Port some tiny testcases that apply to our corp impl of the rdv hasher
to OSS as well. This is in preparation for cutting over to the OSS
impl exclusively.
Updates tailscale/corp#46471
Signed-off-by: Amal Bansode <amal@tailscale.com>
The rendezvous hasher for traffic steering loadbalancing was flawed.
By plainly using the FNV-1a hash value, the result often reflected the
magnitude of the most significant bits in the hash seed, meaning the
hash function was not diffusive (aka missing the Avalanche Effect).
Popular wisdom seems to be that the output of FNV-1a should be mixed
with some large numbers to perturb more output bits. Borrow concepts
from other (Rust, Java) libraries by using the mix13 variant of 64-bit
finalizers by David Stafford.
Modify the fuzz test that asserts this fairness. Adjust a few
constants like client count and candidate count to more closely
reflect real-world scenarios and practical probabilities. Tighten
the bounds for distribution from 50% to +-20%.
Updates tailscale/corp#46471
Signed-off-by: Amal Bansode <amal@tailscale.com>
In PR #19682, we introduced the traffic package which provides a
traffic.Scores.SortNodes method that uses rendezvous hashing to
break ties by equally distribute the “best” node for any given client.
This PR adds a fuzzer to make sure this algorithm is not wildly unfair.
Updates #17366
Updates tailscale/corp#33033
Signed-off-by: Simon Law <sfllaw@tailscale.com>
In PR tailscale/corp#30448, we originally decided to break ties using
SHA256 for our rendezvous hashing algorithm. Now that we’ve had some
experience with it, we think that FNV-1a is a better choice. It
distributes bits evenly, it’s much faster, and it doesn’t need to be
cryptographically secure. The FNV designers recommend FNV-1a over the
deprecated FNV-1.
This PR makes the switch and updates the related tests, since changing
the algorithm changes which stable pick gets selected. As of 2026-05,
this is the best time to make this change, since there are almost no
clients in the wild with traffic steering enabled.
Updates #17366
Updates tailscale/corp#29964
Updates tailscale/corp#29966
Updates tailscale/corp#33033
Signed-off-by: Simon Law <sfllaw@tailscale.com>
The traffic package contains helpers for evaluating traffic steering
scores and picking appropriate nodes. These were extracted from
ipnlocal.suggestExitNodeUsingTrafficSteering so they can be reused by
the new routecheck package to probe exit nodes in priority order.
Updates #17366
Updates tailscale/corp#33033
Signed-off-by: Simon Law <sfllaw@tailscale.com>
Amal Bansode