RIP实验手册-07RIP防环机制

1、2011cntc国际互联网技术中心文档类别实验手册作者:柯闲松version : 1.0date : 2011/10/15rip基本特征7 : rip的防环机制此文档详细介绍了 r1p的各种计时器目录rip实验七:rip的防环机制第一章实验准备11丄实验目的11.2实验top图113 ip地址规划表11.4基本配置2第二章rip的防环机制32.1水平分割32.2路由毒化72.3毒性逆转132.4 hold down 计时器162.5触发更新22第三章 实验总结23第一章实验准备:l1实验目的本实验重点研究rip路由协'议的一种优化机制防环机制本实验重点硏 究了五种防环机制的基本原理和应

2、用背景。12实验top图1.3 ip地址规划表sl/o34.1.1.3/24sl/123.1.1.3/24loopo3.3.3.3/241.4基本配置首先进行基本配置，r1/r2/r3/r4的接口等按上表信息配置。完成之后,通过ping命令测试连通性，以检查基本配置的正确性。r1可以uz_12.1.1.1为源地址，去ping通r2的.12.1.1.2接口的地址了。(rlping通r2的截图粘在此处rl#ping 12.1.1.2 source 12.1.1.1type escape sequenee to abortssending 5， 100-byte icmp echos to 12.1

3、.1.2 timeout is 2 seconds:packet sent with a source address ofsuccess rate is 100 percent (5/5)， round-trip min/avg/max = 64/80/112 msr1可以以14.1.1.1为源地址，去ping通r4的14.1.1.4接口的地址了。(rlping通r4的截图粘在此处rl#ping 14.1.1.4 source 14.1.1<1type escape sequence to abort.sending 5, 100-byte icmp echos totimeout i

4、s 2 seconds:packet sent with a source address of 14.1.1.1success rate is 100 percent (5/5)， roundtrip min/avg/max = 32/52/72 msr3可以以23.1.1.2为源地址，去ping通r2的23.1.1.2接口的地址了。r3ping通r2的截图粘在此处r3#ping 23.1.1.2 source 23.1.1.3type escape sequenee to abort.sending 5， 100-byte icmp echos to 23.1.1.2， timeout i

5、s 2 seconds:packet sent with a source address of 23.1.1.3success rate is 100 percent (5/5)， round-trip min/avg/max = 64/70/96 ms r3#|r3可以uz_34.1.1.3为源地址，去ping通r4的34.1.1.4接口的地址了 o(r3ping通r4的截图粘在此处r3#ping 34.1.1.4 source 34.1.1.3type escape sequenee to abort.sending 5， 100-byte icmp echos to 34.1.1.4

6、timeout is 2 seconds:packet sent with a source address of 34.1.1<3success rate is 100 percent (5/5)， round-trip min/avg/max = 40/73/132 ms第二章rip的防环机制2.1水平分割水平分割是距离矢量路由协议的最基本的防环机制。rip路由协议在进行路由更新时,会把从邻居路由器学来的update再发送给相邻路由器。如果a发送给b的路由更新zb又回传给了 a，此时a是（是/否）_会将这些路由装入rib中，这是因为 发送全部路由。但是这样会存在出现路由环路的危险。水

7、平分割的防环机制要求路由器，从某个 接口接受到的路由条目，不再会从此接口发送出去。network例如上图，r1的rib中会有y网段的路由条目，但是在r1发给r2的update中仅仅带有x网段z r2同理仅带有y网段z这样r1去往x网段的下一跳就永远不可能为_12.1丄2而r2去往y网段的下一跳就永远不可能为_12.1.1.1o这样便排除了路由环路的隐患。起到了防环的效果。为了验证水平分割这种防环机制，需要在r1和r2上启动rip路由协议。首先完成基本配置。在r1上配rip路由协议，把r1的s1/0接口和loop 0接口启动ripo（r1的配置粘在下面）rl(c on fig )#厂0口1：0

8、ripr1(config-router)#network 12.1.1.0r1(config-router)#network 1.1.1.0rl(config-router)#在r2上配rip路由协议，把r2的s1/1接口和loop 0接口启动ripo(r2的配置粘在下面)r2(config)#router ripr2(config-router)#network 12.1.1.0r2(config-touted)#network 2220r2(config-router)#|观察r1的rib ,我们发现r1学到了_2.0.00/8 路由。(r1的rib粘在下面gateway of lastr

