[Dependent on PR#21335] Feature/bgp flap high bgp phase 2

[PriyanshTratiya]

Description of PR

Summary:
Fixes # (issue)

This PR adds the high‑scale BGP admin flap tests that build on top of the refactoring done in PR #21335. It introduces new test cases and utilities to exercise BGP IPv6 convergence and scale behavior under repeated admin shutdown/startup (“flap”) scenarios for BGP sessions and interfaces.

Key Points:

• Implements new high‑scale BGP admin flap test cases reusing the generalized connection‑handling logic introduced in PR Refactoring/high bgp phase 2 #21335.
• Adds parameterized flows to flap:
  • Individual BGP sessions,
  • Subsets of ports,
  • All ports/sessions, at scale.
• Extends helper methods to:
  • Drive repeated admin shut/no‑shut cycles,
  • Measure convergence and recovery time after each flap,
  • Validate BGP IPv6 routes and neighbor states remain stable after repeated flaps.
• Integrates the new flap scenarios with existing BGP IPv6 convergence and scale tests, keeping configuration and connection behaviors consistent with the refactored framework.
• Improves logging and per‑iteration reporting for easier debugging of failures during long‑running flap cycles.

Dependency:

• Functionally depends on the refactoring from PR #21335. The helper methods and parameters introduced there are used here for BGP admin flap scenarios.

Type of change

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

Back port request

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

Approach

What is the motivation for this PR?

To validate BGP IPv6 convergence and stability under high‑scale and repeated admin flap scenarios, we want dedicated test coverage for:

• Repeated shut/no‑shut of BGP neighbors and interfaces at scale,
• Ensuring routes re‑converge within expected bounds,
• Detecting potential regressions in control‑plane stability and convergence times when links or sessions are frequently toggled.

How did you do it?

• Added new BGP flap test flows in tests/bgp/test_ipv6_bgp_scale.py (and related helpers) that:
  • Use the refactored connection control APIs (shutdown_connections, connection_type, shutdown_all_connections, etc.) to drive admin flaps.
  • Allow configuration of:
    • Number of flap iterations,
    • Target connection type (session vs. port, subset vs. all),
    • Wait times between flap and verification.
  • After each flap cycle, verify:
    • BGP sessions return to Established,
    • Expected IPv6 routes are fully present,
    • No unexpected route loss or long‑term neighbor instability.
• Reused/refined existing helper functions for command execution, logging, and validation so that the flap tests share as much code as possible with the convergence/scale tests added.
• Kept the test logic parameter‑driven to make future extensions (e.g., different neighbor sets, different topologies) straightforward.

How did you verify/test it?

• Ran the new BGP flap tests on:
  • t0-isolated-d2u510s2 topology
  • Platform: Broadcom Arista-7060X6-64PE-B-C512S2
• Verified:
  • BGP sessions recover to Established after each flap iteration,
  • IPv6 routes re‑converge as expected,
  • No persistent errors or unexpected failures in the test logs.

Any platform specific information?

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

Documentation

#21437

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).