Re: [Nolug] ISP failover w/DNS

I kind of figured that was the case, as I've never seen a failover router
that didn't have a built in forwarder. But in the case where you didn't
have any other option, I was thinking the first way to list the DNS servers
would probably give you the least amount of delay at least. Like I said,
purely hypothetical, though. You're probably right though, I bet every
router that does failover does this already.

On Sat, May 14, 2011 at 1:38 PM, John Souvestre <johns@sstar.com> wrote:

> Hi Chris.
>
>
>
> Any time you reference a DNS resolver that you can’t reach you will
> experience a delay before trying the next DNS resolver in the list. You
> want to avoid this situation!
>
>
>
> Any router you use should for a load balancing or failover function should
> have at least a DNS forwarder built in. Furthermore, when the external DNS
> resolvers are defined in it, they should be per input feed. Thus the router
> knows which external DNS resolvers to use based on which line(s) is up.
>
>
>
> Regards,
>
>
>
> John
>
> John Souvestre - New Orleans LA - (504) 454-0899
>
>
>
> *From:* owner-nolug@stoney.kellynet.org [mailto:
> owner-nolug@stoney.kellynet.org] *On Behalf Of *Chris Jones
> *Sent:* Saturday, May 14, 2011 1:28 pm
> *To:* nolug@nolug.org
> *Subject:* [Nolug] ISP failover w/DNS
>
>
>
> I was thinking about a project I'm working on for a client of mine.
> They're going to have 2 ISP's piped into their network, and use a router
> that does failover. I probably won't even need to do this in my case, but I
> was just thinking if setting up dual internet w/ failover becomes more
> common, this is a situation that could easily be encountered. Most of my
> clients that would ever want internet redundancy probably have their own DNS
> server anyways. :) I know some of you guys work for ISP's, and there are
> even a couple of CCNP's on here I believe. I consider myself very
> knowledgeable about TCP/IP, but probably nothing like what you have to know
> to get a CCNP or CCIE. (actually, CCNA/CCNP is probably what I should work
> on next)
>
> The thing I was thinking about, is if you have 2 ISP's, each one has their
> own DNS servers. Let's hypothetically say the ISP's are Cox and AT&T (they
> aren't actually, for geographical reasons), and each ISP has 2 DNS servers.
> Set Cox as the primary ISP, and if that goes down, it fails over to the
> slower AT&T line. If you set the computers behind the firewall to Cox's DNS
> servers, when it fails over to AT&T, it will probably lose access to Cox's
> DNS servers. So, what would be the "best practices" way to combine the two
> sets of DNS servers on a network? Obviously most operating systems will let
> you put even more than 2 DNS servers, so you can just list them all, which
> is probably fine to do if the router doesn't have its own built in DNS
> forwarder. (so you could set the PC's to just use 192.168.1.1 as their DNS,
> and the router will route the DNS requests on its own)
>
> But, what order should you do it for best performance and reliability? I'm
> thinking one of two orders:
>
> Order #1:
> Cox DNS 1
> AT&T DNS 1
> Cox DNS 2
> AT&T DNS 2
>
> Order #2:
> Cox DNS 1
> Cox DNS 2
> AT&T DNS 1
> AT&T DNS 2
>
>
>

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Received on 05/14/11