Can forwarders list really work?

Kevin Darcy kcd at daimlerchrysler.com
Wed Jan 10 23:00:28 UTC 2001


I think parallel forwarding would be messy and wasteful. A better solution
would be to use forwarders *adaptively*, based on how quickly they answer. By
extension, this means a non-responsive forwarder would soon get "penalized" and
used hardly at all. In addition to load-balancing, therefore, it also offers a
"soft" form of failover. BIND 8.2.3, still in beta, supposedly implements this
logic.

Why are you using forwarding at all? If you have full Internet connectivity,
you may be better off just running your own caching server. Are you doing it
for performance or because you don't have full Internet connectivity? If for
performance, try just using a caching-only server temporarily and measure the
results. You might find that it performs just as well (or even better! because
you're eliminating a forwarding "hop" for at least some queries) without the
additional complication and points of failure associated with forwarding. Even
if forwarding performs better under normal circumstances, if you have full
Internet connectivity you may wish to change that "forward only" to "forward
first". This will allow you to resolve Internet names even if both sets of
ISP's nameservers are down or unavailable.


- Kevin

Igor Shabaltas wrote:

> Hi Folks,
>
> There is a network with two internet connections: to ISP-1 and to ISP-2.
> There are three name servers (Bind-8.2.2p7) - one 'internal' and two
> 'external'.
> Internal DNS server (IP 10.x.x.x) has next options:
> ...
> forward only;
> forwarders { isp.1.sub.ip; isp.2.sub.ip; };
> ...
>
> Where:
> isp.1.sub.ip - real IP address of DNS server in subnetwork connected to
> ISP-1
> isp.2.sub.ip - real IP address of DNS server in subnetwork connected to
> ISP-2
>
> All requests from internal network are going to internal DNS server.
> The aim: when any one connection to internet is down, DNS requests will be
> resolved succesfully through other one.
>
> Good idea?
> What we have in reality?
>
> If ISP-2 is down all still work perfectly.
> If ISP-1 is down you can resolve your request, but it takes a long time. As
> a rule you need to make three or four requests to get correct answer.
> So, only first IP in forwarders list is actually useful.
>
> How is it possible to deside this  problem and make this scheme alive?
>
> May be in the next versions of Bind we can have an option like 'forward only
> parallel'  to make the parallel requests to all forwarders at the same time?
> Why not? :-)
> Or is it just my fault and I forgot to include some options? Help!
>
> Any suggestions, comments?
>
> Thanks in advance,
> --
> Igor Shabaltas






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