Re: Win2k3 DNS

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Date: Wed, 1 Sep 2004 23:13:01 +0100

In message <c1.01.2sT7q9$5AJ@J.de.Boyne.Pollard.localhost>, Jonathan de
Boyne Pollard <J.deBoynePollard@Tesco.NET> writes

>TL> This is indeed the case. I suppose the issue on whether to forward or
>TL> not depends on your bandwidth and where you're going to.
>
>It depends from more than that.

First - good catch, I was being over simplistic.

> The choice between having a forwarding and having a resolving proxy
>DNS server involves such decision criteria as the proximity of one's
>own proxy DNS server to the rest of Internet; the cost, size, and usage
>of the link between one and one's ISP; the DNS namespace that the
>forwardee presents; the security of the forwardee; and the shape of
>hole that one is capable of knocking into one's firewall.

Indeed. Design of the DNS service does depend on those items.
Ultimately, though, it's all down to your "bandwidth", in the wider
sense of the word. In the UK, we're close to a main root server, my main
ISP's DNS server seems very quick, and fast and relatively full. Same at
my other ISP.

>TL> And if your ISP's DNS is even close to being reasonable, it's
>TL> cache is up to date.
>
>If "up to date" means "populated with relevant information", then this
>is false. _Entirely reasonable_ caching proxy DNS servers can, if the
>user population exceeds a critical threshold size, end up *not* holding
>relevant information in their caches, when the size of the combined
>"working set" sizes of the queries issued by all of the individual
>customers exceeds the size alloted to the cache. Thrashing thus commences.

An 'unreasonable' service, IMHO. But point taken.

>TL> No, you don't have to forward, but I suspect most smaller users
>TL> probably would benefit from this. Don't you agree?
>
>Yes, I do not. I, as a customer of my ISP, don't use forwarding in
>part because my ISP's proxy DNS servers are chronically unreliable. I
>regularly read reports from other customers, in my ISP's private
>newsgroups, of DNS problems, that I simply don't experience because I
>am using my own resolving proxy DNS server rather than the proxy DNS
>servers provided by my ISP.

True - experience varies by ISP.

>Ironically, it is not the size of the customer that matters. It is the
>size of the ISP. ISPs with large numbers of customers are likely to
>see a very low locality of reference in the queries sent to their proxy
>DNS servers, whereas ISPs with small numbers of customers are likely to
>see a higher locality of reference.

Indeed.

It's clearly important that you investigate all aspects of an ISPs
service. At the end of the day, you end up balancing a bunch of factors:
cost, speed, transit speed, quality of service, nntp/ftp/smtp/pop3
services, etc.

> ISPs encourage their customers to use their caching proxy servers
>primarily for _their own_ benefits.

ALL ISPs try to optimise services for their own benefits. :-)

Thanks for adding some good detail to the details of what to look for. I
must get around to writing this up for www.reskit.net/dns.

Thomas

-- 
Thomas Lee  doctordns@gmail.com

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