OSPFv2特殊区域---NSSA区域

NSSA区域原理

NSSA区域 no-so-stub-area，次末梢区域。
NSSA区域能够将外部路由引入并传播到整个OSPF自治域中，同时又不会学习来自OSPF网络其它区域的5类LSA
在这里插入图片描述
OSPF规定Stub区域是不能引入外部路由的，这样可以避免大量外部路由对Stub区域路由器带宽和存储资源的消耗。对于既需要引入外部路由又要避免外部路由带来的资源消耗的场景，Stub区域就不再满足需求了。因此Stub区域的变形——NSSA区域就产生了。
7类LSA
• 7类LSA是为了支持NSSA区域而新增的一种LSA类型，用于描述引入的外部路由信息。
• 7类LSA由NSSA区域的自治域边界路由器（ASBR）产生，其扩散范围仅限于边界路由器所在的NSSA区域。
• NSSA区域的区域边界路由器（ABR）收到7类LSA时，会有选择地将其转化为5类LSA，以便将外部路由信息通告到OSPF网络的其它区域。
• 缺省路由也可以通过7类LSA来表示，用于指导流量流向其它自治域。
为了将NSSA区域引入的外部路由发布到其它区域，需要把Type-7 LSA转化为Type-5 LSA以便在整个OSPF网络中通告。
• option字段P用于告知转化路由器该条7类LSA是否需要转化。
• 进行转化的是NSSA区域中Router ID最大的区域边界路由器（ABR）。
• 只有P置位并且Forwarding Address不为0的Type-7 LSA才能转化为Type-5 LSA。Forwarding Address用来表示发送的某个目的地址的报文将被转发到Forwarding Address所指定的地址。
• 满足以上条件的缺省7类LSA也可以被转化。
• 区域边界路由器产生的7类LSA不会置位P-bit。
注意事项
• 在NSSA区域中，可能同时存在多个边界路由器。为了防止路由环路产生，边界路由器之间不计算对方发布的缺省路由。
NSSA和Totally NSSA
• NSSA区域允许引入少量通过本区域的ASBR到达的外部路由，但不允许其他区域的外部路由ASE LSA（Type5 LSA）在区域内传播。即到达自治系统外部的路由只能通过本区域的ASBR到达。
• Totally NSSA区域既不允许其他区域的外部路由ASE LSA（Type5 LSA）在区域内传播，也不允许区域间路由（Type3 LSA）在区域内传播。

注意：
如果希望到达自治系统外部的路由通过该区域的ASBR到达，而其它外部路由通过其它区域出去。此时，ABR会产生一条Type7LSA的缺省路由，通告到整个NSSA区域内。这样，除了某少部分路由通过NSSA的ASBR到达，其它路由都可以通过NSSA的ABR到达其它区域的ASBR出去。

如果希望所有的外部路由只有通过本区域NSSA的ASBR到达。则必须在ASBR上手动通过命令进行配置，使ASBR产生一条缺省NSSA lSA（Type7 LSA），通告到整个NSSA区域内。这样，所有的外部路由就只能通过本区域NSSA的ASBR到达。
两种情况的区别是：
在ABR上无论路由是否存在缺省路由0.0.0.0，都会产生Type7LSA的缺省路由。
在ASBR上只有当路由表中存在缺省路由0.0.0.0时，才会产生Type7LSA的缺省路由。
因为缺省路由指示在本NSSA区域内泛洪，并没有泛洪到整个OSPF域中，所以本NSSA区域内的路由器在找不到路由之后可以从该NSSA的ASBR出去，但不能实现其他OSPF域的路由从这个出口出去。Type7LSA缺省路由不会再ABR上转换成Type5LSA缺省路由泛洪到整个OSPF域。

always参数：
ASBR已经有缺省路由，执行default-route-advertise命令，将在整个OSPF区域中通告缺省路由0.0.0.0。
ASBR没有缺省路由，执行default-route-advertise命令时按照以下需求选择是否配置always参数。
如果配置always参数，无论ASBR是否有缺省路由都将在整个OSPF区域中通告缺省路由0.0.0.0，并且不再计算来自其他设备的缺省路由。
如果没有配置always参数，ASBR的路由表中必须有激活的非OSPF（BGP除外）缺省路由时才生成缺省路由的LSA。

