Network Requirements
- Configure OSPF for all devices, and divide the devices into two areas, Area 0 and Area 1.
- On the ABR, configure inter-area route filtration. According to route filtration, Area 0 does not allow injection of route 20.0.3.0/24, and 10.0.3.0/24 is not allowed to flood into other areas.
Network Topology
Figure 7-7 Networking for Configure Route Filtration on Inter-Area OSPF Routes
Configuration Steps
Step 1: Create VLANs, and add ports to the required VLANs. (Omitted)
Step 2: Configure IP addresses for the ports. (Omitted)
Step 3: Configure an OSPF process and let the interface cover different areas.
#Configure Device1.
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Device1#configure terminal
Device1(config)#router ospf 100
Device1(config-ospf)#router-id 1.1.1.1
Device1(config-ospf)#network 10.0.1.0 0.0.0.255 area 0
Device1(config-ospf)#network 10.0.2.0 0.0.0.255 area 0
Device1(config-ospf)#network 10.0.3.0 0.0.0.255 area 0
Device1(config-ospf)#exit
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#Configure Device2.
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Device2#configure terminal
Device2(config)#router ospf 100
Device2(config-ospf)#router-id 2.2.2.2
Device2(config-ospf)#network 10.0.1.0 0.0.0.255 area 0
Device2(config-ospf)#network 20.0.1.0 0.0.0.255 area 1
Device2(config-ospf)#exit
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#Configure Device3.
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Device3#configure terminal
Device3(config)#router ospf 100
Device3(config-ospf)#router-id 3.3.3.3
Device3(config-ospf)#network 20.0.1.0 0.0.0.255 area 1
Device3(config-ospf)#network 20.0.2.0 0.0.0.255 area 1
Device3(config-ospf)#network 20.0.3.0 0.0.0.255 area 1
Device3(config-ospf)#exit
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#Query the OSPF LSDB and routing table of Device2.
Device2#show ip ospf database
OSPF Router with ID (2.2.2.2) (Process ID 100)
Router Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Link count
1.1.1.1 1.1.1.1 329 0x8000005b 0xa6d5 3
2.2.2.2 2.2.2.2 324 0x80000051 0xb007 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 324 0x8000004e 0x9d2e
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.1.0 2.2.2.2 324 0x8000004e 0xac25 20.0.1.0/24
20.0.2.0 2.2.2.2 324 0x8000004d 0xad23 20.0.2.0/24
20.0.3.0 2.2.2.2 259 0x80000001 0x3be0 20.0.3.0/24
Router Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Link count
2.2.2.2 2.2.2.2 334 0x80000055 0x4f51 1
3.3.3.3 3.3.3.3 335 0x80000059 0xca7a 3
Net Link States (Area 1)
Link ID ADV Router Age Seq# CkSum
20.0.1.2 3.3.3.3 340 0x80000001 0xeb17
Summary Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Route
10.0.1.0 2.2.2.2 365 0x80000001 0xc95f 10.0.1.0/24
10.0.2.0 2.2.2.2 319 0x80000001 0xc85e 10.0.2.0/24
10.0.3.0 2.2.2.2 256 0x80000001 0xbd68 10.0.3.0/24
Device2#show ip route
Codes: C - connected, S - static, R - RIP, O - OSPF, OE-OSPF External, M Management
D - Redirect, E - IRMP, EX - IRMP external, o - SNSP, B BGP, i-ISIS
Gateway of last resort is not set
C 10.0.1.0/24 is directly connected, 00:06:13, vlan2
O 10.0.2.0/24 [110/2] via 10.0.1.1, 00:05:22, vlan2
O 10.0.3.0/24 [110/2] via 10.0.1.1, 00:05:22, vlan2
C 20.0.1.0/24 is directly connected, 00:06:19, vlan3
O 20.0.2.0/24 [110/2] via 20.0.1.2, 00:05:32, vlan3
O 20.0.3.0/24 [110/2] via 20.0.1.2, 00:05:32, vlan3
C 127.0.0.0/8 is directly connected, 94:42:22, lo0
In the OSPF database of Device2, three inter-area LSAs are generated respectively for Area 0 and Area 1.The intra-area routes of the areas have also been added into the routing table.
#Query the routing table of Device1.
Device1#show ip route
Codes: C - connected, S - static, R - RIP, O - OSPF, OE-OSPF External, M Management
D - Redirect, E - IRMP, EX - IRMP external, o - SNSP, B BGP, i-ISIS
Gateway of last resort is not set
C 10.0.1.0/24 is directly connected, 00:08:41, vlan2
C 10.0.2.0/24 is directly connected, 37:59:10, vlan3
C 10.0.3.0/24 is directly connected, 38:05:36, vlan4
O 20.0.1.0/24 [110/2] via 10.0.1.2, 00:07:55, vlan2
O 20.0.2.0/24 [110/3] via 10.0.1.2, 00:07:55, vlan2
O 20.0.3.0/24 [110/3] via 10.0.1.2, 00:06:50, vlan2
C 127.0.0.0/8 is directly connected, 70:07:32, lo0
Device1 has learnt routes of Area 1.
