思路：分析需求
要求1.首先R4有给定的换回路由，其他的环回路由和骨干链路的都需要配置在192.168.1.0/24网段 。
要求2：给定区域OSPF，R3的环回需在area0内
要求3：area0区域内无BDR，有且仅有R3为DR
要求4：R4的环回不能宣告，全网可达
解：
第一步：划分网段
三个环回接口+两个骨干链路 --- 5 //至少需要5个网段
2^n-2>5 ---- n至少为3 //借3位
192.168.1.0 /24+3
192.168.1.0/27 --- 骨干链路
此时R3-R4需要两个地址 --- /30 192.168.1.0 /30
而R1-R3需要三个地址 ---/29 192.168.1.8/29
192.168.1.32/27 ---R1的环回接口
192.168.1.33/27
192.168.1.64/27 ---R2的环回接口
192.168.1.65/27
192.168.1.96/27 ----R3的环回接口
192.168.1.97/27
开始配置R1-R4的接口和环回地址
//R1
[R1-GigabitEthernet0/0/0]ip address 192.168.1.9 29
Nov 15 2021 23:50:13-08:00 R1 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP
on the interface GigabitEthernet0/0/0 has entered the UP state.
[R1]interface l 0
[R1-LoopBack0]ip a
[R1-LoopBack0]ip address 192.168.1.33 27
[R1-LoopBack0]q
//R2
[R2-GigabitEthernet0/0/0]ip address 192.168.1.10 29
Nov 15 2021 23:50:38-08:00 R2 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP
on the interface GigabitEthernet0/0/0 has entered the UP state.
[R2]int
[R2]interface l 0
[R2-LoopBack0]ip a
[R2-LoopBack0]ip address 192.168.1.65 27
[R2-LoopBack0]q
//R3
[R3-GigabitEthernet0/0/0]ip address 192.168.1.11 29
Nov 15 2021 23:51:06-08:00 R3 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP
on the interface GigabitEthernet0/0/0 has entered the UP state.
[R3-GigabitEthernet0/0/0]int
[R3-GigabitEthernet0/0/0]int g0/0/1
[R3-GigabitEthernet0/0/1]ip address 192.168.1.2 30
Nov 15 2021 23:51:36-08:00 R3 %%01IFNET/4/LINK_STATE(l)[1]:The line protocol IP
on the interface GigabitEthernet0/0/1 has entered the UP state.
[R3-GigabitEthernet0/0/1]q
[R3]int
[R3]interface l 0
[R3-LoopBack0]ip
[R3-LoopBack0]ip a
[R3-LoopBack0]ip address 192.168.1.97 27
[R3-LoopBack0]q
//R4
[R4-GigabitEthernet0/0/0]ip address 192.168.1.1 30
Nov 15 2021 23:50:38-08:00 R2 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP
on the interface GigabitEthernet0/0/0 has entered the UP state.
[R2]int
[R2]interface l 0
[R2-LoopBack0]ip a
[R2-LoopBack0]ip address 4.4.4.1 24
[R2-LoopBack0]q
经过检查，没有配置错误，现在开始配置OSPF协议
//R1
[R1]os
[R1]ospf 1
[R1]ospf 1 r
[R1]ospf 1 router-id 1.1.1.1
[R1-ospf-1]area 0
[R1-ospf-1-area-0.0.0.0]net
[R1-ospf-1-area-0.0.0.0]network 192.168.1.33 0.0.0.255
[R1-ospf-1-area-0.0.0.0]ne
[R1-ospf-1-area-0.0.0.0]network 192.168.1.9 0.0.0.0
//R2
[R2]
[R2]oss
[R2]osp
[R2]ospf 1 r
[R2]ospf 1 router-id 2.2.2.2
[R2-ospf-1]area
[R2-ospf-1]area 0
[R2-ospf-1-area-0.0.0.0]ne
[R2-ospf-1-area-0.0.0.0]network 192.168.1.10 0.0.0.255
//R3
[R3]
[R3]os
[R3]ospf 1 r
[R3]ospf 1 router-id 3.3.3.3
[R3-ospf-1]ara
[R3-ospf-1]are
[R3-ospf-1]area 1
[R3-ospf-1-area-0.0.0.1]net
[R3-ospf-1-area-0.0.0.1]network 192.168.1.2 0.0.0.0
//另一个区域
[R3]ospf 1 r
[R3]ospf 1 router-id 3.3.3.3
[R3-ospf-1]ar
[R3-ospf-1]area 0
[R3-ospf-1-area-0.0.0.0]netw
[R3-ospf-1-area-0.0.0.0]network 192.168.1.97 0.0.0.255
//R4
[R4]ospf 1 router-id 4.4.4.4
Info: The configuration succeeded. You need to restart the OSPF process to valid
ate the new router ID.
