redundant servers

[Mark_Andrews at isc.org]

> Ok here is my scenario i have 3 registered domains and two Freebsd boxes 
> running bind 9 postfix 2 and apache 2.  These servers are on separate 
> networks server one is master for itself and slave for the remaining 2 
> domains on the server 2.  Server 2 is slave for server 1 and master for 
> a couple of its own domains yet only has one ip address.  This i seem to 
> have figured out over the past couple of years what is confusing me 
> right now is how do i get the servers to back each other up i mean  if 
> one goes down  the other one takes over dns web page mail sever 
> everything.  seems like a great concept but how do i achieve this i 
> think i got the dns stuff  but what about the rest dns seems to be 
> everything in these situations so  i hope this is not to far off topic

	At the DNS level as server is a master or slave FOR A ZONE.

	For mail you add MX records with higher preference values
	which refer to the other machine which will *queue* the mail
	while the machine is down.  You will have to tell the other
	machines that they are to relay mail for the other machines.

	machine1.example.net.	MX 0 machine1.example.net.
	machine1.example.net.	MX 10 machine2.example.net.
	machine1.example.net.	MX 10 machine3.example.net.

	machine2.example.net.	MX 0 machine2.example.net.
	machine2.example.net.	MX 10 machine1.example.net.
	machine2.example.net.	MX 10 machine3.example.net.

	machine3.example.net.	MX 0 machine3.example.net.
	machine3.example.net.	MX 10 machine2.example.net.
	machine3.example.net.	MX 10 machine3.example.net.

--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org