Going in circles without a real-time clock

Original Article ↗ Hacker News Discussion ↗

Bootstrapping Time & DNSSEC / NTP Deadlocks

  • Main failure mode: devices without RTC start far from real time, fail DNSSEC validation for NTP pool domains, and thus can’t reach NTP to fix their clocks.
  • Some argue enabling DNSSEC on ntp.org undermines its mission because many clients will be badly skewed; others counter that without DNSSEC, MITM attackers can redirect NTP and feed malicious time.
  • Suggested workarounds:
    • Temporarily disable time-based DNSSEC checks on boot.
    • Use last-known-good time plus TLS certificates/OCSP ranges to narrow current time.
    • Use HTTP Date header for insecure but simple bootstrapping.
    • Use tools like tlsdate-style approaches or Roughtime (not widely deployed yet).
    • OpenWrt example: start DNS with “no timecheck” until NTP syncs once.

WireGuard and Time Synchronization

  • WireGuard relies on a per‑peer monotonic counter (often derived from time) for key rotation and replay protection.
  • Not strictly wall‑clock synchronized, but large backward jumps or skew can break sessions; some report peers needing restarts after clock corrections.
  • People try systemd ordering (start WireGuard after time-sync.target), with uncertain reliability.

RTC Modules, GPS, and Time Servers

  • Many recommend adding an RTC or GPS to Pis and routers:
    • Cheap I2C RTCs (~$1) work well for most, but others report fragile hardware.
    • GPS + PPS gives microsecond‑level accuracy; several run Pi-based stratum‑1 servers.
    • Projects exist that bundle overlayFS, GPS, and chrony to make robust time servers.
  • Counterpoint: RTCs add BOM cost, board space, batteries, and still have drift/failure modes; some designs intentionally omit them and rely on network time.

Raspberry Pi Ecosystem & Reliability

  • Repeated complaints about:
    • Lack of RTC on older Pis and Pi 5 requiring a separate battery.
    • SD card corruption under write‑heavy workloads; mitigations include overlayFS, high‑endurance cards, or moving OS to USB/NVMe.
  • Some claim Pis are increasingly unsuitable for “production” compared to small x86 PCs; others are happy using them as low‑power desktops, GPIO controllers, and NTP servers.

DHCP and Other Time-Bootstrapping Ideas

  • Several want DHCP to provide a coarse current timestamp for RTC‑less devices.
  • Critics note time is more security‑sensitive than IP configuration; trusting DHCP time can enable certificate abuse.
  • Proposed compromise: treat DHCP-supplied time as a one‑shot bootstrap, bounded by other local timestamps and not used for long‑term trust.