IS-IS Lab 23 Several L1 Areas Attached to a Single Router

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Download Lab: VIRL | EVE-NG | GNS3


Image requirements:

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


Introduction:  
Multiple L1 areas can be configured on the single router with the help of IS-IS tags. Every IS-IS L1 area must use an L1/L2 router to communicate with devices outside of its area. If there are multiple L1 areas in topology, concentrated in one physical location to form the border with the L2 area, there would be a lot of L1/L2 nodes to make it happen, this configuration introduces complexity and unnecessary consumption of resources. In this lab, you will configure a single router attached to multiple L1 areas and one L2 area to conserve resources and implement the neat design to ease future troubleshooting.


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



Topology: 




Scenario: 
Most of the routers in the topology have been configured to route IPv4 and IPV6 using IS-IS except "A" routers, this group of routers has one node A1 which is L1/L2 router and it will connect several L1 areas to the L2 area. Router A1 will run four different IS-IS processes, one to connect to the core over L2 adjacency, and three other processes will be configured for L1 areas. IS-IS processes for L1 areas named after its area ID


Lab tasks: 

1. Configure IS-IS on the router A1 with the default IS-IS process tag to connect to the core infrastructure. IS-type for this process will be L2-only as well as circuit-id for the interface connecting to the C1 router. The area-ID is A00A.

2. Verify that L2 IS-IS neighborship formed between A1 and the core router C1. Confirm that A1 able to ping IP addresses of the loopback0 interfaces of L1 routers B2, D2, and E2, this will ensure that router A1 is successfully communicated with the rest of the topology. 

3. Configure the first L1 area A000, enable IS-IS process A000 on the router A1, router A2 will be configured using the default tag for the IS-IS process. 

4. Verify the proper configuration of the A000 area. Check for neighborship formation between routers A1 and A2. Make sure that node A1 is able to ping A2's loopback0 interfaces' IP address.

5. Proceed to configure the second L1 area A001, router A1 configured with the IS-IS process tag of A001, while all configuration on the A3 will be performed with default parameters.

6. Repeat step 4 for the area A001. 

7. Finally, configure area A002, router A1 has A002 as an IS-IS process tag. Router A4 configured with default parameters. 

8. Again, confirm the proper configuration of area A002. 

9. Test connectivity from L1 "A" routers to router E2. 

10. Understand why connectivity test from L1 "A" routers failed.

11. Implement a solution.

12. Test a solution.


Lab procedure:

Step1: Acess CLI of router A1, enter IS-IS router mode, type the NET address of 49.A00A.0000.0000.00A1.00, change IS-Type to L2 only, then configure IS-IS on the interfaces G0/2 and Lo0 with circuit-type L2, enable IS-IS for both IPv4 and IPv6: 


A1(config)#router  isis
A1(config-router)#net 49.A00A.0000.0000.00A1.00
A1(config-router)#is-type level-2-only 

A1(config-router)#metric-style wide
A1(config-router)#log-adjacency-changes
A1(config-router)#exit

!
A1(config)#interface  g0/2
A1(config-if)#isis circuit-type level-2-only
A1(config-if)#ip router isis
A1(config-if)#ipv6  router isis
A1(config-if)# end 

!
A1(config)#interface  lo0
A1(config-if)#isis circuit-type level-2-only
A1(config-if)#ip router isis
A1(config-if)#ipv6  router isis 



Step2: Verify that A1 has L2 adjacency with router C1, ping other L1 routers in the topology: 

A1#show  isis  neighbors
 System Id       Type Interface     IP Address      State Holdtime Circuit Id
C1              L2   Gi0/2         10.0.0.6        UP    9        C1.02   



