feat(fib): per-class maximum_paths_ebgp / maximum_paths_ibgp (ADR-0066)#263
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Add per-table `[[fib_tables]].maximum_paths_ebgp` and `maximum_paths_ibgp` (FRR's `maximum-paths` / `maximum-paths ibgp`): cap eBGP and iBGP equal-cost groups independently. They coexist with the overall `maximum_paths` — a per-class value overrides it for that class, and an unset class falls back to `maximum_paths` then `1`, so existing configs are byte-for-byte unchanged. The equal-cost group is homogeneous, so the best route's class (`Route::is_ebgp`) selects the cap; the re-cap moves into the per-candidate projection loop (`src/fib.rs`), and `max_install_paths` widens the RIB gather to the max of all three caps so projection can reach any per-class width. Validation applies the same `>= 1` / `<= 256` guardrail to all three (refactored into one helper). No new interop: per-class only changes which cap applies, not the kernel RTA_MULTIPATH install path (covered by M50). Tests: projection per-class cap + fallback (eBGP/iBGP), config round-trip, validation rejects 0 / over-cap for the new fields. Docs: CONFIGURATION (also backfills the missing maximum_paths row), COMPARISON footnote, CHANGELOG.
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Pull request overview
Adds per-class ECMP width caps to FIB table configuration so eBGP and iBGP equal-cost groups can be installed with different maximum path counts, while preserving existing behavior when unset.
Changes:
- Introduces
[[fib_tables]].maximum_paths_ebgpandmaximum_paths_ibgpwith shared validation guardrails (>= 1,<= 256). - Applies per-class capping during FIB projection and widens RIB candidate gathering to the maximum of overall/per-class caps.
- Adds/updates unit tests and updates configuration/docs/changelog to describe the new knobs.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| src/fib.rs | Adds per-class max-path selection during projection and projection tests. |
| src/fib_runtime.rs | Widens RIB gather width to cover overall and per-class caps. |
| src/config/validation.rs | Refactors ECMP cap validation into a shared helper and validates new fields. |
| src/config/tests.rs | Adds parsing/guardrail tests for the new per-class fields. |
| src/config/schema.rs | Extends FibTableConfig schema with new per-class ECMP cap fields and docs. |
| docs/CONFIGURATION.md | Documents maximum_paths plus new per-class ECMP cap fields. |
| docs/COMPARISON.md | Updates multipath feature comparison text to reflect per-class caps availability. |
| CHANGELOG.md | Adds changelog entry describing per-class ECMP caps and semantics. |
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| /// Project configured FIB tables and Loc-RIB install candidates using the | ||
| /// current RIB peer-group map for table allow-list checks. | ||
| #[must_use] | ||
| /// Per-class ECMP width: the eBGP/iBGP override if set, else the table's overall | ||
| /// `maximum_paths`, else 1 (today's single-next-hop behavior). The equal-cost | ||
| /// group is homogeneous, so the best route's class selects the cap. | ||
| fn per_class_max_paths(table: &FibTableConfig, is_ebgp: bool) -> usize { | ||
| if is_ebgp { | ||
| table.maximum_paths_ebgp.or(table.maximum_paths) | ||
| } else { | ||
| table.maximum_paths_ibgp.or(table.maximum_paths) | ||
| } | ||
| .unwrap_or(1) | ||
| .max(1) as usize | ||
| } | ||
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| pub(crate) fn project_fib_intent_with_peer_groups( | ||
| tables: &[FibTableConfig], |
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The per_class_max_paths helper was inserted between the doc comment / #[must_use] and project_fib_intent_with_peer_groups, so the projection function lost its documentation and must-use lint while the helper was mis-documented as doing projection. Move the helper above the doc block so each attribute lands on its intended function.
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ECMP follow-up 2/4 — per-class
maximum_paths_ebgp/maximum_paths_ibgp(ADR-0066)Adds per-table per-class ECMP caps, FRR's
maximum-paths/maximum-paths ibgp:eBGP and iBGP equal-cost groups can carry different install widths.
Semantics (coexist, non-breaking)
maximum_pathsfor that class.maximum_paths, then1— so existing configs are byte-for-byte unchanged.Route::is_ebgp) selects the cap.Change
[[fib_tables]].maximum_paths_ebgp/maximum_paths_ibgpconfig + validation (same>= 1/<= 256guardrail, refactored into one helper).src/fib.rs,per_class_max_paths).max_install_pathswidens the RIB gather tomax(maximum_paths, maximum_paths_ebgp, maximum_paths_ibgp)across tables, so projection can reach any per-class width.Tests
maximum_paths_ebgp_caps_ebgp_group,maximum_paths_ibgp_caps_ibgp_group,per_class_overrides_with_maximum_paths_fallback(projection).fib_tables_per_class_maximum_paths_round_trip+ per-class cases infib_tables_reject_invalid_guardrails(0 / over-cap).No new interop: per-class only changes which cap applies, not the kernel
RTA_MULTIPATHinstall path itself (covered by M50). Docs:CONFIGURATION.md(also backfills the previously-missing
maximum_pathsrow),COMPARISON.mdfootnote,
CHANGELOG.md.Next: Link Bandwidth ext-community parse (PR3), then weighted/unequal-cost multipath (PR4, + ADR).