Cisco BGP-4 Command and Configuration Handbook

1-5 aggregate-address address mask route-map route-map- name

Syntax Description:

• address ” Aggregate IP address.

• mask ” Aggregate mask.

• route-map-name ” Route map used to modify the aggregate's attributes.

Purpose: To create an aggregate entry in the BGP table. An aggregate is created only if a more-specific route of the aggregate exists in the BGP table. This form of the aggregate-address command can be used to modify the aggregate's BGP attributes. The form of the command using the keyword route-map is equivalent to using the keyword attribute-map.

Cisco IOS Software Release: 10.0

Configuration Example: Modifying the Aggregate's Attributes

Figure 1-6 shows Router A learning two routes from Router B and two routes from Router C. Router B aggregates these four routes and modifies the aggregate's metric.

Router A router bgp 1 neighbor 10.1.1.2 remote-as 2 neighbor 172.17.1.2 remote-as 65530 ___________________________________________________________________________ Router B interface loopback 0 ip address 172.16.2.1 255.255.255.0 ! interface loopback 1 ip address 172.16.3.1 255.255.255.0 ! router bgp 2 network 172.16.2.0 mask 255.255.255.0 network 172.16.3.0 mask 255.255.255.0 neighbor 10.1.1.1 remote-as 1 ___________________________________________________________________________ Router C interface loopback 0 ip address 172.16.0.1 255.255.255.0 ! interface loopback 1 ip address 172.16.1.1 255.255.255.0 ! router bgp 65530 network 172.16.0.0 mask 255.255.255.0 network 172.16.1.0 mask 255.255.255.0 neighbor 172.17.1.1 remote-as 1 !

Four loopbacks have been created ”two on Router B and two on Router C. A BGP router can advertise an aggregate only if at least one specific route of the aggregate is in the BGP table. The BGP network commands are necessary on Routers B and C in order to place the routes into the BGP table. Before aggregating the loopback prefixes, you need to verify that the specific routes are in the BGP table on Routers A, B, and C:

rtrA# show ip bgp BGP table version is 35, local router ID is 144.223.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 172.17.1.2 0 0 65530 i *> 172.16.1.0/24 172.17.1.2 0 0 65530 i *> 172.16.2.0/24 10.1.1.2 0 0 2 i *> 172.16.3.0/24 10.1.1.2 0 0 2 i ___________________________________________________________________________ rtrB# show ip bgp BGP table version is 13, local router ID is 172.16.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 10.1.1.1 0 1 65530 i *> 172.16.1.0/24 10.1.1.1 0 1 65530 i *> 172.16.2.0/24 0.0.0.0 0 32768 i *> 172.16.3.0/24 0.0.0.0 0 32768 I ___________________________________________________________________________ rtrC# show ip bgp BGP table version is 35, local router ID is 172.17.1.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 0.0.0.0 0 32768 i *> 172.16.1.0/24 0.0.0.0 0 32768 i *> 172.16.2.0/24 172.17.1.1 0 1 2 i *> 172.16.3.0/24 172.17.1.1 0 1 2 i

Now modify the BGP configuration on Router A to enable the advertisement of the aggregate and to verify that the aggregate is being advertised to Routers B and C:

Router A router bgp 1 aggregate-address 172.16.0.0 255.255.252.0 neighbor 10.1.1.2 remote-as 2 neighbor 172.17.1.2 remote-as 65530

Verify that the aggregate is being advertised:

rtrA# show ip bgp BGP table version is 6, local router ID is 144.223.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 172.17.1.2 0 0 65530 i *> 172.16.0.0/22 0.0.0.0 32768 i *> 172.16.1.0/24 172.17.1.2 0 0 65530 i *> 172.16.2.0/24 10.1.1.2 0 0 2 i *> 172.16.3.0/24 10.1.1.2 0 0 2 I ___________________________________________________________________________ rtrB# show ip bgp BGP table version is 8, local router ID is 172.16.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 10.1.1.1 0 1 65530 i *> 172.16.0.0/22 10.1.1.1 0 1 i *> 172.16.1.0/24 10.1.1.1 0 1 65530 i *> 172.16.2.0/24 0.0.0.0 0 32768 i *> 172.16.3.0/24 0.0.0.0 0 32768 I ___________________________________________________________________________ rtrC# show ip bgp BGP table version is 8, local router ID is 172.16.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 0.0.0.0 0 32768 i *> 172.16.0.0/22 172.17.1.1 0 1 i *> 172.16.1.0/24 0.0.0.0 0 32768 i *> 172.16.2.0/24 172.17.1.1 0 1 2 i *> 172.16.3.0/24 172.17.1.1 0 1 2 i

Now use an attribute-map on Router A to modify the attribute's MED or metric:

Router A router bgp 1 aggregate-address 172.16.0.0 255.255.252.0 attribute-map attrib neighbor 10.1.1.2 remote-as 2 neighbor 172.17.1.2 remote-as 65530 ! route-map attrib permit 10 set metric 50

Verification

Verify that the metric for the attribute has been modified:

rtrA# show ip bgp BGP table version is 6, local router ID is 172.17.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 172.17.1.2 0 0 65530 i *> 172.16.0.0/22 0.0.0.0 50 32768 i *> 172.16.1.0/24 172.17.1.2 0 0 65530 i *> 172.16.2.0/24 10.1.1.2 0 0 2 i *> 172.16.3.0/24 10.1.1.2 0 0 2 I ___________________________________________________________________________ rtrB# show ip bgp BGP table version is 60, local router ID is 172.16.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 10.1.1.1 0 1 65530 i *> 172.16.0.0/22 10.1.1.1 50 0 1 i *> 172.16.1.0/24 10.1.1.1 0 1 65530 i *> 172.16.2.0/24 0.0.0.0 0 32768 i *> 172.16.3.0/24 0.0.0.0 0 32768 I ___________________________________________________________________________ rtrC# show ip bgp BGP table version is 48, local router ID is 172.16.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 0.0.0.0 0 32768 i *> 172.16.0.0/22 172.17.1.1 50 0 1 i *> 172.16.1.0/24 0.0.0.0 0 32768 i *> 172.16.2.0/24 172.17.1.1 0 1 2 i *> 172.16.3.0/24 172.17.1.1 0 1 2 i

Troubleshooting

Step 1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state, see section 8-23.

Step 2. Ensure that at least one specific route in the BGP table is contained in the range of addresses that you want to aggregate using the show ip bgp command.

Step 3. If at least one more-specific route is in the BGP table, go to Step 5.

Step 4. If there is not at least one more-specific route in the BGP table, do the following:

- ” Check the syntax (address and mask) of your BGP network command. Go to Step 2.

- ” If you're redistributing routes (connected, static, or from an IGP), make sure you are using the no auto-summary command. Check the syntax of your redistribution command(s). Go to Step 2.

Step 5. Verify that no filters are blocking the aggregate from being advertised.

Step 6. Verify the syntax of your route map.