BGP鄰居建立與路由發佈

一、實驗拓撲

二、實驗配置

1、建立BGP鄰居

router ospf 1

router-id 10.10.0.2

log-adjacency-changes

redistribute connected metric 1000 metric-type 1 subnets

network 10.10.0.2 0.0.0.0 area 0

network 10.10.1.0 0.0.0.3 area 0

network 10.10.1.4 0.0.0.3 area 0

default-information originate always metric 2000 metric-type 1

router ospf 1

router-id 10.10.0.5

log-adjacency-changes

passive-interface Serial0/0

network 10.10.0.5 0.0.0.0 area 0

network 10.10.1.0 0.0.0.3 area 0

network 10.10.1.8 0.0.0.3 area 0

network 10.20.45.0 0.0.0.3 area 0

default-information originate always metric 2000 metric-type 1

注意：如果AS邊界接口啓動了IGP，必須配置被動接口；禁止在AS間建立IGP鄰居，禁止將AS內部IGP拓撲通告給其他AS，AS間的路由傳播通過BGP。

R2#sh ip bgp summary

BGP router identifier 10.10.0.2, local AS number 10

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.10.0.5 4 10 7 7 1 0 0 00:03:22 0

10.10.23.2 4 30 6 6 1 0 0 00:02:05 0

R2#

R2#sh ip bgp neighbors

BGP neighbor is 10.10.0.5, remote AS 10, internal link

BGP version 4, remote router ID 10.10.0.5

BGP state = Established, up for 00:04:42

Last read 00:00:42, last write 00:00:43, hold time is 180, keepalive interval is 60 seconds

Neighbor capabilities:

Route refresh: advertised and received(old & new)

Address family IPv4 Unicast: advertised and received

Message statistics:

InQ depth is 0

OutQ depth is 0

Sent Rcvd

Opens: 1 1

Notifications: 0 0

Updates: 0 0

Keepalives: 7 7

Route Refresh: 0 0

Total: 8 8

Default minimum time between advertisement runs is 0 seconds

For address family: IPv4 Unicast

BGP table version 1, neighbor version 1/0

Output queue size : 0

Index 1, Offset 0, Mask 0x2

1 update-group member

Sent Rcvd

Prefix activity: ---- ----

Prefixes Current: 0 0

Prefixes Total: 0 0

Implicit Withdraw: 0 0

Explicit Withdraw: 0 0

Used as bestpath: n/a 0

Used as multipath: n/a 0

Outbound Inbound

Local Policy Denied Prefixes: -------- -------

Total: 0 0

Number of NLRIs in the update sent: max 0, min 0

Connections established 1; dropped 0

Last reset never

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 255

Local host: 10.10.0.2, Local port: 24133

Foreign host: 10.10.0.5, Foreign port: 179

Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)

Event Timers (current time is 0x64B654):

Timer Starts Wakeups Next

Retrans 7 0 0x0

TimeWait 0 0 0x0

AckHold 6 5 0x0

SendWnd 0 0 0x0

KeepAlive 0 0 0x0

GiveUp 0 0 0x0

PmtuAger 0 0 0x0

DeadWait 0 0 0x0

iss: 3435368555 snduna: 3435368734 sndnxt: 3435368734 sndwnd: 16206

irs: 2674832881 rcvnxt: 2674833060 rcvwnd: 16206 delrcvwnd: 178

SRTT: 264 ms, RTTO: 1169 ms, RTV: 905 ms, KRTT: 0 ms

minRTT: 140 ms, maxRTT: 860 ms, ACK hold: 200 ms

Flags: active open, nagle

IP Precedence value : 6

Datagrams (max data segment is 536 bytes):

Rcvd: 11 (out of order: 0), with data: 6, total data bytes: 178

Sent: 14 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 7, total data bytes: 178

BGP neighbor is 10.10.23.2, remote AS 30, external link

BGP version 4, remote router ID 10.10.0.3

BGP state = Established, up for 00:03:33

..........

