Network monitoring

Javier Palacios javiplx at
Mon Jul 28 17:44:26 UTC 2008

> What I have is a wireless AP on a small network (a Netgear AP), and it
> does have SNMP but I didn't see the docs on accessing it or polling it.
> What I'd like to do is have a way for my Linux system to periodically
> poll the AP (or the network), get a basic list of items on the network,
> and if anything comes up as "new" or "foreign" to just alert me about it
> so I know and have a record of it.

The tools are net-snmp. They allow you to get a single value, or to
traverse a tree.
Just in case, I'll give you a very short intro to snmp, just in case.
Each variable is identified by a long dot separated number (the OID).
There are ways that allow you to use sensible names for that, and that
will happen with net-snmp out of the box if you don't use any
extensions provided by your AP manufacturer. The most useful command
will be probably snmptable, that shows you a table in terse format.
Running `snmptable ifTable` will show you info about your interfaces
(similar to `ifconfig -a`). I know there is a table showing the MAC,
IP address and port number, but I don't remember the name (this is for
wired switches at least).
You probably need to use a community name (version 2c, usually is
'public' to query.
And if you configure the snmptrap host on your AP to a linux box, and
run there the snmptrapd, you will get notified (via syslog, but can be
also piped to email) about events such a new address given or a device
plugged/unplugged. Unless you use traps, you will need some kind of
crontab polling.

Javier Palacios

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