OSPF ABR Type 3 LSA

2023-01-31 07:44

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Feature Overview
The OSPF ABR Type 3 LSA Filtering feature extends the ability of an ABR that is running the OSPF protocol to filter type 3 link-state advertisements (LSAs) that are sent between different OSPF areas.This feature allows only packets with specified prefixes to be sent from one area to another area and restricts all packets with other prefixes. This type of area filtering can be applied out of a specific OSPF area, into a specific OSPF area, or into and out of the same OSPF areas at the same time. This feature is supported by the addition of the area filter-list command in router configuration mode.

Benefits
The OSPF ABR Type 3 LSA Filtering feature gives the administrator improved control of route distribution between OSPF areas.

拓扑说明：

R3的S2/1与R5的S2/1通过FR连接
R4的S2/0与R5的S2/0通过FR连接
R3,R4和R6的F0/0通过以太网交换机连接
R3 S2/1: 1.1.35.3/24 F0/0: 1.1.46.3/24
R4 S2/0: 1.1.45.4/24 F0/0: 1.1.46.4/24
R5 S2/0: 1.1.45.5/24 S2/1: 1.1.35.5/24
R6 F0/0: 1.1.46.6/24

实验目的

在R3上过滤LSA3，看过滤前后的区别

初始配置
R3
conf t
int f0/0
ip add 1.1.46.3 255.255.255.0
no shut
int s2/1
ip add 1.1.35.3 255.255.255.0
encap f
no arp f
no frame inv
frame map ip 1.1.35.5 315 b
no shut
router ospf 1
nei 1.1.35.5
net 1.1.35.3 0.0.0.0 a 0
net 1.1.46.3 0.0.0.0 a 1
end

R4
conf t
int f0/0
ip add 1.1.46.4 255.255.255.0
no shut
int s2/0
ip add 1.1.45.4 255.255.255.0
encap f
no arp f
no frame inv
frame map ip 1.1.45.5 405 b
band 64
no shut
router ospf 1
nei 1.1.45.5
net 1.1.45.4 0.0.0.0 a 0
net 1.1.46.4 0.0.0.0 a 1
end

R5
conf t
int s2/0
ip add 1.1.45.5 255.255.255.0
encap f
no arp f
no frame inv
frame map ip 1.1.45.4 504 b
no shut
int s2/1
ip add 1.1.35.5 255.255.255.0
encap f
no arp f
no frame inv
frame map ip 1.1.35.3 513 b
no shut
router ospf 1
net 1.1.35.5 0.0.0.0 a 0
net 1.1.45.5 0.0.0.0 a 0
end

R6
conf t
int f0/0
ip add 1.1.46.6 255.255.255.0
no shut
router ospf 1
net 1.1.46.6 0.0.0.0 a 1
end

校验：

R3#sh ip ospf data

……

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.35.0        1.1.46.3        127         0x80000004 0x00049D
1.1.35.0        1.1.46.4        129         0x80000004 0x003947
1.1.45.0        1.1.46.3        123         0x80000001 0x001E3C
1.1.45.0        1.1.46.4        221         0x80000005 0x00466F

注意到R3发送的LSA3中有1.1.35.0/24网段。

R6(config-router)#do sh 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

     1.0.0.0/24 is subnetted, 3 subnets
O IA    1.1.35.0 [110/65] via 1.1.46.3, 00:01:44, FastEthernet0/0
O IA    1.1.45.0 [110/129] via 1.1.46.3, 00:01:40, FastEthernet0/0
C       1.1.46.0 is directly connected, FastEthernet0/0

R6(config-router)#do sh ip ospf data

……

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.35.0        1.1.46.3        4           0x80000001 0x000A9A
1.1.35.0        1.1.46.4        1491        0x80000005 0x003748
1.1.45.0        1.1.46.3        1542        0x80000002 0x001C3D
1.1.45.0        1.1.46.4        1491        0x80000006 0x004470

R6也可以通过R3访问到1.1.35.0/24网段

在R3上过滤通往AREA1的LSA-3

conf t

ip prefix-list TO_A1 deny 1.1.35.0/24

ip prefix-list TO_A1 permit 0.0.0.0/8 le 32

router ospf 1

area 1 filter-list prefix TO_A1 in

end

R3(config-router)#do sh ip ospf data

……

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.35.0        1.1.46.4        515         0x80000004 0x003947
1.1.45.0        1.1.46.3        509         0x80000001 0x001E3C
1.1.45.0        1.1.46.4        607         0x80000005 0x00466F

R3已经过滤1.1.35.0/24网段

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 3 subnets
O IA    1.1.35.0 [110/1627] via 1.1.46.4, 00:00:02, FastEthernet0/0
O IA    1.1.45.0 [110/129] via 1.1.46.3, 00:00:02, FastEthernet0/0
C       1.1.46.0 is directly connected, FastEthernet0/0

R6(config-router)#do sh ip ospf data

……

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.35.0        1.1.46.4        1427        0x80000005 0x003748
1.1.45.0        1.1.46.3        1479        0x80000002 0x001C3D
1.1.45.0        1.1.46.4        1427        0x80000006 0x004470

R6从R4上收到1.1.35.0/24网段

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ABR OSPF LSA

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