BGP - Aggregation
December 16th, 2008 in
BGP | tags:
BGP aggregation In this post I will talk about BGP route aggregation. For the purpose of this post I used the diagram below. As you can see I configured several loopback addresses on router R5, on router R2 I will configure aggregation of these ip-addresses while on router R4 there will be no aggregation.
Let’s configure the aggregation :
R5 :
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interface Loopback0
ip address 5.5.5.5 255.255.255.255
!
interface Loopback221
ip address 22.22.22.1 255.255.255.255
!
interface Loopback222
ip address 22.22.22.2 255.255.255.255
!
interface Loopback223
ip address 22.22.22.3 255.255.255.255
!
interface Loopback224
ip address 22.22.22.4 255.255.255.255
!
interface Loopback225
ip address 22.22.22.5 255.255.255.255
!
interface Loopback226
ip address 22.22.22.6 255.255.255.255
!
interface Loopback441
ip address 44.44.44.1 255.255.255.255
!
interface Loopback442
ip address 44.44.44.2 255.255.255.255
!
interface Loopback443
ip address 44.44.44.3 255.255.255.255
!
interface Loopback444
ip address 44.44.44.4 255.255.255.255
!
interface Loopback445
ip address 44.44.44.5 255.255.255.255
!
interface Loopback446
ip address 44.44.44.6 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.25.5 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet2/0
ip address 10.10.45.5 255.255.255.0
duplex auto
speed auto
!
router bgp 65005
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
network 5.5.5.5 mask 255.255.255.255
network 22.22.22.1 mask 255.255.255.255
network 22.22.22.2 mask 255.255.255.255
network 22.22.22.3 mask 255.255.255.255
network 22.22.22.4 mask 255.255.255.255
network 22.22.22.5 mask 255.255.255.255
network 22.22.22.6 mask 255.255.255.255
network 44.44.44.1 mask 255.255.255.255
network 44.44.44.2 mask 255.255.255.255
network 44.44.44.3 mask 255.255.255.255
network 44.44.44.4 mask 255.255.255.255
network 44.44.44.5 mask 255.255.255.255
network 44.44.44.6 mask 255.255.255.255
neighbor 10.10.25.2 remote-as 65002
neighbor 10.10.25.2 send-community
neighbor 10.10.45.4 remote-as 65004
neighbor 10.10.45.4 send-community
no auto-summary
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R2 :
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interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.12.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet1/0
ip address 10.10.25.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet2/0
no ip address
shutdown
duplex auto
speed auto
!
router bgp 65002
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
aggregate-address 22.22.22.0 255.255.255.248
aggregate-address 44.44.44.0 255.255.255.248
neighbor 10.10.12.1 remote-as 65001
neighbor 10.10.12.1 send-community
neighbor 10.10.25.5 remote-as 65005
neighbor 10.10.25.5 send-community
no auto-summary
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R4 :
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interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.14.4 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet1/0
ip address 10.10.45.4 255.255.255.0
duplex auto
speed auto
!
router bgp 65004
no synchronization
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 4.4.4.4 mask 255.255.255.255
neighbor 10.10.14.1 remote-as 65001
neighbor 10.10.14.1 send-community
neighbor 10.10.45.5 remote-as 65005
neighbor 10.10.45.5 send-community
no auto-summary
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R1 :
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.12.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet1/0
ip address 10.10.13.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet2/0
ip address 10.10.14.1 255.255.255.0
duplex auto
speed auto
!
router bgp 65001
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 10.10.12.2 remote-as 65002
neighbor 10.10.12.2 send-community
neighbor 10.10.14.4 remote-as 65004
neighbor 10.10.14.4 send-community
no auto-summary
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If we would configure the aggregation like this the following will be the “sh ip bgp” output on router R1 :
R1 :
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R1#sh ip bgp
BGP table version is 19, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 10.10.12.2 0 0 65002 i
*> 4.4.4.4/32 10.10.14.4 0 0 65004 i
* 5.5.5.5/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
*> 22.22.22.0/29 10.10.12.2 0 0 65002 i
* 22.22.22.1/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 22.22.22.2/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 22.22.22.3/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 22.22.22.4/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 22.22.22.5/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 22.22.22.6/32 10.10.12.2 0 65002 65005 i
Network Next Hop Metric LocPrf Weight Path
*> 10.10.14.4 0 65004 65005 i
*> 44.44.44.0/29 10.10.12.2 0 0 65002 i
* 44.44.44.1/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 44.44.44.2/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 44.44.44.3/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 44.44.44.4/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 44.44.44.5/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
* 44.44.44.6/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
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As you can see router R2 advertises a /29 network but also all networks as /32 networks.
If we only want router R2 to advertise the /29 network without additionally specifying all /32 networks we would have to configure bgp like below on router R2 :
R2 :
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R2#sh run | section bgp
router bgp 65002
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
aggregate-address 22.22.22.0 255.255.255.248 summary-only
aggregate-address 44.44.44.0 255.255.255.248 summary-only
neighbor 10.10.12.1 remote-as 65001
neighbor 10.10.12.1 send-community
neighbor 10.10.25.5 remote-as 65005
neighbor 10.10.25.5 send-community
no auto-summary
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On router R1 this would be the “sh ip bgp” output :
R1 :
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R1#sh ip bgp
BGP table version is 19, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 10.10.12.2 0 0 65002 i
*> 4.4.4.4/32 10.10.14.4 0 0 65004 i
* 5.5.5.5/32 10.10.12.2 0 65002 65005 i
*> 10.10.14.4 0 65004 65005 i
*> 22.22.22.0/29 10.10.12.2 0 0 65002 i
*> 22.22.22.1/32 10.10.14.4 0 65004 65005 i
*> 22.22.22.2/32 10.10.14.4 0 65004 65005 i
*> 22.22.22.3/32 10.10.14.4 0 65004 65005 i
*> 22.22.22.4/32 10.10.14.4 0 65004 65005 i
*> 22.22.22.5/32 10.10.14.4 0 65004 65005 i
*> 22.22.22.6/32 10.10.14.4 0 65004 65005 i
*> 44.44.44.0/29 10.10.12.2 0 0 65002 i
*> 44.44.44.1/32 10.10.14.4 0 65004 65005 i
*> 44.44.44.2/32 10.10.14.4 0 65004 65005 i
*> 44.44.44.3/32 10.10.14.4 0 65004 65005 i
*> 44.44.44.4/32 10.10.14.4 0 65004 65005 i
Network Next Hop Metric LocPrf Weight Path
*> 44.44.44.5/32 10.10.14.4 0 65004 65005 i
*> 44.44.44.6/32 10.10.14.4 0 65004 65005 i
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As you can see only the /29 prefix is now advertised by router R2.