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CCNP Route Lab 3-3, OSPF Virtual Links and Area Summarization

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CCNP Route Lab 3-3, OSPF Virtual Links and Area Summarization

Topology

ccnp-route-lab-ospf-virtual-links-area-summarization

Objectives

  • Configure multi-area OSPF on a router.
  • Verify multi-area behavior.
  • Create an OSPF virtual link.
  • Summarize an area.
  • Generate a default route into OSPF.

Background
You are responsible for configuring the new network to connect your company’s engineering, marketing, and accounting departments, represented by loopback interfaces on each of the three routers. The physical devices have just been installed and connected by serial cables. Configure multiple-area OSPF to allow full connectivity between all departments.

In addition, R1 has a loopback interface representing a connection to the Internet. This connection will not be added into OSPF. R3 will have four additional loopback interfaces representing connections to branch offices.

Note: This lab uses Cisco 1841 routers with Cisco IOS Release 12.4(24)T1 and the Advanced IP Services image c1841 -advipservicesk9-mz.124-24.T1 .bin. You can use other routers (such as a 2801 or 2811) and Cisco IOS Software versions if they have comparable capabilities and features. Depending on the router model and Cisco IOS Software version, the commands available and output produced might vary from what is shown in this lab.

Required Resources

  • 3 routers (Cisco 1841 with Cisco IOS Release 12.4(24)T1 Advanced IP Services or comparable)
  • Serial and console cables

Step 1: Configure addressing and loopbacks.
Using the addressing scheme in the diagram, apply IP addresses to the serial interfaces on R1, R2, and R3. Create loopbacks on R1, R2, and R3, and address them according to the diagram.

R1# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)# interface loopback 1
R1(config-if)# description Engineering Department
R1(config-if)# ip address 10.1.1.1 255.255.255.0
R1(config-if)# interface loopback 30
R1(config-if)# ip address 172.30.30.1 255.255.255.252
R1(config-if)# interface serial 0/0/0
R1(config-if)# ip address 10.1.12.1 255.255.255. 0
R1(config-if)# clockrate 64000
R1(config-if)# no shutdown
R2# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# interface loopback 2
R2(config-if)# description Marketing Department
R2(config-if)# ip address 10. 1.2.1 255.255.255.0
R2(config-if)# interface serial 0/0/0
R2(config-if)# ip address 10.1.12.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)# interface serial 0/0/1
R2(config-if)# ip address 10.1.23.2 255.255.255.0
R2(config-if)# clockrate 64000
R2(config-if)# no shutdown
R3# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)# interface loopback 3
R3(config-if)# description Accounting Department
R3(config-if)# ip address 10.1.3.1 255.255.255.0
R3(config-if)# interface loopback 100
R3(config-if)# ip address 192.168.100.1 255.255.255.0
R3(config-if)# interface loopback 101
R3(config-if)# ip address 192.168.101.1 255.255.255.0
R3(config-if)# interface loopback 102
R3(config-if)# ip address 192.168.102.1 255.255. 255.0
R3(config-if)# interface loopback 103
R3(config-if)# ip address 192.168.103.1 255.255.255.0
R3(config-if)# interface serial 0/0/1
R3(config-if)# ip address 10.1.23.3 255.255.255.0
R3(config-if)# no shutdown

Step 2: Add interfaces into OSPF.
a. Create OSPF process 1 on all three routers. Using the network command, configure the subnet of the serial link between R1 and R2 to be in OSPF area 0. Add loopback 1 on R1 and loopback 2 on R2 into OSPF area 0.

Note: The default behavior of OSPF for loopback interfaces is to advertise a 32-bit host route. To ensure that the full /24 network is advertised, use the ip ospf network point-to-point command. Change the network type on the loopback interfaces so that they are advertised with the correct subnet.

R1(config)# router ospf 1
R1(config-router)# network 10.1.12.0 0.0.0.255 area 0
R1(config-router)# network 10.1.1.0 0.0.0.255 area 0
R1(config-router)# exit
R1(config)# interface loopback 1
R1(config-if)# ip ospf network point-to-point
R2(config)# router ospf 1
R2(config-router)# network 10.1.12.0 0.0.0.255 area 0
R2(config-router)# network 10.1.2.0 0.0.0.255 area 0
R2(config-router)# exit
R2(config)# interface loopback 2
R2(config-if)# ip ospf network point-to-point

b. Verify that you can see OSPF neighbors in the show ip ospf neighbors output on both routers. Verify that the routers can see each other’s loopback with the show ip route command.