R3#sh ip bgp summary

BGP router identifier 10.10.0.3, local AS number 30

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.10.23.1 4 10 9 9 1 0 0 00:05:35 0

10.30.34.2 4 40 6 7 1 0 0 00:03:50 0

R4#sh ip bgp summary

BGP router identifier 10.10.0.4, local AS number 40

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.20.45.1 4 10 0 0 0 0 0 never Idle //TCP建立不成功

10.30.34.1 4 30 9 8 1 0 0 00:05:24 0

R4#

R5#sh ip bgp summary

BGP router identifier 10.10.0.5, local AS number 10

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.10.0.2 4 10 12 12 1 0 0 00:08:35 0

10.20.24.2 4 40 0 0 0 0 0 never Idle//注意沒有建立鄰居

TCP建立不成功，這裏的原因是配錯IP

我們查看一下R5的BGP配置

router bgp 10

no synchronization

bgp log-neighbor-changes

network 10.10.0.0 mask 255.255.0.0

neighbor 10.10.0.2 remote-as 10

neighbor 10.10.0.2 update-source Loopback0

neighbor 10.20.24.2 remote-as 40 //錯誤所在低級錯誤

no auto-summary

我們改正過來

R5(config)#router bgp 10

R5(config-router)#no neighbor 10.20.24.2 remote-as 40

R5(config-router)#nei 10.20.45.2 remote-as 40

R5#sh ip bgp sum

BGP router identifier 10.10.0.5, local AS number 10

BGP table version is 13, main routing table version 12

3 network entries using 351 bytes of memory

6 path entries using 312 bytes of memory

7/3 BGP path/bestpath attribute entries using 868 bytes of memory

4 BGP AS-PATH entries using 96 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 1627 total bytes of memory

BGP activity 6/3 prefixes, 10/4 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.10.0.2 4 10 82 81 12 0 0 01:17:12 3

10.20.45.2 4 40 7 2 0 0 0 00:00:00 2

建立成功！！

2、BGP配置及調試（路由發佈：靜態注入）

R2(config)#ip route 10.10.0.0 255.255.0.0 null 0 //配置了一條靜態路由

R2(config)#router bgp 10

R2(config-router)#net 10.10.0.0 mask 255.255.0.0 //注入這條靜態路由

R2(config-router)#end

*Mar 1 02:16:13.491: %SYS-5-CONFIG_I: Configured from console by console

R2#sh 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 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 11 subnets, 4 masks

S 10.10.0.0/16 is directly connected, Null0

C 10.10.1.0/30 is directly connected, Ethernet1/0

O 10.10.0.1/32 [110/101] via 10.10.1.6, 00:37:53, Serial0/0

C 10.10.0.2/32 is directly connected, Loopback0

O 10.10.5.0/24 [110/110] via 10.10.1.6, 00:37:53, Serial0/0

C 10.10.1.4/30 is directly connected, Serial0/0

O 10.10.0.5/32 [110/101] via 10.10.1.2, 00:37:53, Ethernet1/0

O 10.10.0.6/32 [110/201] via 10.10.1.2, 00:37:53, Ethernet1/0

O 10.10.1.8/30 [110/200] via 10.10.1.2, 00:37:53, Ethernet1/0

O 10.10.1.12/30 [110/200] via 10.10.1.6, 00:37:53, Serial0/0

C 10.10.23.0/30 is directly connected, Serial0/1

R2#sh ip bgp

BGP table version is 2, local router ID is 10.10.0.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete //BGP的屬性：源頭