9、esort is not set1.0.0.0/24 is subnetted, 1 subnetsc2110 is directly connected, loopbackgr 2.0.0.0/8 120/1 via 12.1.1.2, 00:00:08, seriall/012.0.0.0/24 is subnetted 1 subnetsc12.1.2.0 is directly connected? seriall/014.0.0.0/24 is subnetted? 1 subnetsc14.1.1.0 is directly connected seriall/1ri 观察r2的r

10、ib我们发现r2学到了_1.0.00/8路由。(r2的rib粘在下面gateway of last resort is not setrcccr2#le0<0.0/8 120/1 via 12.1.1.1, 00:00:05? seriall/12.0.0.0/24 is subnetted丿 1 subnets2.2.2.0 is directly connected， loopbacko23.0.0.0/24 is23.1.1.0 is12.0.0.0/24 is12.1.1.0 issubnetted, 1 subnets directly connected? seriall/0

11、 subnetted， 1 subnets directly connected? seriall/1两台路由器不知道对方环回口的路由，现在两台路由器均学习到了对方的环回口的路由，由此可以说明之前进行的rip路由协议的配置无误。在r1上开启debug ip rip命令。cr1的debug信息截图粘在下面）rlttdebug ip riprip protocol debugging is onr1#*mar100:34:55.483:*mar100:34:55.487:*mar100:34:56.075:*mar100:34:56.075:*mar100:34:56.075:rl#*mar100

12、:35:00.207:*mar100:35:00.207:*mar100:35:00.211:*mar100:35:00.211:rl#unallrip: received vl update from 12.1.1.2 on seriall/02.0.0.0 in 1 hopsrip: sending vl update to 255.255.255.255 via seriall/0 (12.1.1.1) rip: build update entriesnetwork 1.0.0.0 metric 1rip: sending vl update to 255255255255 via l

13、oopbacko (l.l.l.l) rip: build update entriesnetwork 2.0.0.0 metric 2network 12.0.0.0 metric 1all possible debugging has beenturned offrl#观察r1的debug信息，发现r2给r1发送的update中仅带有2.0.0.0路由。在r2上开启debug ip rip命令。（r2的debug信息截图粘在下面）r2#debug ip riprip protocol debugging is onr2#*mar*mar*mar*mar*marr2#*marmar*mar*

14、marr2#r2#un11111111100:34:55.183:00:34:55.183:00:34:55.187；00:34:55.863:00:34:55.867:00:34:59.303:00:34:59.303；00:34:59.307：00:34:59.307：allrip: sending vl update to 255255255.255 via seriall/1 (12.1.1.2) rip: build update entriesnetwork 2.0.0.0 metric 1rip:received vl update from 12.1.1.1 on serial

15、l/11.0.0.0 in 1 hopssending vl update to build update entries network networkrip:rip:255.255.255.255 via loopbacko (2.2.2.2)1.0.0.0 metric 212.0.0.0 metric 1turned offall possible debugging has beenr2#观察r2的debug信息，发现r2给r1发送的update中仅带有2.0.0.0路由 °上述实验现象说明：r1在给r2发update时，不会把2.0.0.0路由返给 r2。 r2 同样不会

16、把_1.0.0.0路由返给rio2.2路由毒化回顾rip路由协议的基本特性，得知rip路由协议是以hops作为度量,如 果某路由的hops达到16 匕即为不可达该路由会从rib中删除。如果某台路由器得知某路由失效了，会向它的邻居路由器，发送关于该条目 的16跳的update ,这种现象叫做路由毒化。接收到该条目的邻居，便会得知此网段已经失效，立即从rib中删除该条目。不需要等待_180秒无效计时器超时之后删除该条目。update ：xhops unreach able:y在多冗余链路的环形网络中，如果不向全网及时通知失效的路由，也会存在出现路由环路的隐患。现在，模拟出下图的网络环境，来验证如果

17、不及时通知失 效的路由，是否有出现路由环路的隐患。现在将3三路由器均启动rip路由协'议。己置完成之后检查r1/r2/r3的路由表,是否网络达到收敛。r1 的 rib :cr1的r1b截图粘在下面gateway of last resort is not set1.0.0<0/241.1.1.0is subnetted 1 subnetsis directly connacted， loopbacko2-0.0-0/8 120/1 via 12.1.1.2, 00:00:08, seriall/03.0.0,0/8 120/1 via 13.1.1.3, 00:00:07, fa

