Hello everyone,
Thanks for all the great replies on my question about Round Robin
DNS addressing! Turns out the answer is in the latest O'Reilly DNS
book and since I have an ancient one, I guess this is a giant hint
to go spend money again on updated books. :-) I have included
some of the other suggestions as well.
Kathy Kost
kathyk@wolfenet.com
Thanks to:
Gustavo Chaves <gustavo@cpqd.br>
Brian Wells <brian@www.klondyke.net>
Jim Harmon <jharmon@telecnnct.com>
Craig Raskin <raskin@asiaonline.net.tw>
Karl E. Vogel <vogelke@c17mis.region2.wpafb.af.mil>
Parthiv Shah <parthiv@nscc.com>
bismark@alta.Jpl.Nasa.Gov (Bismark Espinoza)
My original question:
I haven't found any documentation on this so here's the question.
I'm noticing some addresses out there (use www.sun.com as an example) that
are assigned multiple ip addresses within dns. I'm assuming that if you
try to get to www.sun.com and the first ip address doesn't answer, it goes
to the next address? Is this how that works? I'm trying to figure out how to
do that with a web server to ensure 7x24 hour up time; i.e., have two mirrored
sites, but have the traffic routed to the second box if I have the first one
down for maintenance. I wasn't aware that you could do this within dns. If
this is how it works, could someone explain to me how it is set up within the
DNS tables? If my assumption is wrong, any other ideas for my 7x24 hour situation?
The Answers
-----------
>From Gustavo:
I'm just reading the book `DNS and BIND', by Paul Albitz and Cricket
Liu, from O'Reilly. I'm not a DNS expert but I think the answer is in
that book.
On page 211 there's a section entitled `Load Sharing Between Mirrored
Servers' that explains how DNS can do what you want. If you use BIND
version 4.8.3 (the one distributed with stock Solaris-2.5.1, unless
you apply the recommended patches, which install BIND 4.9.3) you'd be
without luck, I guess. However, since BIND 4.9.3 you could simply go
ahead and put several A records in your zone files for your mirrored
server and BIND would rotate them upon every request. The example
given in the book is as follows:
foo.bar.baz. 60 IN A 192.1.1.1
foo.bar.baz. 60 IN A 192.1.1.2
foo.bar.baz. 60 IN A 192.1.1.3
Upon the first query for foo.bar.baz's A records BIND would return the
three records in the given order. On the second query, it would
return them rotated (2,3,1), and then (3,1,2) and on and on.
>From Craig:
(discusses a load balancing name server)
check out:
http://www-leland.stanford.edu/~schemers/docs/lbnamed/lbnamed.html
>From Karl:
This is called "round robin" addressing. I think it's mentioned in the
current BIND operations guide, which is included with the source.
ftp://ftp.vix.com/pub/bind/release/4.9.5/bind-4.9.5-REL.tar.gz
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