BGP邻居关系建立深入探讨(一):默认路由
是自己的心得,谁看到了,大家探讨一下吧,不知道自己分析的对不对
R2----------------R3--------------------R4
R2和R3之间是ospf total stub区域,在area 1.R3和R4之间是ospf backbone(area 0)
r4#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/129] via 10.1.34.3, 08:27:11, Serial0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 10.1.34.3, 08:27:11, Serial0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback0
5.0.0.0/32 is subnetted, 1 subnets
O 5.5.5.5 [110/65] via 10.1.45.5, 08:27:11, Serial1
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.1.12.0 [110/192] via 10.1.34.3, 08:27:11, Serial0
O IA 10.1.23.0 [110/128] via 10.1.34.3, 08:27:11, Serial0
C 10.1.45.0 is directly connected, Serial1
C 10.1.34.0 is directly connected, Serial0
r2#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
Gateway of last resort is 10.1.23.3 to network 0.0.0.0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 2 subnets
C 10.1.12.0 is directly connected, Serial0
C 10.1.23.0 is directly connected, Serial1
O*IA 0.0.0.0/0 [110/65] via 10.1.23.3, 09:05:59, Serial1
r4#sh ip b summary
BGP router identifier 2.2.2.2, local AS number 1
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
2.2.2.2 4 1 62 62 0 0 0 08:01:03 Active
r4#
r4#sh tcp b
r4#sh ru | b r b
router bgp 1
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 1 这里没有update source lo 0
no auto-summary
!
ip classless
no ip pim bidir-enable
!
!
!
line con 0
logging synchronous
line aux 0
line vty 0 4
!
end
r4#
SP_Access_Server_1>2
[Resuming connection 2 to 1-r2 ... ]
09:2#
r2#sh
09:26:04: TCP: checksum failure <10.1.34.4,11188> <2.2.2.2,179>
r2#sh ru | b r b
router bgp 1
no synchronization
bgp router-id 4.4.4.4
bgp cluster-id 33686018
bgp log-neighbor-changes
neighbor 4.4.4.4 remote-as 1
neighbor 4.4.4.4 update-source Loopback0
no auto-summary
!
ip classless
no ip pim bidir-enable
!
!
!
line con 0
logging synchronous
line aux 0
line vty 0 4
!
end
r2#
09:26:08: TCP: checksum failure <10.1.34.4,11188> <2.2.2.2,179>
r2#
09:26:14: BGP: 4.4.4.4 multihop open delayed 15544ms (no route)
r2#
09:26:16: TCP: checksum failure <10.1.34.4,11188> <2.2.2.2,179>
r2#
09:26:30: BGP: 4.4.4.4 multihop open delayed 11840ms (no route)
r2#
09:26:41: BGP: 4.4.4.4 multihop open delayed 10304ms (no route)
r2#
09:26:52: BGP: 4.4.4.4 multihop open delayed 10480ms (no route)
r2#
09:27:02: BGP: 4.4.4.4 multihop open delayed 10144ms (no route)
r2#
09:27:12: BGP: 4.4.4.4 multihop open delayed 14032ms (no route)
r2#
r2#sh
09:27:26: BGP: 4.4.4.4 multihop open delayed 16384ms (no route)
r2#sh ip b su
BGP router identifier 4.4.4.4, local AS number 1
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
4.4.4.4 4 1 62 62 0 0 0 08:02:59 Active
r2#cle
r2#clear
r2#clear ip b *
r2#
r2#
09:28:20: BGP: 4.4.4.4 went from Active to Idle
r2#
09:28:32: TCP: checksum failure <10.1.34.4,11189> <2.2.2.2,179>
r2#
09:28:34: TCP: checksum failure <10.1.34.4,11189> <2.2.2.2,179>
r2#
09:28:38: TCP: checksum failure <10.1.34.4,11189> <2.2.2.2,179>
r2#
09:28:41: BGP: 4.4.4.4 went from Idle to Active
09:28:41: BGP: 4.4.4.4 open active, delay 5004ms
r2#
09:28:46: BGP: 4.4.4.4 multihop open delayed 19168ms (no route)
09:28:46: TCP: checksum failure <10.1.34.4,11189> <2.2.2.2,179>
r2#
09:29:05: BGP: 4.4.4.4 multihop open delayed 10208ms (no route)
r2#
SP_Access_Server_1>4
[Resuming connection 4 to 1-r4 ... ]
r2因为使用默认路由所以不能主动发起tcp连接,因为r4没有做环回口的update source ,所以,它的更新源是出接口s0(10.1.34.4),而r2做了update source lo 0,其更新源是环回口,这时候从r4主动发起的tcp连接,r2收到这个请求后,尝试用自己的环回口地址(2.2.2.2)对r4发起更新的源地址(10.1.34.4)做相应,而r2没有neighbor这个地址,所以会出现tcp 校验和错误,并且向r4发送tcp rst,要求重新发起tcp连接.
