目录
第一章 OSPF协议特性与配置
实验 1-4 OSPF Stub区域与NSSA区域
学习目的
·掌握OSPF的Stub区域的配置
·掌握OSPF的NSSA区域的配置
·观察LSA Type7的内容
·理解LSA Type7与Type5之间的转化关系
拓扑图
图1-4 OSPF Stub区域与NSSA区域
场景
你是公司的网络管理员。现在公司的网络中有五台AR G3路由器，其中R2、R3和R4在公司总部。R5在公司分部。R5通过专线与公司总部的R3相连。R1在公司的另外一个分部，通过专线与公司总部的R2相连。
网段10.0.23.0/24、10.0.2.0/24、10.0.3.0/24属于区域0。
网段10.0.35.0/24属于区域1，区域1为NSSA区域。R5的Loopback0接口不属于OSPF区域。
网段10.0.24.0/24属于区域3。R4的Loopback0接口连接到Internet，需要配置一条缺省路由。
网段10.0.12.0/24、10.0.1.0/24属于区域2，区域2为Stub区域。
同时为了明确设备的Router-ID，你配置设备使用固定的地址作为Router-ID。
学习任务
步骤一.基础配置与IP编址
给所有路由器配置IP地址和掩码。配置时注意所有的Loopback接口配置掩码均为24位，模拟成一个单独的网段。
<R1>system-view
Enter system view, return user view with Ctrl+Z.
[R1]interface Serial 1/0/0
[R1-Serial1/0/0]ip address 10.0.12.1 24
[R1-Serial1/0/0]quit
[R1]interface LoopBack 0
[R1-LoopBack0]ip address 10.0.1.1 24
[R1-LoopBack0]quit
<R2>system-view
Enter system view, return user view with Ctrl+Z.
[R2]interface Serial 1/0/0
[R2-Serial1/0/0]ip address 10.0.12.2 24
[R2-Serial1/0/0]quit
[R2]interface Serial 2/0/0
[R2-Serial2/0/0]ip address 10.0.23.2 24
[R2-Serial2/0/0]quit
[R2]interface GigabitEthernet 0/0/0
[R2-GigabitEthernet0/0/0]ip address 10.0.24.2 24
[R2-GigabitEthernet0/0/0]quit
[R2]interface LoopBack 0
[R2-LoopBack0]ip address 10.0.2.2 24
[R2-LoopBack0]quit
<R3>system-view
Enter system view, return user view with Ctrl+Z.
[R3]interface Serial 2/0/0
[R3-Serial2/0/0]ip address 10.0.23.3 24
[R3-Serial2/0/0]quit
[R3]interface Serial 3/0/0
[R3-Serial3/0/0]ip address 10.0.35.3 24
[R3-Serial3/0/0]quit
[R3]interface LoopBack 0
[R3-LoopBack0]ip address 10.0.3.3 24
[R3-LoopBack0]quit
<R4>system-view
Enter system view, return user view with Ctrl+Z.
[R4]interface GigabitEthernet 0/0/0
[R4-GigabitEthernet0/0/0]ip address 10.0.24.4 24
[R4-GigabitEthernet0/0/0]quit
[R4]interface LoopBack 0
[R4-LoopBack0]ip address 10.0.4.4 24
[R4-LoopBack0]quit
<R5>system-view
Enter system view, return user view with Ctrl+Z.
