[TRM] Implement VRF MDT Support in Terraform Provider

[tech-of-all-trades]

This PR adds support for TRM VRF Multicast Distribution Tree (MDT) configuration in the Terraform Provider.

Overview

This PR adds comprehensive support for TRM VRF Multicast Distribution Tree (MDT) configuration to the iosxe_vrf resource, enabling MVPN multicast routing with MDT trees for IOS-XE devices.

This extends the iosxe_vrf resource with 9 new MDT-related attributes that map to the following CLI commands:

CLI Command	Terraform Attribute	Description
mdt default <addr>	ipv4_mdt_default_address	MDT default group IPv4 address
mdt auto-discovery vxlan	ipv4_mdt_auto_discovery_vxlan	Enable BGP auto-discovery for VxLAN
mdt auto-discovery vxlan inter-as	ipv4_mdt_auto_discovery_vxlan_inter_as	Enable Inter-AS for VxLAN
mdt auto-discovery interworking vxlan-pim	ipv4_mdt_auto_discovery_interworking_vxlan_pim	Enable VxLAN-PIM interworking
mdt auto-discovery interworking vxlan-pim inter-as	ipv4_mdt_auto_discovery_interworking_vxlan_pim_inter_as	Enable Inter-AS for interworking
mdt overlay use-bgp	ipv4_mdt_overlay_use_bgp	Enable BGP overlay signaling
mdt overlay use-bgp spt-only	ipv4_mdt_overlay_use_bgp_spt_only	Enable SPT-only mode
mdt data <addr> <wildcard>	ipv4_mdt_data_multicast	Data MDT group ranges (list)
mdt data threshold <thresh_rate>	ipv4_mdt_data_threshold	MDT switching threshold (Kbps)

Technical Implementation

YANG Model Analysis

• Verified support in IOS-XE YANG models 17.12.1 and 17.15.1
• YANG path: /Cisco-IOS-XE-native:native/vrf/definition[name=%s]/address-family/ipv4/mdt/*
• Used config-mvpn-mdt-grouping from Cisco-IOS-XE-ip.yang

Key Design Decisions

1. XPath Notation: Used xpath attribute to handle YANG choice/case structures properly

   • Auto-discovery options are within a choice statement (mutually exclusive)
   • XPath bypasses intermediate containers for correct NETCONF operations

2. Test Exclusions: Added exclude_test: true to interworking attributes

   • VxLAN and interworking auto-discovery are mutually exclusive (YANG choice)
   • Tests validate VxLAN auto-discovery; interworking remains available for users
   • Prevents test failures due to mutual exclusivity conflicts

3. Data Structures:

   • ipv4_mdt_data_multicast is a list supporting multiple group ranges
   • Each range has composite key (address + wildcard)

Example Usage

resource "iosxe_vrf" "trm_vrf" {
  name                = "TRM_VRF"
  description         = "TRM VRF with MDT configuration"
  rd                  = "65000:100"
  address_family_ipv4 = true
  
  # MDT Configuration
  ipv4_mdt_default_address                = "239.1.1.1"
  ipv4_mdt_auto_discovery_vxlan           = true
  ipv4_mdt_auto_discovery_vxlan_inter_as  = true
  ipv4_mdt_overlay_use_bgp                = true
  ipv4_mdt_overlay_use_bgp_spt_only       = true
  
  ipv4_mdt_data_multicast = [
    {
      address  = "239.1.2.0"
      wildcard = "0.0.0.255"
    }
  ]
  
  ipv4_mdt_data_threshold = 50
}

Files Modified

• gen/definitions/vrf.yaml - Added MDT attribute definitions
• internal/provider/model_iosxe_vrf.go - Generated model structs
• internal/provider/resource_iosxe_vrf.go - Generated resource CRUD logic
• internal/provider/resource_iosxe_vrf_test.go - Generated acceptance tests
• internal/provider/data_source_iosxe_vrf.go - Generated data source
• internal/provider/data_source_iosxe_vrf_test.go - Generated data source tests
• docs/resources/vrf.md - Updated documentation with MDT examples
• docs/data-sources/vrf.md - Updated data source documentation
• examples/resources/iosxe_vrf/resource.tf - Updated example configuration

Testing

• ✅ Acceptance tests pass on IOS-XE device
• ✅ All MDT attributes correctly serialized to NETCONF XML
• ✅ State refresh correctly reads back MDT configuration
• ✅ Mutual exclusivity properly handled (VxLAN vs interworking)

Compatibility

YANG model compatibility verified for both 17.12.1 and 17.15.1

• Minimum IOS-XE Version: 17.12.1
• Recommended Version: 17.15.1
• Breaking Changes: None (backward compatible)

Related Issues

Resolves: Issue 398 (internal)

Notes for Reviewers

1. The interworking attributes are excluded from tests but remain fully functional for user configuration
2. Auto-discovery methods (VxLAN vs interworking) are mutually exclusive by design (YANG choice statement)
3. All MDT features are under the IPv4 address-family; IPv6 MDT support could be added in a future PR if needed