We were under the impression that with KRC and R8 you only need port 5721 opened. I found an article which states port 3478 TCP and UDP must also be opened outbound.
Has anyone found this to be a problem when not opening this port?
I discussed this with a colleague recently and we opened port 3478 on a remote clients firewall and noticed the speed of KRC to that client seemed faster and more responsive.
Does this mean, that I should allow this port inbound to Kaseya server?
Port 3478 is not required.
When Remote Control is initiated the admin/viewer machine and the agent communicate through the VSA to setup the session. Both sides will then make an outbound STUN request (on port 3478 - see: http://en.wikipedia.org/wiki/STUN) to "learn" their public IPs and will then try to setup a peer-to-peer session directly between the admin/viewer and the agent.
Typically, a direct connection is faster than one relayed through the VSA, so Kaseya Remote Control will try multiple techniques/technologies to find the best connection available.
If a peer to peer connection cannot be established, the admin/viewer and the agent will "talk" through a connection relayed through the VSA (using the existing port 5721 port from agent to VSA).