isisd: Fix missing neighbor address Sub-TLVs after link-params change

[cscarpitta]

When link-params are removed from an interface, Zebra notifies IS-IS via the zebra_if_update_link_params hook, triggering isis_mpls_te_update(). That function calls isis_link_params_update(), which resets ext->status to keep only SR-related Sub-TLV flags — clearing EXT_NEIGH_ADDR and EXT_NEIGH_ADDR6, which control advertisement of the IPv4 and IPv6
Neighbor Address Sub-TLVs, so those Sub-TLVs disappear from the Extended IS Reachability TLV.

Fix by calling isis_mpls_te_circuit_ip_update() after isis_link_params_update() in isis_mpls_te_update() when MPLS-TE is active. This re-evaluates the adjacency's known IP addresses and restores EXT_NEIGH_ADDR/EXT_NEIGH_ADDR6 if appropriate, causing the IPv4 and IPv6 Neighbor Address Sub-TLVs to be advertised again.

[greptile-apps]

Greptile Summary

This PR fixes a bug where IPv4/IPv6 Neighbor Address Sub-TLVs (EXT_NEIGH_ADDR/EXT_NEIGH_ADDR6) disappear from the IS-IS Extended IS Reachability TLV after a link-params remove-and-readd cycle on an interface.

Root cause: isis_link_params_update() resets ext->status to only SR-related flags when HAS_LINK_PARAMS(ifp) is false (i.e., link-params removed), clearing the neighbor address bits. When link-params are re-added, isis_link_params_update() explicitly does not re-set neighbor addresses (delegating that to adjacency events), so the Sub-TLVs remain absent.

Fix: Call isis_mpls_te_circuit_ip_update() immediately after isis_link_params_update() in isis_mpls_te_update() when MPLS-TE is active, matching the existing pattern in isis_mpls_te_enable() (lines 102-103). This re-evaluates adjacency IP addresses and restores the neighbor address flags.

Key changes:

• isisd/isis_te.c: 3-line fix adding a conditional call to isis_mpls_te_circuit_ip_update() in isis_mpls_te_update()
• tests/topotests/isis_te_topo1/test_isis_te_topo1.py: New test_step11() that removes and re-adds link-params on r1-eth0 and verifies all 4 routers see the correct TED
• tests/topotests/isis_te_topo1/reference/ted_step11.json: New reference TED state confirming remote-address and remote-address-v6 are present after the re-add

Confidence Score: 5/5

• This PR is safe to merge — the fix is minimal, well-targeted, and consistent with the existing pattern already used in isis_mpls_te_enable()
• The 3-line code change mirrors an identical call sequence already present in isis_mpls_te_enable() (lines 102-103 of isis_te.c), guarded by the correct IS_MPLS_TE condition. The fix is idempotent, adds no new state, and is covered by a new topotest that exercises the exact failing scenario across all 4 routers.
• No files require special attention

Important Files Changed

Filename	Overview
isisd/isis_te.c	Minimal targeted fix: adds isis_mpls_te_circuit_ip_update() call after isis_link_params_update() in isis_mpls_te_update(), guarded by the same IS_MPLS_TE condition, matching the existing pattern in isis_mpls_te_enable()
tests/topotests/isis_te_topo1/test_isis_te_topo1.py	New test_step11() exercises the remove-and-readd link-params scenario on r1-eth0; correctly uses polling via compare_ted_json_output to wait for convergence across all 4 routers
tests/topotests/isis_te_topo1/reference/ted_step11.json	New reference TED snapshot for step 11; r1's edges include local-address/remote-address and local-address-v6/remote-address-v6, confirming neighbor address Sub-TLVs are restored after link-params re-add

Sequence Diagram

sequenceDiagram
    participant Z as Zebra
    participant TE as isis_mpls_te_update()
    participant LP as isis_link_params_update()
    participant IP as isis_mpls_te_circuit_ip_update()
    participant LSP as lsp_regenerate_schedule()

    Note over Z,LSP: "no link-params" on interface
    Z->>TE: zebra_if_update_link_params hook
    TE->>LP: isis_link_params_update(circuit, ifp)
    Note over LP: HAS_LINK_PARAMS=false<br/>→ resets ext->status<br/>→ clears EXT_NEIGH_ADDR/EXT_NEIGH_ADDR6
    LP-->>TE: returns
    TE->>IP: isis_mpls_te_circuit_ip_update(circuit) [NEW]
    Note over IP: Re-evaluates adj IPv4/IPv6 addrs<br/>→ restores EXT_NEIGH_ADDR/EXT_NEIGH_ADDR6<br/>if adjacency has known addresses
    IP-->>TE: returns
    TE->>LSP: lsp_regenerate_schedule(area, ...)
    Note over LSP: Re-advertises TLV with<br/>Neighbor Address Sub-TLVs intact

Loading

_{Last reviewed commit: 70ceffa}

[donaldsharp]

@Mergifyio backport stable/10.6 stable/10.5

[mergify]

backport stable/10.6 stable/10.5

✅ Backports have been created

Details

• #21212 isisd: Fix missing neighbor address Sub-TLVs after link-params change (backport #21204) has been created for branch stable/10.6
• #21213 isisd: Fix missing neighbor address Sub-TLVs after link-params change (backport #21204) has been created for branch stable/10.5