R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.1.2.1 0 FULL/ - 00:00:38 10.1.12.2 Serial0/0/0
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
10.0.0.0/24 is subnetted, 3 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
O 10.1.2.0 [110/65] via 10.1.12.2, 00:00:10, Serial0/0/0
C 10.1.1.0 is directly connected, Loopback1
172.30.0.0/30 is subnetted, 1 subnets
C 172.30.30.0 is directly connected, Loopback30
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.30.30.1 0 FULL/ - 00:00:35 10.1.12.1 Serial0/0/0
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
10.0.0.0/24 is subnetted, 4 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
C 10.1.2.0 is directly connected, Loopback2
O 10.1.1.0 [110/65] via 10.1.12.1, 00:00:30, Serial0/0/0
C 10.1.23.0 is directly connected, Serial0/0/1

c. Add the subnet between R2 and R3 into OSPF area 23 using the network command. Add loopback 3 on R3 into area 23.

R2(config)# router ospf 1
R2(config-router)# network 10.1.23.0 0.0.0.255 area 23
R3(config)# router ospf 1
R3(config-router)# network 10.1.23.0 0.0.0.255 area 23
R3(config-router)# network 10.1.3.0 0.0.0.255 area 23
R3(config-router)# exit
R3(config)# interface loopback 3
R3(config-if)# ip ospf network point-to-point

d. Verify that this neighbor relationship comes up with the show ip ospf neighbors command.

R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.30.30.1 0 FULL/ - 00:00:36 10.1.12.1 Serial0/0/0
192.168.103.1 0 FULL/ - 00:00:36 10.1.23.3 Serial0/0/1

e. Using a Tcl script, verify connectivity to all interfaces from any router, with the exception of loopback 30 on R1, and R3 loopbacks 100 through 103.

R1# tclsh
R1(tcl)#
foreach address {
10.1.1.1
10.1.2.1
10.1.3.1
10.1.12.1
10.1.12.2
10.1.23.2
10.1.23.3
172.30.30.1
192.168.100.1
192.168.101.1
192.168.102.1
192.168.103.1

Step 3: Create a virtual link.
a. Add loopbacks 100 through 103 on R3 to the OSPF process in area 100 using the network command. Change the network type to advertise the correct subnet mask.

R3(config)# router ospf 1
R3(config-router)# network 192.168.100.0 0.0.3.255 area 100
R3(config-router)# exit
R3(config)# interface loopback 100
R3(config-if)# ip ospf network point-to-point
R3(config-if)# interface loopback 101
R3(config-if)# ip ospf network point-to-point
R3(config-if)# interface loopback 102
R3(config-if)# ip ospf network point-to-point
R3(config-if)# interface loopback 103
R3(config-if)# ip ospf network point-to-point

b. Look at the output of the show ip route command on R2. Notice that the routes to those networks do not appear. The reason for this behavior is that area 100 on R3 is not connected to the backbone. It is only connected to area 23. If an area is not connected to the backbone, its routes are not advertised outside of its area.

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
10.0.0.0/24 is subnetted, 5 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
O 10.1.3.0 [110/65] via 10.1.23.3, 00:01:00, Serial0/0/1
C 10.1.2.0 is directly connected, Loopback2
O 10.1.1.0 [110/65] via 10.1.12.1, 00:03:10, Serial0/0/0
C 10.1.23.0 is directly connected, Serial0/0/1

What would happen if routes could pass between areas without going through the backbone?
Routing loops might occur because any route could get advertised to different areas. By passing through the backbone, type 3 LSAs are generated by their respective areas and not sent back in. You can get around this situation by creating a virtual link. A virtual link is an OSPF feature that creates a logical extension of the backbone area across a regular area, without actually adding any physical interfaces into area 0.

Note: Prior to creating a virtual link you need to identify the OSPF router ID for the routers involved (R2 and R3), using a command such as show ip ospf, show ip protocols or show ip ospf interface. The output for the show ip ospf command on R1 and R3 is shown below.

R2# show ip ospf
Routing Process "ospf 1" with ID 10.1.2.1
<output omitted>
R3# show ip ospf
Routing Process "ospf 1" with ID 192.168.103.1
<output omitted>

c. Create a virtual link using the area transit_area virtual-link router-id OSPF configuration command on both R2 and R3.

