Advanced Round Robin Implementation

[Laurent Verhoest]

In article <MoCE3.146$zE6.6864 at burlma1-snr2>,
  Barry Margolin <barmar at bbnplanet.com> wrote:
>
> >  Is it possible or not ?
>
> Not with DNS.  Round robin simply reorders the responses each time, so
some
> clients will get them in the order x.y.z.w,x.y.z.w2, while others will
get
> them in the order x.y.z.w2,x.y.z.w.  Some applications try all the
> addresses they get until they succeed in connecting, but many just try
the
> first one and give up.
>

not exactly, you can improve this : you can 'trick' DNS by setting low
TTL values for those particular records :

www 1 IN x.y.z.w
www 1 IN x.y.z.w2

This way, clients will get this first IP *almost* always in the first
place.

> >  Because i think that yahoo, microsoft and others, for example, must
> >have many
> >servers to answer the dns queryes, but when one of them is down the
> >address must
> >not be the answer from a query, because the request won't get
responde
> >and will return a "host down" status.
>
> Are you talking about DNS servers, or web servers?  Multiple DNS
servers
> are usually implemented by having multiple NS records pointing to
different
> hostnames.  DNS servers try all the NS records until succeess.
>
> If you're talking about web servers, the most common solution is to
use a
> multiplexer like Cisco Local Director.  This is a NAT-like device that
has
> one IP address and forwards connections to several real server
addresses.
> It monitors the servers, and if one of them goes down it stops
forwarding
> connections to it.
>

true. This is not the original purpose of DNS.

NCPM does it (from HP, works on HP-UX and Windoze NT), so does lbnamed
(an improved dns server in perl, based on BIND, but I didn't try it).

> --
> Barry Margolin, barmar at bbnplanet.com
> GTE Internetworking, Powered by BBN, Burlington, MA

--
Laurent.


Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.