L1-L2 Area Routing with a Single Instance
IS-IS supports a two-level hierarchy for handling and scaling the functionality of large networks. The Level-1 (L1) area is mainly for Leaf networks, and the Level-2 (L2) area is the backbone area connecting Level-1 areas. In this example, R3 and R4 are configured as Level-1 routers, and reside in the Level-1 area. R1 and R2 are configured as Level-1-2 routers, and connect these two Level-1 areas with a backbone Level-2 area. You can configure Level-1-2 routers with single or multiple instances: This configuration shows the single-instance version of the Level-1-2 router.
Topology
Figure 13-106: Single-Instance L1-L2 Area Routing
Configuration
R1
#configure terminal | Enter configure mode. |
|---|---|
(config-if)#commit | Commit candidate configuration to the running configuration |
(config)#interface eth1 | Enter interface mode. |
(config-if)#ip address 20.20.20.1/24 | Configure IP address on interface. |
(config-if)#ip router isis ABC | Enable IS-IS routing on the interface eth1 for area ABC. |
(config-if)#isis circuit-type level-2-only | Set the circuit type for the interface eth1. |
(config-if)#exit | Exit interface mode. |
(config)#interface eth2 | Enter interface mode. |
(config-if)#ip address 30.30.30.1/24 | Configure IP address on interface. |
(config-if)#ip router isis ABC | Enable IS-IS routing on the interface eth2 for area ABC. |
(config-if)#isis circuit-type level-1 | Set the circuit type for interface eth2 to level 1. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis ABC | Create an IS-IS routing instance for area ABC. |
(config-router)#net 52.0000.0000.0001.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#commit | Commit candidate configuration to the running configuration |
R2
(config)#interface eth1 | Enter interface mode. |
(config-if)#ip router isis bb | Enable IS-IS routing on the interface eth1 for area bb. |
(config-if)#ip address 20.20.20.2/24 | Configure IP address on interface. |
(config-if)#isis circuit-type level-2-only | Set the circuit type for the interface eth1 to level-2 only. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#interface eth2 | Enter interface mode. |
(config-if)#ip address 40.40.40.1/24 | Configure IP address on interface. |
(config-if)#ip router isis bb | Enable IS-IS routing on interface eth2 for area bb. |
(config-if)#isis circuit-type level-1 | Set the circuit type for interface eth2 to level 1. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis bb | Create an IS-IS routing instance for area bb. |
(config-router)#net 50.0000.0000.0002.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-if)#commit | Commit candidate configuration to the running configuration |
R3
(config)#interface eth2 | Enter interface mode. |
(config-if)#ip address 30.30.30.2/24 | Configure IP address on interface. |
(config-if)#ip router isis xyz | Enable IS-IS routing on the interface eth2 for area xyz. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis xyz | Create an IS-IS routing instance for area xyz. |
(config-router)#is-type level-1 | Set the IS level for this area (xyz) as level-1. |
(config-router)#net 52.0000.0000.0003.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-if)#commit | Commit candidate configuration to the running configuration |
R4
(config)#interface eth2 | Enter interface mode. |
(config-if)#ip address 40.40.40.2/24 | Configure IP address on interface. |
(config-if)#ip router isis aa | Enable IS-IS routing on the interface eth2 for area aa. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode. |
(config)#router isis aa | Create an IS-IS routing instance for area aa. |
(config-router)#is-type level-1 | Set the IS level for this area (aa) as level-1. |
(config-router)#net 50.0000.0000.0004.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-if)#commit | Commit candidate configuration to the running configuration |
Validation
R1#
R1#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 1
Total number of adjacencies: 2
Tag ABC: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth1 5254.002a.230a Up 20 L2 IS-IS
0000.0000.0003 eth2 5254.00a8.940d Up 6 L1 IS-IS
R2#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 1
Total number of adjacencies: 2
Tag bb: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.00dc.0b76 Up 8 L2 IS-IS
0000.0000.0004 eth2 5254.00e2.aece Up 7 L1 IS-IS
R3#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 0
Total number of adjacencies: 1
Tag xyz: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth2 5254.00a1.6afe Up 23 L1 IS-IS
R4#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 0
Total number of adjacencies: 1
Tag aa: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth2 5254.007e.5ade Up 25 L1 IS-IS
