关于OSPF中LSA5产生的路由和LSA7产生的同一条路由的优先使用规测。
关于OSPF中LSA5产生的路由和LSA7产生的同一条路由的优先使用规测。
R1配置：
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 14.1.1.1 255.255.255.0
duplex auto
speed auto
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
redistribute static metric 21 subnets
network 1.1.1.1 0.0.0.0 area 0
network 12.1.1.0 0.0.0.255 area 0
!
ip classless
ip route 44.1.1.0 255.255.255.0 14.1.1.2
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/24 is subnetted, 1 subnets
O IA 34.1.1.0 [110/3] via 12.1.1.2, 00:10:30, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
32.0.0.0/24 is subnetted, 1 subnets
O IA 32.1.1.0 [110/2] via 12.1.1.2, 00:10:30, FastEthernet0/0
4.0.0.0/32 is subnetted, 1 subnets
O E2 4.4.4.4 [110/20] via 12.1.1.2, 00:10:30, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
44.0.0.0/24 is subnetted, 1 subnets
S 44.1.1.0 [1/0] via 14.1.1.2
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, FastEthernet0/1
R1#
配置中R1上写了一条到R4 loop1 ip=44.1.1.0网段的静态路由，然后把这条路由重分发到了OSPF域内。
在看R4的配置：
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface Loopback1
ip address 44.1.1.1 255.255.255.0
!
interface FastEthernet0/0
ip address 34.1.1.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 14.1.1.2 255.255.255.0
duplex auto
speed auto
!
router ospf 1
log-adjacency-changes
area 1 nssa
redistribute connected subnets
network 34.1.1.0 0.0.0.255 area 1
!
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/24 is subnetted, 1 subnets
C 34.1.1.0 is directly connected, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/4] via 34.1.1.1, 00:09:28, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
O 32.1.1.0 [110/2] via 34.1.1.1, 00:09:28, FastEthernet0/0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback0
12.0.0.0/24 is subnetted, 1 subnets
O IA 12.1.1.0 [110/3] via 34.1.1.1, 00:09:28, FastEthernet0/0
44.0.0.0/24 is subnetted, 1 subnets
C 44.1.1.0 is directly connected, Loopback1
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, FastEthernet0/1
R4作为ASBR路由器，把路由器R4 connect的路由41.1.1.0重分发到OSPF域内。
当41.1.1.0那条路由通过R4发布到ospf域内的时候，他会以LSA7的类型广播到nssa区域，所以R3，R2的链路状态数据库内都会有着条路由的LSA7的链路状态通告。
而41.1.1.0那条路由也通过R1发布到ospf域内，这时候他会以lsa5的类型广播到area0内（本来可以广播到整个ospf域内，但是area1是NSSA区域，不会接受外部lsa也就是lsa5。这样在41.1.1.0这个lsa5会在R1，R2产生。
R2# show ip ospf database
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
1.1.1.1 1.1.1.1 1693 0x8000000A 0x00D11A 2
2.2.2.2 2.2.2.2 1034 0x80000009 0x007F78 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
12.1.1.2 2.2.2.2 1034 0x80000007 0x00060A
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
32.1.1.0 2.2.2.2 788 0x8000000C 0x00887E
34.1.1.0 2.2.2.2 1786 0x8000000B 0x007A8A
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 1414 0x8000000D 0x00784E 1
3.3.3.3 3.3.3.3 1411 0x80000011 0x00A7BA 2
4.4.4.4 4.4.4.4 1754 0x8000000A 0x000BAB 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
32.1.1.2 3.3.3.3 799 0x80000008 0x00DA0E
34.1.1.1 3.3.3.3 1818 0x80000003 0x0039AB
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
1.1.1.1 2.2.2.2 1035 0x80000005 0x00D054
12.1.1.0 2.2.2.2 1035 0x80000005 0x0041DA
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
4.4.4.4 4.4.4.4 1754 0x80000005 0x00C685 0
14.1.1.0 4.4.4.4 1736 0x80000001 0x00B996 0
44.1.1.0 4.4.4.4 1754 0x80000005 0x002A04 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
4.4.4.4 2.2.2.2 1787 0x80000003 0x009BC4 0
14.1.1.0 2.2.2.2 1737 0x80000001 0x008AD7 0
44.1.1.0 1.1.1.1 1589 0x80000004 0x0078F1 0
