Add IPv6-only management mode support for running tests

[opcoder0]

Description of PR

This change adds support for running tests in IPv6-only management mode:

• Add --ipv6_only_mgmt pytest option and -6 flag for run_tests.sh
• Add ipv6_only_mgmt_enabled fixture in conftest.py
• Update tests/common/devices/base.py to use IPv6 address when mode is enabled
• Skip IPv4 mgmt sanity check when mgmt_ip is IPv6 in sanity_check/checks.py
• Use ping6 for IPv6 management addresses in reboot.py
• Add retry logic for chrony service startup in ansible playbook
• Update documentation with instructions for running tests with IPv6

Summary:
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511

Approach

What is the motivation for this PR?

Support to run tests in IPv6 only management network environment

How did you do it?

Modify deploy mini graph configuration and related scripts.

How did you verify/test it?

On internal pipelines. This is additional work to the infrastructure changes that were made earlier #22310

Any platform specific information?

None

Supported testbed topology if it's a new test case?

NA

Documentation

Updated.

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[StormLiangMS]

Review: IPv6-Only Management Mode Support

Approve ✅ — well-structured, clean design. A few items to discuss below.

Architecture (good)

• Class-level flag on AnsibleHostBase set by session-scoped fixture, checked in __init__ — clean, no global state leaking.
• Fixture ordering enforced — ipv6_only_mgmt_enabled injected as dependency of fixture_duthosts, guaranteeing the flag is set before any SonicHost.__init__ calls.
• Backward compatible — default is False, no behavior change unless flag is explicitly passed.

---

Issues

1. (Medium) ping6 may not exist on all Linux distros

In reboot.py:

ping_cmd = "ping6" if is_ipv6_address(str(duthost.mgmt_ip)) else "ping"

On newer distros (Ubuntu 22.04+), ping6 is a symlink to ping and may not exist. The portable alternative is ping -6. This runs on the test server (localhost), not the DUT, so it depends on the sonic-mgmt container's OS.

2. (Low) Missing ansible_hostv6 — silent fallback to IPv4

In base.py:

if self.is_ipv6_only_mgmt() and ansible_hostv6:
    self.mgmt_ip = ansible_hostv6
else:
    self.mgmt_ip = ansible_host  # falls back silently

If --ipv6_only_mgmt is set but ansible_hostv6 is not defined in inventory, it silently falls back to IPv4 with no indication. Consider logging a warning: "IPv6-only mode requested but ansible_hostv6 not defined for {hostname}, falling back to IPv4."

3. (Low) _mgmt_ipv4 not used anywhere

self._mgmt_ipv4 = ansible_host  # "Keep IPv4 available for reference"

Set but never read. Fine if for future use, otherwise dead code.

4. (Question) Other ping calls in the codebase

Only reboot.py::collect_mgmt_config_by_console was updated. Any other test that does localhost.shell(f"ping ... {duthost.mgmt_ip}") will break in IPv6-only mode. May be worth a utility function like ping_mgmt(duthost, localhost) that auto-selects ping/ping6, or a broader grep to confirm no other call sites exist.

---

Internal PR #20116

Reviewed — config-only (9 new ipv6.yml files for internal labs with IPv6 NTP/DNS/syslog/TACACS addresses). No code logic, straightforward.

Chrony retry

Unrelated to IPv6 flag but reasonable for environments where NTP may be slower to start. No concerns.

[mssonicbld]

/azp run

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[opcoder0]

Thank you @StormLiangMS for the comments. I have addressed 1 and 2. For (3) - may be useful for troubleshooting hence left it as-is. For (4) hope to fix them and any other issues as part of IPv6 only tests I am running.

[StormLiangMS]

Review: Needs minor fix before merge

Summary: Clean implementation of IPv6-only management mode. Fixture design, run_tests.sh wiring, sanity check skip, ping6 handling, and documentation are all solid. One bug to fix:

---

🐛 Bug: Spurious warning in normal (non-IPv6) mode (tests/common/devices/base.py)

The else branch fires in two cases:

1. IPv6 mode NOT requested (normal operation — the common case)
2. IPv6 mode requested BUT ansible_hostv6 is undefined

But the warning is unconditional — so in every normal test run, every DUT init logs "IPv6-only mode requested but ansible_hostv6 not defined". Suggested fix:

if self.is_ipv6_only_mgmt() and ansible_hostv6:
    self.mgmt_ip = ansible_hostv6
    self.mgmt_ipv6 = ansible_hostv6
    self._mgmt_ipv4 = ansible_host
    logger.debug(...)
elif self.is_ipv6_only_mgmt():
    logger.warning(
        "IPv6-only mode requested but ansible_hostv6 not defined for %s, "
        "falling back to IPv4.", hostname)
    self.mgmt_ip = ansible_host
    self.mgmt_ipv6 = None
else:
    self.mgmt_ip = ansible_host
    self.mgmt_ipv6 = ansible_hostv6

---

Minor observations (non-blocking):

• _mgmt_ipv4 is only set in the IPv6 branch — consider initializing self._mgmt_ipv4 = None before the if/else to avoid potential AttributeError in future code.
• host_vars.get("ansible_host") changes behavior from KeyError to silent None if ansible_host is missing — probably fine but worth noting.
• Chrony retry fix is useful but tangential to IPv6 — could be a separate PR.

Positives: Fixture ordering via duthosts dependency is clean, ping -6 over ping6 is the right cross-distro choice, docs are thorough, is_ipv6_address is already imported in checks.py ✅.

[opcoder0]

Review: Needs minor fix before merge

Summary: Clean implementation of IPv6-only management mode. Fixture design, run_tests.sh wiring, sanity check skip, ping6 handling, and documentation are all solid. One bug to fix:

🐛 Bug: Spurious warning in normal (non-IPv6) mode (tests/common/devices/base.py)

Thank you. I have fixed it now.

[mssonicbld]

/azp run

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[StormLiangMS]

LGTM