tests: add BGP unnumbered VLAN subinterface topotest

[sudharr86]

Summary

Add a topotest for BGP unnumbered sessions over VLAN subinterfaces.

Why

BGP unnumbered should continue to establish sessions and exchange routes when the peering interface is a VLAN subinterface. The test coverage makes that behavior explicit.

Changes

• Add a two-router BGP unnumbered topology using VLAN subinterfaces.
• Verify neighbor establishment and route propagation through the topology.

Related

• Design proposal: BGP unnumbered over VLAN subinterfaces sonic-net/SONiC#2414

Validation

• git diff --check upstream/master..HEAD
• PYTHONPYCACHEPREFIX=/private/tmp/codex-pycache-frr python3 -m py_compile tests/topotests/bgp_unnumbered_subif/test_bgp_unnumbered_subif.py
• Reviewed the diff for unintended references.

[riw777]

Please use the unified config rather that protocol config files

[sudharr86]

Please use the unified config rather that protocol config files

yes fixing it. thanks

[sudharr86]

Updated this to use unified frr.conf files for both routers and load them with load_frr_config. Thanks.

[riw777]

Updated this to use unified frr.conf files for both routers and load them with load_frr_config. Thanks.

Thanks! Please let me know when you're ready for final review on this ... this far everything looks good, just waiting on the move from draft to "ready" state.

[sudharr86]

Updated this to use unified frr.conf files for both routers and load them with load_frr_config. Thanks.

Thanks! Please let me know when you're ready for final review on this ... this far everything looks good, just waiting on the move from draft to "ready" state.

@riw777 this can be merged. Thanks.

[greptile-apps]

Greptile Summary

This PR adds a new topotest (bgp_unnumbered_subif) verifying that BGP unnumbered sessions establish and exchange routes over VLAN subinterfaces, filling a gap left by the existing bgp_unnumbered test which only covers physical interfaces.

• Adds five test cases covering session bring-up, route propagation, link-down/restore, and BGP peer removal without crash, using VLAN subinterfaces (r1-eth0.100, r1-eth0.200) created via router.net.add_vlan.
• The add_vlan/del_iface lifecycle and the BGP helper functions (_bgp_summary_check, _check_route_present) follow the same patterns used in bfd_vrflite_topo1 and other existing FRR topotests; previously flagged issues (unused _check_route_absent helper and unread success bindings) have been resolved.

Confidence Score: 5/5

Safe to merge — this is a new self-contained topotest with no changes to existing code or configs.

The test adds five well-scoped cases, follows the same add_vlan/del_iface lifecycle used in bfd_vrflite_topo1, and checks BGP state via the correct JSON keys (interface name for unnumbered peers in show bgp summary, prefix keys in show bgp ipv4 unicast). Previously flagged dead code and unread return values have both been cleaned up. No defects found.

No files require special attention.

Important Files Changed

Filename	Overview
tests/topotests/bgp_unnumbered_subif/test_bgp_unnumbered_subif.py	Core test logic: five test cases covering session establishment, route exchange, link-down/restore, and peer removal. Uses well-established FRR topotest patterns; helpers are used correctly and previously flagged dead code has been removed.
tests/topotests/bgp_unnumbered_subif/r1/frr.conf	R1 FRR config: BGP AS 65001 with unnumbered peers on r1-eth0.100 and r1-eth0.200, loopback 10.10.10.1/32 redistributed into BGP. Config is correct.
tests/topotests/bgp_unnumbered_subif/r2/frr.conf	R2 FRR config: BGP AS 65002 with unnumbered peers on r2-eth0.100 and r2-eth0.200, loopback 10.10.10.2/32 redistributed. Symmetric and correct.
tests/topotests/bgp_unnumbered_subif/init.py	Empty init file marking the directory as a Python package — standard for FRR topotests.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant T as Test Runner
    participant R1 as R1 (AS 65001)
    participant R2 as R2 (AS 65002)

    Note over T,R2: setup_module
    T->>R1: add_vlan r1-eth0.100 / r1-eth0.200
    T->>R2: add_vlan r2-eth0.100 / r2-eth0.200
    T->>R1: load_frr_config (r1/frr.conf)
    T->>R2: load_frr_config (r2/frr.conf)
    R1-->>R2: IPv6 ND RA on .100 and .200
    R2-->>R1: IPv6 ND RA on .100 and .200

