Firewall Wizards: failover and dns

[Lyndon David <lyndond () sentinet co uk>]

Dear All,

I am looking at the following situation.

Company A is big and multinational. As a service to employees on the
road it offers
an application which uses a web browser as a front end and enforces
access restriction
by use of one time token cards and mandating that everything is kept (a
little)
secret by SSL.

Company A now wants to improve resilliance. The have datacenters in
three
continents and so the basic idea is to put up three copies. Now the dns
entry will
point to one of them, if that fails then the contents of the dns will be
changed (not
by hand) to point at the secondary etc. Use a very short ttl on the dns
entry and
things should start again after a short while.

Questions.

Has anyone tried this before.
If they did, did it work OK
What is available to do the dns changing bit.
Is this a good idea or are there better.

Anyhow, I would just like to start a thread to discuss options for high
availability
for big organisations that have a big world wide internal network and
multiple
Internet access points in different countries.

Thanks

Lyndon David