BGP Route Summary aggregate-address command

Route Summary using aggregate-address command

The aggregate-address command can be used to generate BGP aggregate routes. The syntax of the command is as follows

The route specified in the aggregate-address command is placed in the BGP table, becomes the best path, and is advertised to other BGP neighbors. However, the condition for using the aggregate-address command is that at least one route within the scope of the aggregate route must exist in the BGP table. If no routes within the scope of the aggregation exist in the BGP table, the aggregate route cannot be generated and advertised.

Path Attributes for Aggregate Route

Recall that BGP route has several path attributes attached to it. Naturally, aggregate route generated by the aggregate-address command will also have path attributes added to it. The following attributes are added by default to the aggregate route generated by aggregate-address command.

• ORIGIN:IGP
• NEXT_HOP:0.0.0.0
• AS_PATH: empty
• WEIGHT:32768
• LOCAL_PREFERENCE:100
• MED: none
• AGGREGATOR: Local AS number and Router ID
• ATOMIC-AGGREGATE

The Well Known Mandatory attribute (ORIGIN/NEXT_HOP/AS_PATH) of the aggregate route generated by the aggregate-address command is the same as the route generated by the network command. ATOMIC-AGGREGATE is the flag indicating that it is an aggregated route. The AGGREGATOR is marked with the AS number and router ID of the local router that generated the aggregated route.

aggregate-address command options

And the aggregate-address command has various options. If you type “?” in the middle of a command and get help, you will see the following.

R1(config-router)#aggregate-address 200.100.0.0 255.255.0.0 ?
advertise-map  Set condition to advertise attribute
as-set         Generate AS set path information
attribute-map  Set attributes of aggregate
nlri           Nlri aggregate applies to
route-map      Set parameters of aggregate
summary-only   Filter more specific routes from updates
suppress-map   Conditionally filter more specific routes from updates

A summary of each option is as follows

• advertise-map
  Specify the pre-aggregation route for which you want the aggregate route to inherit attributes
• as-set
  Inherit the AS number and COMMUNITY attribute of the route before aggregation
• attribute-map
  Set attributes for aggregate routes
• route-map
  Same as attribute-map
• summary-only
  Suppress all routes before aggregation
• suppress-map
  Selective Aggregation. Specify the route to be suppressed among the routes before aggregation.

These options should be considered from two perspectives.

• What to do with the attributes of the aggregate route
• How to handle pre-aggregation routes

The options for “what to do with aggregate route attributes” are as-set, advertise-map, attribute-map, and route-map.The options for “how to handle pre-aggregation routes” are summary-only and suppress-map.

Related article

The options for the aggregate-address command are described in detail in the following article.

N-Study

aggregte-address command : summary-only opiton | N-Study

https://www.n-study.com/en/bgp-detail/aggregate-address-summary-only/

The summary-only option is an option regarding "how to handle routes pre-aggregation". The option summary-only advertises only aggregate route. This section describes the summary-only option in more detail.

N-Study

aggregte-address command : attribute-map opiton | N-Study

https://www.n-study.com/en/bgp-detail/aggregate-address-attribute-map/

The attribute-map is an option for "what to do with the attributes of the aggregate route". The attribute-map allows attributes to be added to the aggregate route.

N-Study

aggregte-address command : as-set opiton | N-Study

https://www.n-study.com/en/bgp-detail/aggregate-address-as-set/

The as-set is an option for “what to do with the attributes of the aggregate route”. The as-set option allows the aggregate route to inherit attributes of the pre-aggregate routes.

N-Study

aggregte-address command : advertise-map opiton | N-Study

https://www.n-study.com/en/bgp-detail/aggregate-address-advertise-map/

This section describes advertise-map, an option of the aggregate-address command that generates BGP aggregate routes.

N-Study

BGP Selective Aggregation : suppress-map | N-Study

https://www.n-study.com/en/bgp-detail/selective-aggregateion-suppress-map/

This section describes the suppress-map option of the aggregate-address command for selective aggregation. suppress-map option allows you to determine the pre-aggregation routes that are not advertised.