实验配置

在这里插入图片描述

配置步骤

1.将各设备的IP地址完成配置。

<Huawei>system-view 
[Huawei]sysname  AR1
[AR1]interface  GigabitEthernet 0/0/0
[AR1-GigabitEthernet0/0/0]ip address  10.1.12.1 24
[AR1-GigabitEthernet0/0/0]quit
[AR1]<Huawei>system-view 
[Huawei]sysname  AR2	
[AR2]interface  GigabitEthernet 0/0/0
[AR2-GigabitEthernet0/0/0]ip address  10.1.12.2 24 
[AR2-GigabitEthernet0/0/0]quit	
[AR2]interface GigabitEthernet 0/0/1
[AR2-GigabitEthernet0/0/1]ip address  10.1.23.2 24
[AR2-GigabitEthernet0/0/1]quit
[AR2]<Huawei>system-view 
[Huawei]sysname  AR3	
[AR3]interface  GigabitEthernet 0/0/1
[AR3-GigabitEthernet0/0/1]ip address  10.1.23.3 24
[AR3-GigabitEthernet0/0/1]quit	
[AR3]interface  GigabitEthernet 0/0/2
[AR3-GigabitEthernet0/0/2]ip address  10.1.34.3 24
[AR3-GigabitEthernet0/0/2]quit
[AR3]<Huawei>system-view 
[Huawei]sysname  AR4	
[AR4]interface  GigabitEthernet 0/0/2
[AR4-GigabitEthernet0/0/2]ip address  10.1.34.4 24
[AR4-GigabitEthernet0/0/2]quit
[AR4]interface  GigabitEthernet 0/0/0
[AR4-GigabitEthernet0/0/0]ip address  10.1.45.4 24 
[AR4-GigabitEthernet0/0/0]quit
[AR4]<Huawei>system-view 
[Huawei]sysname  AR5
[AR5]interface  GigabitEthernet 0/0/0
[AR5-GigabitEthernet0/0/0]ip address  10.1.45.5 24
[AR5-GigabitEthernet0/0/0]quit
[AR5]interface LoopBack 0
[AR5-LoopBack0]ip address  10.1.1.1 32
[AR5-LoopBack0]quit
[AR5]

2.配置OSPF协议，将各网段IP地址通告。

[AR1]ospf 1 router-id  1.1.1.1
[AR1-ospf-1]area  1	
[AR1-ospf-1-area-0.0.0.1]network  10.1.12.0 0.0.0.255
[AR1-ospf-1-area-0.0.0.1]quit
[AR1-ospf-1][AR2]ospf 1 router-id  2.2.2.2
[AR2-ospf-1]area  0
[AR2-ospf-1-area-0.0.0.0]network  10.1.23.0 0.0.0.255
[AR2-ospf-1-area-0.0.0.0]quit
[AR2-ospf-1]area  1
[AR2-ospf-1-area-0.0.0.1]network  10.1.12.0 0.0.0.255
[AR2-ospf-1-area-0.0.0.1]quit
[AR2-ospf-1][AR3]ospf 1 router-id  3.3.3.3
[AR3-ospf-1]area  0
[AR3-ospf-1-area-0.0.0.0]network  10.1.23.0 0.0.0.255
[AR3-ospf-1-area-0.0.0.0]quit 
[AR3-ospf-1]area 2	
[AR3-ospf-1-area-0.0.0.2]network  10.1.34.0 0.0.0.255
[AR3-ospf-1-area-0.0.0.2]quit
[AR3-ospf-1][AR4]ospf 1 router-id  4.4.4.4
[AR4-ospf-1]area 2	
[AR4-ospf-1-area-0.0.0.2]network  10.1.34.0 0.0.0.255
[AR4-ospf-1-area-0.0.0.2]qui
[AR4-ospf-1]

3.在AR4和AR5设备配置静态路由。

[AR4]ip route-static 10.1.1.1 32 10.1.45.5 [AR5]ip route-static 0.0.0.0 0.0.0.0 10.1.45.4

