if tha nagios server is on one side of both links and you have servers on the other side, pinging those servers tells you the link is up. But that's not enough because you wouldn't know if the link is down or if the server is turned off. so you need to check some snmp service on the machine (possibly using check_nt) ping the machine (checking if it's on but possibly not responsing but you would know the link is still up) check the status of the port on the router which the link connects to (via SNMP most routers can this) and ping the router itself to see if it's on. this way you would have almost all possible failures at a glance.
I avoided talking about the network part before the router...
I don't know how to use the windows SNMP via nagios, sorry.
EDIT: The routers MIB structure should be better documented than the X25 cards one.. any way if you need you probably can just make an snmpwalk of the MIBs and search the info you need... (had to this for SUN hardware MIBs. that wasn't fun... :evil:
Edited Fri Mar 18 2005, 11:57PM ]