Distributing DNS load via DHCP
dhcp1 at thehobsons.co.uk
Fri Dec 16 18:03:33 UTC 2011
Jeff Wieland wrote:
>We have a fairly large pool of address, and we'd like to distribute
>the DNS load on this pool between two DNS servers.
How about just :
range 192.168.128.11 192.168.77.254;
option domain-name-servers 192.168.1.6, 192.168.1.5;
range 192.168.78.1 192.168.143.254;
option domain-name-servers 192.168.1.5, 192.168.1.6;
In the long term, once all addresses have been used one then the
distribution of leases between pools will be more or less random. In
the short term, you could make whichever pool gets used first*
smaller until it's full and devices have been forced into the other
pool - and then enlarge the pool a bit until both are at full size.
* In 3.x and below, unused addresses were used "top down" (ie highest
address first) due to the way the internal hashing worked. It looks
like 4.x does it bottom up.
However, I'm not sure this will entirely achieve what you want. For
example, if one of the DNS servers goes down for any reason, then I
believe some (all ?) versions of Windows will put the "dead" server
to the bottom of it's query order - and leave it there indefinitely
(ie until one of the other servers goes down). At my last job, I know
some of my colleagues in other divisions were using this trick to
have clients query an internal server before going external - which
broke the first time the internal server went down.
And on that note, some clients will query all the servers anyway for
non-resolving addresses. What my colleagues were doing was to have an
internal server which resolved internal domains. If that failed to
give an answer, then the Windows client would try the next server (an
external one) which resolved external addresses.
If that is still how they work, then your clients would query one
server, get nxdomain response, and then query the other for the same
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