snmp4sbc

SNMP for Single Board Computers (i.e. "BeagleBone Black" or "Raspberry Pi")

Introduction

This project is to share my experience using SNMP to manage a fleet of single board computers such as BeagleBone Black (etc) or the Raspberry Pi (etc).

SNMP is mature and well documented, there are several decent books and a great open source implementation provided by the Net-SNMP agent and utilities. I share some advice about configuring and using Net-SNMP and end with extending the agent to monitor GPIO.

I am writing this in November, 2024 and the current source version of Net-SNMP is 5.9.4

The Players

WRT54GL Wireless Access Point (all client IP address via DHCP)

host	IP address	interface	role	type	operating system
bb11	192.168.1.109	wlan0	agent	beaglebone black wireless	Debian 10 Buster
rpi4e	192.168.1.113	wlan0	agent	raspberry pi 4	2024-03-15 64bit rPi OS
waifu	192.168.1.126	wlp0s20f3	manager	Lenovo Notebook P/N 21FVX001US	Ubuntu 22.04.5 LTS (Jammy Jellyfish)

The Plan (Raspberry Pi)

1. Simple Start (Notification/Trap)
   1. Goal: use the snmptrap(1) utility to generate notifications from a rPi to a manager host running tcpdump(8), which demonstrates routing between machines on UDP 162.
   2. On the agent (rPi) install the SNMP utilities by running apt-get install snmp, which (in November, 2024) installs the Net-SNMP v5.9.3 utilities.
   3. On the manager, invoke tcpdump(8) (might need to be root) as tcpdump -v port 162
   4. On the agent (rPi), tweak trap-demo.sh to have the correct IP address of your manager and then invoke it.
   5. On the manager, tcpdump(8) should look similar to this:

      22:46:40.250146 IP (tos 0x0, ttl 64, id 2503, offset 0, flags [DF], proto UDP (17), length 122) 192.168.1.113.58095 > waifu.snmp-trap:  { SNMPv2c { V2Trap(79) R=212351885  system.sysUpTime.0=17714770 S:1.1.4.1.0=E:8072.2.3.0.1 E:8072.2.3.2.1=123456 } }
      

   6. snmptrapd(8) could also be used by the manager to log trap messages.
2. Simple "Read Only" Agent
   1. Goal: introduce a minimal SNMP agent configuration (rPi), and interrogate it from a manager host.
   2. On the agent (rPi) install the SNMP agent by running apt-get install snmpd, which (in November, 2024) installs the Net-SNMP v5.9.3 SNMP agent.
      1. Verify working installation by invoking systemctl status snmpd, the response should be similar to this:

      ● snmpd.service - Simple Network Management Protocol (SNMP) Daemon.
           Loaded: loaded (/lib/systemd/system/snmpd.service; enabled; preset: enabled)
           Active: active (running) since Sat 2024-11-30 07:59:56 UTC; 7h ago
         Main PID: 1232 (snmpd)
            Tasks: 1 (limit: 8731)
              CPU: 29.445s
           CGroup: /system.slice/snmpd.service
                   └─1232 /usr/sbin/snmpd -LOw -u Debian-snmp -g Debian-snmp -I -smux mteTrigger mteTrigger> 
      

   3. Surprisingly (for a systemd(1) service) journalctl(1) does not contain the agent logs. snmpd(8) logs to /var/log/snmpd.log
   4. Now update the agent (rPi) configuration, use simple.conf by copying it to overwrite /etc/snmp/snmpd.conf
   5. Restart the agent (rPi) by invoking systemctl restart snmpd
   6. Request the system MIB contents by invoking snmpwalk -v 2c -c public 192.168.1.113 1.3.6.1.2.1.1 (replace the address 192.168.1.113 with the IP address of your rPi). The result should look like:

      SNMPv2-MIB::sysDescr.0 = STRING: Linux rpi4e 6.6.31+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.6.31-1+rpt1 (2024-05-29) aarch64
      SNMPv2-MIB::sysObjectID.0 = OID: NET-SNMP-MIB::netSnmpAgentOIDs.10
      DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (19905) 0:03:19.05
      SNMPv2-MIB::sysContact.0 = STRING: "hax4bux”
      SNMPv2-MIB::sysName.0 = STRING: rpi4e
      SNMPv2-MIB::sysLocation.0 = STRING: "shasta"
      (etc, etc..)
      

