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Chapter 29
| IP Routing Commands
Border Gateway Protocol (BGPv4)
as-set – Generates autonomous system set information for the AS path
attribute, indicating that a route originated in multiple autonomous
systems.
summary-only – Sends the summary routes only, ignoring more specific
routes.
Command Mode
Router Configuration
Default Setting
No aggregate routes are defined.
Command Usage
◆
Using this command without any keywords will create an aggregate entry in
the routing table if any more specific routes are available in the specified range.
The aggregate route does not include any individual route attributes (e.g., AS-
Path or Community). It is advertised as coming from this autonomous system
and has the atomic aggregate attribute set to indicate that some information
may be missing.
◆
Using the as-set keyword creates an aggregate route where the advertised
path is an AS-Set that consists of all elements contained in all of paths being
summarized. AS-Set information can be used to avoid routing loops because it
records where the route has been. If a router notes its own AS number in the
AS-Set of the aggregate update, it will drop the aggregate to prevents loop.
However, when aggregating tens or hundreds of routes, avoid advertising
routing information in this manner, since this route may be frequently
withdrawn and updated as AS path reachability information for the
summarized routes changes.
◆
Using the summary-only keyword creates the aggregate route, while at the
same time suppressing advertisements of more specific routes to all neighbors.
Example
Console(config-router)#aggregate-address 100.1.0.0 255.255.0.0 summary-only
Console(config-router)#aggregate-address 100.2.0.0 255.255.0.0 summary-only
as-set
Console(config-router)#aggregate-address 100.3.0.0 255.255.0.0 as-set
Console(config-router)#end
Console#show ip bgp
BGP table version is 0, local router ID is 192.168.0.4
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S Stale, R Removed
Origin codes: i - IGP, e - EGP, ? - incomplete
Network
Next Hop
*>i192.168.0.0/24
0.0.0.0
Metric LocPrf Weight Path
– 930 –
0
32768 i
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