A1#show  isis  protocol 
IS-IS Router: <Null Tag>
  System Id: 0000.0000.00A1.00  IS-Type: level-2
  Manual area address(es):
        49.a00a
  Routing for area address(es):
        49.a00a
  Interfaces supported by IS-IS:
        Loopback0 - IP - IPv6
        GigabitEthernet0/2 - IP - IPv6
  Redistribute:
    static (on by default)
  Distance for L2 CLNS routes: 110
  RRR level: none
  Generate narrow metrics: none
  Accept narrow metrics:   none
  Generate wide metrics:   level-1-2
  Accept wide metrics:     level-1-2


A1#ping 192.168.0.7
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.7, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/7/9 ms
 

A1#ping 192.168.0.9
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.9, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/5 ms
 

A1#ping 2001:DB8:b:0:1::d
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:B:0:1::D, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 2/5/11 ms
A1#



Step3: Configure router A1 for L1 area A000, first enter router IS-IS mode with process tag of A000 then assign the NET address of 49.A000.1000.0000.00A1.00, leave default IS-type, configure metric style wide. Enable interface G0/1 for IPv4 and IPv6 with a process tag of A000. Configure IS-IS on the router A3 with the default tag, assign NET of 49.A000.0000.0000.00A2.00, change IS-Type to L1, enable interfaces G0/1 and loopback0 for both IPv4 and IPv6 IS-IS:

A1(config)#router isis A000
A1(config-router)#net 49.A000.1000.0000.00A1.00
A1(config-router)#metric-style wide
A1(config-router)#log-adjacency-changes
A1(config-router)#exit

!
A1(config)#interface  g0/1
A1(config-if)#ip router isis  A000
A1(config-if)#ipv6 router isis A000

A1(config-if)# end
!
!
A2(config)#router isis
A2(config-router)#net  49.A000.0000.0000.00A2.00
A2(config-router)#log-adjacency-changes
A2(config-router)#is-type level-1
A2(config-router)#metric-style wide
A2(config-router)#exit

!
A2(config)#interface  range  g0/1, lo0
A2(config-if-range)#ip router isis
A2(config-if-range)#ipv6  router isis
A2(config-if-range)#isis circuit-type level-1



Step4: Verify proper IS-IS configuration in the area A000:

A1#show  isis  neighbors 
Tag null:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
C1              L2   Gi0/2         10.0.0.6        UP    27       A1.01             

Tag A000:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A2              L1   Gi0/1         10.0.0.26       UP    9        A2.01     


A2#show  isis  neighbors 
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A1              L1   Gi0/1         10.0.0.25       UP    29       A2.01             
A2#

This output shows that A1 has two neighbors, one L2 neighbor for the null tag which is the C1 router. Another neighbor router A2 which appears under the A000 tag. This means that both of these neighbors are in separate IS-IS topologies. Displaying database on the router A1 will prove that each process tag has its own database:

A1#show  isis  database
Tag null:
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000009   0xEB2B                 682/*         0/0/0
A1.01-00            * 0x00000002   0x2B9D                 645/*         0/0/0
B1.00-00              0x00000007   0xA811                 732/1198      0/0/0
B1.02-00              0x00000003   0x465F                 739/1198      0/0/0
C1.00-00              0x00000008   0x74B8                 685/1199      0/0/0
C2.00-00              0x00000008   0x9B50                 869/1198      0/0/0
C2.01-00              0x00000003   0x4A3B                 883/1198      0/0/0
C2.03-00              0x00000003   0xBEA4                 800/1198      0/0/0
D1.00-00              0x00000007   0x2A43                 765/1198      0/0/0
D1.02-00              0x00000003   0x5214                 659/1198      0/0/0
E1.00-00              0x00000007   0x4C17                 965/1198      0/0/0

Tag A000:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00              0x00000005   0x05F0                 691/1199      0/0/0
A2.01-00              0x00000001   0x82CE                 692/1199      0/0/0
A1.00-00            * 0x00000004   0xB25B                 692/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000004   0xCE87                 698/*         0/0/0
A1#

Ping loopback0's IP addresses of A2:

A1#ping 192.168.0.9
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.9, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/6 ms

A1#ping 2001:Db8:b:0:1::b
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:B:0:1::B, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/5 ms
A1#

Successful ping indicates that area A000 has been configured properly.