3. Configure SNMP agent to generate start/shutdown traps
   1. Goal: configure the SNMP agent (rPi) to generate SNMPv2-MIB::coldStart and UCD-SNMP-MIB::ucdShutDown
   2. On the manager, invoke tcpdump(8) as tcpdump -v port 162
   3. On the agent (rPi) update the configuration by copying simple_with_trap.conf to replace /etc/snmp/snmpd.conf
      1. Update the IP address to match your manager
   4. Restart the agent (rPi) by invoking systemctl restart snmpd
   5. On the agent (rPi) install the SNMP agent by running apt-get install snmpd, which (in November, 2024) installs the Net-SNMP v5.9.3 SNMP agent.
   6. Note that when you restart the agent, a trap is now generated to announce "coldStart" From tcpdump(8) it looks like:

      09:19:32.472153 IP (tos 0x0, ttl 64, id 54386, offset 0, flags [DF], proto UDP (17), length 123) 192.168.1.113.52157 > waifu.snmp-trap:  { SNMPv2c { V2Trap(80) R=133045648  system.sysUpTime.0=21 S:1.1.4.1.0=S:1.1.5.1 S:1.1.4.3.0=E:8072.3.2.10 } } 
      
      

   7. If you restart the agent (rPi) again, there will be two traps: One for "shut down" and then "cold start".
4. Use MIB names instead of raw OID
   1. Goal: refer to objects by name instead of using raw OID. A component of SNMP is the Management Information Base (MIB)
   2. The agent and utilities share a common configuration file "/etc/snmp/snmp.conf"
   3. On your manager, locate the "snmp.conf" file and update the "mibdirs" variable
      1. On my manager, "/usr/share/snmp/mibs" contains enough freely available MIB to work.
   4. Verify you can now reference items by name instead of OID
      1. snmpwalk -v 2c -c public 192.168.1.113 system
5. Monitor Raspberry Pi using the "Host Resources MIB"
   1. Goal: access host resources such as date/time, file systems, CPU, memory, etc.
   2. The HOST-RESOURCES-MIB defines how to access this information.
   3. Example: snmpwalk -v 2c -c public 192.168.1.113 host

      HOST-RESOURCES-MIB::hrSystemUptime.0 = Timeticks: (1117912) 3:06:19.12
      HOST-RESOURCES-MIB::hrSystemDate.0 = STRING: 2024-11-30,20:25:29.0,+0:0
      HOST-RESOURCES-MIB::hrSystemInitialLoadDevice.0 = INTEGER: 393216
      HOST-RESOURCES-MIB::hrSystemInitialLoadParameters.0 = STRING: "coherent_pool=1M 8250.nr_uarts=0 snd_bcm2835.enable_headphones=0 snd_bcm2835.enable_headphones=1 snd_bcm2835.enable_hdmi=1 snd_b"
      HOST-RESOURCES-MIB::hrSystemNumUsers.0 = Gauge32: 5
      HOST-RESOURCES-MIB::hrSystemProcesses.0 = Gauge32: 206
      HOST-RESOURCES-MIB::hrSystemMaxProcesses.0 = INTEGER: 0
      HOST-RESOURCES-MIB::hrMemorySize.0 = INTEGER: 7997476 KBytes
      HOST-RESOURCES-MIB::hrStorageIndex.1 = INTEGER: 1
      (etc, etc...)
      

The Plan (BeagleBone Black)

1. Net-SNMP installation notes
2. Register BeagleBone boot via notification/trap and share IP address
3. Configure agent to share useful system identification
4. Extend agent to share GPIO status