Hello,
>is it also implemented by the microsoft's DNS version
>as well ?
Don't know.
>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 ?
Correct. Try $> nslookup snap.com . You get:
206.132.166.65, 206.132.166.66, 206.132.166.61,
206.132.166.62 206.132.166.63, 206.132.166.64
This may not be round robin'd, but that's what you get
when you lookup a name that is round robin'd.
>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....
NO! It has no relation to the application making the
request. Each request would(ideally) receive a
different address, but it depends on the TTL you specify
for the A records (see below):
When setting up a round robin scheme (on Unix, at least)
you need to give a TTL for each A record that is very
small. Basically, this tells the server to shuffle the
record often(ideally, every lookup gets a different
address) Here's how I set up the DNS entries (BIND 8):
www.foo.com. 1 IN A 192.168.0.1
www.foo.com. 1 IN A 192.168.0.2
www.foo.com. 1 IN A 192.168.0.3
www.foo.com. 1 IN A 192.168.0.4
Then, in the reverse lookup file:
1.0.168.192.in-addr.arpa. IN PTR www.foo.com.
2.0.168.192.in-addr.arpa. IN PTR www.foo.com.
3.0.168.192.in-addr.arpa. IN PTR www.foo.com.
4.0.168.192.in-addr.arpa. IN PTR www.foo.com.
The TTL of 1 sec in the A record portion basically
changes the returned address every second. This also
seems to work with BIND4.9, and BIND4.83 has some patch
that can be applied to get this to work.
The order in which you get addresses in response to
successive requests (i.e. ping www.foo.com) seems to be
random, you don't get .1 then .2 then .3 then .4 .
To get a simple overview, there is one page(p. 285 I
think) to look at in the O'Reilly book DNS & BIND by
Paul Albitz and Cricket Lui.
Good Luck,
-Vance
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