R2(config)# router ospf 1
R2(config-router) # area 23 virtual-link 192.168.103.1
R3(config)# router ospf 1
R3(config-router)# area 23 virtual-link 10.1.2.1

Note: To ensure that the router ID of the virtual link endpoints remains constant, you can statically configure the OSPF router ID of the virtual link endpoints using the router-id command.

d. After you see the adjacency over the virtual interface come up, issue the show ip route command on R2 and see the routes from area 100. You can verify the virtual link with the show ip ospf neighbor and show ip ospf interface commands.

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
10.0.0.0/24 is subnetted, 5 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
O 10.1.3.0 [110/65] via 10.1.23.3, 00:01:35, Serial0/0/1
C 10.1.2.0 is directly connected, Loopback2
O 10.1.1.0 [110/65] via 10.1.12.1, 00:01:35, Serial0/0/0
C 10.1.23.0 is directly connected, Serial0/0/1
O IA 192.168.102.0/24 [110/65] via 10.1.23.3, 00:00:05, Serial0/0/1
O IA 192.168.103.0/24 [110/65] via 10.1.23.3, 00:00:05, Serial0/0/1
O IA 192.168.100.0/24 [110/65] via 10.1.23.3, 00:00:57, Serial0/0/1
O IA 192.168.101.0/24 [110/65] via 10.1.23.3, 00:00:16, Serial0/0/1
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.103.1 0 FULL/ - - 10.1.23.3 OSPF_VL0
172.30.30.1 0 FULL/ - 00:00:30 10.1.12.1 Serial0/0/0
192.168.103.1 0 FULL/ - 00:00:30 10.1.23.3 Serial0/0/1
R2# show ip ospf interface
OSPF_VL0 is up, line protocol is up
Internet Address 10.1.23.2/24, Area 0
Process ID 1, Router ID 10.1.2.1, Network Type VIRTUAL_LINK, Cost: 64
Configured as demand circuit.
Run as demand circuit.
DoNotAge LSA allowed.
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:03
Supports Link-local Signaling (LLS)
Index 3/4, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 192.168.103.1 (Hello suppressed)
Suppress hello for 1 neighbor(s)
<output omitted>

When are virtual links useful?
Virtual links are useful when there needs to be a temporary extension of the backbone, either because the backbone became discontiguous or a new area got added onto an existing area.

Why are virtual links a poor long-term solution?
Virtual links are a poor long-term solution because they add processing overhead and basically extend the backbone area onto routers where it might not belong. They can also add a lot of complexity to troubleshooting.

Step 4: Summarize an area.
Loopbacks 100 through 103 can be summarized into one supernet of 192.168.100.0 /22. You can configure area 100 to be represented by this single summary route.

a. Configure R3 (the ABR) to summarize this area using the area area range network mask command.

R3(config)# router ospf 1
R3(config-router)# area 100 range 192.168.100.0 255.255.252.0

b. You can see the summary route on R2 with the show ip route and show ip ospf database commands.

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
10.0.0.0/24 is subnetted, 5 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
O 10.1.3.0 [110/65] via 10.1.23.3, 00:07:25, Serial0/0/1
C 10.1.2.0 is directly connected, Loopback2
O 10.1.1.0 [110/65] via 10.1.12.1, 00:07:25, Serial0/0/0
C 10.1.23.0 is directly connected, Serial0/0/1
O IA 192.168.100.0/22 [110/65] via 10.1.23.3, 00:00:01, Serial0/0/1
R2# show ip ospf database
OSPF Router with ID (10.1.2.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
10.1.2.1 10.1.2.1 341 0x80000003 0x0028DD 4
172.30.30.1 172.30.30.1 1665 0x80000002 0x000E67 3
192.168.103.1 192.168.103.1 1 (DNA) 0x80000003 0x00A374 1
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.1.3.0 10.1.2.1 1268 0x80000001 0x00EFEF
10.1.3.0 192.168.103.1 6 (DNA) 0x80000001 0x00FD5E
10.1.23.0 10.1.2.1 1311 0x80000001 0x0009C3
10.1.23.0 192.168.103.1 6 (DNA) 0x80000001 0x00996F
192.168.100.0 192.168.103.1 1 (DNA) 0x80000002 0x009A04
Router Link States (Area 23)
Link ID ADV Router Age Seq# Checksum Link count
10.1.2.1 10.1.2.1 341 0x80000003 0x00DD8B 2
192.168.103.1 192.168.103.1 342 0x80000003 0x002E57 3
Summary Net Link States (Area 23)
Link ID ADV Router Age Seq# Checksum
10.1.1.0 10.1. 2.1 1321 0x80000001 0x0006DB
10.1.2.0 10.1.2.1 1321 0x80000001 0x0078A8
10.1.12.0 10.1.2.1 1321 0x80000001 0x008255
192.168.100.0 192.168.103.1 157 0x80000002 0x009A04

