Re: [cobalt-developers] Re: Secondary DNS

[Norbert Bollow <nb@xxxxxxxxxxxxxx>]

> I would appreciate your thoughts on that - if my RAQ and its primary DNS
> are up, but Internic has a secondary DNS in place of my primary #, and that
> secondary is down, do browsers (or whatever the mechanism is) *know* to
> look at the other DNS server or do they just report a server not found error?

The DNS system is designed so that the "closest" nameserver (in
some sense) is tried first, but as long as at least one of
your primary and secondary nameservers is working and reachable,
all name lookups will work.

So suppose you have two servers, let's call them 'primary' and
'secondary', with IP addresses XXX.XXX.XXX.XXX and YYY.YYY.YYY.YYY.
Set them up so that 'secondary' exactly mirrors all the websites
at 'primary'. Run named on both servers, but *not*
in the usual configuration of master and slave, but configure
both as masters, with different zone files, as follows:


On the 'primary' server:

; DNS hack for two webservers so that if one server is down or
; unreachable, the other is guaranteed to have completely taken
; its place within five minutes. -- nb@xxxxxxxxxxxxxx
@                IN   SOA     primary.example.com. hostmaster.example.com. (
                              2000120201            ; Serial
                              10800                 ; Refresh
                              1800                  ; Retry
                              3600000               ; Expire
                              300    )              ; Minimum TTL
          604800 IN   NS      primary.example.com.
	  604800 IN   NS      secondary.example.com.
          604800 IN   MX   10 primary.example.com.
          604800 IN   MX   20 secondary.example.com.
	     300 IN   A       XXX.XXX.XXX.XXX
primary   604800 IN   A       XXX.XXX.XXX.XXX
secondary 604800 IN   A       YYY.YYY.YYY.YYY
www       604800 IN   CNAME   example.com.


On the 'secondary' server:

; DNS hack for two webservers so that if one server is down or
; unreachable, the other is guaranteed to have completely taken
; its place within five minutes. -- nb@xxxxxxxxxxxxxx
@                IN   SOA     secondary.example.com. hostmaster.example.com. (
                              2000120201            ; Serial
                              10800                 ; Refresh
                              1800                  ; Retry
                              3600000               ; Expire
                              300    )              ; Minimum TTL
          604800 IN   NS      primary.example.com.
	  604800 IN   NS      secondary.example.com.
          604800 IN   MX   10 primary.example.com.
          604800 IN   MX   20 secondary.example.com.
	     300 IN   A       YYY.YYY.YYY.YYY
primary   604800 IN   A       XXX.XXX.XXX.XXX
secondary 604800 IN   A       YYY.YYY.YYY.YYY
www       604800 IN   CNAME   example.com.



It is then important that you list primary.example.com. and
secondary.example.com. and nothing else as nameservers.

I'm available to help you with setting this up properly
(including mirroring and mail relaying) if desired, for an
hourly fee.

Warm greetings, Norbert.


-- 
Comparitive list of colo providers http://thoughtcenter.com/colocation
Norbert Bollow, Weidlistr.18, CH-8624 Gruet (near Zurich, Switzerland)
Tel +41 1 972 20 59       Fax +41 1 972 20 69        nb@xxxxxxxxxxxxxx