It's all easy today

*Those not terribly interested in networking will rightly skip this thread*
But back in the day making network protocols work together was a black art. Here is a link talking about IPX/IP gateway services..
Capacity Planning for the IntranetWare IPX/IP Gateway
I have also stumbled upon a good article that explains programming and networking. Some appreciation of this is all to the good for networking professionals.
Interaction of TCP/IP with other protocols
TCP/IP Networks - Interaction of TCP/IP and Other Protocols
Interestingly desktop protocols was tested significantly on earlier versions of the CCIE (I can remember it well), with NetBIOS, AppleTalk, DecNet as well as IPX all in the mix. In some senses I think that helped students get a deeper awareness of protocol mechanics.
We still see these things lurking on networks, particularly SNA and DLSW+ use in legacy IBM mainframe environments. Hardly tested at all these days these things. Same for ISDN and X.25 which is still around.
Once we move house, I will be building a legacy network laboratory at home and posting some legacy technical information that may help those struggling in the field with realities that the certification tracks have left far behind.