IPA-taskpacket001：BGP的基本原理
實驗一：BGP路由傳遞原則
實驗目標：掌握BGP的路由傳遞原則
實驗TOP：
基本配置
R1
!
hostname R1
!
no ip domain lookup
!
interface Loopback0
ipaddress 1.1.1.1 255.255.255.0
!
interface Loopback10
ipaddress 10.10.10.10 255.255.255.0
ipospf network point-to-point
!
interface Serial1/0
ipaddress 12.1.1.1 255.255.255.0
!
interface Serial1/1
ipaddress 13.1.1.1 255.255.255.0
!
router ospf 10
router-id 1.1.1.1
network 10.10.10.0 0.0.0.255 area 0
network 12.1.1.0 0.0.0.255 area 0
network 13.1.1.0 0.0.0.255 area 0
!
router bgp 65001
nosynchronization
bgprouter-id 1.1.1.1
network 1.1.1.0 mask 255.255.255.0
neighbor 12.1.1.2 remote-as 65001
neighbor 13.1.1.3 remote-as 65001
noauto-summary
!
R2
!
hostname R2
!
no ip domain lookup
!
interface Loopback0
ipaddress 2.2.2.2 255.255.255.0
!
interface Loopback10
ipaddress 20.20.20.20 255.255.255.0
ipospf network point-to-point
!
interface Serial1/0
ipaddress 24.2.2.2 255.255.255.0
!
interface Serial1/1
ipaddress 12.1.1.2 255.255.255.0
!
router ospf 10
router-id 2.2.2.2
network 12.1.1.0 0.0.0.255 area 0
network 20.20.20.0 0.0.0.255 area 0
network 24.2.2.0 0.0.0.255 area 0
!
router bgp 65001
nosynchronization
bgprouter-id 2.2.2.2
network 2.2.2.0 mask 255.255.255.0
neighbor12.1.1.1 remote-as 65001
neighbor 24.2.2.4 remote-as 65001
noauto-summary
!
R3
!
hostname R3
!
no ip domain lookup
!
interface Loopback0
ipaddress 3.3.3.3 255.255.255.0
!
interface Loopback10
ipaddress 30.30.30.30 255.255.255.0
ipospf network point-to-point
!
interface Serial1/1
ipaddress 13.1.1.3 255.255.255.0
!
interface Serial1/0
ipaddress 34.3.3.3 255.255.255.0
!
router ospf 10
router-id 3.3.3.3
network 13.1.1.0 0.0.0.255 area 0
network 30.30.30.0 0.0.0.255 area 0
network34.3.3.0 0.0.0.255 area 0
!
router bgp 65001
nosynchronization
bgprouter-id 3.3.3.3
network 3.3.3.0 mask 255.255.255.0
neighbor 13.1.1.1 remote-as 65001
neighbor 34.3.3.4 remote-as 65001
no auto-summary
!
R4
!
hostname R4
!
no ip domain lookup
!
interface Loopback0
ipaddress 4.4.4.4 255.255.255.0
!
interface Loopback10
ipaddress 40.40.40.40 255.255.255.0
ipospf network point-to-point
!
interface Serial1/0
ipaddress 24.2.2.4 255.255.255.0
!
interface Serial1/1
ipaddress 34.3.3.4 255.255.255.0
!
Interface Serial1/2
Ip address 45.4.4.4 255.255.255.0
!
Interface Serial1/3
Ip address 46.4.4.4 255.255.255.0
!
router ospf 10
router-id 4.4.4.4
network 40.40.40.0 0.0.0.255 area 0
network 24.2.2.0 0.0.0.255 area 0
network 34.3.3.0 0.0.0.255 area 0
!
router bgp 65001
nosynchronization
bgprouter-id 4.4.4.4
network 4.4.4.0 mask 255.255.255.0
neighbor 24.2.2.2 remote-as 65001
neighbor 34.3.3.3 remote-as 65001
neighbor 45.4.4.5 remote-as 65002
neighbor 46.4.4.6 remote-as 65003
noauto-summary
!