[R5]interface Serial 1/0/0
[R5-Serial1/0/0]ip address 10.0.35.5 24
[R5-Serial1/0/0]quit
[R5]interface LoopBack 0
[R5-LoopBack0]ip address 10.0.5.5 24
[R5-LoopBack0]quit
测试直连链路的连通性。
[R2]ping -c 1 10.0.12.1
PING 10.0.12.1: 56 data bytes, press CTRL_C to break
Reply from 10.0.12.1: bytes=56 Sequence=1 ttl=255 time=30 ms
--- 10.0.12.1 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 30/30/30 ms
[R2]ping -c 1 10.0.24.4
PING 10.0.24.4: 56 data bytes, press CTRL_C to break
Reply from 10.0.24.4: bytes=56 Sequence=1 ttl=255 time=6 ms
--- 10.0.24.4 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 6/6/6 ms
[R2]ping -c 1 10.0.23.3
PING 10.0.23.3: 56 data bytes, press CTRL_C to break
Reply from 10.0.23.3: bytes=56 Sequence=1 ttl=255 time=31 ms
--- 10.0.23.3 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 31/31/31 ms
[R3]ping -c 1 10.0.35.5
PING 10.0.35.5: 56 data bytes, press CTRL_C to break
Reply from 10.0.35.5: bytes=56 Sequence=1 ttl=255 time=38 ms
--- 10.0.35.5 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 38/38/38 ms
步骤二.配置多区域OSPF
在R1上配置Serial 1/0/0及Loopback 0属于区域2，并对所有OSPF区域的Loopback接口，修改其OSPF网络类型为Broadcast类型，以便于OSPF发布Loopback口的真实掩码信息，所有的路由器使用Loopback 0的IP地址作为Router ID。
[R1]ospf 1 router-id 10.0.1.1
[R1-ospf-1]area 2
[R1-ospf-1-area-0.0.0.2]network 10.0.12.1 0.0.0.0
[R1-ospf-1-area-0.0.0.2]network 10.0.1.1 0.0.0.0
[R1-ospf-1-area-0.0.0.2]quit
[R1-ospf-1]quit
[R1]interface LoopBack 0
[R1-LoopBack0]ospf network-type broadcast
[R1-LoopBack0]quit
在R2上配置接口Serial 2/0/0及Loopback 0属于区域0，接口Serial 1/0/0属于区域2，接口GigabitEthernet 0/0/0属于区域3。
[R2]ospf 1 router-id 10.0.2.2
[R2-ospf-1]area 0
[R2-ospf-1-area-0.0.0.0]network 10.0.23.2 0.0.0.0
[R2-ospf-1-area-0.0.0.0]network 10.0.2.2 0.0.0.0
[R2-ospf-1-area-0.0.0.0]quit
[R2-ospf-1]area 2
[R2-ospf-1-area-0.0.0.2]network 10.0.12.2 0.0.0.0
[R2-ospf-1-area-0.0.0.2]quit
[R2-ospf-1]area 3
[R2-ospf-1-area-0.0.0.3]network 10.0.24.2 0.0.0.0
[R2-ospf-1-area-0.0.0.3]qui
[R2-ospf-1]quit
[R2]interface LoopBack 0
[R2-LoopBack0]ospf network-type broadcast
[R2-LoopBack0]quit
在R3上配置接口Serial 2/0/0及Loopback 0属于区域0，接口Serial 3/0/0属于区域1。
[R3]ospf 1 router-id 10.0.3.3
[R3-ospf-1]area 0
[R3-ospf-1-area-0.0.0.0]network 10.0.23.3 0.0.0.0
[R3-ospf-1-area-0.0.0.0]network 10.0.3.3 0.0.0.0
[R3-ospf-1-area-0.0.0.0]quit
[R3-ospf-1]area 1
[R3-ospf-1-area-0.0.0.1]network 10.0.35.3 0.0.0.0
[R3-ospf-1-area-0.0.0.1]quit
[R3-ospf-1]quit
[R3]interface LoopBack 0
[R3-LoopBack0]ospf network-type broadcast
[R3-LoopBack0]quit
在R4上配置接口GigabitEthernet 0/0/0属于区域3，接口Loopback 0不属于任何区域。
[R4]ospf 1 router-id 10.0.4.4
[R4-ospf-1]area 3
[R4-ospf-1-area-0.0.0.3]network 10.0.24.4 0.0.0.0
[R4-ospf-1-area-0.0.0.3]quit
[R4-ospf-1]quit
在R5上配置接口Serial 1/0/0属于区域1，接口Loopback 0不属于OSPF区域。
[R5]ospf 1 router-id 10.0.5.5
[R5-ospf-1]area 1
[R5-ospf-1-area-0.0.0.1]network 10.0.35.5 0.0.0.0
[R5-ospf-1-area-0.0.0.1]quit
[R5-ospf-1]quit
配置完成后，在R1上查看路由器的路由表。
[R1]display ip routing-table
