Want to install Nagios or SNMP plugin

I've been googling around but all of the information related to Nagios is really old. I'd like to be able to monitor my router from my raspberry pi running Nagios.
Any suggestions?

I have installed the SNMPd plug-in and it is working from the command line via:
snmpwalk -v1 -c public router.
I am new to SNMP, but it's my understanding that I need a MIB for Nagios to interpret this data. I have installed snmp-mibs but am unsure how to download the file. This may have become a question for another site, but I would appreciate any help anyone may have.