Step5: Configuring area A001. Enter IS-IS router mode with process tag of A001, assign the NET address of 49.A001.2000.0000.00A1.00, change metric-style to wide, IS-type stays default, configure interface g0/3 for both IPv4 and IPv6 IS-IS using the tag of A001. Configure router A3 with default tag, assign the NET address of 49.A001.0000.0000.00A3.00, change IS-type to L1-only, metric-style is wide, both G0/1 and lo0 are participating for IPv4 and IPv6 IS-IS:

A1(config)#router isis  A001
A1(config-router)#net 49.A001.2000.0000.00A1.00
A1(config-router)#metric-style wide
A1(config-router)#log-adjacency-changes
A1(config-router)#exit


!
A1(config)#interface  g0/3
A1(config-if)#ip router isis A001
A1(config-if)#ipv6 router isis A001

!
!
A3(config)#router isis
A3(config-router)#net 49.A001.0000.0000.00A3.00
A3(config-router)#is-type level-1
A3(config-router)#log-adjacency-changes
A3(config-router)#metric-style wide
A3(config-router)#exit

!
A3(config)#interface range g0/1, lo0
A3(config-if-range)#isis circuit-type level-1
A3(config-if-range)#ip router isis
A3(config-if-range)#ipv6 router isis
A3(config-if-range)# exit 



Step6: Verify IS-IS configuration for area A001:

A1#show  isis  neighbors
Tag null:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
C1              L2   Gi0/2         10.0.0.6        UP    25       A1.01             

Tag A000:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A2              L1   Gi0/1         10.0.0.26       UP    9        A2.01             

Tag A001:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A3              L1   Gi0/3         10.0.0.42       UP    29       A1.01             
A1#

Now router A1 has one more neighbor router A3, under the tag A001.

A1#show  isis  database
Tag null:
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x0000000D   0xE32F                 564/*         0/0/0
A1.01-00            * 0x00000004   0x279F                 917/*         0/0/0
B1.00-00              0x00000009   0xA413                 860/1198      0/0/0
B1.02-00              0x00000005   0x4261                 889/1198      0/0/0
C1.00-00              0x0000000A   0x70BA                 955/1199      0/0/0
C2.00-00              0x0000000A   0x9752                 881/1198      0/0/0
C2.01-00              0x00000005   0x463D                1183/1198      0/0/0
C2.03-00              0x00000005   0xBAA6                 898/1198      0/0/0
D1.00-00              0x00000009   0x2645                 847/1198      0/0/0
D1.02-00              0x00000005   0x4E16                 856/1198      0/0/0
E1.00-00              0x00000009   0x4819                 942/1198      0/0/0

Tag A000:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00              0x00000007   0x01F2                 924/1199      0/0/0
A2.01-00              0x00000003   0x7ED0                 630/1199      0/0/0
A1.00-00            * 0x00000006   0xAE5D                 793/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000006   0xCA89                 880/*         0/0/0

Tag A001:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A3.00-00              0x00000005   0x386F                 940/1196      0/0/0
A1.00-00            * 0x00000004   0xF2AA                 939/*         0/0/0
A1.01-00            * 0x00000001   0x9985                 940/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000004   0x9965                 945/*         0/0/0

A new database for IS-IS process A001 appears at the bottom of the output.

A1#ping 192.168.0.11
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.11, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 2/2/3 ms

A1#ping 2001:DB8:b:0:1::4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:B:0:1::4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/5 ms
A1#

Ping to A3's loopback0 IP addresses confirms that area A001 has been configured successfully.


