Configuring Multi-Area OSPF

Real World Application & Core Knowledge

After completing the first 4 Labs found in the OSPF section you should have a good foundation of configuring OSPF. Now its time to build onto that foundation by learning how to configure multiple area’s in ospf to segregate the routed network for management and resource conservation benefits. Take a step back and look at it this way, designing a network using multiple area’s gives you an easy network to troubleshoot when something blows up. For example facility one is OSPF area 1, facility 2 is OSPF area two, this gives you the ability to isolate network problems to a site/facility level.

You can conserve router resources as a specific router in a given area only has to maintain the database for that configured area. However Area Boarder Routers maintain a copy of the entire OSPF topology thus these routers need to be able to handle such performance requirements such as a Catalyst 6500 layer 3 switch, 7600 Series routers, 7200 series routers, or even 3800/3900 Series Integrated Services Routers.

An online poll done by a highly respectable network media website showed that the average OSPF network contains 50-75 areas. Keep in mind that not every single building has to be its own OSPF area, a general rule of thumb when designing OSPF area’s is that a single area could contain up to 250 routers and a few hundred intra-area routes.

To configure a new area the command is identical to configuring the backbone area but instead of specifying area 0 after the network statement you specify the new area number. Remember Area 0 is the backbone area and all traffic traversing the network from one area to another area MUST!!! traverse the backbone area.

In this lab you will configure six new area’s; one for each router that contains the routers loopback interface. For example; R1′s Loopback0 interface will be in Area 1, R2′s Loopback0 interface will belong in Area 2, etc… On R5 and R6 you will configure area 45 for the FastEthernet network connected to SW1. This configuration will be used for a later lab in the OSPF section.

Review the following command(s);

network ip.ip.ip.ip wc.wc.wc.wc area # – This command is executed in OSPF router configuration mode to specify which interfaces participate in the OSPF process and which OSPF area they belong to.

show ip ospf interface – This command is executed in privileged mode to display interface parameters including which Area particular interfaces belong to.

The following logical topology shown below is used in labs found through out Section 9 – Configuring OSPF;

Lab Prerequisites

• If you completed lab 9-4 you can start where you’ve left off or you can load the Free CCNA Workbook GNS3 topology; start and establish a console session with R1, R2, R3, R4, R5 and SW1 then load their initial configurations included below by copying the config from the textbox and pasting it into the routers console.

Initial Configurations

!################################################## !#  Free CCNA Workbook Lab 9-5 R1 Initial Config  # !################################################## ! enable configure terminal ! hostname R1 no ip domain-lookup ! interface Loopback0  description ### SIMULATED NETWORK ###  ip address 10.55.10.1 255.255.255.0 ! interface Serial1/0  description ### PHYSICAL FRAME RELAY INTERFACE ###  ip address 10.1.245.1 255.255.255.248  encapsulation frame-relay  serial restart-delay 0  frame-relay map ip 10.1.245.5 125 broadcast  frame-relay map ip 10.1.245.4 124 broadcast  frame-relay map ip 10.1.245.2 122 broadcast  no frame-relay inverse-arp  no shut  exit ! router ospf 1  log-adjacency-changes  network 10.1.245.1 0.0.0.0 area 0  neighbor 10.1.245.2  neighbor 10.1.245.4  neighbor 10.1.245.5 ! line con 0  logging sync  no exec-timeout ! end

!################################################## !#  Free CCNA Workbook Lab 9-5 R2 Initial Config  # !################################################## ! enable configure terminal ! hostname R2 no ip domain-lookup ! interface Loopback0  description ### SIMULATED NETWORK ###  ip address 10.55.20.1 255.255.255.0 ! interface Serial1/0  description ### PHYSICAL FRAME RELAY INTERFACE ###  ip address 10.1.245.2 255.255.255.248  encapsulation frame-relay  ip ospf priority 0  serial restart-delay 0  no frame-relay inverse-arp  frame map ip 10.1.245.1 221 broadcast  frame map ip 10.1.245.4 221  frame map ip 10.1.245.5 221  no shut ! interface Serial1/2  ### POINT-TO-POINT LINK TO R3 ###  ip address 10.1.23.1 255.255.255.252  encapsulation ppp  serial restart-delay 0  no shut  exit ! router ospf 1  log-adjacency-changes  network 10.1.245.2 0.0.0.0 area 0 ! line con 0  logging sync  no exec-timeout ! end

!################################################## !#  Free CCNA Workbook Lab 9-5 R3 Initial Config  # !################################################## ! enable configure terminal ! hostname R3 no ip domain-lookup ! interface Loopback0  description ### SIMULATED NETWORK ###  ip address 10.55.30.1 255.255.255.0 ! interface Serial1/1  description ### POINT-TO-POINT LINK TO R2 ###  ip address 10.1.23.2 255.255.255.252  encapsulation ppp  no shut  exit ! line con 0  logging sync  no exec-timeout ! end

!################################################## !#  Free CCNA Workbook Lab 9-5 R4 Initial Config  # !################################################## ! enable configure terminal ! hostname R4 no ip domain-lookup ! interface Loopback0  description ### SIMULATED NETWORK ###  ip address 10.55.40.1 255.255.255.0 ! interface FastEthernet0/0  description ### REAL NETWORK ###  ip address 10.45.1.1 255.255.255.0  no shut ! interface Serial1/0  description ### PHYSICAL FRAME RELAY INTERFACE ###  ip address 10.1.245.4 255.255.255.248  encapsulation frame-relay  ip ospf priority 0  serial restart-delay 0  no frame-relay inverse-arp  frame map ip 10.1.245.1 421 broadcast  frame map ip 10.1.245.2 421  frame map ip 10.1.245.5 421  no shut ! interface Serial1/1  description ### POINT-TO-POINT LINK TO R5 ###  ip address 10.1.45.1 255.255.255.252  encapsulation ppp  serial restart-delay 0  no shut  exit ! router ospf 1  log-adjacency-changes  network 10.1.245.4 0.0.0.0 area 0 ! line con 0  logging sync  no exec-timeout ! end