18、stethernet0/023.0.0.0/8 120/1 via 12.1.1.2, 00:00:08, seriall/0120/1 via 13.1.1.3, 00:00:07, fastethernet0/012.0.0-0/24 is12.1.1.0 is13.0.0-0/24 issubnetted， 1 subnetsdirectly connected， seriall/0 subnetted, 1 subnetsdirectly connectedfastethernet0/0rl#r2 的 rib :(r2的rib截图粘在下面gateway of last resort i

19、s not setrcrccr1.0.0<0/8 120/1 via 12.1<1.1, 00:00:10, seriall/12.0.0.0/24 is subnetted 1 subnets2.2.2.0 is directly connected， loopbacko3.0.0.0/8 120/1 via 23.1.1.3, 00:00:16, seriall/023-0.0.0/24 is23.1.1.0 is12.0.0.0/24 is12.1.1.0 issubnetted， 1 subnetsdirectly connected seriall/0 subnetted

20、 1 subnetsdirectly connected? seriall/113.0.0.0/8 120/1 via 12.1.1.1, 00:00:10, seriall/1120/1 via 23.1.1.3, 00:00:16, seriall/0r?itr3 的 rib :(r3的rib截图粘在下面gateway of last resortis not setr1<0.0.0/8 120/2 via 23.1.1.2, 00:00:22, seriall/1r2.0.0.0/8 120/1 via 23.1.1,2, 00:00:22, seriall/13.0.0.0/24

21、 is subnetted, 1 subnetsc3>3<3.0 is directly connected, loopbacko23.0.0.0/24 is subnetted, 1 subnetsc23.1.1.0 is directly connected seriall/1r 12.0.0.0/8 120/1 via 23.1.1.2, 00:00:22, seriall/1 13.0.0.0/24 is subnetted 1 subnetsc13<1.1.0 is directly connected fastethernet0/0在r1上输入命令debug ip

22、 rip查看r1接收和发送的updateo*mar100:05:17483:rip：received vlupdatefrom13.1.1.3on fastethernet0/0mar100:05:17487:2.0.0.0 in2 hopsmar100:05:17487：23.0.0.0 in1 hopsrl#*mar100:05:18507：rip：received vlupdatefrom12.1.1.2on seriall/0*mar100:05:18.51"2.0.0.0 in1 hopsmar100:05:18 5：1：l：23.0.0.0 in1 hops红色框框出的是

23、r2和r3给r1发送的关于2.0.0.0网段的路由更新，r1 会选择_121.1.2为下一跳”这是因为_r2给r1发的路由更新所携带的跳数小,r1因此会选择12.1.1.2为下一跳。思考：2.0.0.0网段是r2的直连路由条目。如果这条路由失效了 , r2却不 向全网通告失效信息，同时r2也不会向全网发送周期更新，因此r1就有可能 将r3发来的关于2.0.0.0网段2 hops的路由条目装入rib中。r1此时会将 -13.1.1.3设置为下一跳。下面再查看一下r1给r3发送的更新：mar 1 00:05:09.339: rip: sending vl update to 255.255.255

24、.255 via fastethenneto/o (13.1.1.1) mar 1 00:05:09.339: rip: build update entriesmar 1 00:05:09>343:network 1-0.0.0 metric 1mar 1 00:05:09<343:network 2.0.q.q metric 2mar 1 00:05:09.343:network 12.0.0.0 metric 1之前我们假设r2不向全网通告2.0.0.0路由的失效信息，因此r3也同样不会收到该失效信息。上图红色框框岀的是r1给r3发送的关于2.0.0.0路由的更新，因此r3会

25、错误得认为网络中2.0.0.0这条路由发生了变化，下一跳设置为 7-13.1.1.3,跳数改成了2。这样r1和r3将对方设置为了去往2.0.0.0网段的下一跳，于是岀现了路由 环路。现在我们来研究一下路由毒化的具体过程。首先把r1的loop 0接口删除。操作如下：在r1上进行的配置)rl#conf tenter configuration commands one per line end with cntl/zrl(config)#int lo 0rl(config-if)#no ip add观察r2的debug信息，在接收到r1的update中，关于1.0.0.0/8的网段的 hops 为

26、_16o(r2的debug信息截图粘在下面,并用红框框出)r2#debug ip riprip protocol debugging is onr2#*nov 2 22:16:56.947: rip: sending vl update to 255.255.255.255 via loopbacko (2222) *nov 2 22:16:56.947: rip: build update entries*nov222:16:56.951:network1.0.0.0 metric 16*nov222:16:56.951:network3.0.0.0 metric 2*nov222:16:5