    Note over T,R2: Test 1 - Sessions
    R1->>R2: BGP OPEN (r1-eth0.100)
    R2->>R1: BGP OPEN (r2-eth0.100)
    R1->>R2: BGP OPEN (r1-eth0.200)
    R2->>R1: BGP OPEN (r2-eth0.200)
    T->>R1: show bgp summary json → Established
    T->>R2: show bgp summary json → Established

    Note over T,R2: Test 2 - Routes
    R1->>R2: UPDATE 10.10.10.1/32 (connected)
    R2->>R1: UPDATE 10.10.10.2/32 (connected)
    T->>R1: show bgp ipv4 unicast json → 10.10.10.2/32 present
    T->>R2: show bgp ipv4 unicast json → 10.10.10.1/32 present

    Note over T,R2: Test 3 - Link Down
    T->>R1: interface r1-eth0.100 shutdown
    R1-->>R2: BGP NOTIFICATION (r1-eth0.100 down)
    T->>R1: .100 not Established, .200 still Established
    T->>R2: r2-eth0.100 not Established

    Note over T,R2: Test 4 - Link Restore
    T->>R1: interface r1-eth0.100 no shutdown
    R1->>R2: BGP OPEN (r1-eth0.100 re-establishes)
    T->>R1: both .100 and .200 Established
    T->>R1: 10.10.10.2/32 re-learned

    Note over T,R2: Test 5 - Peer Removal
    T->>R1: no neighbor r1-eth0.200 interface remote-as external
    T->>R1: .100 Established, .200 gone from peers
    T->>R1: 10.10.10.2/32 still present (via .100)

    Note over T,R2: teardown_module
    T->>R1: del_iface r1-eth0.100 / r1-eth0.200
    T->>R2: del_iface r2-eth0.100 / r2-eth0.200
    T->>T: stop_topology

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sequenceDiagram
    participant T as Test Runner
    participant R1 as R1 (AS 65001)
    participant R2 as R2 (AS 65002)

    Note over T,R2: setup_module
    T->>R1: add_vlan r1-eth0.100 / r1-eth0.200
    T->>R2: add_vlan r2-eth0.100 / r2-eth0.200
    T->>R1: load_frr_config (r1/frr.conf)
    T->>R2: load_frr_config (r2/frr.conf)
    R1-->>R2: IPv6 ND RA on .100 and .200
    R2-->>R1: IPv6 ND RA on .100 and .200

    Note over T,R2: Test 1 - Sessions
    R1->>R2: BGP OPEN (r1-eth0.100)
    R2->>R1: BGP OPEN (r2-eth0.100)
    R1->>R2: BGP OPEN (r1-eth0.200)
    R2->>R1: BGP OPEN (r2-eth0.200)
    T->>R1: show bgp summary json → Established
    T->>R2: show bgp summary json → Established

    Note over T,R2: Test 2 - Routes
    R1->>R2: UPDATE 10.10.10.1/32 (connected)
    R2->>R1: UPDATE 10.10.10.2/32 (connected)
    T->>R1: show bgp ipv4 unicast json → 10.10.10.2/32 present
    T->>R2: show bgp ipv4 unicast json → 10.10.10.1/32 present

    Note over T,R2: Test 3 - Link Down
    T->>R1: interface r1-eth0.100 shutdown
    R1-->>R2: BGP NOTIFICATION (r1-eth0.100 down)
    T->>R1: .100 not Established, .200 still Established
    T->>R2: r2-eth0.100 not Established

    Note over T,R2: Test 4 - Link Restore
    T->>R1: interface r1-eth0.100 no shutdown
    R1->>R2: BGP OPEN (r1-eth0.100 re-establishes)
    T->>R1: both .100 and .200 Established
    T->>R1: 10.10.10.2/32 re-learned

    Note over T,R2: Test 5 - Peer Removal
    T->>R1: no neighbor r1-eth0.200 interface remote-as external
    T->>R1: .100 Established, .200 gone from peers
    T->>R1: 10.10.10.2/32 still present (via .100)

    Note over T,R2: teardown_module
    T->>R1: del_iface r1-eth0.100 / r1-eth0.200
    T->>R2: del_iface r2-eth0.100 / r2-eth0.200
    T->>T: stop_topology

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_{Reviews (5): Last reviewed commit: "tests: honor expected BGP peer state in ..." | Re-trigger Greptile}

[sudharr86]

Addressed the review cleanup and the PR is ready for final review.

[sudharr86]

@greptile-apps review

[sudharr86]

Added the missing topotest package marker. @greptile-apps review

[sudharr86]

@greptileai rereview

[sudharr86]

Addressed the helper-state check noted in the rereview. @greptileai rereview

[riw777]

looks good