mrambossekandClaude Opus 5
4ae744aae5
A measurement server must prove its own host isn't distorting results:
- sysctl audit (/proc/sys): flags accept_ra on a static host, ICMP
redirects, ICMP rate-limiting of the server's own errors, and disabled
TCP options — each a measurement-fidelity hazard, with the "why".
- egress-MTU self-proof: DF PMTUD probe (IP_MTU_DISCOVER + getsockopt
IP_MTU, no root — Linux-only, stub elsewhere) to external anchors. If the
server's own uplink is below 1500, client MTU tests measure THIS server,
so we say so.
Exposed at GET /admin/selftest (full report) and as server_selftest
{mtu_ok, sysctl_ok} in the profile so clients can trust or skip MTU tests.
Recommended deploy/99-echolot-sysctl.conf + README section.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>