27、6.951:network12.0.0.0 metric 1*nov222:16:56.955:network13.0.0.0 metric 2*nov222:16:56.955:network23.0.0.0 metric 1r2#*nov 2 22:17:11.235: rip: sending vl 叩date to 255255255255 via seriall/1 (12.1.1.2) *nov 2 22:17:11.235: rip: build update entries*nov 2 22:17:11.239: network 1.0.0.0 metric 16*nov 2

28、22:17:11.239:network 2.0.0.0 metric 1*nov 2 22:17:11.239:network 3.0.0.0 metric 2*nov 2 22:17:11.243:network 23.0.0.0 metric 1当r2收到这条路由之后，会得知该路由已经失效，立即从自己的路由表中 删除该条目。(r2的r1b截图粘在下方gateway of lastresort is not set2<0.0>0/24is subnetted.1 subnetscrccr23-0.0-0/24 is23.1.1.0 is12,0.0.0/24 is12.1-1.

29、0 is2.2.2.q is directly connected, loopbacko3.0.0.0/8 120/1 via 23.1.1.3, 00:00:12, seriall/0 subnetted， 1 subnetsdirectly connected， seriall/0 subnetted， 1 subnetsdirectly connected seriall/113<0>0<0/8 120/1 via00:00:08 seriall/1120/1 via 23.1.1.3, 00:00:12, seriall/0r?#再来查看一下r3的路由表。(r3的ri

30、b截图粘在下方gateway of last resort is not setr 2>0.0<0/8 120/1 via 23.1.1.2, 00:00:06, seriall/1 3.0.0.0/24 is subnetted1 subnetsc3.3.3<0 is directly connected? loopbacko23.0.0.0/24 is subnetted? 1 subnetsc23<lel>0 is directly connected seriall/1r 12.0.0.0/8 120/1 via 23.1.1.2, 00:00:06, s

31、eriall/1 120/1 via 13.1.1.1, 00:00:26, fastethernet0/0 13.0.0.0/24 is subnetted 1 subnetsc13.1.1.0 is directly connected fastethernet0/0同样，r3也没有了 1.0.0.0路由的条目了，由此说明了，当rip路由的某条路由失效之后,会向_相连路由通告路由失效的信息。2.3毒性逆转在刚才的实验中，当我们删除r1的loop 0接口后，r1会通告路由失效的信息，但是我们在r2的debug信息中，同样也发现了 r2回给r1的，关于-1.0.0.0网段不可达的信息，rip路

32、由协议的这种防环机制叫做毒性逆转。（r2的debug信息截图粘在此处）r2#debug ip riprip protocol debugging is on r2# *nov 12) 歩nov *nov *nov 1.2) *nov *nov *nov 2) *nov *nov novr2# *novr2# nov *nov nov22:22:15.239:22:22:15.239:22:22:15.243:22:22:15.243:22:22:15.247:22:22:15.247:22:22:15.251:22:22:15.251:22:22:15.251:22:22:15.303:22:

33、22:15.307:22:22:19.175:22:22:19.179:22:22:19.179:*nov 2 22:22:19.179:rip: sending vl flash update torip: build flash update entries network 1.0.0.0 metric 16rip: sending vl flash update torip: build flash update entries network 1-0.0.0 metric 16rip: sending vl flash update to255.255.255.255255.255.2

34、55.255255255255255viaviaviarip: build flash update entriesnetwork 1.0.0.0 metric 16received vl update from 23.1.1.3 on seriall/0rip:rip:1.0.0.0 in 16 hops (inaccessible)received vl update from 23.1.1.3 on seriall/01.0.0.0 in 16 hops (inaccessible)3.0.0.0 in 1 hops2 孑0込0 口seriall/0 (23.1.seriall/1 (1

35、2.1.loopbacko (2.2.2x=1在现网当中，毒性逆转与路由毒化通常是作为双保险"的防环机制。设计 路由毒化的目的是及时向全网通告路由的失效信息，而毒性逆转会回传路由的不 可达信息,纠正之前自己发出的错误得路由信息继续分析下面这张网络。现在将r1的loop 0 口重新开启，网络重新收敛。现在将 r3 的 s1/1 接口 shutdown ,在 r1 上开 debug ip riprip：rip：1111100：42：06<187： 00:42:06 ：19“ 00:42:06 19：1： 00:42:06.191：00：42：07963： 00:42:07967:

36、00:42:07967: 00：42：07>967：received vl update from 12*1«1.2 on seriall/0 2<0<0<0 in 1 hops3>0<0<0 in 2 hops23.q.q.q in 1 hopsreceived vl update from 13.1.1.3 on fastethernet0/0 2.0.0.0 in 16 hops (inaccessible)3<0<0<0 in 1 hops23.0.0.0 in 16 hops (inaccessible)发现r1刚