#Query the routing table of Device3.
Device3#show ip route
Codes: C - connected, S - static, R - RIP, O - OSPF, OE-OSPF External, M Management
D - Redirect, E - IRMP, EX - IRMP external, o - SNSP, B BGP, i-ISIS
Gateway of last resort is not set
O 10.0.1.0/24 [110/2] via 20.0.1.1, 00:08:44, vlan2
O 10.0.2.0/24 [110/3] via 20.0.1.1, 00:08:33, vlan2
O 10.0.3.0/24 [110/3] via 20.0.1.1, 00:07:30, vlan2
C 20.0.1.0/24 is directly connected, 00:09:31, vlan2
C 20.0.2.0/24 is directly connected, 37:59:57, vlan3
C 20.0.3.0/24 is directly connected, 38:03:35, vlan4
C 127.0.0.0/8 is directly connected, 61:26:38, lo0
Device3 has learnt routes of Area 0.
Step 4: Configure a route filtration policy.
#Configure Device2.
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Device2(config)#ip prefix-list 1 deny 10.0.3.0/24
Device2(config)#ip prefix-list 1 permit 0.0.0.0/0 le 32
Device2(config)#ip prefix-list 2 deny 20.0.3.0/24
Device2(config)#ip prefix-list 2 permit 0.0.0.0/0 le 32
Device2(config)#exit
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Prefix list 1 filters out network 10.0.3.0/24 and allows all other networks. Prefix list 2 filters out network 20.0.3.0/24 and allows all other networks.
Step 5: On the ABR, configure filtration of inter-area routes and invoke the matching rules of a prefix list.
#Configure Device2.
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Device2(config)#router ospf 100
Device2(config-ospf)#area 0 filter-list prefix 1 out
Device2(config-ospf)#area 0 filter-list prefix 2 in
Device2(config-ospf)#exit
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Step 6: Check the result.
#Query OSPF LSDB of Device2.
Device2#show ip ospf database
OSPF Router with ID (2.2.2.2) (Process ID 100)
Router Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Link count
1.1.1.1 1.1.1.1 679 0x8000005b 0xa6d5 3
2.2.2.2 2.2.2.2 673 0x80000051 0xb007 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 673 0x8000004e 0x9d2e
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.1.0 2.2.2.2 673 0x8000004e 0xac25 20.0.1.0/24
20.0.2.0 2.2.2.2 673 0x8000004d 0xad23 20.0.2.0/24
Router Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Link count
2.2.2.2 2.2.2.2 683 0x80000055 0x4f51 1
3.3.3.3 3.3.3.3 684 0x80000059 0xca7a 3
Net Link States (Area 1)
Link ID ADV Router Age Seq# CkSum
20.0.1.2 3.3.3.3 689 0x80000001 0xeb17
Summary Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Route
10.0.1.0 2.2.2.2 714 0x80000001 0xc95f 10.0.1.0/24
10.0.2.0 2.2.2.2 668 0x80000001 0xc85e 10.0.2.0/24
Comparing the result with the result of Step 2, the LSA of network 20.0.3.0/24 has been deleted from Area 0 in the OSPF database. Similarly, the LSA of network 10.0.3.0/24 has been deleted from Area 1.
#Query the routing table of Device1.
Device1#show ip route
Codes: C - connected, S - static, R - RIP, O - OSPF, OE-OSPF External, M - Management
D - Redirect, E - IRMP, EX - IRMP external, o - SNSP, B - BGP, i-ISIS
Gateway of last resort is not set
C 10.0.1.0/24 is directly connected, 00:12:57, vlan2
C 10.0.2.0/24 is directly connected, 38:03:25, vlan3
C 10.0.3.0/24 is directly connected, 38:09:52, vlan4
O 20.0.1.0/24 [110/2] via 10.0.1.2, 00:12:11, vlan2
O 20.0.2.0/24 [110/3] via 10.0.1.2, 00:12:11, vlan2
C 127.0.0.0/8 is directly connected, 70:11:48, lo0
The route 20.0.3.0/24 does not exist in the routing table of Device1.
#Query the routing table of Device3.
Device3#show ip route
Codes: C - connected, S - static, R - RIP, O - OSPF, OE-OSPF External, M Management
D - Redirect, E - IRMP, EX - IRMP external, o - SNSP, B BGP, i-ISIS
Gateway of last resort is not set
O 10.0.1.0/24 [110/2] via 20.0.1.1, 00:13:09, vlan2
O 10.0.2.0/24 [110/3] via 20.0.1.1, 00:12:58, vlan2
C 20.0.1.0/24 is directly connected, 00:13:56, vlan2
C 20.0.2.0/24 is directly connected, 38:04:22, vlan3
C 20.0.3.0/24 is directly connected, 38:08:00, vlan4
C 127.0.0.0/8 is directly connected, 64:31:03, lo0
The route 10.0.3.0/24 does not exist in the routing table of Device3.
Switch
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