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IPv6-Only Management Network Configuration for Virtual Testbed

This document explains how to use the --ipv6-only-mgmt flag to configure virtual testbeds with IPv6-only management networks.

Overview

The --ipv6-only-mgmt flag allows you to configure a virtual DUT (Device Under Test) with IPv6-only management network settings, including:

  • IPv6 management IP address (using ansible_hostv6 from inventory)
  • IPv6 NTP servers
  • IPv6 DNS servers
  • IPv6 TACACS servers (using PTF container's IPv6 address)
  • IPv6 syslog servers
  • IPv6 SNMP servers
  • IPv6 management routes

Usage

Basic Usage

To deploy a virtual testbed with IPv6-only management configuration:

Generate Minigraph

Generate minigraph for IPv6 only management address is only required for Virtual testbed.

./testbed-cli.sh [-t testbed-file] [-m inventory] gen-mg <testbed-name> <inventory> <vault-password-file> --ipv6-only-mgmt

Deploy Minigraph

./testbed-cli.sh deploy-mg <testbed-name> <inventory> <vault-password-file> --ipv6-only-mgmt

Examples

  1. Deploy minigraph with IPv6-only management:

    ./testbed-cli.sh deploy-mg vms-sn2700-t0 lab ~/.password --ipv6-only-mgmt

  2. Generate and deploy minigraph with IPv6-only management for virtual testbed:

    # generate minigraph
./testbed-cli.sh -t vtestbed.yaml -m veos_vtb gen-mg vms-kvm-t0 veos_vtb ~/.password --ipv6-only-mgmt
# deploy minigraph
./testbed-cli.sh -t vtestbed.yaml -m veos_vtb deploy-mg vms-kvm-t0 veos_vtb ~/.password --ipv6-only-mgmt

  3. Test minigraph with IPv6-only management:

    ./testbed-cli.sh -t vtestbed.yaml -m veos_vtb test-mg vms-kvm-t0 veos_vtb ~/.password --ipv6-only-mgmt

Prerequisites

1. Testbed Configuration

The testbed must have ptf_ipv6 defined in the testbed.yaml file:

- conf-name: vms-sn2700-t0
  group-name: vms1-3
  topo: t0
  ptf_image_name: docker-ptf
  ptf: ptf_vms1-3
  ptf_ip: 10.255.0.180/24
  ptf_ipv6: 2001:db8:1::10/64    # Required for IPv6-only management
  server: server_1
  vm_base: VM0100
  dut:
    - str-msn2700-01
  inv_name: lab

2. Inventory Configuration

The device should have ansible_hostv6 defined in the inventory file:

str-msn2700-01:
  ansible_host: 10.250.0.101
  ansible_hostv6: fc00:2::101
  mgmt_subnet_mask_length: 24

3. IPv6 Configuration Files

IPv6 service configurations are defined in:

  • group_vars/lab/ipv6.yml - For lab inventory
  • group_vars/sonic/ipv6.yml - For lab inventory (depending on the inventory group)
  • group_vars/vm_host/ipv6.yml - For vm_host inventory

Virtual Testbed IPv6 Addressing Scheme

For virtual testbeds, we use the following IPv6 addressing:

Network Purpose IPv6 Prefix Notes
Management Network fc00:2::/64 ULA prefix for DUT management
PTF Backplane fc0a::/64 Defined in vm_host/main.yml
Local Server fc00:1::/64 ULA for syslog, SNMP
Google DNS 2001:4860:4860::/64 Public DNS servers

Configuration Details

IPv6 Service Addresses

When --ipv6-only-mgmt is used, the following services use IPv6:

Service IPv6 Address Notes
NTP fec0::ffff:afa:2 Local testbed NTP server (primary)
NTP 2001:4860:4806:: Google IPv6 NTP (fallback)
TACACS PTF's ptf_ipv6 From testbed.yaml
Syslog fec0::1 Testbed gateway
SNMP fec0::1 Testbed gateway

Management IP Configuration

  • The DUT's management IP uses ansible_hostv6 instead of ansible_host
  • The subnet mask length defaults to /64
  • IPv6 management routes are configured for proper connectivity

TACACS Integration

When using PTF TACACS servers (default behavior):

  • IPv4 mode: Uses testbed's ptf_ip
  • IPv6 mode: Uses testbed's ptf_ipv6 (with CIDR notation stripped)

The TACACS server runs on the PTF container, which must have IPv6 connectivity to the DUT.