Step7: Configuring area A002. Router A1 configured with the tag of A002, has the NET address of 49.A002.3000.0000.00A1.00, metric-style is wide, IS-type remains the default, interface G0/4 enabled for both IPv4 and IPv6 IS-IS with tag A002. Router A4 configured with the default tag. Has the NET address of 49.A002.0000.0000.00A4.00, IS-type changed to L1-only, metric-style is wide, interfaces G0/1 and Lo0 are both participating in the IPv4 and IPv6 IS-IS with circuit-type L1:

A1(config)#router isis A002
A1(config-router)#net 49.A002.3000.0000.00A1.00
A1(config-router)#metric-style wide
A1(config-router)#log-adjacency-changes
A1(config-router)#exit
!
A1(config)#interface g0/4
A1(config-if)#ip router isis A002
A1(config-if)#ipv6 router isis A002
A1(config-if)#exit
!

!
A4(config)#router  isis
A4(config-router)#net 49.A002.0000.0000.00A4.00
A4(config-router)#is-type level-1
A4(config-router)#metric-style wide
A4(config-router)#log-adjacency-changes
A4(config-router)#exit 

!
A4(config)#interface range g0/1, lo0
A4(config-if-range)#isis circuit-type level-1
A4(config-if-range)#ip router isis
A4(config-if-range)#ipv6  router isis
A4(config-if-range)# exit 



Step8: Lastly verify the area A002

A1#show  isis  neighbors Tag null:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
C1              L2   Gi0/2         10.0.0.6        UP    29       A1.01             

Tag A000:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A2              L1   Gi0/1         10.0.0.26       UP    9        A2.01             

Tag A001:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A3              L1   Gi0/3         10.0.0.42       UP    29       A1.01             

Tag A002:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A4              L1   Gi0/4         10.0.0.46       UP    8        A4.01             
A1#

Now the output shows the complete outcome, router A1 as intended has four neighbors one with L2 adjacency and three with L1 adjacencies. Three L1 areas have been attached to a single router. Router A1 has four separate IS-IS topologies as shown in the output below:

A1#show  isis  database

Tag null:
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000010   0xDD32                 665/*         0/0/0
A1.01-00            * 0x00000006   0x23A1                 541/*         0/0/0
B1.00-00              0x0000000C   0x9E16                1008/1198      0/0/0
B1.02-00              0x00000008   0x3C64                1145/1198      0/0/0
C1.00-00              0x0000000C   0x6CBC                 505/1199      0/0/0
C2.00-00              0x0000000D   0x9155                1145/1198      0/0/0
C2.01-00              0x00000007   0x423F                 692/1198      0/0/0
C2.03-00              0x00000008   0xB4A9                1064/1198      0/0/0
D1.00-00              0x0000000C   0x2048                1033/1198      0/0/0
D1.02-00              0x00000008   0x4819                1084/1198      0/0/0
E1.00-00              0x0000000B   0x441B                 587/1198      0/0/0

Tag A000:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00              0x00000009   0xFCF4                 480/1199      0/0/0
A2.01-00              0x00000006   0x78D3                 964/1199      0/0/0
A1.00-00            * 0x00000009   0xA860                 999/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000009   0xC48C                1197/*         0/0/0

Tag A001:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A3.00-00              0x00000008   0x3272                1160/1199      0/0/0
A1.00-00            * 0x00000006   0xEEAC                 535/*         0/0/0
A1.01-00            * 0x00000003   0x9587                 421/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000006   0x9567                 470/*         0/0/0

Tag A002:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A4.00-00              0x00000007   0xCAE8                 771/1199      0/0/0
A4.01-00              0x00000002   0x64C7                 768/1199      0/0/0
A1.00-00            * 0x00000006   0xDFB7                 773/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000004   0xC11A                 726/*         0/0/0
A1#

Confirm connectivity to router A4:

A1#ping 192.168.0.12
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.12, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 2/2/3 ms

A1#ping 2001:DB8:b:0:1::5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:B:0:1::5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/8 ms
A1#

The result of ping is positive, proves that area A002 has been enabled in the right way.


