All nameservers unresponsive when master is down

[Sam Pointer]

My domain `hpdsc.com` has 2 "actual" nameservers which we present to the
world as 4 "logical" nameservers. The 2 boxes are multihomed and all 4
addresses are given as valid namesevers for the domain (we have 2 leased
lines and this removes a single point of failure).

My whois informations is:

 Domain servers in listed order:

   NS2.HPDSC.COM                212.158.99.195
   NS3.HPDSC.COM                195.167.246.3
   NS4.HPDSC.COM                195.167.246.4
   NS1.HPDSC.COM                212.158.99.194	The like-typed nameservers
are actually the same nameserver on the same box (multihomed).

The relevant part of the Zone data is:

hpdsc.com.      IN      SOA     ns1.hpdsc.com. dnsadmin.hpdsoftware.com. (
                                        1018281163      ; Serial
                                        7200            ; refresh (2 hour)
                                        3600            ; retry (1 hours)
                                        604800          ; expire (1 week)
                                        1               ; neg. cache
                                        )
...
hpdsc.com.      NS      ns1.hpdsc.com.
hpdsc.com.      NS      ns2.hpdsc.com.
hpdsc.com.      NS      ns3.hpdsc.com.
hpdsc.com.      NS      ns4.hpdsc.com.
...

ns1.hpdsc.com.          IN A            212.158.99.194
ns2.hpdsc.com.          IN A            212.158.99.195
ns3.hpdsc.com.          IN A            195.167.246.3
ns4.hpdsc.com.          IN A            195.167.246.4


However, if I stop BIND running on ns1 (which is also ns3 if referenced by
it's alternative IP address) then the whole Zone stops resolving. And I
can't for the life of me work out why. If you want to tell me to "FAQ off"
then please do.

Any help/pointers/soothing words of calm would be most appreciated: I'm
terrified on ns1/ns3 falling over! I'm running BIND9.
_________________________________________


Sam Pointer - HPD Software Ltd.
Email:   sam.pointer at hpdsoftware.com

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