DNS Server Specification

Jim Reid jim at rfc1035.com
Thu Oct 26 23:00:53 UTC 2000


>>>>> ">" == 9Nine9  <null at void.net> writes:

    >> Does anyone have any suggestions or know of documentation that
    >> describes the hardware specifications for a machine running
    >> BIND under a given load?

    >> I have about 300 users browsing the internet whose requests
    >> will be cached and forwarded by BIND, mail server(s) for these
    >> users, and a 1000 hit per day webserver, and maybe e-com in the
    >> future.

    >> Any suggestions?  I'm tight on hardware right now but I'm
    >> thinking of using a 250 MHz alpha.  Will it be adequate??

It depends. How much memory does it have? How much of that can the
name server use? What sort of query rate will your server get? Will
your box be running other (resource-hungry) applications? Will the
server be using DNSSEC and digitally signing its DNS data? How long's
this piece of string in my hand?

As a general rule, DNS is not CPU intensive. CPU only becomes a factor
when the name server is under very high loads: say several hundred
queries per second or more. few servers get that sort of load: they're
generally run by people who have been in the business of Big DNS for a
long time. Tens of queries/second could be a problem for a CPU if
DNSSEC is involved and crypto has to be used to validate every query
and answer.

Name servers like to use RAM. They also want to have all their address
space resident: faulting in pages of cache from disk for DNS lookups
are bad news. The amount of RAM depends on the number of different
names your users lookup, how often they do that and how long those
names get cached for. Usually the size of the name server's cache
stabilises after 1-2 weeks running. DNS data tends to have cache TTL
values of 1-2 weeks at most. If your name server is serving zones, a
rough rule of thumb is 1 Kb of data for each zone{} statement plus 100
bytes for every resource record in the zone. More RAM will be needed
on top of this for the non-local names that your local users and
applications lookup in the DNS.



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