ngtcp2 — Path MTU black hole above a threshold

Pass

Recovered: detected the black hole 1 time(s) and settled on a 1293-byte path MTU (360 datagram(s) swallowed).

The client did what the clause requires.

What was measured

Client

ngtcp2 — ngtcp2 + nghttp3 (direct), 3c23148

Test

Path MTU black hole above a threshold — q-pmtu-blackhole

Clause

RFC 9000 §14, RFC 8899 (SHOULD)

Class

resilience — Recovered rather than giving up.

Required behaviour

Detect the black hole, probe down to a working size, and keep the connection. Path-MTU discovery is driven past the limit on this port, so it engages on every connection.

Measured

2026-09-18

Reproduce it

The suite is the judge, so the reproduction is to point the same client at the same test and let the server report what it saw.

SESSION=$(curl -sX POST https://conformance.pqcrypta.com/session | jq -r .id)
# then drive ngtcp2 at the test URL and read the verdict:
curl -s https://conformance.pqcrypta.com/report/$SESSION.json | jq '.results["q-pmtu-blackhole"]'