At least I think it's that host because when dissabling the vpn I'm no longer able to ping the same IP. I set up a vpn with the firewall/router and I'm able to ping to the internal IP of that host. Now the second network which requires monitoring is also on a .x network (with the same netmask). To monitor this network I put up a vpn on, being the external (provided by the ISP) IP. The same IP address can be used on different switches. NOTE: Different interfaces cannot have overlapping IP addresses or subnets. The command applies only between the mgmt interface and an internal interface. Just a thought, could you initiate a tunnelled peer to peer connection between the (problem) remote hosts and the Nagios machine? At the moment I'm monitoring a .x network with nagios (which is working like it's supposed to). You can use the set allow-subnet-inteface command to allow two interfaces to include the same IP address in the same subnet. They know this problem excists but they realised too late. Things like these require them to set up contracts and what not (out of the scope of my knowledge). But seeing how those networks are actual customers you can't just go and start changing things, because it will have an effect on actual people and their job. I already suggested changing those few networks so that they wouldn't have this problem. The process to info overlaps is simple: calculate the range of addresses in each subnet, and then compare the lists. So the person above me is actually the head of sysadmins over at this company. The ability to recognize when two subnets overlap that is, the address range in the two subnets overlap can be very useful on the ICND2 and CCNA exams, as well as the ROUTE and CCIE exams. The last couple of months of my education (don't know the correct word for it) we are required to do an internship at an external company.

Easyvpn overlapping subnets