IS-IS

IS-IS (Intermediate System to Intermediate System) is a link-state interior gateway protocol that uses Dijkstra’s algorithm to calculate optimal routing paths through a network. Originally designed for ISO’s Connectionless Network Service (CLNS), IS-IS has been extended to support IP routing and is widely deployed in service provider networks. The protocol uses Network Entity Titles (NETs) for router identification, supports hierarchical routing through level-1 and level-2 adjacencies, and provides fast convergence with minimal routing overhead. IS-IS features include flexible metric structures, area-based network segmentation, and MPLS traffic engineering extensions for comprehensive enterprise and carrier routing solutions.

Diagram

Classes

routing (iosxe.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
isis_processes	List	`[isis_processes]`	No

isis_processes (iosxe.devices.configuration.routing)

Name	Type	Constraint	Mandatory
area_tag	String		Yes
nets	List	`[nets]`	No
metric_style_wide	Boolean	`true`, `false`	No
metric_style_narrow	Boolean	`true`, `false`	No
metric_style_transition	Boolean	`true`, `false`	No
log_adjacency_changes	Boolean	`true`, `false`	No
log_adjacency_changes_all	Boolean	`true`, `false`	No

nets (iosxe.devices.configuration.routing.isis_processes)

Name	Type	Constraint	Mandatory	Default Value
tag	String		Yes

IS-IS provides scalable, efficient routing through its two-level hierarchy and flexible metric system. Configure the area tag, NET values, metric style, and interface-level metrics to fit your network topology.

Examples

IS-IS Process with Wide Metrics and Point-to-Point Interface

Cisco IOS-XE CLI Equivalent:

router isis TEST
 net 49.0001.1920.0000.2001.00
 metric-style wide
 log-adjacency-changes all
!
interface GigabitEthernet2
 ip address 10.1.1.1 255.255.255.252
 ip router isis TEST
 isis network point-to-point

iosxe:
  devices:
    - name: router1
      configuration:
        routing:
          isis_processes:
            - area_tag: TEST
              nets:
                - tag: 49.0001.1920.0000.2001.00
              metric_style_wide: true
              log_adjacency_changes: true
              log_adjacency_changes_all: true
        interfaces:
          ethernets:
            - type: GigabitEthernet
              id: "2"
              ipv4:
                address: 10.1.1.1
                address_mask: 255.255.255.252
              isis:
                area_tag: TEST
                network_point_to_point: true

IS-IS Narrow and Transition Metric Styles

Cisco IOS-XE CLI Equivalent:

router isis NARROW
 net 49.0002.1920.0000.2002.00
 metric-style narrow
!
router isis TRANSITION
 net 49.0003.1920.0000.2003.00
 metric-style transition

iosxe:
  devices:
    - name: router1
      configuration:
        routing:
          isis_processes:
            - area_tag: NARROW
              nets:
                - tag: 49.0002.1920.0000.2002.00
              metric_style_narrow: true
            - area_tag: TRANSITION
              nets:
                - tag: 49.0003.1920.0000.2003.00
              metric_style_transition: true

IS-IS Interface Metrics per Level

Cisco IOS-XE CLI Equivalent:

router isis TEST
 net 49.0001.1920.0000.2001.00
 metric-style wide
!
interface GigabitEthernet2
 ip router isis TEST
 isis metric 100 level-1
 isis metric 200 level-2

iosxe:
  devices:
    - name: router1
      configuration:
        routing:
          isis_processes:
            - area_tag: TEST
              nets:
                - tag: 49.0001.1920.0000.2001.00
              metric_style_wide: true
        interfaces:
          ethernets:
            - type: GigabitEthernet
              id: "2"
              ipv4:
                address: 10.1.1.1
                address_mask: 255.255.255.252
              isis:
                area_tag: TEST
                ipv4_metric_levels:
                  - level: level-1
                    value: 100
                  - level: level-2
                    value: 200