09
r4#
r4#cle
r4#clear ip b *
r4#
09:29:25: BGP: 2.2.2.2 went from Active to Idle
r4#
09:29:45: BGP: 2.2.2.2 went from Idle to Active
09:29:45: BGP: 2.2.2.2 open active, delay 8368ms
r4#
09:29:53: BGP: 2.2.2.2 open active, local address 10.1.34.4 其出接口的更新源
09:29:53: TCB004F26A4 created
09:29:53: TCB004F26A4 setting property TCP_WINDOW_SIZE (0) 4FDE76
09:29:53: TCB004F26A4 setting property TCP_TOS (11) 4FDE75
09:29:53: TCB004F26A4 bound to 10.1.34.4.11190
09:29:53: TCP: sending SYN, seq 3358096071, ack 0
09:29:53: TCP0: Connection to 2.2.2.2:179, advertising (after MSS set) MSS 536
09:29:53: TCP0: state was CLOSED -> SYNSENT [11190 -> 2.2.2.2(179)]
09:29:53: TCP0: state was SYNSENT -> CLOSED [11190 -> 2.2.2.2(179)]
09:29:53: TCP0: bad seg from 2.2.2.2 -- closing connection: seq 0 ack 3358096072 rcvnxt 0 rcvwnd 0
09:29:53: TCP0: connection closed - remote sent RST
09:29:53: TCB 0x4F26A4 destroyed
09:29:53: BGP: 2.2.2.2 open failed: Connection refused by remote host
r4#
因为r2没有对r4的tcp连接做出响应,以它向r4发送tcp RST
----------------------------------------------------------------------------
如果把r2的update source lo 0去掉:
r2(config)#router bgp 1
r2(config-router)#
09:43:00: BGP: 4.4.4.4 multihop open delayed 10564ms (no route)
09:44:16: TCP: checksum failure <10.1.34.4,11196> <2.2.2.2,179>
r2(config-router)#no
09:44:18: TCP: checksum failure <10.1.34.4,11196> <2.2.2.2,179>
r2(config-router)#no neighbor 4.4.4.4 update-source Loopback0
09:44:22: TCP: checksum failure <10.1.34.4,11196> <2.2.2.2,179>
r2(config-router)#end
r2#
SP_Access_Server_1>4
[Resuming connection 4 to 1-r4 ... ]
09:
r4>en
09:41:53: BGP: 2.2.2.2 open active, local address 0.0.0.0
09:41:53: TCB0079170C created
09:41:53: TCB0079170C setting property TCP_WINDOW_SIZE (0) 4FDE76
09:41:53: TCB0079170C setting property TCP_TOS (11) 4FDE75
09:41:53: TCB0079170C bound to 0.0.0.0.11195
09:41:53: TCP: sending SYN, seq 2734427470, ack 0
09:41:53: TCP0: Connection to 2.2.2.2:179, advertising (after MSS set) MSS 536
09:41:53: TCP0: state was CLOSED -> SYNSENT [11195 -> 2.2.2.2(179)]
09:42:07: TCP0: timeout #3 - timeout is 16000 ms, seq 2734427470
r4#conf t
Enter configuration commands, one per line. End with CNTL/Z.
