Re: Information & Power /Alexandria library

Alejandro Dubrovsky (
Tue, 4 May 1999 02:21:03 +1000 (GMT+1000)

On Sun, 2 May 1999, Michael S. Lorrey wrote:

> Ross A. Finlayson wrote:
> >
> > The biggest threat to the entirety of regular Internet WWW functionality is DNS,
> > in terms of global connectivity, although any size of DNS names might be cached
> > anywhere.
> The entire DNS database is updated regularly on every web server at
> every ISP, so there is not threat to its being destroyed. Thats why they
> are called name servers. When you request a page from a site, your ISP's
> webserver looks up the DNS and its corresponding IP address, then
> queries the network for the data from that IP address. The routers take
> that query and send it to the next closer router, etc. The system does
> not query network solutions' registry every time.

Each DNS at each ISP holds a minuscule share of the entire database, most definitely not the entire database. It can cache requests that go through it but that only for a short time (usually one hour) and only of the request done on it. A DNS usually only holds the IP table for whatever domains it is acting as a master or as a secondary for, and usually you only have two servers knowing the IPs for a subdomain. Whatever ISP you are using does not have a clue what IP corresponds to but the root servers know who the dns master for is (, who still doesn't know the ip but it knows that the master dns for is, and so on. This system enables each dns to respond quickly to name lookups since they only have to hold a couple of name to ip matchings but it does mean that it is fragile. If the 7 or 8 root servers were taken down all cross domain lookups (eg from .edu to .com, or from .gov to .uk) would fail after the corresponding caches expire (1 to 3 hours). chau
Alejandro Dubrovsky