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Routing Tables: Public
Destinations : 16 Routes : 16
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.0.1.0/24 Direct 0 0 D 10.0.1.1 LoopBack0
10.0.1.1/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.0.1.255/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.0.2.0/24 OSPF 10 1562 D 10.0.12.2 Serial1/0/0
10.0.3.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.12.0/24 Direct 0 0 D 10.0.12.1 Serial1/0/0
10.0.12.1/32 Direct 0 0 D 127.0.0.1 Serial1/0/0
10.0.12.2/32 Direct 0 0 D 10.0.12.2 Serial1/0/0
10.0.12.255/32 Direct 0 0 D 127.0.0.1 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
10.0.35.0/24 OSPF 10 4686 D 10.0.12.2 Serial1/0/0
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32Direct 0 0 D 127.0.0.1 InLoopBack0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
测试全网的连通性。
[R1]ping -c 1 10.0.35.5
PING 10.0.35.5: 56 data bytes, press CTRL_C to break
Reply from 10.0.35.5: bytes=56 Sequence=1 ttl=253 time=114 ms
--- 10.0.35.5 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 114/114/114 ms
[R1]ping -c 1 10.0.3.3
PING 10.0.3.3: 56 data bytes, press CTRL_C to break
Reply from 10.0.3.3: bytes=56 Sequence=1 ttl=254 time=74 ms
--- 10.0.3.3 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 74/74/74 ms
[R1]ping -c 1 10.0.24.4
PING 10.0.24.4: 56 data bytes, press CTRL_C to break
Reply from 10.0.24.4: bytes=56 Sequence=1 ttl=254 time=34 ms
--- 10.0.24.4 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 34/34/34 ms
步骤三.配置将外部路由引入到OSPF
将R5的Loopback0接口网段10.0.5.0/24引入到OSPF区域。使用默认配置进行路由引入。
[R5]ospf 1
[R5-ospf-1]import-route direct
配置完成后，在R1上查看该路由，并测试网络连通性。
[R1]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 7 Routes : 7
OSPF routing table status : <Active>
Destinations : 7 Routes : 7
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.0.2.0/24 OSPF 10 1562 D 10.0.12.2 Serial1/0/0
10.0.3.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.5.0/24 O_ASE 150 1 D 10.0.12.2 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
10.0.35.0/24 OSPF 10 4686 D 10.0.12.2 Serial1/0/0
10.0.35.3/32 O_ASE 150 1 D 10.0.12.2 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
[R1]ping -c 1 10.0.5.5
PING 10.0.5.5: 56 data bytes, press CTRL_C to break
Reply from 10.0.5.5: bytes=56 Sequence=1 ttl=253 time=111 ms
--- 10.0.5.5 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 111/111/111 ms
在R4上配置缺省路由，下一跳为Loopback0接口。并将该缺省路由引入到OSPF区域，定义为类型1，代价值为20，不使用永久发布。
[R4]ip route-static 0.0.0.0 0.0.0.0 LoopBack 0
[R4]ospf 1
[R4-ospf-1]default-route-advertise type 1 cost 20
[R4-ospf-1]quit
配置完成后，在R1上查看该缺省路由学习的情况。并测试网络的连通性。
[R1]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 8 Routes : 8
OSPF routing table status : <Active>
Destinations : 8 Routes : 8
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 1583 D 10.0.12.2 Serial1/0/0
10.0.2.0/24 OSPF 10 1562 D 10.0.12.2 Serial1/0/0
