Pi using LAN and WLAN

I plan to use two RPi3 B+'s communicating with each other. So far I have only one, and am testing its use using a laptop with Ubuntu 14.04. WLAN (via WiFi) works without any real hitches, but I would prefer direct-wired, and have bought a crossover cable to try this. But I cannot get communication, even though pinging in both directions works using the IP addresses. Any ideas?

Hey John,

What are you using SSH for communication and how are you connecting? There are a few jobs that the router does such as assigning names to IP addresses.