bgpd: Print neighbor link type correctly according to local-as

[ton31337]

Closes #21474

[greptile-apps]

Greptile Summary

This PR fixes bgpd/bgp_vty.c to correctly classify a neighbor as an internal link when local-as <AS> no-prepend replace-as is configured with the same AS as the remote peer, adding the missing p->change_local_as && p->as == p->change_local_as check. It also aligns the external-link detection to use CHECK_FLAG(p->as_type, AS_EXTERNAL) instead of a raw equality comparison, consistent with how AS_INTERNAL is already checked. A new router r5 and associated topotest are added to cover this scenario end-to-end.

Confidence Score: 5/5

Safe to merge — targeted display-logic fix with a new topotest covering the reported scenario.

All changes are narrowly scoped to the neighbor link-type classification in bgp_show_peer. The new change_local_as guard is correctly gated on a non-zero value before the equality check, the CHECK_FLAG alignment for AS_EXTERNAL is a consistency improvement with no behaviour change in practice (enum values are powers-of-two and are not combined), and the topotest directly validates both the previously-broken and the already-correct cases. No P0 or P1 issues found.

No files require special attention.

Vulnerabilities

No security concerns identified. The change only affects display/classification logic in show bgp neighbors output and does not touch authentication, data handling, or network reachability decisions.

Important Files Changed

Filename	Overview
bgpd/bgp_vty.c	Adds change_local_as equality check to correctly classify iBGP peers when local-as masking is active; also fixes as_type == AS_EXTERNAL to CHECK_FLAG for consistency with the AS_INTERNAL path.
tests/topotests/bgp_remote_as_auto/test_bgp_remote_as_auto.py	Adds _bgp_neighbors test verifying correct nbrExternalLink/nbrInternalLink classification, and extends _bgp_converge to include r5 in the established-peers check.
tests/topotests/bgp_remote_as_auto/r1/frr.conf	Adds neighbor 192.168.1.5 with local-as 65005 no-prepend replace-as to simulate the iBGP masking scenario under test.
tests/topotests/bgp_remote_as_auto/r5/frr.conf	New router configuration for r5 (AS 65005) with remote-as auto, forming the iBGP-masking peer for r1 in the new test case.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[bgp_show_peer: determine link type] --> B{p->as == p->local_as?}
    B -- Yes --> E[Internal / Confed-Internal Link]
    B -- No --> C{p->change_local_as != 0\nAND p->as == p->change_local_as?}
    C -- Yes --> E
    C -- No --> D{CHECK_FLAG as_type AS_INTERNAL?}
    D -- Yes --> E
    D -- No --> F{p->as != 0\nOR CHECK_FLAG as_type AS_EXTERNAL?}
    F -- Yes --> G[External / Confed-External Link]
    F -- No --> H[Unspecified Link]

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[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[riw777]

looks good