Ssh proxy forwarding to nagios remote host


Hello everyone,

The scenario with my problem is that:
Nagios server is running in our local network, we got 6 nagios hosts locating in our customers data center, 3 on tier1(have public IP address, nrpe is running), and other 3 on tier2(just have private IP address, if we want to login to tier2, have to login to tier1 first, then login to tier2).

Now I need to monitor tier2 hosts with Nagios, is it possible open a proxy on tier1 host, then forward to tier2 to make the Nagios server communicate with nrpe running in hosts on tier2?

Set up a VPN should solve the problem, but it will take a very very long time and involve complex things. So I am thinking is it possible to use the proxy forwarding or create a tunnel to make Nagios work?

Any suggestion will be helpful.