Network Next Hop Metric LocPrf Weight Path

*> 10.10.0.0/16 0.0.0.0 0 32768 i //這裏的i表示IGP

注意：weight是cisco的私有值，不是BGP屬性，不能在BGP鄰居間傳播，只在BGP本路由器內有效。Cisco裏首選weight值最高的路由。

R5(config)# ip route 10.10.0.0 255.255.0.0 null 0

R5(config)#router bgp 10

R5(config-router)#net 10.10.0.0 mask 255.255.0.0

注意：R5上發佈這條路由是爲了備份

R3(config)#ip route 10.30.0.0 255.255.0.0 null 0

R3(config)#router bgp 30

R3(config-router)#net 10.30.0.0 mask 255.255.0.0

R4(config)#ip route 10.40.0.0 255.255.0.0 null 0

R4(config)#router bgp 40

R4(config-router)#net 10.40.0.0 mask 255.255.0.0

查看各設備BGP表

R2#sh ip bgp

BGP table version is 13, local router ID is 10.10.0.2

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

* i10.10.0.0/16 10.10.0.5 0 100 0 i //從IBGP鄰居學到的？

*> 0.0.0.0 0 32768 i //靜態注入的IGP

*> 10.30.0.0/16 10.10.23.2 0 0 30 i

*>i10.40.0.0/16 10.20.45.2 0 100 0 40 i //不會改變下一跳？

* 10.10.23.2 0 30 40 i

問題：什麼叫IGP？從IBGP鄰居學到的爲什麼也是i? （這裏的i是指path那裏的標記）

解答：i是表示該路由在來源路由器那裏是IGP。（來源路由器指最先發起該條路由的路由器）

* i10.10.0.0/16

最前面的i是指該路由是內部路由，即從IBGP學來的BGP路由。

R5#sh ip bgp

BGP table version is 13, local router ID is 10.10.0.5

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

* i10.10.0.0/16 10.10.0.2 0 100 0 i //

*> 0.0.0.0 0 32768 i

* 10.30.0.0/16 10.20.45.2 0 40 30 i

*>i 10.10.23.2 0 100 0 30 i

*> 10.40.0.0/16 10.20.45.2 0 0 40 i

//cisco首選weight值最高的路由；其他廠家，選擇本地始發的路由

本地始發的路由下一跳0.0.0.0，向BGP鄰居通告時，將下一跳改爲自己。

//選擇AS-PATH最短的路由

BGP只把最優的路由通告給它的鄰居，以及基於鄰居的水平分割。

上面R2將10.30.0.0傳給IBGP鄰居R5時不改變下一跳。

R3#sh ip bgp

BGP table version is 12, local router ID is 10.10.0.3

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

* 10.10.0.0/16 10.30.34.2 0 40 10 i

*> 10.10.23.1 0 0 10 i

*> 10.30.0.0/16 0.0.0.0 0 32768 i //本地始發路由

* 10.40.0.0/16 10.10.23.1 0 10 40 i

*> 10.30.34.2 0 0 40 i

R4#sh ip bgp

BGP table version is 21, local router ID is 10.10.0.4

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

*> 10.10.0.0/16 10.20.45.1 0 0 10 i

* 10.30.34.1 0 30 10 i

* 10.30.0.0/16 10.20.45.1 0 10 30 i//下一跳改爲自己

*> 10.30.34.1 0 0 30 i

*> 10.40.0.0/16 0.0.0.0 0 32768 i

上面R3與R4：R3的本地始發路由下一跳爲0.0.0.0 ，向BGP鄰居R4通告時，將下一跳改爲自己.