R5
!
Hostname R5
!
no ip domain lookup
!
interface Loopback0
ipaddress 5.5.5.5 255.255.255.0
!
interface Serial1/0
ipaddress 45.4.4.5 255.255.255.0
!
router bgp 65002
nosynchronization
bgprouter-id 5.5.5.5
network 5.5.5.0 mask 255.255.255.0
neighbor 45.4.4.4 remote-as 65001
noauto-summary
!
R6
!
hostnameR6
!
interfaceLoopback0
ip address 6.6.6.6 255.255.255.0
!
interfaceSerial1/0
ip address 46.4.4.6 255.255.255.0
!
routerbgp 65003
no synchronization
bgp router-id 6.6.6.6
network 6.6.6.0 mask 255.255.255.0
neighbor 46.4.4.4 remote-as 65001
no auto-summary
!
批註：路由器接口默認是關閉的，所以應將對應的接口開啓
基本配置完成之後，我們開始檢查BGP對等體關係是否正常建立
R1#show ip bgp summary
BGP router identifier 1.1.1.1, local AS number 65001
BGP table version is 4, main routing table version 4
3 network entries using 303 bytes of memory
3 path entries using 144 bytes of memory
2 BGP path attribute entries using 120 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 567 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 65001 10 10 4 0 0 00:05:28 1
13.1.1.3 4 65001 9 9 4 0 0 00:04:42 1
R1#
//R1此時已經正常與R2和R3建立iBGP對等體關係
R2#show ip bgp summary
BGP router identifier 2.2.2.2, local AS number 65001
BGP table version is 4, main routing table version 4
5 network entries using 505 bytes of memory
5 path entries using 240 bytes of memory
4 BGP path attribute entries using 240 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1033 total bytes of memory
BGP activity 5/0 prefixes, 5/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.1 4 65001 11 11 4 0 0 00:06:13 1
24.2.2.4 4 65001 11 9 4 0 0 00:04:51 3
R2#
//R2此時已經正常與R1和R4建立iBGP對等體關係
R3#show ip bgp summary
BGP router identifier 3.3.3.3, local AS number 65001
BGP table version is 4, main routing table version 4
5 network entries using 505 bytes of memory
5 path entries using 240 bytes of memory
4 BGP path attribute entries using 240 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1033 total bytes of memory
BGP activity 5/0 prefixes, 5/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
13.1.1.1 4 65001 10 10 4 0 0 00:05:53 1
34.3.3.4 4 65001 12 10 4 0 0 00:05:16 3
R3#
//R3此時已經正常與R1和R4建立iBGP對等體關係
R4#show ip bgp summary
BGP router identifier 4.4.4.4, local AS number 65001
BGP table version is 6, main routing table version 6
5 network entries using 505 bytes of memory
5 path entries using 240 bytes of memory
4 BGP path attribute entries using 240 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1033 total bytes of memory
BGP activity 5/0 prefixes, 5/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
24.2.2.2 4 65001 11 13 6 0 0 00:06:13 1
34.3.3.3 4 65001 11 13 6 0 0 00:06:13 1
45.4.4.5 4 65002 9 11 6 0 0 00:04:34 1
46.4.4.6 4 65003 9 11 6 0 0 00:04:10 1
R4#
//R4此時已經正常與R2和R3建立iBGP對等體關係，並且與R5和R6建立eBGP對等體關係
R5#show ip bgp summary
BGP router identifier 5.5.5.5, local AS number 65002
BGP table version is 6, main routing table version 6
