I have heard that the NT nameserver code does round-robin, but have no
experience running dns on NT. Microsoft claims to do their entire Internet
presence using NT servers, so I decided to query their nameserver:
> nslookup microsoft.com dns1.microsoft.com
Server: dns1.microsoft.com
Address: 131.107.1.7
Name: microsoft.com
Addresses: 207.46.130.14, 207.46.130.149, 207.46.130.150, 207.46.131.137
207.46.131.28, 207.46.131.30
> nslookup microsoft.com dns1.microsoft.com
Server: dns1.microsoft.com
Address: 131.107.1.7
Name: microsoft.com
Addresses: 207.46.130.149, 207.46.130.150, 207.46.131.137, 207.46.131.28
207.46.131.30, 207.46.130.14
Yep, that's what round-robin looks like. A dns query of a name will cause all
of the addresses associated with that name to be returned by the nameserver; a
subsequent query will cause the same addresses to be returned, but in a
different order. The application that made the query will try using the first
address in the response. There is essentially only one form of query to a
nameserver - nslookup and resolvers (a query from an application such as a web
browser is sent to the local machine's resolver - gethostbyname) both get the
same answer from the nameserver.
While round-robin is useful for load sharing, in no way can it be considered
"load balancing". It dumbly hands out the addresses regardless of the actual
load on any of the machines.
And it has only a weak capability in providing redundancy. It will hand out the
address first of a dead machine (if it's that address' turn). But some client
applications, if they get no response from the first address, will try the
second (and some apps won't).
Tony Rall
Tally <[EMAIL PROTECTED]> on 10/22/1999 15:24:10
I was browsing the archives of this list for more
info on Round Robin DNS. From the discussion
and further reading of whatever I could gather
it seems that Round Robin is implemented by BIND.
is it also implemented by the microsoft's DNS
version
as well ?
also if I were to a nslookup for www.domain.com
then this would give me a list of IP addresses that
a named.hosts file (as in a typical unix DNS box)
would have. correct ? however if an appliation such
as a HTTP request would make to a web server,
then it would just return one IP address from the
whole lot, ie it would implement the "round robin
method of dns".... correct ?
if this correct then, it would mean that BIND
returns
DNS query answers depending upon the appliation
requesting a dns query... is this correct ? i guess
this is so....
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