r4(config)#
r4(config)#
r4(config)#
r4(config)#
09:42:07: TCP: (11195) -> 2.2.2.2(179)
09:42:23: TCP0: state was SYNSENT -> CLOSED [11195 -> 2.2.2.2(179)]
09:42:23: TCB 0x79170C destroyed
09:42:23: BGP: 2.2.2.2 open failed: Connection timed out; remote host not responding
09:42:25: TCP: sending RST, seq 0, ack 2256687541
09:42:25: TCP: sent RST to 5.5.5.5:11251 from 4.4.4.4:179
09:44:23: BGP: 2.2.2.2 open active, local address 0.0.0.0
09:44:23: TCB0079170C created
09:44:23: TCB0079170C setting property TCP_WINDOW_SIZE (0) 4FDE76
09:44:23: TCB0079170C setting property TCP_TOS (11) 4FDE75
09:44:23: TCB0079170C bound to 0.0.0.0.11196
09:44:23: TCP: sending SYN, seq 2486109609, ack 0
09:44:23: TCP0: Connection to 2.2.2.2:179, advertising (after MSS set) MSS 536
09:44:23: TCP0: state was CLOSED -> SYNSENT [11196 -> 2.2.2.2(179)]
09:44:25: TCP: sending RST, seq 0, ack 3114400074
09:44:25: TCP: sent RST to 5.5.5.5:11252 from 4.4.4.4:179
09:44:37: TCP0: timeout #3 - timeout is 16000 ms, seq 2486109609
09:44:37: TCP: (11196) -> 2.2.2.2(179)
r4(config)#end
r4#
r4#sh ip
09:44:52: %SYS-5-CONFIG_I: Configured from console by console
r4#sh ip b su
BGP router identifier 2.2.2.2, local AS number 1
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
2.2.2.2 4 1 62 62 0 0 0 08:20:14 Active
5.5.5.5 4 1 10 11 0 0 0 08:19:05 Idle (Admin)
10.1.45.5 4 1 15 15 0 0 0 08:26:35 Idle (Admin)
r4#
09:44:53: TCP0: state was SYNSENT -> CLOSED [11196 -> 2.2.2.2(179)]
09:44:53: TCB 0x79170C destroyed
09:44:53: BGP: 2.2.2.2 open failed: Connection timed out; remote host not responding
r4#
因为对于r2其更新源是10.1.12.1,连基本的update source lo 0都没有,连发送一个rst都没有,所以超时.
r4#
r4#
r4#
09:46:53: BGP: 2.2.2.2 open active, local address 0.0.0.0
09:46:53: TCB0079170C created
09:46:53: TCB0079170C setting property TCP_WINDOW_SIZE (0) 4FDE76
09:46:53: TCB0079170C setting property TCP_TOS (11) 4FDE75
09:46:53: TCB0079170C bound to 0.0.0.0.11197
09:46:53: TCP: sending SYN, seq 1906822626, ack 0
09:46:53: TCP0: Connection to 2.2.2.2:179, advertising (after MSS set) MSS 536
09:46:53: TCP0: state was CLOSED -> SYNSENT [11197 -> 2.2.2.2(179)]
r4#
-------------------------------------------------------------------------
在r4上打上update source lo 0
r4(config)#router bgp 1
r4(config-router)#nei 2.2.2.2 up lo0
r4(config-router)#end
这时候 bgp邻居建立起来了.
看debug信息
09:51:53: BGP: 2.2.2.2 open active, local address 4.4.4.4
09:51:53: TCB0079170C created
09:51:53: TCB0079170C setting property TCP_WINDOW_SIZE (0) 4FDE76
09:51:53: TCB0079170C setting property TCP_TOS (11) 4FDE75 协商tcp窗口大小
09:51:53: TCB0079170C bound to 4.4.4.4.11199
09:51:53: TCP: sending SYN, seq 1260969948, ack 0
09:51:53: TCP0: Connection to 2.2.2.2:179, advertising (after MSS set) MSS 536
09:51:53: TCP0: state was CLOSED -> SYNSENT [11199 -> 2.2.2.2(179)]
09:51:54: TCP0: state was SYNSENT -> ESTAB [11199 -> 2.2.2.2(179)] tcp3次握手
09:51:54: TCB0079170C connected to 2.2.2.2.179
09:51:54: BGP: 2.2.2.2 went from Active to OpenSent
09:51:54: BGP: 2.2.2.2 sending OPEN, version 4, my as: 1 主动发送open
09:51:54: BGP: 2.2.2.2 send message type 1, length (incl. header) 45
09:51:54: BGP: 2.2.2.2 rcv message type 1, length (excl. header) 26
09:51:54: BGP: 2.2.2.2 rcv OPEN, version 4
09:51:54: BGP: 2.2.2.2 rcv OPEN w/ OPTION prameter len: 16
