Network Requirements
- Configure OSPF for all devices, and divide the devices into two areas, Area 0 and Area 1.
- To decrease the number of inter-area routes, inter-area routes are summarized on the ABR. The routes in Area 0 are summarized to form 10.0.0.0/16. The routes in Area 1 are summarized to form 20.0.0.0/16.
Network Topology
Figure 7-6 Networking for Configure Route Summary 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 1419 0x80000007 0x4f81 3
2.2.2.2 2.2.2.2 1414 0x80000004 0x4bb9 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 1419 0x80000001 0x38e0
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.1.0 2.2.2.2 1437 0x80000001 0x47d7 20.0.1.0/24
20.0.2.0 2.2.2.2 1363 0x80000001 0x46d6 20.0.2.0/24
20.0.3.0 2.2.2.2 1363 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 1368 0x80000004 0xe70b 1
3.3.3.3 3.3.3.3 1341 0x80000006 0x6138 3
Net Link States (Area 1)
Link ID ADV Router Age Seq# CkSum
20.0.1.1 2.2.2.2 1368 0x80000001 0x24e3
Summary Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Route
10.0.1.0 2.2.2.2 1442 0x80000001 0xc95f 10.0.1.0/24
10.0.2.0 2.2.2.2 1409 0x80000001 0xc85e 10.0.2.0/24
10.0.3.0 2.2.2.2 1409 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, 00:30:31, vlan2
O 10.0.2.0/24 [110/2] via 10.0.1.1, 00:23:37, vlan2
O 10.0.3.0/24 [110/2] via 10.0.1.1, 00:23:37, vlan2
C 20.0.1.0/24 is directly connected, 02:09:10, vlan3
O 20.0.2.0/24 [110/2] via 20.0.1.2, 00:22:51, vlan3
O 20.0.3.0/24 [110/2] via 20.0.1.2, 00:22:51, vlan3
C 127.0.0.0/8 is directly connected, 05:28:14, 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 OSPF LSDB and routing table of Device1.
Device1#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 100)
Router Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Link count
1.1.1.1 1.1.1.1 249 0x80000008 0x4d82 3
2.2.2.2 2.2.2.2 191 0x80000005 0x49ba 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 471 0x80000002 0x36e1
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.1.0 2.2.2.2 251 0x80000002 0x45d8 20.0.1.0/24
20.0.2.0 2.2.2.2 1988 0x80000001 0x46d6 20.0.2.0/24
20.0.3.0 2.2.2.2 1988 0x80000001 0x3be0 20.0.3.0/24
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, 00:25:11, vlan2
C 10.0.2.0/24 is directly connected, 00:24:58, vlan3
C 10.0.3.0/24 is directly connected, 00:24:44, vlan4
O 20.0.1.0/24 [110/2] via 10.0.1.2, 00:14:59, vlan2
O 20.0.2.0/24 [110/3] via 10.0.1.2, 00:14:12, vlan2
O 20.0.3.0/24 [110/3] via 10.0.1.2, 00:14:12, vlan2
C 127.0.0.0/8 is directly connected, 116:19:42, lo0
The OSPF database of Device1 contains three inter-area LSAs, and the three routes have been added into the routing table.
#Query the OSPF LSDB and routing table of Device3.
Device3#show ip ospf database
OSPF Router with ID (3.3.3.3) (Process ID 100)
Router Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Link count
2.2.2.2 2.2.2.2 532 0x80000005 0xe50c 1
3.3.3.3 3.3.3.3 506 0x80000007 0x5f39 3
Net Link States (Area 1)
Link ID ADV Router Age Seq# CkSum
20.0.1.1 2.2.2.2 532 0x80000002 0x22e4
Summary Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Route
10.0.1.0 2.2.2.2 82 0x80000002 0xc760 10.0.1.0/24
10.0.2.0 2.2.2.2 382 0x80000002 0xc65f 10.0.2.0/24
10.0.3.0 2.2.2.2 262 0x80000002 0xbb69 10.0.3.0/24
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, 00:24:04, vlan2
O 10.0.2.0/24 [110/3] via 20.0.1.1, 00:24:04, vlan2
O 10.0.3.0/24 [110/3] via 20.0.1.1, 00:24:04, vlan2
C 20.0.1.0/24 is directly connected, 02:09:51, vlan2
C 20.0.2.0/24 is directly connected, 02:07:21, vlan3
C 20.0.3.0/24 is directly connected, 02:07:09, vlan4
C 127.0.0.0/8 is directly connected, 360:20:45, lo0
Similarly, the OSPF database of Device3 contains three inter-area LSAs, and the three routes have been added into the routing table.
