Fix ipv6 vtysh bgp command - bgp/test_bgp_update_replication.py

[justin-wong-ce]

Description of PR

Summary: Fix invalid command for reading bgp infomration on ipv6-only topologies
Fixes #28020

Type of change

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

Back port request

• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605

Tracking issue/work item for backport/cherry-pick request (GitHub issue or Microsoft ADO):
Failure type:

Tested branch

• master
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• N/A

Test result

• 202605: Arista internal build from Sep 17th, 2026 - bgp/test_bgp_update_replication.py passes.

bgp/test_bgp_update_replication.py::test_bgp_update_replication[qspf201-default] PASSED [100%]
...
--------------------------------------------- generated xml file: /data/tests/logs/tr.xml ---------------------------------------------
============================================ 1 passed, 1710 warnings in 3929.73s (1:05:29) ============================================

Approach

What is the motivation for this PR?

How did you do it?

How did you verify/test it?

Any platform specific information?

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

Documentation

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