test(interop): prove import next-hop self on the wire

[lance0]

Depends on #2978. M114 fails on main until #2978 lands, so keep this draft until that merges.

What it adds

M114 is a containerlab leg for import next-hop self. The topology:

• an FRR eBGP source (AS 65002) sends two IPv4 prefixes to rustbgpd (AS 65001);
• rustbgpd's inline import policy sets next-hop self on 198.51.100.0/24 and leaves the control prefix 198.51.101.0/24 unchanged;
• two FRR 10.7.1 receivers take the routes, one over iBGP and one as a route_server_client.

The driver asserts the following:

• rustbgpd's best routes carry 10.114.0.1, the local address of the source session, for the rewritten prefix, and 10.114.0.2 for the control prefix. This passes on main too, which places the defect in export.
• Each receiver's pre-policy Adj-RIB-In (received-routes, with soft-reconfiguration inbound) holds 10.114.0.1 for the rewritten prefix and 10.114.0.2 for the control prefix.
• A tshark sidecar in rustbgpd's namespace, built from the existing Dockerfile.bmpsink, checks every UPDATE that carries either prefix to either receiver. Each such UPDATE must have exactly one NEXT_HOP attribute with the expected address and no MP_REACH_NLRI. The capture must also contain no NOTIFICATION.
• Both receiver sessions stay on their first connection.

The job is wired into interop.yml as m114, with a single attempt and no retry. It is listed in docs/interop.md.

Local results

Each run below used a fresh deployment of this branch's topology and driver.

origin/main (a2c741431): 19 passed, 4 failed. Both receivers get the received next hop:

FAIL frr-ibgp received 198.51.100.0/24 with next hop '10.114.0.2', expected 10.114.0.1
FAIL frr-rs received 198.51.100.0/24 with next hop '10.114.0.2', expected 10.114.0.1
FAIL wire: to 10.114.1.2 198.51.100.0/24: 1 UPDATE(s), NEXT_HOP counts [1], MP_REACH counts [0], next hops ['10.114.0.2']
FAIL wire: to 10.114.2.2 198.51.100.0/24: 1 UPDATE(s), NEXT_HOP counts [1], MP_REACH counts [0], next hops ['10.114.0.2']

origin/main merged with #2978 (934a0dba5): 23 passed, 0 failed.

Scope

Extended Next Hop is not negotiated in this lab, so the IPv4 MP_REACH fallback that #2978 also fixes remains covered by its unit tests only. FRR advertises Extended Next Hop only over IPv6 transport.

[Copilot]

🟡 Changes recommended

The wire checker can pass after parser failure or overlook MP_REACH-only advertisements.

2 open findings

• Propagate Python parse failures to prevent false CI passes · New
• Reject MP_REACH_NLRI to prevent missed forbidden announcements · New

What changed in this PR

Adds M114 interoperability coverage for #2978, verifying import next-hop self reaches iBGP and route-server clients correctly.

Changes:

• Adds an FRR topology with rewritten and unchanged control prefixes.
• Checks receiver routes, captured UPDATEs, and session stability.
• Registers a single-attempt CI job and documents coverage.

File	Description
tests/​interop/​scripts/​test-m114-import-next-hop-self-frr.sh	Runs route, wire, and session assertions.
tests/​interop/​m114-import-next-hop-self-frr.clab.yml	Defines the four-node lab.
tests/​interop/​configs/​rustbgpd-m114-import-next-hop-self.toml	Configures import rewriting and passthrough peers.
tests/​interop/​configs/​frr-bgpd-m114-source.conf	Advertises test and control prefixes.
tests/​interop/​configs/​frr-bgpd-m114-rs.conf	Configures the route-server receiver.
tests/​interop/​configs/​frr-bgpd-m114-ibgp.conf	Configures the iBGP receiver.
docs/​interop.md	Documents M114 coverage and limitations.
.github/​workflows/​interop.yml	Adds M114 to required interop checks.

🧠 Review effort: Balanced

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[Copilot]

🟢 Approval recommended

No blocking issues remain, and prerequisite #2978 is confirmed merged.

1 open finding

• Reject MP_REACH_NLRI to prevent missed forbidden announcements

1 resolved since last review

• Propagate Python parse failures to prevent false CI passes

🧠 Review effort: Balanced

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