Step 4: On the ABR, configure inter-area route summary. Now Device2 is the ABR.
#On Device2, summarize the routes in Area 0 to form route 10.0.0.0/16, and summarize the routes in Area 1 to form route 20.0.0.0/16.
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Device2(config)#router ospf 100
Device2(config-ospf)#area 0 range 10.0.0.0/16
Device2(config-ospf)#area 1 range 20.0.0.0/16
Device2(config-ospf)#exit
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Step 5: Check the result.
#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 1.1.1.1 305 0x80000009 0x4b83 3
2.2.2.2 2.2.2.2 297 0x80000006 0x47bb 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 527 0x80000003 0x34e2
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.0.0 2.2.2.2 23 0x80000001 0x52cd 20.0.0.0/16
Router Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Link count
2.2.2.2 2.2.2.2 277 0x80000006 0xe30d 1
3.3.3.3 3.3.3.3 332 0x80000008 0x5d3a 3
Net Link States (Area 1)
Link ID ADV Router Age Seq# CkSum
20.0.1.1 2.2.2.2 317 0x80000003 0x20e5
Summary Link States (Area 1)
Link ID ADV Router Age Seq# CkSum Route
10.0.0.0 2.2.2.2 26 0x80000001 0xd455 10.0.0.0/16
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
O 10.0.0.0/16 [110/1] is directly connected, 00:00:31, null0
C 10.0.1.0/24 is directly connected, 00:40:31, vlan2
O 10.0.2.0/24 [110/2] via 10.0.1.1, 00:33:37, vlan2
O 10.0.3.0/24 [110/2] via 10.0.1.1, 00:33:37, vlan2
O 20.0.0.0/16 [110/1] is directly connected, 00:00:27, null0
C 20.0.1.0/24 is directly connected, 02:19:10, vlan3
O 20.0.2.0/24 [110/2] via 20.0.1.2, 00:32:51, vlan3
O 20.0.3.0/24 [110/2] via 20.0.1.2, 00:32:51, vlan3
C 127.0.0.0/8 is directly connected, 05:38:14, lo0
Comparing the result with the result of Step 2, you will find that only one summarized inter-area LSA is generated respectively for Area 0 and Area 1 in the OSPF database of Device2. Similarly, a summary route with the output interface being Null0 is automatically added into the routing table.
#Query the OSPF LSDB and routing table of Device1.
Device1#show ip ospf database
OSPF Router with ID (1.1.1.1) (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 1338 0x80000009 0x4b83 3
2.2.2.2 2.2.2.2 1332 0x80000006 0x47bb 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# CkSum
10.0.1.2 2.2.2.2 1563 0x80000003 0x34e2
Summary Link States (Area 0)
Link ID ADV Router Age Seq# CkSum Route
20.0.0.0 2.2.2.2 90 0x80000001 0x52cd 20.0.0.0/16
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, 00:40:11, vlan2
C 10.0.2.0/24 is directly connected, 00:39:58, vlan3
C 10.0.3.0/24 is directly connected, 00:39:44, vlan4
O 20.0.0.0/16 [110/2] via 10.0.1.2, 00:02:18, vlan2
C 127.0.0.0/8 is directly connected, 116:44:42, lo0
On Device1, you will find that the OSPF database contains only the summarized inter-area LSA, and the routing table leans only the summary route 20.0.0.0/16 of Area 1. Similarly, Device3 learns only the summary route 10.0.0.0/16 of Area 0.
Switch
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