5 network entries using 505 bytes of memory
5 path entries using 240 bytes of memory
4 BGP path attribute entries using 240 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1033 total bytes of memory
BGP activity 5/0 prefixes, 5/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
45.4.4.4 4 65001 11 9 6 0 0 00:04:53 4
R5#
//R5此時已經正常與R4建立eBGP對等體關係
R6#show ip bgp summary
BGP router identifier 6.6.6.6, local AS number 65003
BGP table version is 6, main routing table version 6
5 network entries using 505 bytes of memory
5 path entries using 240 bytes of memory
4 BGP path attribute entries using 240 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1033 total bytes of memory
BGP activity 5/0 prefixes, 5/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
46.4.4.4 4 65001 11 9 6 0 0 00:04:56 4
R6#
//R6此時已經正常與R4建立eBGP對等體關係
調試：
1．IBGP路由器從直連IBGP對等體學來的路由條目不會再傳送給另外一個直連IBGP對等體。
如下圖所示，如果R3不會將自己從iBGP對等體R1學習到的1.1.1.0/24網段傳遞給另一個iBGP對等體R4證明此結論正確。
首先我們查看R3的bgp表：
R3#show ip bgp
BGP table version is 4, local router ID is3.3.3.3
Status codes: s suppressed, d damped, hhistory, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -incomplete
Network Next Hop Metric LocPrf Weight Path
*>i1.1.1.0/24 13.1.1.1 0 100 0 i
*> 3.3.3.0/24 0.0.0.0 0 32768 i
*>i4.4.4.0/24 34.3.3.4 0 100 0 i
* i5.5.5.0/24 45.4.4.5 0 100 0 65002 i
* i6.6.6.0/24 46.4.4.6 0 100 0 65003 i
//我們發現R3學習到了R1的lo0
再來查看R4的BGP表
R4#show ip bgp
BGP table version is 6, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i -internal,
r RIB-failure, SStale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*> 5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//我們發現R4並沒有學習到了R1的lo0
2．IBGP路由器會將自己從其他IBGP對等體學來的條目傳給自身直連的EBGP對等體。
如果R5學習到R3的3.3.3.0/24路由條目，確定此結論正確。
首先我們查看R4的BGP表
R4#show ip bgp
BGP table version is 6, local router ID is4.4.4.4
Status codes: s suppressed, d damped, hhistory, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -incomplete
Network Next Hop Metric LocPrf Weight Path
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*> 5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//R4學習到R3的路由
再來查看R5的BGP表
R5#show ip bgp
BGP table version is 6, local router ID is5.5.5.5
Status codes: s suppressed, d damped, hhistory, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -incomplete
Network Next Hop Metric LocPrf Weight Path
*> 2.2.2.0/24 45.4.4.4 0 65001 i
*>3.3.3.0/24 45.4.4.4 0 65001 i
*> 4.4.4.0/24 45.4.4.4 0 0 65001 i
*> 5.5.5.0/24 0.0.0.0 0 32768 i
*> 6.6.6.0/24 45.4.4.4 0 65001 65003 i
R5#
//我們發現R5確實學習到了R3 的路由，證明上結論沒有問題
3．從EBGP對等體學來的路由條目會傳遞給自身直連的IBGP對等體。
如果R4從eBGP對等體R5學習到5.5.5.0/24網段可以傳遞給iBGP對等體R3，則可證明結論正確
那麼首先我們查看R4的BGP表
R4#show ip bgp
BGP table version is 6, local router ID is4.4.4.4
Status codes: s suppressed, d damped, hhistory, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -incomplete
Network Next Hop Metric LocPrf Weight Path