R1#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag ABC: VRF : default
Destination Metric Next-Hop Interface Tag
C 20.20.20.0/24 10 -- eth1 0
C 30.30.30.0/24 10 -- eth2 0
L2 40.40.40.0/24 20 20.20.20.2 eth1 0
R2#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag bb: VRF : default
Destination Metric Next-Hop Interface Tag
C 20.20.20.0/24 10 -- eth1 0
L2 30.30.30.0/24 20 20.20.20.1 eth1 0
C 40.40.40.0/24 10 -- eth2 0
R3#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag xyz: VRF : default
Destination Metric Next-Hop Interface Tag
L1 0.0.0.0/0 10 30.30.30.1 eth2 0
C 30.30.30.0/24 10 -- eth2 0
R4#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag aa: VRF : default
Destination Metric Next-Hop Interface Tag
L1 0.0.0.0/0 10 40.40.40.1 eth2 0
C 40.40.40.0/24 10 -- eth2 0
R1#show isis topology
Tag ABC: VRF : default
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0001 --
0000.0000.0003 10 0000.0000.0003 eth2 5254.00a8.940d
IS-IS paths to level-2 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0001 --
0000.0000.0002 10 0000.0000.0002 eth1 5254.002a.230a
R2#show isis topology
Tag bb: VRF : default
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0002 --
0000.0000.0004 10 0000.0000.0004 eth2 5254.00e2.aece
IS-IS paths to level-2 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0001 10 0000.0000.0001 eth1 5254.00dc.0b76
0000.0000.0002 --
R3#show isis topology
Tag xyz: VRF : default
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0001 10 0000.0000.0001 eth2 5254.00a1.6afe
0000.0000.0003 --
R4#show isis topology
Tag aa: VRF : default
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
0000.0000.0002 10 0000.0000.0002 eth2 5254.007e.5ade
0000.0000.0004 --
R1#show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2,
ia - IS-IS inter area, E - EVPN,
v - vrf leaked
* - candidate default
IP Route Table for VRF "default"
C 10.12.30.0/24 is directly connected, eth0, 00:27:08
C 20.20.20.0/24 is directly connected, eth1, 00:16:57
C 30.30.30.0/24 is directly connected, eth2, 00:15:48
i L2 40.40.40.0/24 [115/20] via 20.20.20.2, eth1, 00:15:05
C 127.0.0.0/8 is directly connected, lo, 00:27:08
Gateway of last resort is not set
R2#show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2,
ia - IS-IS inter area, E - EVPN,
v - vrf leaked
* - candidate default
IP Route Table for VRF "default"
C 10.12.30.0/24 is directly connected, eth0, 00:27:17
C 20.20.20.0/24 is directly connected, eth1, 00:17:13
i L2 30.30.30.0/24 [115/20] via 20.20.20.1, eth1, 00:16:18
C 40.40.40.0/24 is directly connected, eth2, 00:15:36
C 127.0.0.0/8 is directly connected, lo, 00:27:17
Gateway of last resort is not set
R3#show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2,
ia - IS-IS inter area, E - EVPN,
v - vrf leaked
* - candidate default
IP Route Table for VRF "default"
Gateway of last resort is 30.30.30.1 to network 0.0.0.0
i*L1 0.0.0.0/0 [115/10] via 30.30.30.1, eth2, 00:16:47
C 10.12.30.0/24 is directly connected, eth0, 00:27:46
C 30.30.30.0/24 is directly connected, eth2, 00:16:52
C 127.0.0.0/8 is directly connected, lo, 00:27:46
R4#show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2,
ia - IS-IS inter area, E - EVPN,
v - vrf leaked
* - candidate default
IP Route Table for VRF "default"
Gateway of last resort is 40.40.40.1 to network 0.0.0.0
i*L1 0.0.0.0/0 [115/10] via 40.40.40.1, eth2, 00:16:26
C 10.12.30.0/24 is directly connected, eth0, 00:27:20
C 40.40.40.0/24 is directly connected, eth2, 00:16:36
C 127.0.0.0/8 is directly connected, lo, 00:27:20
R1#show isis database
Tag ABC: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00* 0x00000005 0xE66E 1165 1/0/0
0000.0000.0003.00-00 0x00000004 0xDC80 1164 0/0/0
0000.0000.0003.01-00 0x00000002 0x10C8 1163 0/0/0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00* 0x00000005 0xD0D8 1148 0/0/0
0000.0000.0001.01-00* 0x00000002 0x1FBA 1109 0/0/0
0000.0000.0002.00-00 0x00000005 0x7219 1189 0/0/0
R2#show isis database
Tag bb: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0002.00-00* 0x00000005 0x9583 1179 1/0/0
0000.0000.0004.00-00 0x00000004 0x8B95 1177 0/0/0
0000.0000.0004.01-00 0x00000002 0x2FA6 1177 0/0/0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00 0x00000005 0xD0D8 1116 0/0/0
0000.0000.0001.01-00 0x00000002 0x1FBA 1078 0/0/0
0000.0000.0002.00-00* 0x00000005 0x7219 1160 0/0/0
R3#show isis database
Tag xyz: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00 0x00000005 0xE66E 1094 1/0/0
0000.0000.0003.00-00* 0x00000004 0xDC80 1095 0/0/0
0000.0000.0003.01-00* 0x00000002 0x10C8 1094 0/0/0
R4#show isis database
Tag aa: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0002.00-00 0x00000005 0x9583 1105 1/0/0
0000.0000.0004.00-00* 0x00000004 0x8B95 1105 0/0/0
0000.0000.0004.01-00* 0x00000002 0x2FA6 1105 0/0/0
Last modified date: 10/16/2023