37、刚收到r3发来的16跳信息后，会将23.0.0.0条目从rib中删mar mar *mar *marrl#*mar *mar *mar *mar除，但是r2此时还未探测出链路失效z因此还会正常给r1发送关于 -23.0.0.0的路由，如上图红框框出的部分。此时r1还会认为去往23.0.0.0网段拥有_2个下一跳,因此会继续将关于23.0.0.0网段的信息回传给_r3。*mar100:42:12.271:rip: sending vl update to 255.255.255.255 via fastethernet0/0 (13.1.1.1)*mar100:42:12.271:rip: bi

38、dld updateentries*mar100:42:12.275:network 1.0.0.0metric 11 00:42:12.275：network 12.0.0.0 metric 11 00:42:12.279：network 23.0.0.0 metric 2*mar100:42:12.275:network 2.0.0.0metric 2因此，r1给_r3发送的_23.0.0.0路由其实是一条错误得路由,如果r3接收了这条路由,会存在出现路由环路的隐患。但是r1在接收到r3发来的关于23.0.0.0不可达的update后，会回传一条_可达的路由。见下图,红框框出的部分。rl#

39、 恤 恤 恤 恤 恤 恤ii(r1的包含上述路由的debug信息截图粘在此处2 22:44:31.795: rip: sending vl update to 255.255.255.255 via fastethernet0/0 (13.1.1.1)2 22:44:31.795: rip: build update entriesnetwork 1.0.0.0 metric 1network 2,000 metric 2network 12.0.0.0 metric 1network 23.0.0.0 metric 22 22:44:31.799:2 22:44:31.799:2 22:44

40、:31.799:2 22:44:31.803:即时r3给r1传递过错误得路由，但是因为毒性逆转机制，r1给r3回传了正确路由，纠正了 r3收到的错误路由，避免了路由环路的岀现。2.4 hold down 计时器hold down计时器是思科私有的一个计时器，当某条路由80秒后还未收到路由更新，该路由条目的状态会变为无计时该路由被 锁定，进入了 hold down状态。现在将r3的s1/1接重新开启z待网络重新收敛。为了使得某条路由 条目的计时器超时，需要被动路由器的某个接口来完成。我们将r3的fo/o接 口被动。操作如下：(将被动r3的fo/o的操作截图粘在下面)r3#conf tenter

41、configuration commandone per line. end w辻h cntl/z. r3(config)#router ripr3(config-router)#pa s sr3(config-router)#passive-interface f0/0|在r：上show ip route跟踪3.0.0.0路由的时间变化。一段时间之后，在r1的路由表中，该条目进入了 possibly down状态。(r1的rib截图粘在下面gateway of last resort is not set1.0.0.0/24 is subnetted 1 subnetsc r r r1.1.

42、1.0 is directly connected loopback02.0.0.0/8 120/1 via 12.1.1.2, 00:00:20, seriall/03.0.0.0/8 120/1 via 13.1.1.3, 00:02:08, fastethernet0/023.0.0.0/8 120/1 via 12.1.1.2, 00:00:20, seriall/0 120/1 via 13.1.1.3 00:02:08, fastethernet0/012.0.0.0/24 is subnetted， 1 subnetsc12.1.1.0 is directly connected

43、 seriall/013.0.0.0/24 is subnetted 1 subnetscrl#13.1.1.0 is directly connected fastethernet0/0*nov *nov *nov *nov3 19:18:59.611: rip: sending vl update to 255255255255 via seriall/0 (12.1.1.1)3 19:18:59.611: rip: build update entries3 19:18:59.615:network 1.0.0.0 metric 13 19:18:59.615:network 3.0.0

44、.0 metric 2gateway of last resort is not set1.0.0.0/24 is subnetted, 1 subnetsc 1.1.1.0 is directly connected, loopbackor2.0.0.0/8 120/1 via 12.1.1.2, 00:00:09, seriall/0r3.0.0.0/8 120/1 via 13.1.1.3, 00:02:24, fastethernet0/0r 23.0.0.0/8 120/1 via 12.1.1.2, 00:00:0% seriall/0 120/1 via 13.1.1.3, 00

45、:02:24, fastethernet0/0 12.0.0.0/24 is subnetted, 1 subnetsc 12.1.1.0 is directly connected seriall/0 13.0.0.0/24 is subnetted, 1 subnetsc 13.1.1.0 is directly connected fastethernet0/0gateway of last resort is not set1.0.0.0/24 is subnetted, 1 subnetsc1.1.1.0 is directly connected, loopbackor2.0.0.

