OSPF常见LSA类型及特殊区域
初学OSPF很容易被各种LSA类型和特殊区域搞晕，但是为了更好的掌握OSPF这个广泛使用的动态路由协议，还是需要搞清楚了LSA的来源、包含信息和传播区域，以及各种特殊区域存在的LSA类型。
###LSA类型###
LSA1：Router LSA
所有运行OSPF的路由器都产,描述了路由器所有接口、链路及他们的 Cost 值。只在本区域内传播
LSA2：Network LSA
由MA类型网络内的DR、BDR产生，包含所有DRother的RID，也包含自己的RID。只在本区域内传播
LSA3：Network Summary LSA
由ABR产生，通告其他区域的路由信息， Link ID 为目标网段的 ID。在整个OSPF域内传播
LSA4：ASBR Summary LSA
由ABR产生，通告ASBR路由器的地址。在整个OSPF域内传播
LSA5：AS External LSA
由ASBR产生，通告OSPF域外的路由信息。在整个OSPF域内传播
LSA7：NSSA External LSA
由NSSA特殊区域内的ASBR产生，通告OSPF域外的路由信息。只在本区域内传播，经过ABR时转换为LSA5在整个OSPF域内传播。
###特殊区域###
Stub Area：阻拦4、5类LSA进入，并自动下发默认路由 ，不允许重发布外部路由
Totally Stub Area：阻拦3、4、5类LSA，并自动下发默认路由，不允许重发布外部路由
Not-So-Stubby Area（NSSA）：阻拦4、5类LSA，需手动下发默认路由，允许重发布外部路由
Totally NSSA：阻拦3、4、5类LSA，并自动下发默认路由，允许重发布外部路由
R1配置
int f1/0
ip add 192.168.12.1 255.255.255.0
clock rate 64000
no sh
!
router ospf 1
router-id 1.1.1.1
network 192.168.12.1 0.0.0 area 1
!
R2配置
int f1/0
ip add 192.168.12.2 255.255.255.0
no sh
int s0/1
ip add 192.168.23.2 255.255.255.0
clock rate 64000
no sh
!
router ospf 1
router-id 2.2.2.2
network 192.168.12.2 0.0.0.0 area 1
network 192.168.23.2 0.0.0.0 area 0
!
R3配置
int s0/1
ip add 192.168.23.3 255.255.255.0
no sh
int s0/0
ip add 192.168.34.3 255.255.255.0
clock rate 64000
no sh
!
router ospf 1
router-id 3.3.3.3
network 192.168.23.3 0.0.0.0 area 0
network 192.168.34.3 0.0.0.0 area 2
!
R4配置
int s0/0
ip add 192.168.34.4 255.255.255.0
no sh
int lo 0
ip add 4.4.4.4 255.255.255.0
!
router ospf 1
router-id 4.4.4.4
network 192.168.34.4 0.0.0.0 a 2
redistribute connect subnet
!
R1与R2通过F口连接属于MA网络，R1存在1、2、3、4、5类LSA
R1#sh ip ospf da
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 1111 0x80000007 0x003EEE 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 1111 0x80000003 0x008B21
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.23.0 2.2.2.2 1111 0x80000003 0x001C56
192.168.34.0 2.2.2.2 1111 0x80000003 0x002502
Summary ASB Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
4.4.4.4 2.2.2.2 610 0x80000003 0x00871A
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
4.4.4.0 4.4.4.4 807 0x80000003 0x00DAA7 0
R1路由表存在3类LSA学到的路由(O IA) 和5类LSA学到的R4重发布到OSPF进程的外部路由4.4.4.0/24 (O E2)
R1#sh ip ro
------------------Omit----------------------
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet1/0
4.0.0.0/24 is subnetted, 1 subnets
O E2 4.4.4.0 [110/20] via 192.168.12.2, 01:23:30, FastEthernet1/0
O IA 192.168.23.0/24 [110/65] via 192.168.12.2, 01:30:29, FastEthernet1/0
O IA 192.168.34.0/24 [110/129] via 192.168.12.2, 01:30:29, FastEthernet1/0
把Area 1设置成Stub区域后,R1上只剩下1、2、3类LSA，同时通过5类LSA学到的外部路由4.4.4.0/24消失，但多了一条通过三类LSA学到的默认路由（O*IA）
R1#sh ip os da
OSPF Router with ID (192.168.12.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 5 0x8000000F 0x004CDA 1
192.168.12.1 192.168.12.1 5 0x80000002 0x004712 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 5 0x80000001 0x0056E7
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 158 0x80000001 0x0075C0
192.168.23.0 2.2.2.2 143 0x80000006 0x00343D
192.168.34.0 2.2.2.2 143 0x80000006 0x003DE8
R1#sh ip ro
---------------Omit-------------------
Gateway of last resort is 192.168.12.2 to network 0.0.0.0
C 192.168.12.0/24 is directly connected, FastEthernet1/0
O IA 192.168.23.0/24 [110/65] via 192.168.12.2, 00:00:58, FastEthernet1/0
O IA 192.168.34.0/24 [110/129] via 192.168.12.2, 00:00:58, FastEthernet1/0
O*IA 0.0.0.0/0 [110/2] via 192.168.12.2, 00:00:58, FastEthernet1/0
把Area 1设置为Totally Stub区域后，3类LSA从3条变成一条，同时路由信息也只有一条三类默认路由（O*IA）
R1#sh ip os da
OSPF Router with ID (192.168.12.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 16 0x80000011 0x003EE7 1
192.168.12.1 192.168.12.1 13 0x80000004 0x00391F 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.1 192.168.12.1 15 0x80000001 0x007C54
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 539 0x80000001 0x0075C0
R1#sh ip ro
-----------------------omit---------------------------
Gateway of last resort is 192.168.12.2 to network 0.0.0.0
C 192.168.12.0/24 is directly connected, FastEthernet1/0