c. Notice on R3 that OSPF has generated a summary route pointing toward Null0.

R3# 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
10.0.0.0/24 is subnetted, 5 subnets
O 10.1.12.0 [110/128] via 10.1.23.2, 00:01:18, Serial0/0/1
C 10.1.3.0 is directly connected, Loopback3
O 10.1.2.0 [110/65] via 10.1.23.2, 00:01:18, Serial0/0/1
O 10.1.1.0 [110/129] via 10.1.23.2, 00:01:18, Serial0/0/1
C 10.1.23.0 is directly connected, Serial0/0/1
C 192.168.102.0/24 is directly connected, Loopback102
C 192.168.103.0/24 is directly connected, Loopback103
C 192.168.100.0/24 is directly connected, Loopback100
C 192.168.101.0/24 is directly connected, Loopback101
O 192.168.100.0/22 is a summary, 00:01:19, Null0

This behavior is known as sending unknown traffic to the “bit bucket.” This means that if the router advertising the summary route receives a packet destined for something covered by that summary but not in the routing table, it drops it.

What is the reasoning behind this behavior?
The reason that summaries generate local routes to Null0 is that when a router creates a summary address, it should have routes to all the existent more-specific routes. If the router lacks a more-specific route for a prefix within the summary, it is assumed that the route does not exist, and packets destined for that prefix should be dropped. If the route did not exist, bandwidth could be wasted if this router has a less specific route (such as a default route) and forwards the packet to the route until it is dropped further down the line.

The discard route also solves another problem. Depending on the contents of the routing table, a routing loop can be formed between two routers, one receiving a summary route from the second one, while the second one uses the first one as its default gateway. If a packet for a nonexistent component of the summary route was received and there was no discard route installed in the second router, the packet would loop between the routers until its TTL was decremented to 0.

Step 5: Generate a default route into OSPF.
You can simulate loopback 30 on R1 to be a connection to the Internet. You do not need to advertise this specific network to the rest of the network. Instead, you can just have a default route for all unknown traffic to go to R1 .

a. To have R1 generate a default route, use the OSPF configuration command default-information originate always. The always keyword is necessary for generating a default route in this scenario.Without this keyword, a default route is generated only into OSPF if one exists in the routing table.

R1(config)# router ospf 1
R1(config-router)# default-information originate always

b. Verify that the default route appears on R2 and R3 with the show ip route command.

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 10.1.12.1 to network 0.0.0.0
10.0.0.0/24 is subnetted, 5 subnets
C 10.1.12.0 is directly connected, Serial0/0/0
O 10.1.3.0 [110/65] via 10.1.23.3, 00:10:36, Serial0/0/1
C 10.1.2.0 is directly connected, Loopback2
O 10.1.1.0 [110/65] via 10.1.12.1, 00:00:19, Serial0/0/0
C 10.1.23.0 is directly connected, Serial0/0/1
O*E2 0.0.0.0/0 [110/1] via 10.1.12.1, 00:00:09, Serial0/0/0
O IA 192.168.100.0/22 [110/65] via 10.1.23.3, 00:00:19, Serial0/0/1
R3# 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 10.1.23.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 5 subnets
O 10.1.12.0 [110/128] via 10.1.23.2, 00:00:35, Serial0/0/1
C 10.1.3.0 is directly connected, Loopback3
O 10.1.2.0 [110/65] via 10.1.23.2, 00:00:35, Serial0/0/1
O 10.1.1.0 [110/129] via 10.1.23.2, 00:00:35, Serial0/0/1
C 10.1.23.0 is directly connected, Serial0/0/1
C 192.168.102.0/24 is directly connected, Loopback102
C 192.168.103.0/24 is directly connected, Loopback103
C 192.168.100.0/24 is directly connected, Loopback100
C 192.168.101.0/24 is directly connected, Loopback101
O*E2 0.0.0.0/0 [110/1] via 10.1.23.2, 00:00:26, Serial0/0/1
O 192.168.100.0/22 is a summary, 00:03:28, Null0

c. You should be able to ping the interface connecting to the Internet from R2 or R3, despite never being advertised into OSPF.

