igpcost

Documentation

Overview

Package igpcost carries the IGP metric of a resolved next-hop from whoever computes it to whoever ranks paths by it.

The producer is sysrib's next-hop resolver, which walks the unified Loc-RIB; the consumer is BGP best-path selection (RFC 4271 Section 9.1.2.2 (e), the "lowest interior cost to the NEXT_HOP" tiebreak). Both sides are optional: sysrib runs with no BGP engine compiled in (//go:build ze_bgp), and the BGP engine runs with no Loc-RIB wired. Keeping the seam here, in a leaf that neither side owns, lets each register or read independently -- previously sysrib pushed directly into the BGP RIB package, which pinned the engine into every binary.

An unset seam yields cost 0, the same value BGP already used before a resolver existed: every next-hop compares equal on that tiebreak and selection falls through to the next rule.

Index

• func Lookup(addr netip.Addr) uint32
• func Set(fn Func)
• type Func

Functions

func Lookup

func Lookup(addr netip.Addr) uint32

Lookup returns the interior cost to addr, or 0 when no resolver is registered. Zero is the documented "no interior cost known" value, not an error: it makes the IGP-cost tiebreak a no-op rather than a failure.

func Set

func Set(fn Func)

Set registers the IGP cost lookup. Called by sysrib once its next-hop resolver exists. A nil fn clears the seam (Lookup then reports 0).

Types

type Func

type Func func(addr netip.Addr) uint32

Func returns the interior (IGP) cost to reach addr.