Step9: Test if routers A2, A3, and A4 able to ping IP address in another L1 area

A2#ping 192.168.0.8Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.8, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
A2#



A3#ping 192.168.0.8Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.8, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
A3#


A4#ping 192.168.0.8Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.8, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
A4#



All three routers failed to ping E2's IP address, the next step hypothesizes what is happening with connectivity.


Step10: To understand the issue occurring in the previous step, further investigation is required, starting from router A2 identify if node learns any IS-IS prefixes:

A2#show ip router isis
Codes: L - local, 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, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set


A2#show ipv6 route isis
IPv6 Routing Table - default - 4 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       RL - RPL, O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1
       OE2 - OSPF ext 2, ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
       la - LISP alt, lr - LISP site-registrations, ld - LISP dyn-eid
       lA - LISP away, a - Application
A2#


From the empty routing table for IS-IS protocol, the conclusion can be drawn that L1/L2 router A1 does not send any routes to this node, a question rises why not? 

Let's interrogate local IS-IS database: 

A2#show  isis  database 
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00            * 0x00000011   0xECFC                 968/*         0/0/0
A2.01-00            * 0x0000000D   0x6ADA                 983/*         0/0/0
A1.00-00              0x00000010   0x9A67                 906/1199     0/0/0
A2#


Ok! This output of the database shows quite interesting information, the LSP of router A1 does not have ATT bit set to 1 instead it is set to 0. Recall that by default every L1 IS-IS area is like OSPF's totally stub area and the nearest L1/L2 router suppose to send its LSP with an attached bit set to 1 then the L1 router will install default route into its routing table but in this case, it does not! 

Why A1 which is configured to be L1/L2 node does not advertise its LSP with ATT bit set to 1? Switching thoughts to router A1! Examine A1 database:

A1#show isis database

Tag null:
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000018   0xCD3A                 925/*         0/0/0
A1.01-00            * 0x0000000E   0x13A9                 568/*         0/0/0
B1.00-00              0x00000013   0x901D                 382/1198      0/0/0
B1.02-00              0x0000000F   0x2E6B                 393/1198      0/0/0
C1.00-00              0x00000014   0x5CC4                 594/1199      0/0/0
C2.00-00              0x00000015   0x815D                 894/1198      0/0/0
C2.01-00              0x0000000F   0x3247                 745/1198      0/0/0
C2.03-00              0x00000010   0xA4B1                1186/1198      0/0/0
D1.00-00              0x00000014   0x1050                1152/1198      0/0/0
D1.02-00              0x00000010   0x3821                 928/1198      0/0/0
E1.00-00              0x00000014   0x3224                 968/1198      0/0/0

Tag A000:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00              0x00000012   0xEAFD                 908/1199      0/0/0
A2.01-00              0x0000000E   0x68DB                 953/1199      0/0/0
A1.00-00            * 0x00000011   0x9868                 920/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000011   0xB494                1140/*         0/0/0

Tag A001:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A3.00-00              0x00000010   0x227A                1073/1199      0/0/0
A1.00-00            * 0x0000000E   0xDEB4                 783/*         0/0/0
A1.01-00            * 0x0000000B   0x858F                 697/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x0000000E   0x856F                 549/*         0/0/0

Tag A002:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A4.00-00              0x0000000F   0xBAF0                 886/1199      0/0/0
A4.01-00              0x0000000A   0x54CF                 530/1199      0/0/0
A1.00-00            * 0x0000000E   0xCFBF                 780/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x0000000C   0xB122                 685/*         0/0/0
A1# 


This output shows that the database contains four distinct IS-IS topologies identified by IS-IS process tags: 

Tag "null" has the database for L2 area A00A which brings connection to the rest of topology only for router A1, meaning that router A1 and its subnets accessible to the rest of routers in the topology who connected by any means to L2 backbone.