10.0.3.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.5.0/24 O_ASE 150 1 D 10.0.12.2 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
10.0.35.0/24 OSPF 10 4686 D 10.0.12.2 Serial1/0/0
10.0.35.3/32 O_ASE 150 1 D 10.0.12.2 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
[R1]ping -c 1 10.0.4.4
PING 10.0.4.4: 56 data bytes, press CTRL_C to break
Reply from 10.0.4.4: bytes=56 Sequence=1 ttl=254 time=39 ms
--- 10.0.4.4 ping statistics ---
1 packet(s) transmitted
1 packet(s) received
0.00% packet loss
round-trip min/avg/max = 39/39/39 ms
步骤四.配置区域2为Stub区域
在R1上查看路由信息。注意刚才看到的默认路由是外部路由（O_ASE），是通过R4发布的第五类LSA学习到的。
[R1]display ospf lsdb
OSPF Process 1 with Router ID 10.0.1.1
Link State Database
Area: 0.0.0.2
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 10.0.2.2 10.0.2.2 12 48 80000003 1562
Router 10.0.1.1 10.0.1.1 11 60 80000003 0
Sum-Net 10.0.35.0 10.0.2.2 33 28 80000001 3124
Sum-Net 10.0.24.0 10.0.2.2 33 28 80000001 1
Sum-Net 10.0.3.0 10.0.2.2 33 28 80000001 1562
Sum-Net 10.0.2.0 10.0.2.2 33 28 80000001 0
Sum-Net 10.0.23.0 10.0.2.2 34 28 80000001 1562
Sum-Asbr 10.0.4.4 10.0.2.2 34 28 80000001 1
Sum-Asbr 10.0.5.5 10.0.2.2 34 28 80000001 3124
AS External Database
Type LinkState ID AdvRouter Age Len Sequence Metric
External 0.0.0.0 10.0.4.4 1049 36 80000002 20
External 10.0.5.0 10.0.5.5 1350 36 80000001 1
External 10.0.35.0 10.0.5.5 1350 36 80000001 1
External 10.0.35.3 10.0.5.5 1350 36 80000001 1
[R1]display ospf lsdb ase 0.0.0.0
OSPF Process 1 with Router ID 10.0.1.1
Link State Database
Type : External
Ls id : 0.0.0.0
Adv rtr : 10.0.4.4
Ls age : 504
Len : 36
Options : E
seq# : 80000002
chksum : 0xa981
Net mask : 0.0.0.0
TOS 0 Metric: 20
E type : 1
Forwarding Address : 0.0.0.0
Tag : 1
Priority : Low
在R1和R2上配置区域2为Stub区域。
[R1]ospf 1
[R1-ospf-1]area 2
[R1-ospf-1-area-0.0.0.2]stub
[R1-ospf-1-area-0.0.0.2]quit
[R1-ospf-1]quit
[R2]ospf 1
[R2-ospf-1]area 2
[R2-ospf-1-area-0.0.0.2]stub
[R2-ospf-1-area-0.0.0.2]quit
[R2-ospf-1]quit
配置完成后，在R1上对比之前的路由表，查看路由信息学习情况。这时可以看到，刚才的外部路由消失了，默认路由也变成了内部路由。
[R1]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 6 Routes : 6
OSPF routing table status : <Active>
Destinations : 6 Routes : 6
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
10.0.2.0/24 OSPF 10 1562 D 10.0.12.2 Serial1/0/0
10.0.3.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.12.2 Serial1/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
10.0.35.0/24 OSPF 10 4686 D 10.0.12.2 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
查看R1的LSDB，可以看到描述外部路由的LSA也消失了，默认路由是由一条第三类LSA学习到的。
[R1]display ospf lsdb
OSPF Process 1 with Router ID 10.0.1.1
Link State Database
Area: 0.0.0.2
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 10.0.2.2 10.0.2.2 182 48 80000003 1562
Router 10.0.1.1 10.0.1.1 182 60 80000004 0
Sum-Net 0.0.0.0 10.0.2.2 183 28 80000001 1
Sum-Net 10.0.35.0 10.0.2.2 183 28 80000001 3124
Sum-Net 10.0.24.0 10.0.2.2 183 28 80000001 1