[R4-ospf-1]ar
[R4-ospf-1]area 1
[R4-ospf-1-area-0.0.0.1]netw
[R4-ospf-1-area-0.0.0.1]network 192.168.1.1 0.0.0.0此时没有检查OSPF表，除了R4的4.4.4.0 /24没有宣告地址无法ping通
//R1
[R1]display ospf peer
OSPF Process 1 with Router ID 1.1.1.1
Neighbors
Area 0.0.0.0 interface 192.168.1.9(GigabitEthernet0/0/0)'s neighbors
Router ID: 2.2.2.2 Address: 192.168.1.10
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.10 BDR: 192.168.1.11 MTU: 0
Dead timer due in 37 sec
Retrans timer interval: 4
Neighbor is up for 00:00:49
Authentication Sequence: [ 0 ]
Router ID: 3.3.3.3 Address: 192.168.1.11
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.10 BDR: 192.168.1.11 MTU: 0
Dead timer due in 30 sec
Retrans timer interval: 5
Neighbor is up for 00:00:43
Authentication Sequence: [ 0 ]
//R2和R3同理
[R2]display ospf peer
OSPF Process 1 with Router ID 2.2.2.2
Neighbors
Area 0.0.0.0 interface 192.168.1.10(GigabitEthernet0/0/0)'s neighbors
Router ID: 1.1.1.1 Address: 192.168.1.9
State: Full Mode:Nbr is Slave Priority: 1
DR: 192.168.1.9 BDR: 192.168.1.10 MTU: 0
Dead timer due in 40 sec
Retrans timer interval: 0
Neighbor is up for 00:03:48
Authentication Sequence: [ 0 ]
Router ID: 3.3.3.3 Address: 192.168.1.11
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.9 BDR: 192.168.1.10 MTU: 0
Dead timer due in 31 sec
Retrans timer interval: 4
Neighbor is up for 00:01:12
Authentication Sequence: [ 0 ]
//R4
<R4>display ospf peer
OSPF Process 1 with Router ID 4.4.4.4
Neighbors
Area 0.0.0.1 interface 192.168.1.1(GigabitEthernet0/0/0)'s neighbors
Router ID: 3.3.3.3 Address: 192.168.1.2
State: Full Mode:Nbr is Slave Priority: 1
DR: 192.168.1.1 BDR: 192.168.1.2 MTU: 0
Dead timer due in 33 sec
Retrans timer interval: 5
Neighbor is up for 00:31:53
Authentication Sequence: [ 0 ]
开始配置area0的BR和BDR
//R1
[R1]int
[R1]interface g0/0/0
[R1-GigabitEthernet0/0/0]os
[R1-GigabitEthernet0/0/0]ospf d
[R1-GigabitEthernet0/0/0]ospf dr-priority ?
INTEGER<0-255> Router priority value
[R1-GigabitEthernet0/0/0]ospf dr-priority 0
//R2
[R2]int
[R2]interface g0/0/0
[R2-GigabitEthernet0/0/0]os
[R2-GigabitEthernet0/0/0]ospf d
[R2-GigabitEthernet0/0/0]ospf dr-priority 0此时再次查看area表内的内容
[R3]display ospf peer
OSPF Process 1 with Router ID 3.3.3.3
Neighbors
Area 0.0.0.0 interface 192.168.1.11(GigabitEthernet0/0/0)'s neighbors
Router ID: 1.1.1.1 Address: 192.168.1.9
State: Full Mode:Nbr is Slave Priority: 0
DR: 192.168.1.11 BDR: None MTU: 0
Dead timer due in 30 sec
Retrans timer interval: 5
Neighbor is up for 00:00:57
Authentication Sequence: [ 0 ]
Router ID: 2.2.2.2 Address: 192.168.1.10
State: Full Mode:Nbr is Slave Priority: 0
DR: 192.168.1.11 BDR: None MTU: 0
Dead timer due in 36 sec
Retrans timer interval: 4
Neighbor is up for 00:00:29
Authentication Sequence: [ 0 ]
Neighbors
Area 0.0.0.1 interface 192.168.1.2(GigabitEthernet0/0/1)'s neighbors
Router ID: 4.4.4.4 Address: 192.168.1.1
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.1 BDR: 192.168.1.2 MTU: 0
Dead timer due in 32 sec
Retrans timer interval: 5
Neighbor is up for 00:05:46
Authentication Sequence: [ 0 ] 此时已经没有BDR，只有BR
尝试ping联通
[R3]ping 192.168.1.1
PING 192.168.1.1: 56 data bytes, press CTRL_C to break
Reply from 192.168.1.1: bytes=56 Sequence=1 ttl=255 time=30 ms
Reply from 192.168.1.1: bytes=56 Sequence=2 ttl=255 time=30 ms
Reply from 192.168.1.1: bytes=56 Sequence=3 ttl=255 time=20 ms
Reply from 192.168.1.1: bytes=56 Sequence=4 ttl=255 time=30 ms
Reply from 192.168.1.1: bytes=56 Sequence=5 ttl=255 time=30 ms
--- 192.168.1.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 20/28/30 ms
结束