[Quoted paragraphs are not in the original order...]

> When I telnet into my mac, I seem to only be able to open a few ports 
> before things get strange.  I get the message:
> 
> Connected to localhost.
> Escape character is '^]'.
> telnetd: All network ports in use.
> Connection closed by foreign host.
[...]
> I can run 10 HTTP daemons, sendmail, inetd, cu, slattach, X, xterms, 
> xclock. . . . ftp. . . . quite successfully with no problems or 
> slowdowns, no "running out of ports", "no more processes" etc.  So I 
> don't think it's really out of resources.

No, it *is* really out of certain resources; ptys, as you noticed
below, and also as rlogin complained to you.

> I noticed in /dev/ that I only had four ptyp's.  My sparc20 has 16 of 
> them in /dev/ptyp, 16 in /dev/ptyq, 16 in /dev/ptyr, for a total of 48 
> pseudoterminals.

There could be maximum of 64 ptys (/dev/ptys0 through /dev/ptysf besides
the ones you listed above).

> Any idea how to create more of them?  Or is this the answer.  I don't 
> know how to use MAKEDEV, but I fear I'll have to learn.

Go to /dev directory and type:

./MAKEDEV pty0

That'll make 12 more ptys (ptyp4 through ptypf).  I think the default
number of ptys for GENERIC configuration is 16, so it may not help
even if you created more ptys by "./MAKEDEV pty1" (which will make
devices ptyq0 through ptyqf).

ken