Sum-Net 10.0.3.0 10.0.2.2 183 28 80000001 1562
Sum-Net 10.0.2.0 10.0.2.2 184 28 80000001 0
Sum-Net 10.0.23.0 10.0.2.2 184 28 80000001 1562
查看这条LSA的详细信息，可以发现这条默认路由是由R2发布的，这就验证了将一个区域配置为Stub区域以后，ABR会阻断第四、五类LSA向该区域发送，并通过三类LSA向该区域内泛洪一条默认路由指向ABR自己。
[R1]display ospf lsdb summary 0.0.0.0
OSPF Process 1 with Router ID 10.0.1.1
Area: 0.0.0.2
Link State Database
Type : Sum-Net
Ls id : 0.0.0.0
Adv rtr : 10.0.2.2
Ls age : 114
Len : 28
Options : None
seq# : 80000001
chksum : 0x1f31
Net mask : 0.0.0.0
Tos 0 metric: 1
Priority : Low
在R2上将区域2配置为no-summary的完全Stub区域。
[R2]ospf 1
[R2-ospf-1]area 2
[R2-ospf-1-area-0.0.0.2]stub no-summary
[R2-ospf-1-area-0.0.0.2]quit
[R2-ospf-1]quit
查看R1的路由表，这时发现通过OSPF学习到的路由条目只剩一条默认路由了。
[R1]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 1 Routes : 1
OSPF routing table status : <Active>
Destinations : 1 Routes : 1
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 OSPF 10 1563 D 10.0.12.2 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
查看R1的LSDB信息，发现除了R1和R2产生的第一类LSA以外，只剩一条由R2发布的三类LSA。
验证了在完全Stub区域中ABR会阻断了第三、四、五类LSA，并生成一条三类LSA，通告一条指向自己的默认路由。
[R1]display ospf lsdb
OSPF Process 1 with Router ID 10.0.1.1
Link State Database
Area: 0.0.0.2
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 10.0.2.2 10.0.2.2 167 48 80000004 1562
Router 10.0.1.1 10.0.1.1 166 60 80000006 0
Sum-Net 0.0.0.0 10.0.2.2 549 28 80000001 1
步骤五.配置区域1为NSSA区域
查看R3的路由表，R5发布的10.0.5.0/24是以外部路由的形式出现的。
[R3]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 7 Routes : 7
OSPF routing table status : <Active>
Destinations : 6 Routes : 6
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 1583 D 10.0.23.2 Serial2/0/0
10.0.1.0/24 OSPF 10 3124 D 10.0.23.2 Serial2/0/0
10.0.2.0/24 OSPF 10 1562 D 10.0.23.2 Serial2/0/0
10.0.5.0/24 O_ASE 150 1 D 10.0.35.5 Serial3/0/0
10.0.12.0/24 OSPF 10 3124 D 10.0.23.2 Serial2/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.23.2 Serial2/0/0
OSPF routing table status : <Inactive>
Destinations : 1 Routes : 1
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.0.35.3/32 O_ASE 150 1 10.0.35.5 Serial3/0/0
在查看R5的路由表和LSDB信息。R5从R4学习到一条外部路由，其余的路由均是内部路由。R5通过第五类LSA向外发布了网络10.0.5.0/24。
[R5]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 7 Routes : 7
OSPF routing table status : <Active>
Destinations : 7 Routes : 7
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 3145 D 10.0.35.3 Serial1/0/0
10.0.1.0/24 OSPF 10 4686 D 10.0.35.3 Serial1/0/0
10.0.2.0/24 OSPF 10 3124 D 10.0.35.3 Serial1/0/0
10.0.3.0/24 OSPF 10 1562 D 10.0.35.3 Serial1/0/0
10.0.12.0/24 OSPF 10 4686 D 10.0.35.3 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.35.3 Serial1/0/0
10.0.24.0/24 OSPF 10 3125 D 10.0.35.3 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
[R5]display ospf lsdb
OSPF Process 1 with Router ID 10.0.5.5
Link State Database
Area: 0.0.0.1
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 10.0.5.5 10.0.5.5 882 48 80000004 1562
Router 10.0.3.3 10.0.3.3 1309 48 80000003 1562