46、0/8 120/1 via 12.1.1.2, 00:00:01, seriall/0r3.0.0.0/8 120/1 via 13.1.1.3, 00:02:45, fastethernet0/0r 23.0.0.0/8 120/1 via 12.1.1.2, 00:00:01, seriall/0120/1 via 13.1.1.3, 00:02:45, fastethernet0/012.0.0.0/24 is subnetted, 1 subnetsc12.1.1.0 is directly connectedseriall/013.0.0.0/24 is subnetted, 1 s

47、ubnetsc13.1.1.0 is directly connected fastethernet0/0rl#*nov 3 19:19:31.635: rip: received vl update from 12.1.1.2 on seriall/0nov 3 19:19:31.639:2.0.0.0 in 1 hopsnov 3 19:19:31.639:3.0.0.0 in 2 hopsnov 3 19:19:31.639:23.0.0.0 in 1 hops同时在r1上开启debug ip rip ,发现r1在给r2发送的路由更新中关于3.0.0.0 路由的 hops 变为了16。（

48、r1的debug信息截图粘在下面）gateway of last resort is not set1.0.0.0/24 is subnettedj 1 subnetsc 1.1.1.0 is directly connected loopbackgr2.0.0.0/8 120/1 via 12.1.1.2, 00:00:14, seriall/0r3.0.0.0/8 is possibly down, routing via 13.1.1.3 fas社thernet0/0r 2300.0/8 120/1 via 12.1.1.2, 00:00:14, seriall/0120/1 via 1

49、3.1.1.3, 00:00:08, fastethern吐0/0 12.000/24 is subnetted, 1 subnetsc 12.1.1.0 is directly connected seriall/013.0.0.0/24 is subnetted 1 subnetsc 13.1.1.0 is directly connected fastethernet0/0rl#gateway of last resort is not set1.0.0.0/24 is subnetted 1 subnetsc1.1.1.0 is directly connected loopback0

50、r2.0.0.0/8 120/1 via 12.1.1.2, 00:00:26, seriall/0r3<0.0.0/8 is possibly down， routing via 13.1.1.3 fastethernet0/0r 23.0.0.0/8 120/1 via 12.1.1.2, 00:00:26, seriall/012.0.0.0/24 is subnetted， 1 subnetsc12.1.1.0 is directly connected seriall/013.0.0.0/24 is subnetted 1 subnetsc13.1.1.0 is directl

51、y connected, fastethernet0/0rl#*nov3 19:20:00.479:rip:received vl update from 12.1.1.2 on seriall/0*nov3 19:20:00.483:2.0.0.0 in 1 hops*nov3 19:20:00.483:3.0.0.0 in 2 hops*nov3 19:20:00.483:23.0.0.0 in 1 hops*nov3 19:20:03.079:rip:sending vl update to 255.255.255.255 via fastethernet0/0 (13.1.1.1)*n

52、ov3 19:20:03.079:rip:build update entries*nov3 19:20:03.079:network 1.0.0-0 metric 1*nov3 19:20:03-079:network 2.0.0.0 metric 2*nov3 19:20:03.079:network 3.0.0.0 metric 16*nov3 19:20:03.079:network 12.0.0.0 metric 1*nov3 19:20:03.079:network 23.0.0.0 metric 2|在hold down时间下取消r3的f0/0接口的被动状态在r1观察debug信

53、息，发现r1可以收到r2和r3发来的3.0.0.0路由的更新。（r1的debug信息截图粘在下面）gateway of last resort is not set1.0.0.0/24 is subnetted, 1 subnetsc1.1.1.0 is directly connected, loopbackor 2.0.0.0/8 120/1 via 12.1.1.2 00:00:23, seriall/0r 23.0.0.0/8 120/1 via 12.1.1.2, 00:00:23, seriall/0120/1 via 13.1.1-3 00:00:17， fastethernet0/0 12.0.0.0/24 is subnetted1 subnetsc12<1.1.0 is directly connected, seriall/013.0.0.0/24 is subnetted， 1 subnetsc13.1.1.0 is directly connected fastethernet0/0rl#*nov 3 19:20:50.527: rip: sending vl update to 255.255.255.255 via seriall/0 (12.1.1.1)*nov 3 19:20:50.527: rip: build updat