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*>5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//我們發現R4學習到了5.5.5.0的路由
再來查看R3的bgp表
R3#show ip bgp
BGP table version is 4, local router ID is3.3.3.3
Status codes: s suppressed, d damped, hhistory, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i1.1.1.0/24 13.1.1.1 0 100 0 i
*> 3.3.3.0/24 0.0.0.0 0 32768 i
*>i4.4.4.0/24 34.3.3.4 0 100 0 i
*i5.5.5.0/24 45.4.4.5 0 100 0 65002 i
* i6.6.6.0/24 46.4.4.6 0 100 0 65003 i
R3#
//我們發現R3也學習到了5.5.5.0/24，說明R4會傳遞R5的5.5.5.0/24網段
4．從EBGP對等體學來的路由條目會傳遞給其他EBGP對等體。
我們可以在R5和R6上測試，觀察R4從eBGP對等體R6學習到的6.6.6.0/24是否會傳遞給eBGP對等體R5
首先，我們查看R4的bgp表
R4#show ip bgp
BGP table version is 6, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, >best, i - internal,
rRIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*> 5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//我們發現R4學習到了R6的6.6.6.0/24
再來查看R5的bgp表
R5#showip bgp
BGPtable version is 6, local router ID is 5.5.5.5
Statuscodes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origincodes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>2.2.2.0/24 45.4.4.4 0 65001 i
*>3.3.3.0/24 45.4.4.4 0 65001 i
*>4.4.4.0/24 45.4.4.4 0 0 65001 i
*>5.5.5.0/24 0.0.0.0 0 32768 i
*> 6.6.6.0/24 45.4.4.4 0 65001 65003 i
//此時R5也同樣學習到R6的6.6.6.0/24網絡，證明結論沒有問題
5．從IBGP對等體學來的路由條目再傳送給EBGP對等體，下一跳會改成自己的出口。
我們測試R2的2.2.2.0/24網段在傳遞給iBGP對等體R4後，由R4在傳遞給直連的eBGP對等體，下一跳是否修改？
首先，我們查看R4的BGP表
R4#showip bgp
BGPtable version is 6, local router ID is 4.4.4.4
Statuscodes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origincodes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*>4.4.4.0/24 0.0.0.0 0 32768 i
*>5.5.5.0/24 45.4.4.5 0 0 65002 i
*>6.6.6.0/24 46.4.4.6 0 0 65003 i
//我們發現此時R4從iBGP對等體R2學習到的2.2.2.0/24網段的下一跳爲R2的出口IP地址24.2.2.2
再來查看R5的BGP表
R5#showip bgp
BGPtable version is 6, local router ID is 5.5.5.5
Statuscodes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origincodes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 2.2.2.0/24 45.4.4.4 0 65001 i
*>3.3.3.0/24 45.4.4.4 0 65001 i
*>4.4.4.0/24 45.4.4.4 0 0 65001 i
*>5.5.5.0/24 0.0.0.0 0 32768 i
*>6.6.6.0/24 45.4.4.4 0 65001 65003 i
R5#
//我們發現R5學習到的2.2.2.0/24的下一跳已經更改爲R4 的出口45.4.4.4
6．從EBGP對等體學來的路由條目再傳送給IBGP對等體，下一跳不會更改爲自己的出口。
這裏測試R4從eBGP對等體R5學習到的5.5.5.0/24在傳遞給iBGP對等體R2，下一跳是否更改
首先，我們查看R4的BGP表
R4#show ip bgp
BGP table version is 6, localrouter ID is 4.4.4.4
Status codes: s suppressed, ddamped, 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
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*> 5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//我們發現R4學習到的5.5.5.0/24網段的下一跳IP地址是45.4.4.5
我們再來查看R2的BGP表
R2#show ip bgp
BGP table version is 4, localrouter ID is 2.2.2.2
Status codes: s suppressed, ddamped, 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
*>i1.1.1.0/24 12.1.1.1 0 100 0 i
*> 2.2.2.0/24 0.0.0.0 0 32768 i
*>i4.4.4.0/24 24.2.2.4 0 100 0 i
* i5.5.5.0/24 45.4.4.5 0 100 0 65002 i