Sum-Net 10.0.24.0 10.0.3.3 65 28 80000003 1563
Sum-Net 10.0.12.0 10.0.3.3 819 28 80000001 3124
Sum-Net 10.0.3.0 10.0.3.3 65 28 80000003 0
Sum-Net 10.0.2.0 10.0.3.3 65 28 80000003 1562
Sum-Net 10.0.1.0 10.0.3.3 812 28 80000001 3124
Sum-Net 10.0.23.0 10.0.3.3 65 28 80000003 1562
Sum-Asbr 10.0.4.4 10.0.3.3 602 28 80000002 1563
AS External Database
Type LinkState ID AdvRouter Age Len Sequence Metric
External 10.0.5.0 10.0.5.5 882 36 80000002 1
External 10.0.35.0 10.0.5.5 883 36 80000002 1
External 10.0.35.3 10.0.5.5 883 36 80000002 1
External 0.0.0.0 10.0.4.4 586 36 80000003 20
配置R3和R5的区域1为NSSA区域。
[R3]ospf 1
[R3-ospf-1]area 1
[R3-ospf-1-area-0.0.0.1]nssa
[R3-ospf-1-area-0.0.0.1]quit
[R3-ospf-1]quit
[R5]ospf 1
[R5-ospf-1]area 1
[R5-ospf-1-area-0.0.0.1]nssa
[R5-ospf-1-area-0.0.0.1]quit
[R5-ospf-1]quit
待邻居关系重新建立后，在R3上查看路由表。
[R3]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 7 Routes : 7
OSPF routing table status : <Active>
Destinations : 6 Routes : 6
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 1583 D 10.0.23.2 Serial2/0/0
10.0.1.0/24 OSPF 10 3124 D 10.0.23.2 Serial2/0/0
10.0.2.0/24 OSPF 10 1562 D 10.0.23.2 Serial2/0/0
10.0.5.0/24 O_NSSA 150 1 D 10.0.35.5 Serial3/0/0
10.0.12.0/24 OSPF 10 3124 D 10.0.23.2 Serial2/0/0
10.0.24.0/24 OSPF 10 1563 D 10.0.23.2 Serial2/0/0
OSPF routing table status : <Inactive>
Destinations : 1 Routes : 1
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.0.35.3/32 O_NSSA 150 1 10.0.35.5 Serial3/0/0
此时，R5通告的外部路由是以O_NSSA的形式出现在路由表里的。
再查看R5的路由表。
[R5]display ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
----------------------------------------------------------------------------
Public routing table : OSPF
Destinations : 7 Routes : 7
OSPF routing table status : <Active>
Destinations : 7 Routes : 7
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_NSSA 150 1 D 10.0.35.3 Serial1/0/0
10.0.1.0/24 OSPF 10 4686 D 10.0.35.3 Serial1/0/0
10.0.2.0/24 OSPF 10 3124 D 10.0.35.3 Serial1/0/0
10.0.3.0/24 OSPF 10 1562 D 10.0.35.3 Serial1/0/0
10.0.12.0/24 OSPF 10 4686 D 10.0.35.3 Serial1/0/0
10.0.23.0/24 OSPF 10 3124 D 10.0.35.3 Serial1/0/0
10.0.24.0/24 OSPF 10 3125 D 10.0.35.3 Serial1/0/0
OSPF routing table status : <Inactive>
Destinations : 0 Routes : 0
刚才默认路由是以外部路由（O_ASE）的形式出现的，现在该默认路由变成了NSSA区域的外部路由（O_NSSA）。
查看R5的LSDB。
[R5]display ospf lsdb
OSPF Process 1 with Router ID 10.0.5.5
Link State Database
Area: 0.0.0.1
Type LinkState ID AdvRouter Age Len Sequence Metric
Router 10.0.5.5 10.0.5.5 811 48 80000007 1562
Router 10.0.3.3 10.0.3.3 811 48 80000007 1562
Sum-Net 10.0.24.0 10.0.3.3 929 28 80000005 1563
Sum-Net 10.0.12.0 10.0.3.3 929 28 80000005 3124
Sum-Net 10.0.3.0 10.0.3.3 929 28 80000005 0
Sum-Net 10.0.2.0 10.0.3.3 929 28 80000005 1562
Sum-Net 10.0.1.0 10.0.3.3 930 28 80000005 3124
Sum-Net 10.0.23.0 10.0.3.3 930 28 80000005 1562
NSSA 10.0.5.0 10.0.5.5 819 36 80000005 1
NSSA 10.0.35.0 10.0.5.5 819 36 80000006 1
