Re: Information & Power /Alexandria library
Alejandro Dubrovsky (s335984@student.uq.edu.au)
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
s335984.student.uq.edu.au but the root servers know who the dns master for
edu.au is (munnari.oz.au), who still doesn't know the ip but it knows that
the master dns for uq.edu.au is krefti.uq.edu.au, 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