Prerequisites: CCNP level skills.
Topology
Task 1
On R4 the following loopbacks should be advertised into BGP. Do not use network statement.
- Loopback 3 = 40.0.0.1/16
- Loopback 4 = 40.1.0.1/16
- Loopback 5 = 40.2.0.1/16
- Loopback 6 = 40.3.0.1/16
- Loopback 7 = 44.4.0.1/19
- Loopback 8 = 44.4.32.1/19
- Loopback 9 = 44.4.64.1/19
- Loopback 10 = 44.4.96.1/19
Summarize all prefixes 40.x.x.x to one prefix only. Summarize prefixes 44.x.x.x but make sure that more specific prefixes are also advertised. Use BGP aggregation command to accomplish this.
Solution
Task 1
On R4 the following loopbacks should be advertised into BGP. Do not use network statement.
- Loopback 3 = 40.0.0.1/16
- Loopback 4 = 40.1.0.1/16
- Loopback 5 = 40.2.0.1/16
- Loopback 6 = 40.3.0.1/16
- Loopback 7 = 44.4.0.1/19
- Loopback 8 = 44.4.32.1/19
- Loopback 9 = 44.4.64.1/19
- Loopback 10 = 44.4.96.1/19
!
ip prefix-list NET_40 seq 5 permit 40.0.0.0/8 le 16
ip prefix-list NET_44 seq 5 permit 44.4.0.0/16 le 19
!
ip prefix-list NET_44 seq 5 permit 44.4.0.0/16 le 19
!
route-map CONN_TO_BGP permit 10
match ip address prefix-list NET_40
!
route-map CONN_TO_BGP permit 20
match ip address prefix-list NET_44
!
router bgp 40
no synchronization
bgp router-id 172.16.104.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.14.1 remote-as 10
neighbor 10.1.24.2 remote-as 20
no auto-summary
match ip address prefix-list NET_40
!
route-map CONN_TO_BGP permit 20
match ip address prefix-list NET_44
!
router bgp 40
no synchronization
bgp router-id 172.16.104.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.14.1 remote-as 10
neighbor 10.1.24.2 remote-as 20
no auto-summary
!
Verification:
Pic. 2 - BGP Prefixes Originated locally on R4.
Notice!
Prefixes originated by the router have next-hop attribute set to '0.0.0.0' and weight set to 32768. Prefixes redistributed use Origin incomplete '?'
Task 2
Summarize all prefixes 40.x.x.x to one prefix only. Summarize prefixes 44.x.x.x but make sure that more specific prefixes are also advertised. Use BGP aggregation command to accomplish this.
R4 Configuration:
!
router bgp 40
no synchronization
bgp router-id 172.16.104.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 summary-only
aggregate-address 44.4.0.0 255.255.128.0
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.14.1 remote-as 10
neighbor 10.1.24.2 remote-as 20
no auto-summary
no synchronization
bgp router-id 172.16.104.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 summary-only
aggregate-address 44.4.0.0 255.255.128.0
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.14.1 remote-as 10
neighbor 10.1.24.2 remote-as 20
no auto-summary
!
Verification:
Pic. 3 - BGP Table on R4.
R4 suppresses 's' more specific routes if 'summary-only' command is used. Only 40.0.0.0/14 is going to be advertised.
If 'summary-only' command is NOT used, the router creates the aggregate route and advertises it with addition to more specific routes.
Pic. 4 - Routing Table on R4.
Similarly to other routing protocols the entry to 'null0' is created for the summary route as a loop prevention mechanism.
Pic. 5 - AS 40 Prefixes Learned on R5 .
Notice!
All prefixes 44.x.x.x AND the summary route are propageted. The prefix 40.x.x.x is the only summary route since 'summary-only' keyword has been used.
