如图，R1在AS1中，R2,R3,R4在一个大AS100中（R2,R3在AS23中，R4在AS4中），5在AS5中。
聚合路由执行最苛刻的条件-- LocPrf最大等。
R2#show route-map
route-map aa, permit, sequence 10
Match clauses:
ip address (access-lists): 1
Set clauses:
local-preference 1000
community internet 1:34464
origin incomplete
Policy routing matches: 0 packets, 0 bytes
route-map aa, permit, sequence 20
Match clauses:
ip address (access-lists): 2
Set clauses:
local-preference 2000
community 3:3392 local-AS
Policy routing matches: 0 packets, 0 bytes
route-map aa, permit, sequence 30
Match clauses:
ip address (access-lists): 3
Set clauses:
local-preference 3000
community 4:37856 no-advertise
Policy routing matches: 0 packets, 0 bytes
route-map aa, permit, sequence 40
Match clauses:
ip address (access-lists): 4
Set clauses:
community no-export
Policy routing matches: 0 packets, 0 bytes
route-map aa, permit, sequence 50
Match clauses:
Set clauses:
Policy routing matches: 0 packets, 0 bytes
R2#show access-lists
Standard IP access list 1
10 permit 200.1.1.0 (16 matches)
Standard IP access list 2
10 permit 200.1.2.0 (16 matches)
Standard IP access list 3
10 permit 200.1.3.0 (16 matches)
Standard IP access list 4
10 permit 200.1.4.0 (16 matches)
R2#show run | s bgp
router bgp 23
bgp router-id 2.2.2.2
bgp log-neighbor-changes
bgp confederation identifier 100
aggregate-address 200.1.0.0 255.255.252.0 as-set
neighbor 3.3.3.3 remote-as 23
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 next-hop-self
neighbor 3.3.3.3 send-community both
neighbor 12.1.1.1 remote-as 1
neighbor 12.1.1.1 route-map aa in
ip bgp-community new-format
R2#show ip bgp
BGP table version is 33, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path> 1.1.1.1/32 12.1.1.1 0 0 1 i
>i 5.5.5.5/32 3.3.3.3 0 100 0 (4) 5 i
> 200.1.0.0/22 0.0.0.0 3000 32768 1 ?
> 200.1.1.0 12.1.1.1 0 1000 0 1 ?
> 200.1.2.0 12.1.1.1 0 2000 0 1 i
> 200.1.3.0 12.1.1.1 0 3000 0 1 i
> 200.1.4.0 12.1.1.1 0 0 1 i
R3#show ip bgp
BGP table version is 29, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path>i 1.1.1.1/32 2.2.2.2 0 100 0 1 i
> 5.5.5.5/32 4.4.4.4 0 100 0 (4) 5 i
>i 200.1.1.0 2.2.2.2 0 1000 0 1 ?
>i 200.1.2.0 2.2.2.2 0 2000 0 1 i
>i 200.1.4.0 2.2.2.2 0 100 0 1 i
R4#show ip bgp
BGP table version is 27, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path> 1.1.1.1/32 2.2.2.2 0 100 0 (23) 1 i
> 5.5.5.5/32 45.1.1.5 0 0 5 i
> 200.1.1.0 2.2.2.2 0 1000 0 (23) 1 ?
> 200.1.4.0 2.2.2.2 0 100 0 (23) 1 i
R4#
R5#show ip bgp
BGP table version is 35, local router ID is 5.5.5.5
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path> 1.1.1.1/32 45.1.1.4 0 100 1 i
> 5.5.5.5/32 0.0.0.0 0 32768 i
> 200.1.1.0 45.1.1.4 0 100 1 ?
R2(config)#route-map aa permit 10
R2(config-route-map)#set as prepend 10 20 30 40 50
R2(config-route-map)#exit
R2(config)#route-map aa per
R2(config)#route-map aa permit 20
R2(config-route-map)#set as prepend 30 40 50
R2#show ip bgp
BGP table version is 36, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path> 1.1.1.1/32 12.1.1.1 0 0 1 i
>i 5.5.5.5/32 3.3.3.3 0 100 0 (4) 5 i
> 200.1.0.0/22 0.0.0.0 3000 32768 {10,20,30,40,50,1} ?
> 200.1.1.0 12.1.1.1 0 1000 0 10 20 30 40 50 1 ?
> 200.1.2.0 12.1.1.1 0 2000 0 30 40 50 1 i
> 200.1.3.0 12.1.1.1 0 3000 0 1 i
*> 200.1.4.0 12.1.1.1 0 0 1 i
R2#show ip bgp 200.1.0.0
BGP routing table entry for 200.1.0.0/22, version 36
Paths: (1 available, best #1, table default, not advertised to any peer)
Not advertised to any peer
Refresh Epoch 1
{10,20,30,40,50,1}, (aggregated by 100 2.2.2.2)
0.0.0.0 from 0.0.0.0 (2.2.2.2)
Origin incomplete, localpref 3000, weight 32768, valid, aggregated, local, best
Community: internet 1:34464 3:3392 4:37856 no-advertise local-AS
原文地址：http://blog.51cto.com/13625527/2104126