Setting Up IPv6 on the PTF Container

Ensure the PTF container has IPv6 configured:

  1. The ptf_ipv6 address from testbed.yaml or vtestbed.yaml is assigned to the PTF container
  2. The TACACS server on PTF must listen on the IPv6 address
  3. Verify IPv6 connectivity between DUT and PTF

Setting Up Local NTP Server

For IPv6-only management networks, external NTP servers may not be reachable. A local NTP server running on the testbed host provides reliable time synchronization.

Deploying the NTP Server

The NTP server runs as a Docker container connected to the management bridge (br1):

cd ansible/
./setup-ntp-server.sh start

This will:

  1. Build the Chrony NTP server Docker image
  2. Create a macvlan network attached to br1
  3. Start the container with both IPv4 and IPv6 addresses

NTP Server Addresses

Protocol Address Notes
IPv4 10.250.0.2 For IPv4 management networks
IPv6 fec0::ffff:afa:2 For IPv6-only management networks

Managing the NTP Server

# Check status
./setup-ntp-server.sh status

# Stop the server
./setup-ntp-server.sh stop

# Restart the server
./setup-ntp-server.sh restart

# Test connectivity
./setup-ntp-server.sh test

# Full cleanup (remove container, network, and image)
./setup-ntp-server.sh clean

Verifying NTP Synchronization

On the DUT, verify NTP is working:

# Check NTP status
show ntp

# Or using chronyc
chronyc sources
chronyc tracking

Configuration Files

The local NTP server is configured as the primary NTP source in:

  • group_vars/sonic/ipv6.yml - For DUTs
  • group_vars/lab/ipv6.yml - For lab devices
  • group_vars/vm_host/ipv6.yml - For VM hosts
  • host_vars/STR-ACS-VSERV-01.yml - Server-specific config

Troubleshooting

Missing ptf_ipv6

Error: IPv6-only management mode requested but ptf_ipv6 is not configured in testbed file

Solution: Add ptf_ipv6 to your testbed entry in testbed.yaml

Missing ansible_hostv6

Issue: Minigraph uses default IPv6 address

Solution: Add ansible_hostv6 to the device entry in the inventory file

DUT Not Reachable After IPv6 Transition

Issue: Playbook fails waiting for DUT after loading minigraph

Solution:

  1. Verify IPv6 routing is configured on the management network
  2. Check that the server/PTF can reach the DUT's IPv6 management address
  3. Ensure the management switch/bridge supports IPv6

IPv6 Services Not Working

Issue: NTP or other services fail after IPv6 transition

Solution:

  1. Verify the IPv6 service addresses are reachable from the DUT
  2. Check firewall rules allow IPv6 traffic
  3. Ensure forced management routes include necessary IPv6 prefixes

NTP Server Not Reachable

Issue: DUT cannot sync time with local NTP server

Solution:

  1. Verify the NTP server is running: 
    ./setup-ntp-server.sh status
  2. Check network connectivity from DUT: 
    # On DUT
ping6 fec0::ffff:afa:2
  3. Verify the macvlan network is attached to br1: 
    docker network inspect sonic-mgmt-ntp-net
  4. Check chrony configuration inside container: 
    docker exec sonic-mgmt-ntp chronyc tracking

Running Tests in IPv6-Only Management Mode

When running tests against a DUT configured with IPv6-only management, you must tell the test framework to use IPv6 addresses.

Using run_tests.sh

Use the -6 flag to enable IPv6-only management mode:

./run_tests.sh -6 -n vms-kvm-t0 -d vlab-01 -c bgp/test_bgp_fact.py -f vtestbed.yaml -i ../ansible/veos_vtb

Using pytest directly

Use the --ipv6_only_mgmt option:

pytest --ipv6_only_mgmt --testbed vms-kvm-t0 --testbed_file vtestbed.yaml --inventory ../ansible/veos_vtb --host-pattern vlab-01 bgp/test_bgp_fact.py

What the IPv6-only flag does

When enabled, the test framework will:

  • Use ansible_hostv6 as the DUT management IP instead of ansible_host
  • Skip IPv4 management connectivity sanity checks
  • Use ping6 for management reachability tests

Important notes

  • The --ipv6_only_mgmt / -6 flag only affects test execution, not deployment
  • The DUT must already be configured with IPv6 management (via deploy-mg --ipv6-only-mgmt)
  • Ensure ansible_hostv6 is defined in the inventory for all DUTs

Reverting to IPv4 Management

To switch back to IPv4 management, simply run deploy-mg without the --ipv6-only-mgmt flag:

./testbed-cli.sh deploy-mg vms-sn2700-t0 lab ~/.password

This will regenerate and deploy a minigraph with IPv4-only management configuration.