Tag "A000" and the rest of IS-IS process tags have the same fate, all of them show that databases for these tags do not have any other LSPs but only A1's LSP. Practically speaking that L1/L2 node for each "tag" is configured to be in both L1 and L2 areas but has no connection to the L2 core router C1 that is why A1 does not technically act as L1/L2 node! 

To fix this problem, think of the A1 router as a physical device that has been connected to three L1 areas, these areas are independent of each other therefore they need three distinct L1/L2 nodes to communicate with the rest of the topology. Router A1 is the only device those areas have been connected to and logical means of communication with L2 backbone has to be provided to each L1 areas separated by tags on the router A1.

Solution: Three more physical links could be added between router C1 and A1 then configure each of interfaces with its own IS-IS tag correlated to each L1 area. But for this lab, only one link is present between those routers, to overcome the problem of a limited amount of physical interfaces, sub-interfaces will be used. Interface G0/2 on both sides will be partitioned to have sub-interfaces G0/2.10 for the tag A000, g0/2.11 for the tag A001, and g0/2.12 for the tag A002. 


Step11: Implement solution: 

Configure router C1: 
C1(config)#interface g0/2.10
C1(config-subif)#encapsulation dot1Q 10
C1(config-subif)#ip address 10.0.1.1 255.255.255.252
C1(config-subif)#ipv6 enable 

C1(config-subif)#ipv6 router isis
C1(config-subif)#ip router isis 

!C1(config)#interface g0/2.11
C1(config-subif)#encapsulation dot1Q 11
C1(config-subif)#ip address 10.0.1.5 255.255.255.252
C1(config-subif)#ipv6 enable 

C1(config-subif)#ipv6 router isis
C1(config-subif)#ip router isis

!
C1(config)#interface g0/2.12
C1(config-subif)#encapsulation dot1Q 12
C1(config-subif)#ip address 10.0.1.9 255.255.255.252
C1(config-subif)#ipv6 enable 

C1(config-subif)#ipv6 router isis
C1(config-subif)#ip router isis



Configure router A1:
A1(config)#interface g0/2.10
A1(config-subif)#encapsulation dot1Q 10 
A1(config-subif)#ip address 10.0.1.2 255.255.255.252
A1(config-subif)#ipv6 enable 

A1(config-subif)#ipv6 router isis A000
A1(config-subif)#ip router isis A000

!A1(config)#interface g0/2.11
A1(config-subif)#encapsulation dot1Q 11
A1(config-subif)#ip address 10.0.1.6 255.255.255.252
A1(config-subif)#ipv6 enable 

A1(config-subif)#ipv6 router isis A001
A1(config-subif)#ip router isis A001

!
A1(config)#interface g0/2.12
A1(config-subif)#encapsulation dot1Q 12
A1(config-subif)#ip address 10.0.1.10 255.255.255.252
A1(config-subif)#ipv6 enable 

A1(config-subif)#ipv6 router isis A002
A1(config-subif)#ip router isis A002



Step12: Test the solution. Begin with verifying IS-IS neighborships on the router A1:

A1#show isis neighbors
Tag null:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
C1              L2   Gi0/2         10.0.0.6        UP    28       A1.01             

Tag A000:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A2              L1   Gi0/1         10.0.0.26       UP    9        A2.01             
C1              L2   Gi0/2.10      10.0.1.1        UP    21       A1.02             

Tag A001:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A3              L1   Gi0/3         10.0.0.42       UP    27       A1.01             
C1              L2   Gi0/2.11      10.0.1.5        UP    21       A1.02             

Tag A002:
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A4              L1   Gi0/4         10.0.0.46       UP    9        A4.01             
C1              L2   Gi0/2.12      10.0.1.9        UP    24       A1.02             
A1#

Router A1 is now having neighborship with router C1 for every L1 tag. Let's see what is going on with the database:

A1#show  isis  database

Tag null:
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00            * 0x00000023   0xB745                 940/*         0/0/0
A1.01-00            * 0x00000018   0xFEB3                1091/*         0/0/0
B1.00-00              0x0000001C   0x7E26                 567/1198      0/0/0
B1.02-00              0x00000018   0x1C74                 686/1198      0/0/0
C1.00-00              0x00000025   0x825D                 407/1199      0/0/0
C2.00-00              0x0000001D   0x7165                 450/1198      0/0/0
C2.01-00              0x00000018   0x2050                 514/1198      0/0/0
C2.03-00              0x00000018   0x94B9                1033/1198      0/0/0
D1.00-00              0x0000001C   0xFF58                 468/1198      0/0/0
D1.02-00              0x00000019   0x262A                 691/1198      0/0/0
E1.00-00              0x0000001D   0x202D                 873/1198      0/0/0
A1.00-00              0x0000001B   0x45A8                1086/1198      0/0/0
A1.02-00              0x00000004   0x8F16                 871/1198      0/0/0
A1.00-00              0x00000018   0x84EA                 462/1198      0/0/0
A1.02-00              0x00000004   0xFE86                1098/1198      0/0/0
A1.00-00              0x00000016   0x4FEA                 513/1198      0/0/0
A1.02-00              0x00000003   0x70F5                 610/1198      0/0/0

Tag A000:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00              0x0000001A   0xDA06                 772/1199      0/0/0
A2.01-00              0x00000017   0x56E4                 975/1199      0/0/0
A1.00-00            * 0x0000001B   0xE19A                1011/*         1/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00              0x00000023   0xB745                 939/1198      0/0/0
A1.01-00              0x00000018   0xFEB3                1090/1198      0/0/0
B1.00-00              0x0000001C   0x7E26                 567/1198      0/0/0
B1.02-00              0x00000018   0x1C74                 686/1198      0/0/0
C1.00-00              0x00000025   0x825D                 407/1199      0/0/0
C2.00-00              0x0000001D   0x7165                 450/1198      0/0/0
C2.01-00              0x00000018   0x2050                 514/1198      0/0/0
C2.03-00              0x00000018   0x94B9                1033/1198      0/0/0
D1.00-00              0x0000001C   0xFF58                 468/1198      0/0/0
D1.02-00              0x00000019   0x262A                 691/1198      0/0/0
E1.00-00              0x0000001D   0x202D                 873/1198      0/0/0
A1.00-00            * 0x0000001B   0x45A8                1087/*         0/0/0
A1.02-00            * 0x00000004   0x8F16                 872/*         0/0/0
A1.00-00              0x00000018   0x84EA                 462/1198      0/0/0
A1.02-00              0x00000004   0xFE86                1098/1198      0/0/0
A1.00-00              0x00000016   0x4FEA                 513/1198      0/0/0
A1.02-00              0x00000003   0x70F5                 610/1198      0/0/0

Tag A001:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A3.00-00              0x00000018   0x1282                 779/1199      0/0/0
A1.00-00            * 0x00000018   0xA252                 467/*         1/0/0
A1.01-00            * 0x00000014   0x7398                 870/*         0/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00              0x00000023   0xB745                 939/1198      0/0/0
A1.01-00              0x00000018   0xFEB3                1090/1198      0/0/0
B1.00-00              0x0000001C   0x7E26                 567/1198      0/0/0
B1.02-00              0x00000018   0x1C74                 686/1198      0/0/0
C1.00-00              0x00000025   0x825D                 407/1199      0/0/0
C2.00-00              0x0000001D   0x7165                 450/1198      0/0/0
C2.01-00              0x00000018   0x2050                 514/1198      0/0/0
C2.03-00              0x00000018   0x94B9                1033/1198      0/0/0
D1.00-00              0x0000001C   0xFF58                 468/1198      0/0/0
D1.02-00              0x00000019   0x262A                 691/1198      0/0/0
E1.00-00              0x0000001D   0x202D                 873/1198      0/0/0
A1.00-00              0x0000001B   0x45A8                1086/1198      0/0/0
A1.02-00              0x00000004   0x8F16                 871/1198      0/0/0
A1.00-00            * 0x00000018   0x84EA                 463/*         0/0/0
A1.02-00            * 0x00000004   0xFE86                1099/*         0/0/0
A1.00-00              0x00000016   0x4FEA                 513/1198      0/0/0
A1.02-00              0x00000003   0x70F5                 610/1198      0/0/0