R3# ping 172.30.30.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.30.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/30/32 ms

d. Use the following Tcl script to verify connectivity to all addresses in the topology.

R1# tclsh
R1(tcl)#
foreach address {
10.1.1.1
10.1.2.1
10.1.3.1
10.1.12.1
10.1.12.2
10.1.23.2
10.1.23.3
172.30.30.1
192.168.100.1
192.168.101.1
192.168.102.1
192.168.103.1
} {
ping $address }

Challenge: Configure OSPF Authentication
Configure OSPF MD5 authentication on the link between R2 and R3, using key ID 1 and the password cisco. Record the commands used below.
Enter the following configuration commands on R2 and R3:

interface serial0/0/1
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 cisco

Router Interface Summary Table

Router Interface Summary
Router Model Ethernet Interface
#1		 Ethernet Interface
#2		 Serial Interface
#1		 Serial Interface
#2
1700 Fast Ethernet 0
(Fa0)		 Fast Ethernet 1
(Fa1)		 Serial 0 (S0) Serial 0/0/1
(S0/0/1)
1800 Fast Ethernet 0/0
(Fa0/0)		 Fast Ethernet 0/1
(Fa0/1)		 Serial 0/0/0
(S0/0/0)		 Serial 0/0/1
(S0/0/1)
2600 Fast Ethernet 0/0
(Fa0/0)		 Fast Ethernet 0/1
(Fa0/1)		 Serial 0/0 (S0/0) Serial 0/1 (S0/1)
2800 Fast Ethernet 0/0
(Fa0/0)		 Fast Ethernet 0/1
(Fa0/1)		 Serial 0/0/0
(S0/0/0)		 Serial 0/0/1
(S0/0/1)
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many interfaces the router has. Rather than list all combinations of configurations for each router class, this table includes identifiers for the possible combinations of Ethernet and serial interfaces in the device. The table does not include any other type of interface, even though a specific router might contain one. For example, for an ISDN BRI interface, the string in parenthesis is the legal abbreviation that can be used in Cisco IOS commands to represent the interface.

Device Configurations (Instructor version)
Router R1

hostname R1
!
interface Loopback1
description Engineering Department
ip address 10.1.1.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback30
ip address 172.30.30.1 255.255.255.252
!
interface Serial0/0/0
ip address 10.1.12.1 255.255.255.0
clock rate 64000
no shutdown
!
router ospf 1
network 10.1.1.0 0.0.0.255 area 0
network 10.1.12.0 0.0.0.255 area 0
default-information originate always
!
end

Router R2

hostname R2
!
interface Loopback2
description Marketing Department
ip address 10.1.2.1 255.255.255.0
ip ospf network point-to-point
!
interface Serial0/0/0
ip address 10.1.12.2 255.255.255.0
no shutdown
!
interface Serial0/0/1
ip address 10.1.23.2 255.255.255.0
clock rate 64000
no shutdown
!
router ospf 1
area 23 virtual-link 192.168.103.1
network 10.1.2.0 0.0.0.255 area 0
network 10.1.12.0 0.0.0.255 area 0
network 10.1.23.0 0.0.0.255 area 23
!
end

Router R3

hostname R3
!
interface Loopback3
description Accounting Department
ip address 10.1.3.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback100
ip address 192.168.100.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback101
ip address 192.168.101.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback102
ip address 192.168.102.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback103
ip address 192.168.103.1 255.255.255.0
ip ospf network point-to-point
!
interface Serial0/0/1
ip address 10.1.23.3 255.255.255.0
no shutdown
!
router ospf 1
area 23 virtual-link 10.1.2.1
area 100 range 192.168.100.0 255.255.252.0
network 10.1.3.0 0.0.0.255 area 23
network 10.1.23.0 0.0.0.255 area 23
network 192.168.100.0 0.0.3.255 area 100
!
end

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