Clean-room, portable C++17 implementation of the PlanB IPv6 LPM algorithm.

Includes: - AVX-512 SIMD path + scalar fallback - Wait-free lookups with rebuild-and-swap dynamic FIB - Benchmarks on synthetic data and real RIPE RIS BGP (~254K prefixes)

Interesting result: on real BGP + uniform random lookups, a plain Patricia trie can sometimes match or beat the SIMD tree due to cache locality and early exits.

Would love feedback, especially comparisons with PopTrie / CP-Trie.

▲

talsania 6 hours ago | parent | next [-]

254K prefixes with skewed distribution means early exits dominate, and no SIMD throughput advantage survives a branch that terminates at depth 3. The interesting edge case is deaggregation events where prefix counts spike transiently and the rebuild-and-swap FIB has to absorb a table that's temporarily 2x normal size

▲

Sesse__ 9 hours ago | parent | prev | next [-]

The obvious question, I guess: How much faster are you than whatever is in the Linux kernel's FIB? (Although I assume they need RCU overhead and such. I have no idea what it all looks like internally.)

▲

zx2c4 8 hours ago | parent [-]

I likewise wonder from time to time whether I should replace WireGuard's allowedips.c trie with something better: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

▲

Sesse__ 7 hours ago | parent [-]

I use Wireguard rarely enough that the AllowedIPs concept gets me every time. It gets easier when I replace it mentally with “Route=” :-)

▲

zx2c4 6 hours ago | parent [-]

It's like a routing table on the way out and an ACL on the way in. Maybe an easier way to think of it.

▲

Sesse__ 5 hours ago | parent [-]

Sure, but how does this differ from a routing table with RPF (which is default in Linux already)?

	▲	zx2c4 5 hours ago \| parent [-]
		It's associated per-peer, so it assures a cryptographic mapping between src ip and public key.

▲

newman314 8 hours ago | parent | prev [-]

I wonder if this would port nicely over to rustybgp.