Tally wrote:
>
> 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....
> Please let me know your views on the implementation
> of round robin dns. also any other info would be
> greatly welcome at this time.
I was under the impression that this was fairly standard.
>From DNS and BIND (3rd edition):
Name servers released since BIND 4.9 have formalized
some load-sharing functionality that has existed in
patches to BIND for sometime. Bryan Beecher wrote
patches to BIND 4.8.3 to implement what he called
"shuffle address records." Thse were address records
of a special type that the name server rotated between
responses. For example, if the domain name foo.bar.baz
had three "shuffled" IP addresses, 192.1.1.1, 192.1.1.2,
and 192.1.1.3, an appropriately patched named server
would give them out first in the order:
192.1.1.1 192.1.1.2 192.1.1.3
then in the order:
192.1.1.2 192.1.1.3 192.1.1.1
and then in the order:
192.1.1.3 192.1.1.1 192.1.1.2
before starting over again with the first order, and
repeating the rotation ad infinitum.
...
BIND 4.9 and later versions do away with the shuffle address
record as a separate record type, subject to special handling.
Instead, a modern name server rotates addresses for any
domain name that has more than one A record. ... The BIND
documentation calls this process round robin.
...
Note that this is really load sharing, not load balancing,
since the name server gives out the addresses in a completely
deterministic way, without regard to the actual load or
capacity of the servers servicing the requests.
Eric Johnson
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