查看個設備的全局路由表

R3>en

R3#sh ip route

10.0.0.0/8 is variably subnetted, 7 subnets, 4 masks

B 10.10.0.0/16 [20/0] via 10.10.23.1, 01:20:27

C 10.10.0.3/32 is directly connected, Loopback0

S 10.30.0.0/16 is directly connected, Null0

C 10.30.3.0/24 is directly connected, Ethernet1/1

C 10.10.23.0/30 is directly connected, Serial0/0

B 10.40.0.0/16 [20/0] via 10.30.34.2, 00:00:03

C 10.30.34.0/30 is directly connected, Serial0/1

10.0.0.0/8 is variably subnetted, 7 subnets, 4 masks

B 10.10.0.0/16 [20/0] via 10.20.45.1, 00:17:49 //鄰居的靜態注入

C 10.10.0.4/32 is directly connected, Loopback0

B 10.30.0.0/16 [20/0] via 10.20.45.1, 00:01:00 //鄰居的靜態注入

S 10.40.0.0/16 is directly connected, Null0 自己的靜態路由管理距離是0

C 10.40.4.0/24 is directly connected, Ethernet1/1

C 10.20.45.0/30 is directly connected, Serial0/1

C 10.30.34.0/30 is directly connected, Serial0/0

注意：不同類型的路由協議優選原則按照管理距離

而BGP自己的路由優選原則是根據那幾個屬性，不要混淆了。。

10.0.0.0/8 is variably subnetted, 11 subnets, 3 masks

S 10.10.0.0/16 is directly connected, Null0 //優選管理距離小的靜態路由

C 10.10.1.0/30 is directly connected, Ethernet1/0

C 10.10.0.2/32 is directly connected, Loopback0

O 10.10.0.5/32 [110/101] via 10.10.1.2, 00:00:03, Ethernet1/0 //IGP

O 10.10.0.6/32 [110/201] via 10.10.1.2, 00:00:03, Ethernet1/0

O 10.10.1.8/30 [110/200] via 10.10.1.2, 00:00:03, Ethernet1/0

O 10.10.1.12/30 [110/210] via 10.10.1.2, 00:00:03, Ethernet1/0

B 10.30.0.0/16 [20/0] via 10.10.23.2, 01:22:20

C 10.10.23.0/30 is directly connected, Serial0/1

B 10.40.0.0/16 [200/0] via 10.20.45.2, 00:16:09

O 10.20.45.0/30 [110/164] via 10.10.1.2, 00:00:03, Ethernet1/0 //遞歸查找

10.0.0.0/8 is variably subnetted, 11 subnets, 3 masks

S 10.10.0.0/16 is directly connected, Null0

C 10.10.1.0/30 is directly connected, Ethernet1/0

O 10.10.0.2/32 [110/101] via 10.10.1.1, 00:00:02, Ethernet1/0

C 10.10.0.5/32 is directly connected, Loopback0

O 10.10.0.6/32 [110/101] via 10.10.1.10, 00:00:02, Serial0/1

C 10.10.1.8/30 is directly connected, Serial0/1

O 10.10.1.12/30 [110/110] via 10.10.1.10, 00:00:02, Serial0/1

B 10.30.0.0/16 [200/0] via 10.10.23.2, 01:32:36

O E1 10.10.23.0/30 [110/1100] via 10.10.1.1, 00:00:02, Ethernet1/0//從R2學來的通過重發布進來OSPF進程的直連路由

B 10.40.0.0/16 [20/0] via 10.20.45.2, 00:17:57

C 10.20.45.0/30 is directly connected, Serial0/0

10.0.0.0/8 is variably subnetted, 11 subnets, 3 masks

O 10.10.1.0/30 [110/200] via 10.10.1.5, 00:00:31, Serial0/1

C 10.10.0.1/32 is directly connected, Loopback0

O 10.10.0.2/32 [110/101] via 10.10.1.5, 00:00:31, Serial0/1

C 10.10.5.0/24 is directly connected, Ethernet1/1

C 10.10.1.4/30 is directly connected, Serial0/1

O 10.10.0.5/32 [110/201] via 10.10.1.5, 00:00:31, Serial0/1

O 10.10.0.6/32 [110/301] via 10.10.1.5, 00:00:31, Serial0/1

O 10.10.1.8/30 [110/300] via 10.10.1.5, 00:00:31, Serial0/1

C 10.10.1.12/30 is directly connected, Ethernet1/0

O E1 10.10.23.0/30 [110/1100] via 10.10.1.5, 00:00:31, Serial0/1

O 10.20.45.0/30 [110/264] via 10.10.1.5, 00:00:31, Serial0/1

O*E1 0.0.0.0/0 [110/2100] via 10.10.1.5, 00:00:31, Serial0/1//從R5學到的重發布缺省

1）R2與R1之間的鏈路爲什麼在數據鏈路層上是一下子up一下子down呢？以致導致學到的這條路由是從R5來的？

2）注意：R1沒有收到BGP路由是因爲，運行BGP的路由器只會把自己的BGP路由表發給自己的BGP鄰居。

10.0.0.0/8 is variably subnetted, 12 subnets, 3 masks

O 10.10.1.0/30 [110/200] via 10.10.1.9, 00:00:23, Serial0/0

O 10.10.0.1/32 [110/301] via 10.10.1.9, 00:00:23, Serial0/0

O 10.10.0.2/32 [110/201] via 10.10.1.9, 00:00:23, Serial0/0

O 10.10.5.0/24 [110/310] via 10.10.1.9, 00:00:23, Serial0/0

O 10.10.1.4/30 [110/300] via 10.10.1.9, 00:00:23, Serial0/0

O 10.10.0.5/32 [110/101] via 10.10.1.9, 00:00:23, Serial0/0

C 10.10.6.0/24 is directly connected, Ethernet1/1

C 10.10.0.6/32 is directly connected, Loopback0

C 10.10.1.8/30 is directly connected, Serial0/0

C 10.10.1.12/30 is directly connected, Ethernet1/0

O E1 10.10.23.0/30 [110/1200] via 10.10.1.9, 00:00:23, Serial0/0

O 10.20.45.0/30 [110/164] via 10.10.1.9, 00:00:23, Serial0/0

O*E1 0.0.0.0/0 [110/2100] via 10.10.1.9, 00:00:24, Serial0/0