> > > On Mon, 1 Sep 2003, Shane Hollis wrote: > > > > The DNs is a semi heiracrchical system from my understanding. The > > > > master DNS ( to use a phrase loosely) are based in the states. My > > > > provider in the states is on the main backbone. Therefore changes get > > > > sent out much more rapidly and from a centrally located place, not > > > > from a little backwater like NZ. > > > > > > > > If I change a DNS here in NZ, it is like injecting an agent into tip > > > > of a whales tail. It takes along time to propogate through the > > > > system. If I inject into the heart it is sent out a lot more quickly > > > > and spreads like a ripple from the centre of the pond, not from the > > > > edge. (some very mixed similes here). > > > > > > That's not how the DNS works. > > > > > > The DNS is organised as a heirachy purely for the purpose of splitting > > > out where answers come from into seperate entities, so that there is no > > > single central set of servers who are responsible for "all" answers. > > > > > > The root servers only know about domain names which are at the global > > > level, and that knowledge is limited to where to find answers. The > > > servers they point to have knowledge about the deeper parts of the DNS, > > > and in turn may point to other servers which inturn know more about > > > even deeper parts. > > >.... > > > I've simplified it, because the queries are not exactly that, but the > > > net effect is the same: We keep looking for an authorative server > > > deeper and deeper into the name. > > > > > > Now, the problem with this system is it takes a while (not long, > > > seconds, but long enough) and that it involves a lot of queries and > > > network traffic as a result. So the answers given are _cached_, which > > > means you get answers quicker, and there's less traffic which means the > > > 'net will actually function. :) > > >...> > > > Thus, how long it takes for a change to propogate has nothing to do > > > with the depth in the tree, it depends on what parts of the answer are > > > cached, and how long they are cached for. > > > > Which is what I was pointing at with my whale analogy ... the more > > authorative or better connected a server the more DNS servers it has > > asking it for changes to information. A little server asks a bigger > > server which asks a bigger server and so on. There is no ultimate server > > for DNS but the better connected and more central a server is the better > > it is for propogating changes.... If there are two little servers, say > > one on my desk and one on your desk and they are both connected to the > > same ISP.... If I change a dns entry on my desk when your server goes to > > ask for changes it wont ask mine, it wil ask the ISP's server. > > no it won't it will ask [a-m].root-servers.net, who will refer it to the > authoritative server for the top level of your domain, and so on down > the chain. > > It will only ask your isp if it is set up to be a caching-only dns > server (which is really only a proxy) (ie a dns server that only queries > one up the chain, the isp's server will then query In New zealand there are an awful lot of businesses who run an internal DNS system that then checks against the ISP. That then gets more complicated when you have buisnesses that are multi national and their servers run in several countries simultaenously. Many sites I have seen have their DNS on their servers looking up from ISP's so that the data only flows between the client and the ISP. this kills an aweful lot of network load across international lines.
Also, I would be surprised if every time a TTL expired or similar that the query always went over seas. Can you imagine what would happen with 100's of millions of people watching a sporting event like the olympics in AU or similar? The international lines would be jammed with requests all over the place. It is more likely the lookups would be handled in country via caching. I have a client who has servers in UK, USA, NZ, AU and Asia. The mail servers are in a replicating cluster. The company is running in a heirarchical structure for naming where the country authority is below the company in the structure e.g. CompanyName/CountryName/City/Office/Person or machine. In some systems countries are not the top most level for networking ... for TCP/IP yes, for other structures no!!. Now these companies will rely on a series of DNs servers to keep things straight. These servers are not always in the same country but may be used across countrys. Do you start to see the problem?This is a very legitimate way to do things to keep internal DNS settings straight and to handle replication as well as DHCP and other problems in a multi national, multi site but homogenous distributed network. Shane Hollis Notes Unlimited New Zealand Ph: 021 465 547 Email: [EMAIL PROTECTED]
