load-balancing in DNS using two A records

Ryan Novosielski novosirj at umdnj.edu
Tue Dec 20 17:45:35 UTC 2011

Hash: SHA1

On 12/20/2011 12:37 PM, Martin T wrote:
> I have seen setups where one domain name has two address records.
> First IP address is in the ISP-A network and the other one is in the
> ISP-B network. In case I execute "host www.<domainname>.com", I always
> get two IP addresses as a reply and they always appear by turns. Am I
> correct, that setup like this provides redundancy as well as
> load-balancing? Is there some common method in BIND to give out IP
> addresses by turns? Last but not least, how do application layer(for
> example www, ssh) handle such setup?

The only thing involved is having two A records for the same name. It's
not truly load-balancing, but it can do the trick in some circumstances.
All applications I've seen ask for and use one IP address. Therefore,
SSH will be sometimes connecting to one server and sometimes another.
Generally with SSH you care what you're connecting to and will also have
individual records for each host to use for that purpose.

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|Y#| |  | |\/| |  \ |\ |  | |Ryan Novosielski - Sr. Systems Programmer
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