Di Posting Oleh : Simple Learning
Kategori : BGP Core Technologies Routing
Prerequisites: CCNP level skills.
Note!
R4 advertises loopbacks as per Task 1 in lab 108.
Topology
Task 1
Configure R4 in such a way that R1 and R2 do not advertise the prefix: 40.1.0.0/16 to any of the BGP routers. R1 and R2 should receive all the prefixes from R4.
Task 2
Configure R1 and R2 so that they aggregate prefixes 40.x.x.x/16 and 44.4.0.0/19 to two prefixes 40.0.0./14 and 44.4.0.0/17 (as per lab 111). Make sure that R5 receives the two summary routes and they show AS 40 in the path.
Solution
Task 1
Configure R4 in such a way that R1 and R2 do not advertise the prefix: 40.1.0.0/16 to any of the BGP routers. R1 and R2 should receive all the prefixes from R4.
!
ip prefix-list NET_40.1.0.0 seq 5 permit 40.1.0.0/16
!
!
route-map SET_COMMUNITY permit 10
match ip address prefix-list NET_40.1.0.0
set community no-advertise
!
route-map SET_COMMUNITY permit 999
!
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 10.1.14.1 send-community
neighbor 10.1.14.1 route-map SET_COMMUNITY out
neighbor 10.1.24.2 remote-as 20
neighbor 10.1.24.2 send-community
neighbor 10.1.24.2 route-map SET_COMMUNITY out
no auto-summary
match ip address prefix-list NET_40.1.0.0
set community no-advertise
!
route-map SET_COMMUNITY permit 999
!
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 10.1.14.1 send-community
neighbor 10.1.14.1 route-map SET_COMMUNITY out
neighbor 10.1.24.2 remote-as 20
neighbor 10.1.24.2 send-community
neighbor 10.1.24.2 route-map SET_COMMUNITY out
no auto-summary
!
Verification:
Pic. 2 - BGP Table on R1.
Pic. 3 - Prefix 40.1.0.0 Details on R1.
Notice!
The prefix 40.1.0.0/16 is marked with the community NO_ADVERTISE and as such, will not be advertised to any peer (R3 here).
Pic. 4 - BGP Table on R5.
Notice!
R5 does not receive 40.1.0.0/16 because neither R1 nor R2 send it towards R3.
Task 2
Configure R1 and R2 so that they aggregate prefixes 40.x.x.x/16 and 44.4.0.0/19 to two prefixes (as per lab 111). Make sure that R5 receives the two summary routes and they show AS 40 in the path.
R1 Configuration:
!
router bgp 10
no synchronization
bgp router-id 172.16.101.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.13.3 remote-as 30
neighbor 10.1.14.4 remote-as 40
no auto-summary
no synchronization
bgp router-id 172.16.101.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.13.3 remote-as 30
neighbor 10.1.14.4 remote-as 40
no auto-summary
!
R2 Configuration:
!
router bgp 20
no synchronization
bgp router-id 172.16.102.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.23.3 remote-as 30
neighbor 10.1.24.4 remote-as 40
no auto-summary
no synchronization
bgp router-id 172.16.102.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.23.3 remote-as 30
neighbor 10.1.24.4 remote-as 40
no auto-summary
!
Notice!
'AS-SET' option is necessary so that R3 and R5 receive AS 40 in the path. Remember that the 'summary-only' keyword removes all ASes from the aggregate except for the one that is aggregating the prefix. But the result of using 'as-set' is that it advertises all attributes (here: AS numbers before aggregation and no-advertise community attribute). Since 40.1.0.0/16 uses the attribute NO_ADVERTISE, the aggregate 40.0.0.0/14 cannot be advertised to R3 and R5 does NOT receive this aggregate either. Check below:
Pic. 5 - BGP Table on R5.
R1 Configuration:
!
route-map REMOVE_COMMUNITY permit 10
set community none
!
router bgp 10
no synchronization
bgp router-id 172.16.101.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only attribute-map REMOVE_COMMUNITY
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.13.3 remote-as 30
neighbor 10.1.14.4 remote-as 40
no auto-summary
set community none
!
router bgp 10
no synchronization
bgp router-id 172.16.101.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only attribute-map REMOVE_COMMUNITY
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.13.3 remote-as 30
neighbor 10.1.14.4 remote-as 40
no auto-summary
!
R2 Configuration:
!
route-map REMOVE_COMMUNITY permit 10
set community none
!
set community none
!
router bgp 20
no synchronization
bgp router-id 172.16.102.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only attribute-map REMOVE_COMMUNITY
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.23.3 remote-as 30
neighbor 10.1.24.4 remote-as 40
no auto-summary
no synchronization
bgp router-id 172.16.102.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
aggregate-address 40.0.0.0 255.252.0.0 as-set summary-only attribute-map REMOVE_COMMUNITY
aggregate-address 44.4.0.0 255.255.128.0 as-set summary-only
neighbor 10.1.23.3 remote-as 30
neighbor 10.1.24.4 remote-as 40
no auto-summary
!
Verification:
Pic. 6 - BGP Table on R3.
Pic. 7 - BGP Table on R5.
Notice!
Thing to remember: the 'attribute-map' sets or removes attributes to the aggregated prefixes which use 'as-set' keyword.
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