4.将Area2配置为NSSA To他利用区域。

[AR3]ospf 1
[AR3-ospf-1]area 2 	
[AR3-ospf-1-area-0.0.0.2]nssa  no-summary[AR4]ospf 1
[AR4-ospf-1]area  2
[AR4-ospf-1-area-0.0.0.2]nssa 
[AR4-ospf-1-area-0.0.0.2]quit

5.在R4设备将静态路由引入到OSPF域中。

[AR4]ospf 1
[AR4-ospf-1]import-route  static

验证结果

1.检查IP地址配置。

[AR1]display  ip interface  brief 
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 2
The number of interface that is DOWN in Physical is 2
The number of interface that is UP in Protocol is 2
The number of interface that is DOWN in Protocol is 2Interface                         IP Address/Mask      Physical   Protocol  
GigabitEthernet0/0/0              10.1.12.1/24         up         up        
GigabitEthernet0/0/1              unassigned           down       down      
GigabitEthernet0/0/2              unassigned           down       down      
NULL0                             unassigned           up         up(s)     
[AR1][AR2]display ip interface  brief 
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 3
The number of interface that is DOWN in Physical is 1
The number of interface that is UP in Protocol is 3
The number of interface that is DOWN in Protocol is 1Interface                         IP Address/Mask      Physical   Protocol  
GigabitEthernet0/0/0              10.1.12.2/24         up         up        
GigabitEthernet0/0/1              10.1.23.2/24         up         up        
GigabitEthernet0/0/2              unassigned           down       down      
NULL0                             unassigned           up         up(s)     
[AR2][AR3]display ip interface  brief 
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 3
The number of interface that is DOWN in Physical is 1
The number of interface that is UP in Protocol is 3
The number of interface that is DOWN in Protocol is 1Interface                         IP Address/Mask      Physical   Protocol  
GigabitEthernet0/0/0              unassigned           down       down      
GigabitEthernet0/0/1              10.1.23.3/24         up         up        
GigabitEthernet0/0/2              10.1.34.3/24         up         up        
NULL0                             unassigned           up         up(s)     
[AR3][AR4]display  ip interface  brief 
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 3
The number of interface that is DOWN in Physical is 1
The number of interface that is UP in Protocol is 3
The number of interface that is DOWN in Protocol is 1Interface                         IP Address/Mask      Physical   Protocol  
GigabitEthernet0/0/0              10.1.45.4/24         up         up        
GigabitEthernet0/0/1              unassigned           down       down      
GigabitEthernet0/0/2              10.1.34.4/24         up         up        
NULL0                             unassigned           up         up(s)     
[AR4][AR5]display ip interface  brief 
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 3
The number of interface that is DOWN in Physical is 2
The number of interface that is UP in Protocol is 3
The number of interface that is DOWN in Protocol is 2Interface                         IP Address/Mask      Physical   Protocol  
GigabitEthernet0/0/0              10.1.45.5/24         up         up        
GigabitEthernet0/0/1              unassigned           down       down      
GigabitEthernet0/0/2              unassigned           down       down      
LoopBack0                         10.1.1.1/32          up         up(s)     
NULL0                             unassigned           up         up(s)     
[AR5]

2.检查OSPF协议邻居建立情况。

[AR2]display  ospf peer  brief OSPF Process 1 with Router ID 2.2.2.2Peer Statistic Information----------------------------------------------------------------------------Area Id          Interface                        Neighbor id      State    0.0.0.0          GigabitEthernet0/0/1             3.3.3.3          Full        0.0.0.1          GigabitEthernet0/0/0             1.1.1.1          Full        ----------------------------------------------------------------------------
[AR2][AR3]display  ospf peer  brief OSPF Process 1 with Router ID 3.3.3.3Peer Statistic Information----------------------------------------------------------------------------Area Id          Interface                        Neighbor id      State    0.0.0.0          GigabitEthernet0/0/1             2.2.2.2          Full        0.0.0.2          GigabitEthernet0/0/2             4.4.4.4          Full        ----------------------------------------------------------------------------
[AR3]

