Very curious

Installed Netware 6.5sp4 on new server #1, very vanilla, goes fine while
creating a new tree, org, etc. Reboots perfect.

Installing same o/s on new server #2, very vanilla, last install phase
configuration has failed five times today always with the same problem.
Second server loses I/P connection to first.

If we plug in the cable to the switch for the second NIC card on the second
server, everything goes back to working and the install completes.

Is it simple? Do we just need to have both NIC cards for each server
plugged into the switch? Or is something amiss here?

Many thanks.