IS-IS Lab 14 Configure Multi-Area

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Download Lab: VIRL | EVE-NG | GNS3

Image requirements:

Cisco IOSv (vios-adventerprisek9-m.vmdk.SPA.156-2.T)

Both IS-IS and OSPF built on the hierarchical principle, but unlike OSPF where every other area must connect back to the core Area 0, IS-IS has a slightly different approach to the multi-area design. Areas in the IS-IS implementation could be Leve-1 and Level-2. Level-1 areas like OSPF's totally stub areas and to communicate between these types of areas IS-IS node has to be configured as an L1/L2 router type. Level-2 area is like OSPF's backbone area but in the IS-IS topology, there could be multiple L2 areas, meaning if a node connected to several L1 areas and two L2 areas, both L2 areas will have in their database prefixes of L1 areas, this approach of having two L2 areas could be used as a redundant design if one L2 area completely failed, traffic will continue to flow over the second L2 area. This lab takes flat topology from the previous lab and partition one L2 topology into multiple areas, core routers C1 and C2 will form an L2 area, then the rest of the routers will be in four L1 areas. 

Nodes Access: 
Enable:       cisco 
Username:  cisco 
Password:   cisco 

Lab tasks: 

1. Core routers C1 and C2 are already configured as needed, begin this lab with configuring Area A000, first, configure nodes A1 and A2 as L1/L2 router type. 

2. The link between A1 and A2 currently supports L2 adjacency only, this lab assumes that the link should be configured as L1 only but in order to prevent loss of connectivity, configure it as L1/L2 adjacency temporarily. 

3. Configure new NET addresses with new area ID for both nodes A1 and A2. 

4. Remove old NET addresses on routers A1 and A2. 

5. Configure the link between A1 and A2 as L1 adjacency only. 

6. Convert router A2 as L1 IS-type only. 

7. Save configurations, verify IS-IS multi-area implementation and connectivity to the router E2. 

8. Repeat tasks in the steps above for areas B000, D000, and E000.


This is how routers configured now:

This is the desired result: C000 is L2 Area only. All other areas are L1.

IPv4, shows IP address of Loopback 0 interfaces:

Lab procedure: 

Step1: Access CLI for A1 and A2, configure routers as L1/L2 IS-type: 

A1(config)#router isis
A1(config-router)#is-type level-1-2 

A2(config)#router isis
A2(config-router)#is-type level-1-2 

Step2: Change "circuit-type to L1/L2 on the link between A1 and A2 nodes:

A1(config)#interface  g0/1
A1(config-if)#isis circuit-type level-1-2 

A2(config)#interface  g0/1
A2(config-if)#isis circuit-type level-1-2 

Step3: Assign the second NET addresses with new AID to routers A1 and A2:

A1(config)#router isis
A1(config-router)#net  49.A000.0000.0000.00A1.00

A2(config)#router isis
A2(config-router)#net  49.A000.0000.0000.00A2.00

Step4: Delete old NET addresses from routers A1 and A2:

A1# show  running-config | section  router isis
router isis
 net 49.c000.0000.0000.00a1.00
 net 49.a000.0000.0000.00a1.00

A1(config)#router isis
A1(config-router)#no  net 49.c000.0000.0000.00a1.00 

A2#show  running-config | section  router isis
router isis
 net 49.c000.0000.0000.00a2.00
 net 49.a000.0000.0000.00a2.00

A2(config)#router isis
A2(config-router)#no  net 49.c000.0000.0000.00a2.00

Step5: Configure G0/1 interfaces on both A1 and A2 as circuit-type L1:

A1(config)#interface  g0/1
A1(config-if)#isis circuit-type level-1

A2(config)#interface  g0/1
A2(config-if)#isis circuit-type level-1

Step6: Change IS-type to L1-only on the router A2:

A2(config)#router isis
A2(config-router)#is-type level-1

Step7: Verify modification of IS-IS configuration on the routers A1 and A2. 

A1#show  isis  neighbors  
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A2              L1   Gi0/1       UP    9        A2.01             
C1              L2   Gi0/2       UP    9        C1.02      

A1#show isis protocol IS-IS Router: <Null Tag>
  System Id: 0000.0000.00A1.00  IS-Type: level-1-2
  Manual area address(es):
  Routing for area address(es):
  Interfaces supported by IS-IS:
        GigabitEthernet0/2 - IP
        GigabitEthernet0/1 - IP
        Loopback0 - IP
    static (on by default)
  Distance for L2 CLNS routes: 110
  RRR level: none
  Generate narrow metrics: level-1-2
  Accept narrow metrics:   level-1-2
  Generate wide metrics:   none

  Accept wide metrics:     none

From the output, you can see that router A1 now has an L1 adjacency only with router A2 and still keeps L2 adjacency with core router C1. Also, AID change from C000 to A000, meaning that A1 now is L1/L2 type of router or from OSPF terminology perspective, it is ABR. 

Verify connectivity to router E2:

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/7/9 ms

Step8: Now that you have transitioned routers A1 and A2 to become part of L1 area A000, using the same tasks performed in steps above, configure the rest of topology according to the second diagram. 


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