We use sortlists quite effectively, but there are some caveats to that approach:
1) If you have clients using "rogue" resolvers without any sortlist
definitions, that will limit the effectiveness of the technique somewhat
2) You need some discipline to keep the sortlist definitions up-to-date as
networks/subnets are renumbered, re-assigned, etc. If you have many
nameservers, it helps to have a centralized/co-ordinated mechanism to
maintain/propagate your nameserver configs (we use Infoblox, for instance)
3) Sortlisting is never a 100% solution and should not be used for applications
which treat connecting to the "wrong" IP (rarely, occasionally) as a *fatal*
error. At the very least, if the app tries to connect to a "wrong" IP, and is
not able to do so (because of routing, firewall rules, ACLs, etc.) it should
fail over in a timely fashion to the next IP in the list. It shouldn't just die.
- Kevin
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Niall O'Reilly
Sent: Monday, January 05, 2015 7:03 AM
To: Christian Kette
Cc: [email protected]; Jeremy C. Reed
Subject: Re: BIND9 Return different IP address based on subnet
At Sat, 3 Jan 2015 19:24:47 +0100,
Christian Kette wrote:
>
> I have found a workaround.
> I defined a different zone for every network
A simpler solution might be to use a sortlist.
From the ARM:
6.2.16.13 The sortlist Statement
The response to a DNS query may consist of multiple resource records
(RRs) forming a resource records set (RRset). The name server will normally
return the RRs within the RRset in an indeterminate order (but see the
rrset-order statement in Section 6.2.16.14). The client resolver code should
rearrange the RRs as appropriate, that is, using any addresses on the local net
in preference to other addresses. However, not all resolvers can do this or are
correctly configured. When a client is using a local server, the sorting can be
performed in the server, based on the client’s address. This only requires
configuring the name servers, not all the clients.
Niall
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