On 12/20/2011 1:22 PM, Matus UHLAR - fantomas wrote:
On 20.12.11 19:37, Martin T wrote:
I have seen setups where one domain name has two address records.
First IP address is in the ISP-A network and the other one is in the
ISP-B network. In case I execute "host www.<domainname>.com", I always
get two IP addresses as a reply and they always appear by turns. Am I
correct, that setup like this provides redundancy as well as
load-balancing?
Kind of. It's much better to have real load-balancing and vailover by
multiple links or L3 load balancers.
Is there some common method in BIND to give out IP
addresses by turns? Last but not least, how do application layer(for
example www, ssh) handle such setup?
bind usually gives all possible addresses for a name in random order.
You can affect this a bit by using "sortlist" statement, where you can
tell BIND which address to prefer for which client (and, intermediate
server may re-sort according to its knowledge)
Just be aware, Wintel clients often choose addresses
out-of-received-sequence according to their notion of "subnet
prioritization" (older OSes) and/or RFC 3484 logic (newer ones), thus
effectively overriding any sortlisting you do on the BIND side.
- Kevin
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