3.在AR1设备检查路由学习情况。

[AR1]display  ip routing-table  protocol  ospf 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPFDestinations : 3        Routes : 3        OSPF routing table status : <Active>Destinations : 3        Routes : 3Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface10.1.1.1/32  O_ASE   150  1           D   10.1.12.2       GigabitEthernet0/0/010.1.23.0/24  OSPF    10   2           D   10.1.12.2       GigabitEthernet0/0/010.1.34.0/24  OSPF    10   3           D   10.1.12.2       GigabitEthernet0/0/0OSPF routing table status : <Inactive>Destinations : 0        Routes : 0
[AR1][AR3]display  ip routing-table protocol  ospf 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPFDestinations : 2        Routes : 2        OSPF routing table status : <Active>Destinations : 2        Routes : 2Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface10.1.1.1/32  O_NSSA  150  1           D   10.1.34.4       GigabitEthernet0/0/210.1.12.0/24  OSPF    10   2           D   10.1.23.2       GigabitEthernet0/0/1OSPF routing table status : <Inactive>Destinations : 0        Routes : 0[AR3][AR4]display  ip routing-table  protocol  ospf 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPFDestinations : 1        Routes : 1        OSPF routing table status : <Active>Destinations : 1        Routes : 1Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface0.0.0.0/0   OSPF    10   2           D   10.1.34.3       GigabitEthernet0/0/2OSPF routing table status : <Inactive>Destinations : 0        Routes : 0[AR4]

5.检查OSPF协议特殊区域数据库。

[AR4]display  ospf lsdb OSPF Process 1 with Router ID 4.4.4.4Link State Database Area: 0.0.0.2Type      LinkState ID    AdvRouter          Age  Len   Sequence   MetricRouter    4.4.4.4         4.4.4.4            472  36    80000006       1Router    3.3.3.3         3.3.3.3            633  36    80000005       1Network   10.1.34.4       4.4.4.4            629  32    80000002       0Sum-Net   0.0.0.0         3.3.3.3            692  28    80000001       1NSSA      10.1.1.1        4.4.4.4            472  36    80000001       1NSSA      0.0.0.0         3.3.3.3            692  36    80000001       1[AR4

6.检查其他区域的OSPF数据库信息。

[AR1]display  ospf lsdb OSPF Process 1 with Router ID 1.1.1.1Link State Database Area: 0.0.0.1Type      LinkState ID    AdvRouter          Age  Len   Sequence   MetricRouter    2.2.2.2         2.2.2.2            115  36    80000005       1Router    1.1.1.1         1.1.1.1            114  36    80000005       1Network   10.1.12.2       2.2.2.2            115  32    80000003       0Sum-Net   10.1.23.0       2.2.2.2            153  28    80000002       1Sum-Net   10.1.34.0       2.2.2.2            745  28    80000002       2Sum-Asbr  3.3.3.3         2.2.2.2            746  28    80000001       1AS External DatabaseType      LinkState ID    AdvRouter          Age  Len   Sequence   MetricExternal  10.1.1.1        3.3.3.3            526  36    80000001       1[AR1]

7.测试地址连通。

[AR1]ping 10.1.1.1PING 10.1.1.1: 56  data bytes, press CTRL_C to breakRequest time outReply from 10.1.1.1: bytes=56 Sequence=2 ttl=252 time=60 msReply from 10.1.1.1: bytes=56 Sequence=3 ttl=252 time=40 msReply from 10.1.1.1: bytes=56 Sequence=4 ttl=252 time=40 msReply from 10.1.1.1: bytes=56 Sequence=5 ttl=252 time=30 ms--- 10.1.1.1 ping statistics ---5 packet(s) transmitted4 packet(s) received20.00% packet lossround-trip min/avg/max = 30/42/60 ms[AR1]ping 10.1.34.4PING 10.1.34.4: 56  data bytes, press CTRL_C to breakReply from 10.1.34.4: bytes=56 Sequence=1 ttl=253 time=50 msReply from 10.1.34.4: bytes=56 Sequence=2 ttl=253 time=30 msReply from 10.1.34.4: bytes=56 Sequence=3 ttl=253 time=30 msReply from 10.1.34.4: bytes=56 Sequence=4 ttl=253 time=40 msReply from 10.1.34.4: bytes=56 Sequence=5 ttl=253 time=30 ms--- 10.1.34.4 ping statistics ---5 packet(s) transmitted5 packet(s) received0.00% packet lossround-trip min/avg/max = 30/36/50 ms[AR1]