实验拓扑
基本配置：
R1
L0:1.1.1.1/32
L1:11.1.1.1/32
E1/0:10.1.12.1/24
E1/1:10.1.14.1/24
R2
L0:2.2.2.2/32
L1:22.2.2.2/32
E1/0:10.1.12.2/24
E1/1:10.1.24.2/24
R4
L0:4.4.4.4/32
L1:44.4.4.4/32
E1/0:10.1.24.4/24
E1/1:10.1.14.4/24
配置IGP（RIP）：
R1
router rip
version 2
network 1.0.0.0
network 10.0.0.0
no auto-summary
R2
router rip
version 2
network 2.0.0.0
network 10.0.0.0
no auto-summary
R4
router rip
version 2
network 4.0.0.0
network 10.0.0.0
no auto-summary
配置BGP：
router bgp 1
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 2.2.2.2 mask 255.255.255.255 backdoor
network 4.4.4.4 mask 255.255.255.255 backdoor
network 11.1.1.1 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 23
neighbor 2.2.2.2 ebgp-multihop 2
neighbor 2.2.2.2 update-source Loopback0
neighbor 4.4.4.4 remote-as 23
neighbor 4.4.4.4 ebgp-multihop 2
neighbor 4.4.4.4 update-source Loopback0
R2
router bgp 23
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255 backdoor
network 2.2.2.2 mask 255.255.255.255
network 22.2.2.2 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 ebgp-multihop 2
neighbor 1.1.1.1 update-source Loopback0
neighbor 4.4.4.4 remote-as 23
neighbor 4.4.4.4 update-source Loopback0
R4
router bgp 23
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255 backdoor
network 4.4.4.4 mask 255.255.255.255
network 44.4.4.4 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 ebgp-multihop 2
neighbor 1.1.1.1 update-source Loopback0
neighbor 2.2.2.2 remote-as 23
neighbor 2.2.2.2 update-source Loopback0
查看R1路由表:origin 为i，表示从IGP 学来的路由。
R1#sh ip bgp
BGP table version is 5, 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, 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
r 2.2.2.2/32 4.4.4.4 0 23 i
r> 2.2.2.2 0 0 23 i
r 4.4.4.4/32 4.4.4.4 0 0 23 i
r> 2.2.2.2 0 23 i
* 22.2.2.2/32 4.4.4.4 0 23 i
*> 2.2.2.2 0 0 23 i
* 44.4.4.4/32 4.4.4.4 0 0 23 i
*> 2.2.2.2 0 23 i
查看22.2.2.2 44.4.4.4的路由表：
R1#sh ip bgp 22.2.2.2
BGP routing table entry for 22.2.2.2/32, version 4
Paths: (2 available, best #2, table default)
Advertised to update-groups:
18
Refresh Epoch 1
23
4.4.4.4 (metric 1) from 4.4.4.4 (4.4.4.4)
Origin IGP, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
23
2.2.2.2 (metric 1) from 2.2.2.2 (2.2.2.2)
Origin IGP, metric 0, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
R1#sh ip bgp 44.4.4.4
BGP routing table entry for 44.4.4.4/32, version 5
Paths: (2 available, best #2, table default)
Advertised to update-groups:
18
Refresh Epoch 1
23
4.4.4.4 (metric 1) from 4.4.4.4 (4.4.4.4)
Origin IGP, metric 0, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
23
2.2.2.2 (metric 1) from 2.2.2.2 (2.2.2.2)
Origin IGP, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
origin皆为IGP。修改 bgp origin-clde 属性，使R1到R2的22.2.2.2 永久的从R4走，到R4的44.4.4.4永久的从R2走。
在R1上配置：
第一步：配置prefix-list
ip prefix-list 22 seq 5 permit 22.2.2.2/32
ip prefix-list 44 seq 5 permit 44.4.4.4/32
第二步：配置route-map
route-map ori-r2 permit 10
match ip address prefix-list 22
set origin incomplete
route-map ori-r2 permit 20
route-map ori-r4 permit 10
match ip address prefix-list 44
set origin incomplete
route-map ori-r4 permit 20
第三步：在BGP中，对相应的邻居in方向调用route-map。
neighbor 2.2.2.2 route-map ori-r2 in
neighbor 4.4.4.4 route-map ori-r4 in
第四步：重置BGP邻居，重新学习路由
clea ip bgp *
查看R1 BGP路由表：
R1#sh ip bgp
BGP table version is 16, 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, 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 0.0.0.0 0 32768 i
r 2.2.2.2/32 4.4.4.4 0 23 i
r> 2.2.2.2 0 0 23 i
r 4.4.4.4/32 4.4.4.4 0 0 23 i
r> 2.2.2.2 0 23 i
*> 11.1.1.1/32 0.0.0.0 0 32768 i
*> 22.2.2.2/32 4.4.4.4 0 23 i
* 2.2.2.2 0 0 23 ?
* 44.4.4.4/32 4.4.4.4 0 0 23 ?
*> 2.2.2.2 0 23 i
此是，BGP表显示从R2学来的22.2.2.2路由，origin-code属性已改为？（incomplete），从R4学来的44.4.4.4路由，属性也改为？（incomplete），优先选择origin-clde为i的路由。
IGP(i)优于EGP(e)优于incomplete(?)的路由。
R1#sh ip bgp 22.2.2.2
BGP routing table entry for 22.2.2.2/32, version 16
Paths: (2 available, best #1, table default)
Advertised to update-groups:
18
Refresh Epoch 1
23
4.4.4.4 (metric 1) from 4.4.4.4 (4.4.4.4)
Origin IGP, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
Refresh Epoch 1
23
2.2.2.2 (metric 1) from 2.2.2.2 (2.2.2.2)
Origin incomplete, metric 0, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
R1#sh ip bgp 44.4.4.4
BGP routing table entry for 44.4.4.4/32, version 15
Paths: (2 available, best #2, table default)
Advertised to update-groups:
18
Refresh Epoch 1
23
4.4.4.4 (metric 1) from 4.4.4.4 (4.4.4.4)
Origin incomplete, metric 0, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
23
2.2.2.2 (metric 1) from 2.2.2.2 (2.2.2.2)
Origin IGP, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
实验完成。
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