Running the rcfg-sim server

rcfg-sim is the SSH server. Each instance binds one IP and a contiguous range of ports, reads a manifest, mmaps the configs, and serves sessions.

A foreground run

./bin/rcfg-sim \
  --listen-ip 127.0.0.1 \
  --port-start 12000 \
  --port-count 100 \
  --manifest /tmp/rcfg-test/manifest.csv \
  --host-key /tmp/rcfg-test/hostkey \
  --metrics-addr 127.0.0.1:9100

This binds ports 12000–12099 on 127.0.0.1. In production you run one instance per IP as a systemd service instead of in the foreground.

Core flags

Flag	Default	Purpose
--listen-ip	10.50.0.1	IP address to bind
--port-start	10000	First port in the contiguous range
--port-count	2500	Number of ports to bind
--manifest	/opt/rcfg-sim/manifest.csv	Authoritative port→config mapping
--host-key	/etc/rcfg-sim/ssh_host_rsa_key	SSH host key (generated if missing)
--metrics-addr	0.0.0.0:9100	Prometheus /metrics + /healthz address (empty disables)
--max-concurrent-sessions	5000	Cap on concurrent sessions (drain)
--log-level	info	error | warn | info | debug

See the full set, including auth, timing, and fault flags, in the CLI reference.

Credentials

Flag	Default	Notes
--username	admin	Currently informational — SSH auth is password-only
--password	admin	Empty string accepts any password
--enable-password	enable123	Cisco enable-mode password

These are the accepted credentials at the transport layer. Per-device credentials in the manifest are what tools should use. How the SSH layer authenticates is controlled by --ssh-auth.

Host keys

If --host-key points at a missing file, the server generates one on first start. Keep the same key across restarts so SSH clients don’t see host-key-changed warnings.

The metrics endpoint

--metrics-addr serves two paths:

• GET /metrics — Prometheus exposition format
• GET /healthz — liveness check

Set --metrics-addr "" to disable the HTTP server entirely. See Metrics.

Next

• SSH authentication modes
• Response timing & jitter
• Concurrency & graceful drain