Hi,
We have been facing this problem where the connections tab in the firewall section is showing huge amounts of connections (somewhere around 20000) and the CPU usage of the router (RB1000) spikes upto 100% from time to time.
How could we trace and limit the hosts responsible for these huge amount of connections.

you can do that by performing a touch from winbox.

Or turn on Traffic Flow, get an external traffic collector and have it generate stats on the top talkers and conversations.