🛸 Hitchhiker's Guide — Phase 03: Management Protocols

Read this if: you need to talk to a BMC/PDU/CDU and "Redfish, IPMI, SNMP" is an alphabet soup. This is the compressed field guide — the tree, the commands, the gotchas.

0. The 30-second mental model

Three ways to talk to hardware out-of-band, three eras:

  • Redfish = the hardware as a REST/JSON tree (modern, secure, the one to master).
  • IPMI = the hardware as a binary command set (legacy, deprecated, still everywhere).
  • SNMP = the hardware as a tree of numbered variables you poll (PDUs/switches).

Senior move: Redfish-first with IPMI/SNMP as fallback drivers behind one interface. If you remember one rule: follow @odata.id links, never hardcode Redfish paths.

1. The Redfish tree (tattoo this)

/redfish/v1                     ServiceRoot (GET, no auth)
├─ /Systems/{id}                the HOST    → PowerState, boot, CPUs; Actions: Reset
├─ /Chassis/{id}                the BOX     → /Power (PSUs, draw, cap), /Thermal (temps, fans)
├─ /Managers/{id}               the BMC     → its firmware, network, VirtualMedia, SerialConsole
├─ /UpdateService               firmware    → returns a TASK
├─ /EventService                push/SSE events
├─ /TaskService                 long ops
└─ /SessionService              login → X-Auth-Token

Which resource owns what (the #1 confusion): System = host power/boot, Chassis = temps/PSUs, Manager = the BMC itself. One node = a System + a Chassis + a Manager.

2. Redfish verbs

WantDo
readGET (follow @odata.id); $expand to inline a collection
power on/off/cyclePOST .../Actions/ComputerSystem.Reset { "ResetType": "..." }
change configPATCH the resource
log inPOST /SessionService/Sessions → use X-Auth-Token → DELETE to log out
firmware updatePOST to UpdateService → 202 + Task → poll Task

Read …@Redfish.AllowableValues for what a field/action accepts — don't guess.

3. IPMI in five commands (ipmitool -I lanplus -H ip -U u -P p ...)

chassis power status|on|off|cycle|reset
sdr list            # sensors + readings + thresholds
sensor list         # detailed sensors
sel list            # the System Event Log (hardware events)
chassis bootdev pxe # boot-once override (Phase 05)
sol activate        # Serial-over-LAN console

Sensor reading = value + thresholds: lnr lc lnc | reading | unc uc unr. Health is "which threshold did it cross." Always lanplus (RMCP+); never plain lan/cipher-0.

4. SNMP in one breath

  • Value = OID (1.3.6.1.2.1.1.3.0 = sysUpTime). MIB = the name↔OID schema. Vendor stuff under 1.3.6.1.4.1.<enterprise>.
  • GET one · GETNEXT the next-in-lexicographic-order · WALK a subtree · GETBULK many · SET write · trap = device → you (UDP 162).
  • snmpwalk -v3 -l authPriv -u user -a SHA -A authpw -x AES -X privpw host OID
  • v1/v2c = cleartext community string (mgmt-net only); v3 = auth+priv (use this).

5. Events: poll vs push vs SSE

latencysteady loadneedsuse when
pollhighhigh at scalenothingmetrics, no-event resources
push subscriptionlowlowyour endpoint reachable by BMCsfleet fault alerts
SSElowlow1 long conn/BMCwhen inbound endpoints are hard

Real telemetry (Phase 07): poll for metrics + subscribe for state changes/faults.

6. Security non-negotiables

  • Redfish: HTTPS + validate the cert (disabling TLS verify is the classic bug), session tokens, least-privilege roles, never log the token.
  • IPMI: lanplus only, disable cipher-0, strong creds, last resort.
  • SNMP: v3 where it matters; v2c read-only + ACL otherwise.
  • All three live ONLY on the isolated management VLAN (Phase 09). Exposed BMCs are a Shodan staple and a fleet-wide compromise.

7. The driver abstraction (the senior pattern)

DeviceDriver(power_state, set_power, read_sensors)
   ├─ RedfishDriver   (preferred)
   ├─ IpmiDriver      (fallback)
   └─ SnmpDriver      (PDUs/switches)
+ unified Reading model so callers don't care where a temp came from

This is the Phase 13 capstone and Phase 07 exporter in one diagram.

8. Vendor variance survival kit

  • Follow links (IDs differ: 1 vs System.Embedded.1 vs UUID).
  • .get() with defaults; tolerate Oem blocks and missing optional fields.
  • Retries/backoff/timeouts (BMCs are flaky); idempotent actions.
  • A per-vendor conformance suite in CI (Phase 11); pin BMC firmware (Phase 08).

9. The "done this before" tells

"Which resource owns that — System, Chassis, or Manager?" · "Are you following the link or hardcoding the path?" · "Is that a Task? Poll it." · "v2c or v3?" · "lanplus, right?" · "Is TLS verification on?" · "Event or poll — and what's the backstop?"

10. How this phase pays off later

  • The driver + unified Reading is the foundation of the Phase 07 exporter and Phase 13 capstone.
  • Tasks are how Phase 08 firmware updates are monitored.
  • EventService/traps feed Phase 07 alerting and Phase 10 RCA.
  • Protocol security is enforced by the Phase 09 management-network isolation.