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From: rlstewart@eng.xyplex.com (Bob Stewart)
Newsgroups: comp.protocols.tcp-ip
Subject: Telnet rotors/connection distribution?
Message-ID: <9101132032.AA04558@xap.xyplex.com>
Date: 13 Jan 91 20:32:00 GMT
References: <1991Jan11.225650.17367@eagle.lerc.nasa.gov>
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We have a rotary capability in our terminal servers.  That won't help you with
PC/Mac to VAX, but I can tell you what I understand of how it works.

DNS will return multiple IP addresses for the same name.  At the name server,
you pick a rotary name and give it the appropriate list of addresses, which
will then go to anything that asks to resolve that name.  I don't know of any
reasonable facility to accomplish load balancing at this point.  DNS wasn't
intended for real-time information.  The catch to this is that most
applications (like Telnet) that do name lookups are pretty stupid about
receiving multiple addresses.  I think what we do in that case is try the
first one, if that doesn't work, we go to the next, and so on.  A slightly
smarter algorith might pick one at random, or keep the whole list and use the
entries in turn for subsequent connections.  As I sit here making all this up,
it strikes me that picking one at random has its features, but that probably
violates the idea (as I recall) that the name server is supposed to put them
in the preferred order.

In your case, all of this implies that you'd probably have to be able to make
some programming changes at the end that originates the connection, requiring
either source code or an armlock on the appropriate vendors.

I'm curious to see if any other suggestions appear, or if anyone is horrified
by our use of DNS.

	Bob