You couldn't talk to an IPX-based NetWare server using IP, and neither could you talk to an IP-based Unix box using IPX. We therefore have to deal with two different protocols
I'll allow that on the point of having the word "based" in there - but whilst we were moving from Netware to MS Winders, we had *both* protocols active on the network for about 3 years.
And for the first 8 months I was one of two (2) people in the entire org that had identities on both sides of the wall. And was the only one who could reset passwords on both sides.