09:51:54: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 6
09:51:54: BGP: 2.2.2.2 OPEN has CAPABILITY code: 1, length 4
09:51:54: BGP: 2.2.2.2 OPEN has MP_EXT CAP for afi/safi: 1/1
09:51:54: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
09:51:54: BGP: 2.2.2.2 OPEN has CAPABILITY code: 128, length 0
09:51:54: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability(old) for all address-families
09:51:54: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
09:51:54: BGP: 2.2.2.2 OPEN has CAPABILITY code: 2, length 0
09:51:54: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability for all address-families bgp能力协商
09:51:54: BGP: 2.2.2.2 went from OpenSent to OpenConfirm
09:51:54: BGP: 2.2.2.2 send message type 4, length (incl. header) 19
09:51:54: BGP: 2.2.2.2 rcv message type 4, length (excl. header) 0
09:51:54: BGP: 2.2.2.2 went from OpenConfirm to Established
09:51:54: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up
09:51:54: BGP: 2.2.2.2 send message type 4, length (incl. header) 19
09:51:54: BGP: 2.2.2.2 send message type 4, length (incl. header) 19
09:51:54: BGP: 2.2.2.2 rcv message type 4, length (excl. header) 0
09:51:54: BGP: 2.2.2.2 rcv message type 4, length (excl. header) 0
r4#
来看看r2的debug信息
09:51:46: TCB004FF288 created
09:51:46: TCP0: state was LISTEN -> SYNRCVD [179 -> 4.4.4.4(11199)]
09:51:46: TCP: sending SYN, seq 1897244048, ack 1260969949
09:51:46: TCP0: Connection to 4.4.4.4:11199, advertising (after MSS set) MSS 536
09:51:46: TCP0: state was SYNRCVD -> ESTAB [179 -> 4.4.4.4(11199)]
09:51:46: TCB0079EF84 callback, connection queue = 1
09:51:46: TCB0079EF84 accepting 004FF288 from 4.4.4.4.11199
09:51:46: BGP: 4.4.4.4 passive open
09:51:46: BGP: 4.4.4.4 went from Active to Idle
09:51:46: BGP: 4.4.4.4 went from Idle to Connect
09:51:47: BGP: 4.4.4.4 rcv message type 1, length (excl. header) 26
09:51:47: BGP: 4.4.4.4 rcv OPEN, version 4
09:51:47: BGP: 4.4.4.4 went from Connect to OpenSent
09:51:47: BGP: 4.4.4.4 sending OPEN, version 4, my as: 1
09:51:47: BGP: 4.4.4.4 rcv OPEN w/ OPTION prameter len: 16
09:51:47: BGP: 4.4.4.4 rcvd OPEN w/ optional parameter type 2 (Capability) len 6
09:51:47: BGP: 4.4.4.4 OPEN has CAPABILITY code: 1, length 4
09:51:47: BGP: 4.4.4.4 OPEN has MP_EXT CAP for afi/safi: 1/1
09:51:47: BGP: 4.4.4.4 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
09:51:47: BGP: 4.4.4.4 OPEN has CAPABILITY code: 128, length 0
09:51:47: BGP: 4.4.4.4 OPEN has ROUTE-REFRESH capability(old) for all address-families
09:51:47: BGP: 4.4.4.4 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
09:51:47: BGP: 4.4.4.4 OPEN has CAPABILITY code: 2, length 0
09:51:47: BGP: 4.4.4.4 OPEN has ROUTE-REFRESH capability for all address-families
09:51:47: BGP: 4.4.4.4 went from OpenSent to OpenConfirm
09:51:47: BGP: 4.4.4.4 send message type 1, length (incl. header) 45
09:51:47: BGP: 4.4.4.4 send message type 4, length (incl. header) 19
09:51:47: BGP: 4.4.4.4 rcv message type 4, length (excl. header) 0
09:51:47: BGP: 4.4.4.4 went from OpenConfirm to Established
09:51:47: %BGP-5-ADJCHANGE: neighbor 4.4.4.4 Up
分析:r4用其环回口向r2的2.2.2.2 发起tcp连接,r2对 r4要求连接的2.2.2.2 做响应,在bgp配置里面正好有这个neighbor项,所以一切正常,但是为什么在不论是在r2还是在r4端clear ip b *,总是r2被动打开?(因为默认路由的关系?<在没有默认路由的时候也是这样好像>还是说其对方看到的neighbor地址较小?还是说在tcp之前的packet里面有一些协商位?)
待续…