O*IA 0.0.0.0/0 [110/2] via 192.168.12.2, 00:02:07, FastEthernet1/0
将Area 1 设置为NSSA区域，R1存在1、2、3类LSA，R1没有学习到R4重发布的外部路由4.4.4.0/24，也没有学习到默认路由，因为NSSA区域的ABR不会自动下发默认路由，需要在ABR（R2）上手动下发默认路由
R1#sh ip os da
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 35 0x80000002 0x00290D 1
2.2.2.2 2.2.2.2 28 0x80000015 0x00CD49 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 28 0x80000001 0x003573
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.23.0 2.2.2.2 135 0x80000003 0x00C1AA
192.168.34.0 2.2.2.2 135 0x80000003 0x00CA56
R1#sh ip ro
------------------------Omit-----------------------
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet1/0
O IA 192.168.23.0/24 [110/65] via 192.168.12.2, 00:03:05, FastEthernet1/0
O IA 192.168.34.0/24 [110/129] via 192.168.12.2, 00:03:05, FastEthernet1/0
此时在R1上开启Loopback 0口 1.1.1.1/24 ，重分布到OSPF进程，R2的F1/0接口将收到一个7类LSA，并学到1.1.1.0/24的路由（O N2）
R2#sh ip os da
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 696 0x8000000B 0x00E196 2
3.3.3.3 3.3.3.3 1701 0x80000006 0x0085F4 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.12.0 2.2.2.2 582 0x80000001 0x00219D
192.168.34.0 3.3.3.3 1701 0x80000004 0x0082DF
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
4.4.4.4 3.3.3.3 1188 0x80000004 0x00E4F7
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 154 0x80000003 0x002D06 1
2.2.2.2 2.2.2.2 591 0x80000015 0x00CD49 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 591 0x80000001 0x003573
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.23.0 2.2.2.2 702 0x80000003 0x00C1AA
192.168.34.0 2.2.2.2 703 0x80000003 0x00CA56
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.0 1.1.1.1 160 0x80000001 0x00EB2D 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.0 2.2.2.2 153 0x80000001 0x0062BC 0
4.4.4.0 4.4.4.4 1446 0x80000004 0x00D8A8 0
R2#sh ip ro
--------------------Omit-------------------------
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet1/0
1.0.0.0/24 is subnetted, 1 subnets
O N2 1.1.1.0 [110/20] via 192.168.12.1, 00:03:04, FastEthernet1/0
4.0.0.0/24 is subnetted, 1 subnets
O E2 4.4.4.0 [110/20] via 192.168.23.3, 00:03:04, Serial0/1
C 192.168.23.0/24 is directly connected, Serial0/1
O IA 192.168.34.0/24 [110/128] via 192.168.23.3, 00:03:04, Serial0/1
由于7类LSA是转换成5类LSA在OSPF域内传播，所以R4收到的是5类LSA，并且学到的路由1.1.1.0/24为 O E2类型
R4#sh ip os database
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum Link count
3.3.3.3 3.3.3.3 1841 0x80000006 0x00411B 2
4.4.4.4 4.4.4.4 1577 0x80000007 0x00E173 2
Summary Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
192.168.12.0 3.3.3.3 723 0x80000001 0x0085F4
192.168.23.0 3.3.3.3 1841 0x80000004 0x00FB71
Summary ASB Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
2.2.2.2 3.3.3.3 833 0x80000001 0x0047A0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.0 2.2.2.2 290 0x80000001 0x0062BC 0
4.4.4.0 4.4.4.4 1579 0x80000004 0x00D8A8 0
R4#sh ip ro
---------------------Omit---------------------
Gateway of last resort is not set
O IA 192.168.12.0/24 [110/129] via 192.168.34.3, 00:14:43, Serial0/0
1.0.0.0/24 is subnetted, 1 subnets
O E2 1.1.1.0 [110/20] via 192.168.34.3, 00:07:28, Serial0/0
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
O IA 192.168.23.0/24 [110/128] via 192.168.34.3, 02:05:39, Serial0/0
C 192.168.34.0/24 is directly connected, Serial0/0
把Area 0 设置为Totally NSSA区域，R1只剩下1、2、3类LSA，自动学习到默认路由（O*IA）
R1#sh ip os da
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 592 0x80000003 0x002D06 1
2.2.2.2 2.2.2.2 1028 0x80000015 0x00CD49 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 1028 0x80000001 0x003573
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 26 0x80000001 0x00FC31
R1#sh ip ro
--------------------Omit-------------------------
Gateway of last resort is 192.168.12.2 to network 0.0.0.0
C 192.168.12.0/24 is directly connected, FastEthernet1/0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
O*IA 0.0.0.0/0 [110/2] via 192.168.12.2, 00:03:05, FastEthernet1/0
虽然Totally Stub和Totally NSSA区域的ABR会阻止其他区域过来的3、4、5类LSA，但在这两个区域内的路由器还是会存在一个3类LSA，这个3类LSA是用来发布默认路由的。