We all know that ping is the most common way to establish layer 3 connectivity. Layer 1 connectivity is established by link light. Layer 2 connectivity is establish by checking if link protocol shows as up (or you see the MAC address), but how about non-ethernet layer 2 connectivity? How about layers 4, 5, 6, and 7?
So, the question is: What are common ways to unequivocally establish connectivity at layers 2, 4, 5, 6, and 7?
Some ideas that pop into my head:
1) telnet to port 80/443 for layer 7 connectivity
2) use netcat (how?)