What limits are there on the number of reverse ssh tunnels?

Question

We have 100+ embedded boards that we need to talk to occasionally.

We've found the best way to do this reliably (there are some strange internet connections out there) is to have the boards open a few reverse ssh tunnels to our server.

Currently each board opens three tunnels, for a total of around 300. The tunnels are inactive most of the time .

Are there any performance implications of this? Assuming we don't run out of ports or file descriptors, what is most likely to trip us up?

Edit: I'm primarily concerned with having several hundred inactive clients connected at once. Only a few of the tunnels will be in active use at any one time.

Answer 1

The limit on active SSH connections is 65,534 minus the number of TCP ports in use on your system -- If we want to be conservative let's just say 60,000 (or for most practical purposes "Unlimited"). You may bump up against other system resource limits however, depending on the machine you're connecting to.

That said you might want to economize on the number of tunnels (do you really need three connections per board?), and if you don't always need the connections up you might want to have the remote site initiate them only when needed.