order of address-records

[Mathias Körber]

> Hi folks,
>=20
> I entered two different address-records for a domins in BIND8. Works =
fine;
> when looking up this domain I get two answers. This means, when one of =
the
> servers is not available, the other one will be taken, right ?
> Okay, when now a browser asks for this domain, he will also get this =
two
> answers (won't he ?)
> Which one will he choose for connecting ? The first one, the=20
> second one, or
> is this decision made by random ?

Normally, the nameserver will return the two records in a round-robin
fashion, ie in one query it will use one first, in the next the other.
As this is also done by the resolving/caching server your client =
(browser)
uses for DNS lookups (unless specifically disabled), it is impossible to =
stop
this at the authoritative server side.

A client should use the addresses in the order they are returned, ie try =
the first
one, and if that fails fall back to the next one and so on.

> In case he will take the first (or last) one, how can I influence=20
> which one
> he will take ?
> The "main" server should be taken first, and only if this one is not
> reachable (or the net-route to this server is overloaded) the other =
server
> should be taken.

Currently this is not really feasible, as the client's local nameserver =
may have turned
round-robin on even if your authoritative servers have not (there is no =
feature in
the DNs protocol telling the querying nameserver that the sequence is =
important, so
it applies it local policy which usually is round-robin).
If you control both the authoritative server and all the =
local/resolving/caching nameservers
that matter to you (ie if this is for in-house use only) you may be able =
to turn round-robin off on
all these servers and get the desired effect.

In future yu will be able to do something like that with SRV records, =
which will have means
to express priority or preference.

There are other means of achieving the desired effect, by putting in =
local-director-style
devices etc which relay the traffic to the servers in any desired =
pattern, but these
rely on means other than the DNS to do what you want.

HTH HAHNY

> Any ideas ?
>=20
> TIA
>=20
> --- Stephan
>=20
>=20
>=20
>=20