Read off a Micromate modem deployed and working for months. Recorded because
this knowledge currently lives only in a modem's web UI, and TMI has seven
working units to diff a misbehaving one against -- the fastest diagnostic
available.
Serial: PAD mode, 115200 8N1, flow control None. (Series III units use 38400 --
a modem moved between series needs this changed and nobody would think to.)
PAD: TCP, auto-answer ON, listening port 9034, destination 50.197.32.91:12345,
idle timeout 2 min, data forwarding 500 ms, MTU 1304, TCP keepalive OFF.
Cellular: APN mw01.VZWSTATIC -- Verizon's static-IP APN, which confirms the fleet
has fixed addresses and rules out any "the IP moved" explanation.
TOPOLOGY this answers: the office ACH listener is on port 12345 at 50.197.32.91,
and field modems listen on 9034 for THOR to dial in. Both were open questions.
Two things worth questioning in the config, flagged as hypothesis not finding:
* TCP keepalive is Off, so nothing detects a half-open session from the modem
side -- the 2-minute idle timeout is the only reaper.
* An idle timer can be held open indefinitely by a client that keeps writing.
THOR polls every 30 s (measured). If it holds a session the unit stopped
answering on and keeps writing into it, each write plausibly resets the idle
timer, the session never ages out, the PAD's single slot stays occupied, and
all new inbound fails -- while ACEmanager answers on its own service.
Whether one-directional traffic resets that timer is NOT confirmed, and the
single-slot behaviour is untested on a real modem. mm_probe --slots tests
the latter directly.
Adds an ordered diff checklist for a misbehaving modem, noting that "listen for
connections" and "destination address" fail in opposite directions -- inbound
broken with call-home working points at the listener; call-home broken with
inbound working points at the destination.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ru8Lg9HkkYvX9VWWo65SmL
serversdownandClaude Opus 5
7b2aa871bd