* i6.6.6.0/24 46.4.4.6 0 100 0 65003 i
R2#
//我們得出R2學習到的5.5.5.0/24網段，下一跳IP地址依然是爲45.4.4.5，沒有改變。
並且在R2的BGP中沒有出現大於號（即最後路徑的標記），那麼R2是不會將它裝入路由表的，我們查看R2的路由表
R2#show ip route bgp
1.0.0.0/24 is subnetted, 1 subnets
B 1.1.1.0 [200/0] via 12.1.1.1, 00:20:10
4.0.0.0/24 is subnetted, 1 subnets
B 4.4.4.0 [200/0] via 24.2.2.4, 00:18:18
R2#
//我們發現R2並沒有將5.5.5.0/24網段裝入路由表，原因是由於在R2的BGP中對應的下一跳地址45.4.4.5所在的網段45.4.4.0/24網段，對於R2 而言不可達造成。我們再來查看R2的IGP路由表：
R2#show ip route
Codes: C - connected, S -static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O -OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 -OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPFexternal type 2
i - IS-IS, su - IS-IS summary, L1 -IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidatedefault, U - per-user static route
o - ODR, P - periodic downloaded staticroute
Gateway of last resort is notset
34.0.0.0/24 is subnetted, 1 subnets
O 34.3.3.0 [110/128] via 24.2.2.4, 00:19:55,Serial1/0
1.0.0.0/24 is subnetted, 1 subnets
B 1.1.1.0 [200/0] via 12.1.1.1, 00:20:02
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
4.0.0.0/24 is subnetted, 1 subnets
B 4.4.4.0 [200/0] via 24.2.2.4, 00:18:10
20.0.0.0/24 is subnetted, 1 subnets
C 20.20.20.0 is directly connected,Loopback10
24.0.0.0/24 is subnetted, 1 subnets
C 24.2.2.0 is directly connected,Serial1/0
40.0.0.0/24 is subnetted, 1 subnets
O 40.40.40.0 [110/65] via 24.2.2.4, 00:19:55,Serial1/0
10.0.0.0/24 is subnetted, 1 subnets
O 10.10.10.0 [110/65] via 12.1.1.1,00:19:55, Serial1/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected,Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
O 13.1.1.0 [110/128] via 12.1.1.1,00:19:55, Serial1/1
30.0.0.0/24 is subnetted, 1 subnets
O 30.30.30.0 [110/129] via 12.1.1.1,00:19:55, Serial1/1
[110/129] via 24.2.2.4,00:19:55, Serial1/0
R2#
//我們發現R2確實沒有對應的45.4.4.0/24網段的路由在IGP路由表中。
補充：如果想讓R2將學習到的5.5.5.0/24，裝入對應的路由表中，我們必須滿足下一跳可達，這裏可以用靜態路由、重發布IGP、next-hop-self等完成可達。
7．從EBGP對等體學來的路由條目，再傳送給EBGP路由器，下一跳更改爲自己的出口。
這裏我們測試R5從eBGP對等體R4學習到R6的6.6.6.0/24網段，下一跳是否會更改
首先，我們查看R4 的BGP表
R4#show ip bgp
BGP table version is 6, localrouter ID is 4.4.4.4
Status codes: s suppressed, ddamped, 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
*>i2.2.2.0/24 24.2.2.2 0 100 0 i
*>i3.3.3.0/24 34.3.3.3 0 100 0 i
*> 4.4.4.0/24 0.0.0.0 0 32768 i
*> 5.5.5.0/24 45.4.4.5 0 0 65002 i
*> 6.6.6.0/24 46.4.4.6 0 0 65003 i
R4#
//我們得出R4學習到R6的6.6.6.0/24網段，下一跳爲R6的出口IP地址46.4.4.6
然後我們查看R5的BGP表
R5#show ip bgp
BGP table version is 6, localrouter ID is 5.5.5.5
Status codes: s suppressed, ddamped, 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
*> 2.2.2.0/24 45.4.4.4 0 65001 i
*> 3.3.3.0/24 45.4.4.4 0 65001 i
*> 4.4.4.0/24 45.4.4.4 0 0 65001 i
*> 5.5.5.0/24 0.0.0.0 0 32768 i
*> 6.6.6.0/24 45.4.4.4 0 65001 65003 i
R5#
//我們發現R5學習到的6.6.6.0/24網段，下一跳變更爲R4 的出口IP地址45.4.4.4
補充：此時我們發現整個網絡沒有收斂，這是由於BGP路由傳遞原則造成，這裏可以採用Full-Mesh、RR等解決方案來完成收斂。