NSSA 10.0.35.3 10.0.5.5 819 36 80000005 1
NSSA 0.0.0.0 10.0.3.3 930 36 80000005 1
发现，刚才的第五类LSA都消失了，外部路由以第七类LSA的形式向外通告。
查看默认路由的明细信息。
[R5]display ospf lsdb nssa 0.0.0.0
OSPF Process 1 with Router ID 10.0.5.5
Area: 0.0.0.1
Link State Database
Type : NSSA
Ls id : 0.0.0.0
Adv rtr : 10.0.3.3
Ls age : 1149
Len : 36
Options : None
seq# : 80000005
chksum : 0x7745
Net mask : 0.0.0.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 0.0.0.0
Tag : 1
Priority : Low
刚才R5上的默认路由是R4通告给它的，而现在这条默认路由的通告者是R3。
从上面的结果我们可知，NSSA区域阻断了外部的第四、五类LSA进入，并且ABR会以第七类LSA的形式，向区域内通告一条默认路由。本区域的外部路由会以第七类LSA的形式，由ASBR向NSSA区域内通告。
NSSA和Stub区域的根本区别是，NSSA区域允许引入外部路由，而Stub区域不可以。
步骤六.观察NSSA给OSPF带来的变化
使用display ospf brief命令查看R3目前所处的OSPF角色，可以看到，在Border Router这个字段有三个值：AREA AS NSSA。AREA表示该路由器是一台ABR，AS表示该路由器是一台ASBR，NSSA表示该路由器至少有一个接口位于NSSA区域。
[R3]display ospf brief
OSPF Process 1 with Router ID 10.0.3.3
OSPF Protocol Information
RouterID: 10.0.3.3 Border Router: AREA AS NSSA
Multi-VPN-Instance is not enabled
Global DS-TE Mode: Non-Standard IETF Mode
Graceful-restart capability: disabled
Helper support capability : not configured
Applications Supported: MPLS Traffic-Engineering
Spf-schedule-interval: max 10000ms, start 500ms, hold 1000ms
Default ASE parameters: Metric: 1 Tag: 1 Type: 2
Route Preference: 10
ASE Route Preference: 150
SPF Computation Count: 14
RFC 1583 Compatible
Retransmission limitation is disabled
Area Count: 2 Nssa Area Count: 1
ExChange/Loading Neighbors: 0
Process total up interface count: 3
Process valid up interface count: 2
Area: 0.0.0.0 (MPLS TE not enabled)
Authtype: None Area flag: Normal
SPF scheduled Count: 14
ExChange/Loading Neighbors: 0
Router ID conflict state: Normal
Area interface up count: 2
Interface: 10.0.3.3 (LoopBack0)
Cost: 0 State: DR Type: Broadcast MTU: 1500
Priority: 1
Designated Router: 10.0.3.3
Backup Designated Router: 0.0.0.0
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
Interface: 10.0.23.3 (Serial2/0/0) --> 10.0.23.2
Cost: 1562 State: P-2-P Type: P2P MTU: 1500
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
Area: 0.0.0.1 (MPLS TE not enabled)
Authtype: None Area flag: NSSA
SPF scheduled Count: 3
ExChange/Loading Neighbors: 0
NSSA Translator State: Elected
Router ID conflict state: Normal
Area interface up count: 1
NSSA LSA count: 0
Interface: 10.0.35.3 (Serial3/0/0) --> 10.0.35.5
Cost: 1562 State: P-2-P Type: P2P MTU: 1500
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
在NSSA区域中，由于不允许第五类LSA存在，所以ASBR是以第七类LSA的形式，向区域内通告外部路由的。但第七类LSA仅允许在NSSA区域内泛洪，NSSA区域的ABR收到这个第七类的LSA后，会将该第七类LSA转换成第五类LSA，然后向其他普通区域发布。
接下来我们在R3上观察7类LSA与5类LSA的转换过程。以10.0.5.0/24为例观察路由信息的传递。对于第七类LSA，Ls id描述了目的网段，Net mask描述了目的网段对应的掩码。Options字段为NP表示该LSA可以被ABR转化成一条第五类LSA，如果Options字段显示此LSA不可以被转换成第五类LSA，则Forwarding Address可以被设置成0.0.0.0；如果Options字段显示此LSA可以被转换成第五类LSA，则Forwarding Address不能被设置0.0.0.0。
在这里，所引入外部路由的下一跳不在OSPF路由域内，Forwarding Address设置为该ASBR上某个OSPF路由域内的Stub网段的接口IP地址。这里使用的地址为R5的Serial 1/0/0的接口地址。
