Trouble with SNMP

dsheltzel used Ask the Experts™
I am completely lost on SNMP

I have read articles and see what SNMP is about, but am trying to understand it further. I am currently setting up Nagios, and need to define SNMP traps and Community strings on my servers and switches. What is the fasteset and best case way to set these up. Is there a super aetricle that explains this information?

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SNMP works in two ways. Either the device (servers, routers, etc) send events to the monitoring server when such events arise (that's called SNMP Traps), or the monitoring server polls each device to get some information. You want to use SNMP traps to immediately know that a switch interface goes down, but you might want to poll your devices regularly to get e.g. Network bandwidth usage graphs (That's what Cacti does).

The polling is quite easy to do even from Nagios with check_snmp, whereas getting traps into Nagios is much more complex and requires passive checks.

There was a nice article on Sys Admin magazine about that :

The other thing to know is that there is something like DNS in SNMP. all SNMP values are referred by OID, which is a suite of number pretty much like an IP address, e.g. .
Of course this is difficult to work with, so to make the analogy with DNS there are files called MIB which contain more information (description, comment, full name, etc). For example the number above turns to

Good luck

The SNMP community strings are for all intents and purposes the password for read-only access (in the case of the public community string) and read-write access (in the case of the private community string). Like any other password, mane these as secure as the hardware and software will allow.

The ideal-world set up is a network management station (NMS) that sends and receives SNMP data from the servers and other devices. In additional, all devices should be configured to send and receive traps ONLY form the NMS.

The best guide I've come across is Essential SNMP by O'Reilly press (Shameless plug:

Hope this helps!


You'll probably have to configure the network gear manually, but if you're using Windows Servers or PCs in a Domain environment there's probably a Group Policy you can define for the domain to configure all the traps you need, and when applied the policy automatically configures the machines.
Not wanting to be picky but questioning the added value of myin68's response compared to MidnightOne and myself, and wondering if an equal split is fair.


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