Prerequisites: CCNP level skills.
Note!
BGP configuration based on Lab 108 (R4 loopbacks already advertised and aggregated).
Topology
Task 1
As per lab 108 R4 aggregates 40.4.x.x/19 range of prefixes to 40.4.0.0/17 but allows more specific ones to be advertised too. Configure R4 to advertise only the aggregate route 44.4.0.0/17.
Task 2
On R4 advertise 44.4.64.0/19 in addition to the aggregate prefix 44.4.0.0/17.
Solution
Task 1
As per lab 108 R4 aggregates 40.4.x.x/19 range of prefixes to 40.4.0.0/17 but allows more specific ones to be advertised too. Configure R4 to advertise only the aggregate route 44.4.0.0/17.
R4 Configuration:
!
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
!
!
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
aggregate-address 40.0.0.0 255.252.0.0 summary-only
aggregate-address 44.4.0.0 255.255.128.0 summary-only
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
aggregate-address 40.0.0.0 255.252.0.0 summary-only
aggregate-address 44.4.0.0 255.255.128.0 summary-only
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 - 44.4.x.x Prefixes on R4.
All 44.4.x.x/19 are being suppressed and only 44.4.0.0/17 is going to be advertised now.
Pic. 3 - AS 40 Originated Prefixes in R5's BGP Table.
On R4 advertise 44.4.64.0/19 in addition to the aggregate prefix 44.4.0.0/17.
R4 Configuration:
!
ip prefix-list PFX_SUPPRESSED seq 5 permit 44.4.0.0/19
ip prefix-list PFX_SUPPRESSED seq 10 permit 44.4.32.0/19
ip prefix-list PFX_SUPPRESSED seq 15 permit 44.4.96.0/19
!
ip prefix-list PFX_SUPPRESSED seq 10 permit 44.4.32.0/19
ip prefix-list PFX_SUPPRESSED seq 15 permit 44.4.96.0/19
!
route-map SUPPRESS permit 10
match ip address prefix-list PFX_SUPPRESSED
!
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 summary-only suppress-map SUPPRESS
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 PFX_SUPPRESSED
!
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 summary-only suppress-map SUPPRESS
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. 4 - AS 40 Originated Prefixesin R5's BGP Table.
Permit statement in prefix-list PFX_SUPPRESSED used by the route-map SUPPRESS filters out more specific routes. What is NOT permitted in the prefix-list will NOT be suppressed by the 'summary-only' option.
