SNMP at home

Several devices on my home network support SNMP. Here’s one way I’m making use of this.

Want to know the last time your router rebooted? Try this:

snmpget -c public server-name system.sysUpTime.0

That UNIX command will work as-is on a Mac. It will also work on Debian Linux but you may have to install the snmp package first and you’ll also have to download the so-called “MIB” to define the “system.sysUptime.0” name.

Without the MIB installed you can still just use the raw low-level object ID:

snmpget -c public server-name

Some (older) Apple airports, most Cisco devices, many routers, and other such networking equipment support SNMP. So, for example, on my (large) home network I have four Cisco WiFi transmitters. I’ve been interested in charting how often the power fails at my house. So I wrote a script to send each WiFi box this command once a day:

nw% snmpget -c public wap-1 system.sysUpTime.0

DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1122240526) 129 days, 21:20:05.26

(Command to server “wap-1” shown) and I record the results. Obviously when there’s been a power failure all the WAPs reboot and now I can know if that has happened (the server these monitoring scripts run on has a UPS so it stays up; otherwise I could of course just look at the server’s own uptime).

If you google snmp system object you will find some pages with more names/OIDs for other variables that might be useful. Also your devices likely have many interesting device-specific parameters you can fetch.  Google is your friend for finding more MIB/OIDs to try.

My pfSense router supports SNMP but you have to enable the SNMP service first (not enabled by default). This may be true on other device types as well so if they don’t respond to SNMP browse through their admin interfaces and see if you have to (i.e., can) enable SNMP.

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