Tag A002:
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A4.00-00              0x00000018   0xA8F9                1058/1199      0/0/0
A4.01-00              0x00000013   0x42D8                 765/1199      0/0/0
A1.00-00            * 0x00000019   0xE209                1151/*         1/0/0
IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A1.00-00              0x00000023   0xB745                 939/1198      0/0/0
A1.01-00              0x00000018   0xFEB3                1090/1198      0/0/0
B1.00-00              0x0000001C   0x7E26                 567/1198      0/0/0
B1.02-00              0x00000018   0x1C74                 686/1198      0/0/0
C1.00-00              0x00000025   0x825D                 407/1199      0/0/0
C2.00-00              0x0000001D   0x7165                 450/1198      0/0/0
C2.01-00              0x00000018   0x2050                 514/1198      0/0/0
C2.03-00              0x00000018   0x94B9                1033/1198      0/0/0
D1.00-00              0x0000001C   0xFF58                 468/1198      0/0/0
D1.02-00              0x00000019   0x262A                 691/1198      0/0/0
E1.00-00              0x0000001D   0x202D                 873/1198      0/0/0
A1.00-00              0x0000001B   0x45A8                1086/1198      0/0/0
A1.02-00              0x00000004   0x8F16                 871/1198      0/0/0
A1.00-00              0x00000018   0x84EA                 462/1198      0/0/0
A1.02-00              0x00000004   0xFE86                1098/1198      0/0/0
A1.00-00            * 0x00000016   0x4FEA                 514/*         0/0/0
A1.02-00            * 0x00000003   0x70F5                 611/*         0/0/0
A1#


The output has changed since the last time, for every L1 tag, there are L2 LSPs from other L2 and L1/L2 routers. Also for the Level 1 IS-IS database, A1's LSP has ATT bit set to 1. 

Next, check router A2, starting with database:

IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime/Rcvd      ATT/P/OL
A2.00-00            * 0x0000001C   0xD608                1158/*         0/0/0
A2.01-00            * 0x00000018   0x54E5                 617/*         0/0/0
A1.00-00              0x0000001D   0xDD9C                1171/1199      1/0/0
A2#


Finally, the LSP from router A1 has an ATT bit set. Next, verify the routing table: 

A2#show ip route isis
Codes: L - local, 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, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.0.25 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/10] via 10.0.0.25, 01:16:57, GigabitEthernet0/1
      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
i L1     10.0.1.0/30 [115/20] via 10.0.0.25, 01:17:13, GigabitEthernet0/1
A2#


A2#show  ipv6  route isis
IPv6 Routing Table - default - 5 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       RL - RPL, O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1
       OE2 - OSPF ext 2, ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
       la - LISP alt, lr - LISP site-registrations, ld - LISP dyn-eid
       lA - LISP away, a - Application
I1  ::/0 [115/10]
     via FE80::F816:3EFF:FE0E:70D3, GigabitEthernet0/1
A2#


For both IPv4 and IPv6, there is default route, router A2 should be able to ping some destinations in other L1 areas:

A2#ping 192.168.0.8
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.8, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 5/6/8 ms
 

A2#ping 2001:DB8:b:0:1::d
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:B:0:1::D, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/11/37 ms
A2#


The same goes for router A3 and A4, they also should be able to ping remote IP addresses of other L1 areas in the topology. 




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