44.1.1.0 2.2.2.2 1588 0x80000001 0x000341 0
R2#
这样看来也就是在R2的lsadb内，对于41.1.1.0这个路由信息，lsa5和lsa7各自有一条。那到底选哪一条做为真正的转发路径呢？
如果按照TCP-IP路由技术的说法就是：区域内路由>区域外路由>ospf域外路由LSA5>OSPF域外路由LSA7。如果按照这个规则则路由表中会出现LSA5产生的路由。
察看R2路由表：
R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/24 is subnetted, 1 subnets
O 34.1.1.0 [110/2] via 32.1.1.2, 00:01:01, FastEthernet0/1
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/2] via 12.1.1.1, 00:01:01, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
C 32.1.1.0 is directly connected, FastEthernet0/1
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O N2 4.4.4.4 [110/20] via 32.1.1.2, 00:01:01, FastEthernet0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
44.0.0.0/24 is subnetted, 1 subnets
O E2 44.1.1.0 [110/20] via 12.1.1.1, 00:01:02, FastEthernet0/0
14.0.0.0/24 is subnetted, 1 subnets
O N2 14.1.1.0 [110/20] via 32.1.1.2, 00:01:02, FastEthernet0/1
R2#
确实是这样。
查看R2内关于该条LSA
R2#show ip ospf database nssa-external 44.1.1.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-7 AS External Link States (Area 1)
LS age: 649
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 44.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000006
Checksum: 0x2805
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 34.1.1.2
External Route Tag: 0
R2#show ip ospf database external 44.1.1.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 352
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 44.1.1.0 (External Network Number )
Advertising Router: 1.1.1.1
LS Seq Number: 80000001
Checksum: 0x74F9
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
发现这俩条了LSA的metric也一样
那我们改变一下R1的配置，增大重新分发时候该路由的度量：
命令：redistribute static subnets metric 25
R2#show ip ospf database external 44.1.1.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 672
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 44.1.1.0 (External Network Number )
Advertising Router: 1.1.1.1
LS Seq Number: 80000004
Checksum: 0xA0C5
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 25
Forward Address: 0.0.0.0
External Route Tag: 0
R2#show ip ospf database nss 44.1.1.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-7 AS External Link States (Area 1)
Routing Bit Set on this LSA
LS age: 1622
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 44.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000006
Checksum: 0x2805
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 34.1.1.2
External Route Tag: 0
检查R2路由表发现：
R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/24 is subnetted, 1 subnets
O 34.1.1.0 [110/2] via 32.1.1.2, 00:01:01, FastEthernet0/1
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/2] via 12.1.1.1, 00:01:01, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
C 32.1.1.0 is directly connected, FastEthernet0/1
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O N2 4.4.4.4 [110/20] via 32.1.1.2, 00:01:01, FastEthernet0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
44.0.0.0/24 is subnetted, 1 subnets
O N2 44.1.1.0 [110/20] via 32.1.1.2, 00:00:31, FastEthernet0/1
14.0.0.0/24 is subnetted, 1 subnets
O N2 14.1.1.0 [110/20] via 32.1.1.2, 00:01:02, FastEthernet0/1
该条路由变成了，O N2 也就是使用了lsa7的路由。也就是说没有按照区域内路由>区域外路由>ospf域外路由LSA5>OSPF域外路由LSA7这个规则。
总结:只有OSPF域内的ABR路由器才有可能同时收到类型LSA5和类型LSA7的同一条LSA，如果这俩条LSA都是以metric-tyoe 2的形式发布进去，并且metric相同的时候，该ABR路由器会优先选择LSA5产生的路由，但是当LSA7 metric大于LSA5 metric的时候 就会优先选择LSA7产生的路由。当lsa5以metric-type 1的类型发布的时候，不管lsa5 metric大小，优先选择lsa5产生的路由。
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