!################################################## !#  Free CCNA Workbook Lab 9-5 R5 Initial Config  # !################################################## ! enable configure terminal ! hostname R5 no ip domain-lookup ! interface Loopback0  description ### SIMULATED NETWORK ###  ip address 10.55.50.1 255.255.255.0 ! interface FastEthernet0/0  description ### REAL NETWORK ###  ip address 10.45.1.2 255.255.255.0  no shut ! interface Serial1/0  description ### PHYSICAL FRAME RELAY INTERFACE ###  ip address 10.1.245.5 255.255.255.248  encapsulation frame-relay  ip ospf priority 0  serial restart-delay 0  no frame-relay inverse-arp  frame map ip 10.1.245.1 521 broadcast  frame map ip 10.1.245.2 521  frame map ip 10.1.245.4 521  no shut ! interface Serial1/1  description ### POINT-TO-POINT LINK TO R4 ###  ip address 10.1.45.2 255.255.255.252  encapsulation ppp  serial restart-delay 0  no shut  exit ! router ospf 1  log-adjacency-changes  network 10.1.245.5 0.0.0.0 area 0 ! line con 0  logging sync  no exec-timeout ! end

!################################################## !#  Free CCNA Workbook Lab 9-5 SW1 Initial Config # !################################################## ! enable configure terminal ! hostname SW1 no ip domain-lookup ! line con 0  logging sync  no exec-timeout ! end

Lab Objectives

• Configure R2′s point-to-point link between R2 and R3 in Area 3.
• Configure each routers Loopback0 interface in its own OSPF area, use the router number as the new OSPF area.
• Configure the point-to-point link between R4 and R5 as well as R4 and R5′s physical LAN interfaces (FastEthernet0/0) in OSPF Area 45.
• Verify that all the new OSPF Inter-Area routes are in R1′s routing table; these are denoted as O*IA routes.

Lab Instruction

Objective 1. – Configure R2′s point-to-point link between R2 and R3 in Area 3.

R2#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R2(config)#router ospf 1 R2(config-router)#network 10.1.23.1 0.0.0.0 area 3 R2(config-router)#end R2#

R3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R3(config)#router ospf 1 R3(config-router)#network 10.1.23.2 0.0.0.0 area 3 R3(config-router)#end R3# %OSPF-5-ADJCHG: Process 1, Nbr 10.55.20.1 on Serial1/1 from LOADING to FULL, Loading Done R3#

Objective 2. – Configure each routers Loopback0 interface in its own OSPF area, use the router number as the new OSPF area.

R1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R1(config)#router ospf 1 R1(config-router)#network 10.55.10.1 0.0.0.0 area 1 R1(config-router)#end R1#

R2#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R2(config)#router ospf 1 R2(config-router)#network 10.55.20.1 0.0.0.0 area 2 R2(config-router)#end R2#

R3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R3(config)#router ospf 1 R3(config-router)#network 10.55.30.1 0.0.0.0 area 3 R3(config-router)#end R3#

R4#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R4(config)#router ospf 1 R4(config-router)#network 10.55.40.1 0.0.0.0 area 4 R4(config-router)#end R4#

R5#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R5(config)#router ospf 1 R5(config-router)#network 10.55.50.1 0.0.0.0 area 5 R5(config-router)#end R5#

Objective 3. – Configure the point-to-point link between R4 and R5 as well as R4 and R5′s physical LAN interfaces (FastEthernet0/0) in OSPF Area 45.

R4#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R4(config)#router ospf 1 R4(config-router)#network 10.1.45.1 0.0.0.0 area 45 R4(config-router)#network 10.45.1.1 0.0.0.0 area 45 R4(config-router)#end R4#

R5#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R5(config)#router ospf 1 R5(config-router)#network 10.1.45.2 0.0.0.0 area 45 %OSPF-5-ADJCHG: Process 1, Nbr 10.55.40.1 on Serial1/1 from LOADING to FULL, Loading Done R5(config-router)#network 10.45.1.2 0.0.0.0 area 45 R5(config-router)#end R5#

Objective 4. – Verify that all the new OSPF Inter-Area routes are in R1′s routing table; these are denoted as O*IA routes.

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

    10.0.0.0/8 is variably subnetted, 9 subnets, 4 masks
O IA    10.55.50.1/32 [110/65] via 10.1.245.5, 00:15:38, Serial1/0
O IA    10.55.40.1/32 [110/65] via 10.1.245.4, 00:15:58, Serial1/0
O IA    10.1.23.0/30 [110/128] via 10.1.245.2, 00:18:13, Serial1/0
O IA    10.55.30.1/32 [110/129] via 10.1.245.2, 00:16:13, Serial1/0
O IA    10.45.1.0/24 [110/65] via 10.1.245.5, 00:07:14, Serial1/0
                    [110/65] via 10.1.245.4, 00:08:31, Serial1/0
O IA    10.1.45.0/30 [110/128] via 10.1.245.5, 00:07:24, Serial1/0
                    [110/128] via 10.1.245.4, 00:08:41, Serial1/0
O IA    10.55.20.1/32 [110/65] via 10.1.245.2, 00:17:02, Serial1/0
C       10.55.10.0/24 is directly connected, Loopback0
C       10.1.245.0/29 is directly connected, Serial1/0
R1#