute is set unless you specify the as-set keyword.)

The as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword, but the path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized. Do not use this form of the aggregate-address command when aggregating many paths, because this route must be continually withdrawn and updated as autonomous system path reachability information for the summarized routes changes.

The summary-only keyword not only creates the aggregate route (for example, 192.*.*.*) but also suppresses advertisements of more-specific routes to all neighbors. If you want to suppress only advertisements to certain neighbors, you may use the neighbor distribute-list command, with caution. If a more-specific route leaks out, all BGP routers will prefer that route over the less-specific aggregate you are generating (using longest-match routing).

The suppress-map keyword creates the aggregate route but suppresses advertisement of specified routes. You can use the match clauses of route maps to selectively suppress some more-specific routes of the aggregate and leave others unsuppressed. IP access lists and autonomous system path access lists match clauses are supported.

The advertise-map keyword selects specific routes that will be used to build different components of the aggregate route, such as AS_SET or community. This form of the aggregate-address command is useful when the components of an aggregate are in separate autonomous systems and you want to create an aggregate with AS_SET, and advertise it back to some of the same autonomous systems. You must remember to omit the specific autonomous system numbers from the AS_SET to prevent the aggregate from being dropped by the BGP loop detection mechanism at the receiving router. IP access lists and autonomous system path access lists match clauses are supported.

The attribute-map keyword allows attributes of the aggregate route to be changed. This form of the aggregate-address command is useful when one of the routes forming the AS_SET is configured with an attribute such as the community no-export attribute, which would prevent the aggregate route from being exported. An attribute map route map can be created to change the aggregate attributes.

This command requires the LAN Enterprise Services license.

Examples

AS-Set Example

This example shows how to create an aggregate BGP address in router configuration mode. The path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized.

switch(config)# router bgp 64496
switch(config-router)# aggregate-address 10.0.0.0 255.0.0.0 as-set

Summary-Only Example

This example shows how to create an aggregate BGP address in address family configuration mode and apply it to the multicast database (SAFI) under the IP Version 4 address family. Because the summary-only keyword is configured, more-specific routes are filtered from updates.

switch(config)# router bgp 64496
switch(config-router)# address-family ipv4 multicast
switch(config-router-af)# aggregate-address 10.0.0.0 255.0.0.0 summary-only

Conditional Aggregation Example

This example shows how to create a route map called MAP-ONE to match on an as-path access list. The path advertised for this route will be an AS_SET consisting of elements contained in paths that are matched in the route map.

switch(config)# ip as-path access-list 1 deny ^1234_
switch(config)# ip as-path access-list 1 permit .*
switch(config)# !
switch(config)# route-map MAP-ONE
switch(config-route-map)# match ip as-path 1
switch(config-route-map)# exit
switch(config)# router bgp 64496
switch(config-router)# address-family ipv4
switch(config-router-af)# aggregate-address 10.0.0.0 255.0.0.0 as-set advertise-map MAP-ONE
switch(config-router-af)# end

Related Commands

Command
Description
route-map
Creates a route map.