43. Aggregate aggregate-address of BGP configuration experiment
1. Experimental Topology
2. Basic configuration
R1 configuration
Interface Loopback0
Ip address 1.1.1.1 255.255.255.0
Interface Serial0/0
Ip address 13.1.1.1 255.255.255.0
Interface FastEthernet1/0
Ip address 124.1.1.1 255.255.255.0
Router ospf 110
Log-adjacency-changes
Network 1.1.1.0 0.0.0.255 area 0
Network 124.1.1.0 0.0.0.255 area 0
Router bgp 1
No synchronization
Bgp router-id 1.1.1.1
Neighbor 2.2.2.2 remote-as 1
Neighbor 2.2.2.2 update-source Loopback0
Neighbor 2.2.2.2 next-hop-self
Neighbor 13.1.1.3 remote-as 3
No auto-summary
R2 configuration
Interface Loopback0
Ip address 2.2.2.2 255.255.255.0
Interface FastEthernet1/0
Ip address 124.1.1.2 255.255.255.0
Router ospf 110
Log-adjacency-changes
Network 2.2.2.0 0.0.0.255 area 0
Network 124.1.1.0 0.0.0.255 area 0
Router bgp 1
No synchronization
Bgp router-id 2.2.2.2
Bgp log-neighbor-changes
Neighbor 1.1.1.1 remote-as 1
Neighbor 1.1.1.1 update-source Loopback0
Neighbor 124.1.1.4 remote-as 4
No auto-summary
R3 configuration
Interface Loopback0
Ip address 3.3.3.3 255.255.255.0
Interface Loopback16
Ip address 202.1.16.3 255.255.255.0
Interface Loopback17
Ip address 202.1.17.3 255.255.255.0
Interface Loopback18
Ip address 202.1.18.3 255.255.255.0
Interface Loopback19
Ip address 202.1.19.3 255.255.255.0
Interface Serial0/0
Ip address 13.1.1.3 255.255.255.0
Router bgp 3
No synchronization
Bgp router-id 3.3.3.3
Bgp log-neighbor-changes
Network 3.3.3.0 mask 255.255.255.0
Network 202.1.16.0
Network 202.1.17.0
Network 202.1.18.0
Network 202.1.19.0
Neighbor 13.1.1.1 remote-as 1
No auto-summary
R4 configuration
Interface Loopback0
Ip address 4.4.4.4 255.255.255.0
Interface FastEthernet1/0
Ip address 124.1.1.4 255.255.255.0
Router bgp 4
No synchronization
Bgp router-id 4.4.4.4
Bgp log-neighbor-changes
Network 4.4.4.0 mask 255.255.255.0
Neighbor 124.1.1.2 remote-as 1
No auto-summary
3. Configure aggregation
BGP aggregation can be done in two ways:
Method 1: manually write a static summary route pointing to the empty interface, and then publish the summary route in the BGP routing process
Method 2: first, network all the detail routes in the BGP routing process and aggregate them with aggregate-address 202.1.16.0255.255.252.0.At this time, both the aggregation route and the detail route will be advertised. Aggregate-address 202.1.16.0255.255.252.0 summary-only will suppress the detail route and mark it as s, and will not send it to other BGP neighbors.
In addition, we can also specify that specific routes are not advertised. The basic steps are as follows:
Ip prefix-list 1 permit 202.1.16.0/23 ge 24 le 24
Route-map YZ permit 10
Match ip address prefix-list 1
Router bgp 3
Aggregate-address 202.1.16.0 255.255.252.0 suppress-map YZ
The second method is to do aggregation at the sender. If aggregation is done at the receiver, the receiver will transmit the aggregation route back to the sender after generating the aggregation route. At this time, packet loss will occur, so the aggregation route should not be sent back. In order to achieve the goal of not being able to transmit, we use BGP's split horizon technology to add the attribute of detail route to the aggregation route, so that when the sender receives the aggregation route, it does not accept the route because it carries its own AS number, aggregate-address 202.1.16.0255.255.252.0 summary-only as-set.
Method 1:
R3 configuration
Ip route 202.1.16.0 255.255.252.0 null0
Router bgp 3
No network 202.1.16.0
No network 202.1.17.0
No network 202.1.18.0
No network 202.1.19.0
Network 202.1.16.0 mask 255.255.252.0
Method 2:
R3 configuration
No ip route 202.1.16.0 255.255.252.0 null0
Router bgp 3
No network 202.1.16.0 mask 255.255.252.0
Network 202.1.16.0
Network 202.1.17.0
Network 202.1.18.0
Network 202.1.19.0
Aggregate-address 202.1.16.0 255.255.252.0
Aggregate-address 202.1.16.0 255.255.252.0 summary-only will suppress the detail route, identified as s, and will not be sent to other BGP neighbors.
Router bgp 3
Aggregate-address 202.1.16.0 255.255.252.0 summary-only
Clear the aggregation on R3 and do the aggregation on R1.
Router bgp 3
No aggregate-address 202.1.16.0 255.255.252.0 summary-only
Router bgp 1
No aggregate-address 202.1.16.0 255.255.252.0 summary-only
Router bgp 1
No aggregate-address 202.1.16.0 255.255.252.0 summary-only as-set
R1 no longer advertises aggregate routes to R3.