[R3]display ospf lsdb nssa 10.0.5.0
OSPF Process 1 with Router ID 10.0.3.3
Area: 0.0.0.0
Link State Database
Area: 0.0.0.1
Link State Database
Type : NSSA
Ls id : 10.0.5.0
Adv rtr : 10.0.5.5
Ls age : 836
Len : 36
Options : NP
seq# : 80000001
chksum : 0xb0c2
Net mask : 255.255.255.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 10.0.35.5
Tag : 1
Priority : Low
查看R3生成的用于描述10.0.5.0/24的第五类LSA。
[R3]display ospf lsdb ase 10.0.5.0
OSPF Process 1 with Router ID 10.0.3.3
Link State Database
Type : External
Ls id : 10.0.5.0
Adv rtr : 10.0.3.3
Ls age : 882
Len : 36
Options : E
seq# : 80000001
chksum : 0x413e
Net mask : 255.255.255.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 10.0.35.5
Tag : 1
Priority : Low
Ls id、Network Mask和Forwarding Address这几个字段的值直接从原来第七类LSA中拷贝。这样，10.0.5.0/24这个网段就被通告到其他区域了。
附加实验: 思考并验证
NSSA区域类型适合用在哪些场景？
分析为什么R3路由器被定义为ASBR？
最终设备配置
<R1>display current-configuration
[V200R007C00SPC600]
#
sysname R1
#
interface Serial1/0/0
link-protocol ppp
ip address 10.0.12.1 255.255.255.0
#
interface LoopBack0
ip address 10.0.1.1 255.255.255.0
ospf network-type broadcast
#
ospf 1 router-id 10.0.1.1
area 0.0.0.2
network 10.0.12.1 0.0.0.0
network 10.0.1.1 0.0.0.0
stub
#
return
<R2>display current-configuration
[V200R007C00SPC600]
#
sysname R2
#
interface Serial1/0/0
link-protocol ppp
ip address 10.0.12.2 255.255.255.0
#
interface Serial2/0/0
link-protocol ppp
ip address 10.0.23.2 255.255.255.0
#
interface GigabitEthernet0/0/0
ip address 10.0.24.2 255.255.255.0
#
interface LoopBack0
ip address 10.0.2.2 255.255.255.0
ospf network-type broadcast
#
ospf 1 router-id 10.0.2.2
area 0.0.0.0
network 10.0.23.2 0.0.0.0
network 10.0.2.2 0.0.0.0
area 0.0.0.2
network 10.0.12.2 0.0.0.0
stub no-summary
area 0.0.0.3
network 10.0.24.2 0.0.0.0
#
return
<R3>display current-configuration
[V200R007C00SPC600]
#
sysname R3
#
interface Serial2/0/0
link-protocol ppp
ip address 10.0.23.3 255.255.255.0
#
interface Serial3/0/0
link-protocol ppp
ip address 10.0.35.3 255.255.255.0
#
interface LoopBack0
ip address 10.0.3.3 255.255.255.0
ospf network-type broadcast
#
ospf 1 router-id 10.0.3.3
area 0.0.0.0
network 10.0.23.3 0.0.0.0
network 10.0.3.3 0.0.0.0
area 0.0.0.1
network 10.0.35.3 0.0.0.0
nssa
#
return
<R4>display current-configuration
[V200R007C00SPC600]
#
sysname R4
#
interface GigabitEthernet0/0/0
ip address 10.0.24.4 255.255.255.0
#
interface NULL0
#
interface LoopBack0
ip address 10.0.4.4 255.255.255.0
ospf network-type broadcast
#
ospf 1 router-id 10.0.4.4
default-route-advertise cost 20 type 1
area 0.0.0.3
network 10.0.24.4 0.0.0.0
#
ip route-static 0.0.0.0 0.0.0.0 LoopBack0
#
return
<R5>display current-configuration
[V200R007C00SPC600]
#
sysname R5
#
interface Serial1/0/0
link-protocol ppp
ip address 10.0.35.5 255.255.255.0
#
interface LoopBack0
ip address 10.0.5.5 255.255.255.0
#
ospf 1 router-id 10.0.5.5
import-route direct
area 0.0.0.1
network 10.0.35.5 0.0.0.0
nssa
#
return