| BGP Route Aggreagation is one of the most complex operations in BGP. Nearly everything can be manipulated or changed. This tutorial shows how to use the varios available options.
The BGP setup is as follows.
Router R1 announces 10 prefixes, some have their initial values changed. The tutorial will work with this values on a step by step basis, sometimes even go back a step to show the effecs of the varios options.
| Prefix | Value |
|---|
| 10.10.10.0 | as-path prepend 1000 2000 3000 |
| 10.10.11.0 | |
| 10.10.20.0 | as-path prepend 777 888 999 |
| 10.10.21.0 | |
| 10.10.30.0 | community 80:300 80:400 additive |
| 10.10.31.0 | community 80:300 80:400 additive |
| 10.10.40.0 | |
| 10.10.41.0 | |
| 10.10.50.0 | |
| 10.10.51.0 | |
Here you can see how this values are set for the prefixes.
ip bgp-community new-format
!
ip prefix-list PL-R2-OUT1 seq 10 permit 10.10.10.0/24
!
ip prefix-list PL-R2-OUT2 seq 10 permit 10.10.20.0/24
!
ip prefix-list PL-R2-OUT3 seq 10 permit 10.10.30.0/24
ip prefix-list PL-R2-OUT3 seq 20 permit 10.10.31.0/24
!
route-map R2-OUT permit 10
match ip address prefix-list PL-R2-OUT1
set as-path prepend 1000 2000 3000
!
route-map R2-OUT permit 20
match ip address prefix-list PL-R2-OUT2
set as-path prepend 777 888 999
!
route-map R2-OUT permit 30
match ip address prefix-list PL-R2-OUT3
set community 80:300 80:400 additive
!
route-map R2-OUT permit 1000
The BGP table of R2 shows the prefixes and the prepended path to some of them. A more detailed look at 10.10.30.0/24 shows the communities.
R2#show ip bgp
BGP table version is 13, local router ID is 172.17.0.2
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
*> 10.10.10.0/24 192.168.100.1 0 0 80 1000 2000 3000 i
*> 10.10.11.0/24 192.168.100.1 0 0 80 i
*> 10.10.20.0/24 192.168.100.1 0 0 80 777 888 999 i
*> 10.10.21.0/24 192.168.100.1 0 0 80 i
*> 10.10.30.0/24 192.168.100.1 0 0 80 i
*> 10.10.31.0/24 192.168.100.1 0 0 80 i
*> 10.10.40.0/24 192.168.100.1 0 0 80 i
*> 10.10.41.0/24 192.168.100.1 0 0 80 i
*> 10.10.50.0/24 192.168.100.1 0 0 80 i
*> 10.10.51.0/24 192.168.100.1 0 0 80 i
R2#show ip bgp 10.10.30.0
BGP routing table entry for 10.10.30.0/24, version 9
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x820
Advertised to update-groups:
1
80
192.168.100.1 from 192.168.100.1 (172.17.0.1)
Origin IGP, metric 0, localpref 100, valid, external, best
Community: 80:300 80:400
Part 2, Setting the Aggregate
Part 3, Component Routes
Part 4, Unsuppress the Suppressed
Part 5, Modification of Attributes
Part 6, Playing with the AS-SET
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