You can now see the last activity of each routers when you put the cursor over the load graph.
Last activity is a user log in, log out or interim updates.
If the router is not sending life signals for some reason, but there was an activity in the last 2 hours, then it will not say "DOWN", it will say "UP, but not sending life signals".
In this case you should turn off any firewalls, especially any SPI Firewalls you may have on your network.
