OT: DNS Failover

[Les Mikesell]

On Wed, 2005-08-31 at 12:11, Thomas Cameron wrote:
> > If you are looking for failover of the looked-up addresses, in many
> > cases you can always give out multiple addresses by including them
> > as A records for the same name.  Browsers seem to be very good at
> > failing over on the client side if some of the returned addresses
> > don't work.
> 
> Have you had success at that?  I've found that Windows clients tend to
> cache DNS results no matter what your TTL is, and to only use the first IP
> address they get until their internal cache expires.  You basically have
> to run ipconfig /flushdns to make a Windows box dump the IP address and
> re-query the DNS server.

Yes, although what I was really testing was the ability of an F5 3dns
box to make the client switch.  It worked with IE *if* both IP's
had been given out initially and subsequently one server stopped
working and the 3dns dropped it from the list.  If only one IP
was initially given out and that one subsequently quit working,
IE would not pick up the new address until you closed all IE windows
and restarted it.  IE is also good about bypassing servers in the
initial list if they don't respond on the first attempt.  I'm not
sure about the case of subsequent failure without a change in
DNS to remove it.  This seems to be very application-dependent,
though - other apps are not so smart about getting multiple addresses
although if you are writing a client you can fix that part yourself.

-- 
  Les Mikesell
    lesmikesell at gmail.com