[IS-IS] Add Advanced IS-IS Support in Terraform Module

[Dan-Dev-Net]

Related Issue(s)

Fixes #505
Depends on: CiscoDevNet/terraform-provider-iosxe#503
Depends on: netascode/nac-iosxe#504

Proposed Changes

This PR extends the Terraform NAC module to support IS-IS routing protocol configuration with complete integration from NAC YAML to device deployment.

New File: iosxe_isis.tf

• Processes IS-IS router configuration from NAC YAML
• Generates iosxe_isis provider resources
• Implements local.isis_processes with proper try() patterns
• Handles area_tag, NETs, metric-style, and log-adjacency-changes

Modified File: iosxe_interfaces.tf

• Extended local.interfaces_loopbacks to include IS-IS configuration
• Added IS-IS boolean flag for presence detection
• Implemented metric levels list processing
• Created iosxe_interface_isis.loopback_isis resource
• Proper depends_on relationships for IS-IS router process

Module Features:

• Translates NAC YAML attributes to provider resource format
• Uses try() patterns with defaults fallback for optional attributes
• Processes NETs as list of objects
• Handles per-level interface metrics (level-1, level-2)
• Follows existing module patterns (consistent with BGP, OSPF)

NAC YAML Format:

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:
  loopbacks:
    - id: 506
      isis:
        ipv4_metric_levels:
          - level: level-1
            value: 100
          - level: level-2
            value: 50

Robot Test(s)

End-to-End NAC Workflow Testing:

Test Environment:

• Device: 10.81.239.57 (IOS-XE 17.15.1)
• NAC YAML: isis-test.nac.yaml
• Module: terraform-iosxe-nac-iosxe

Workflow Validated:

NAC YAML → Module → Provider → Device

Test Steps:

1. Created NAC YAML with IS-IS configuration
2. Ran terraform init - Module loaded successfully
3. Ran terraform plan - Module generated correct resources:
   • iosxe_isis.isis with all attributes
   • iosxe_interface_loopback.loopback with IP
   • iosxe_interface_isis.loopback_isis with metrics
4. Ran terraform apply - All 3 resources created
5. Verified device CLI - Configuration correct
6. Ran terraform apply again - Idempotency verified (no changes)

Results:

• Module correctly translates NAC YAML to provider resources
• All attributes mapped properly (area_tag, NETs, metric-style, metrics)
• Resources applied successfully to device
• Device configuration matches NAC specification
• Idempotency verified - second apply shows no changes
• Dependencies work correctly (interface depends on router process)

Device Verification:

router isis EPIC506-NAC-TEST
 net 49.0001.1721.6025.5002.00
 metric-style wide
 log-adjacency-changes all

interface Loopback506
 ip address 192.0.2.100 255.255.255.255
 isis metric 100 level-1
 isis metric 50 level-2

Code Quality:

• No linter errors
• Follows module coding standards
• Consistent naming conventions
• Proper try() patterns
• Correct depends_on relationships

Cisco IOS-XE Version

• Developed against: IOS-XE 17.15.1 (device tested)
• Compatible with: IOS-XE 17.12.1
• Module version: Compatible with provider v0.5.6+

External Repo Link

CiscoDevNet/terraform-provider-iosxe#503 (Provider PR - must be merged first)
netascode/nac-iosxe#504 (Schema PR - must be merged first)

Checklist

• Latest commit is rebased from develop with merge conflicts resolved
• New or updates to documentation has been made accordingly
• Robot test(s) included or updated for data model updates or additions
• If applicable, external repo link, e.g. Ansible Collection, provided
• Assigned the proper reviewers