Help! I''m a newbie...

Re: Help! I''m a newbie...

From:

Date:

Time:

On 05/02/01 at 16:29, andrew wrote:

> > Is there any tried and true method of knowing exactly when this will
> > switch over so that I know everything is working from the moment the
> > IP switch happens on Network Solutions? How do I know when it has
> > happened?
>
> No, because routers, proxy servers and other switching equipment around the
> internet "cache" (store) the IP addresses of webservers so they don't have
> to ask your nameserver "where" the webserver is every time someone types
> "xyz.com" into their browser.

No. It is resolvers that cache DNS information. Resolvers are software
programs that use the domain name system (DNS) to translate domain names to IP
addresses. Routers and switching equipment do not use domain names, they use
only the numeric addresses of networked machines (IP, ethernet addresses,
etc.) and therefore do not need to know anything about DNS. It's generally
computers that have human interfaces (workstations, etc.) that need to be able
to translate domain names to IP address, since domain names are simply a
convenient way for people to think about such things. It's the resolvers that
you need to consider when talking about DNS caching issues

> You can tell these machines not to remember this information and ask you
> more frequently, which is a good idea to do about 2 weeks before you switch
> the IPs over, but not every machine will obey your wishes. You do this by
> adjusting the "TTL" value (time to live) in the domain information (either
> for a specific machine address or for the domain as a whole). Setting a
> lower value forces (or at least tries to force) the other machine caching
> your information to re-query your nameserver more frequently.
>
> You only want to set lower TTL values before moving the site or server, and
> then return them to their default values afterwards, or your DNS will become
> bogged down answering "where are you" queries all day long.

When and how you adjust TTLs in advance of making a DNS change depends on the
current TTLs of the records you're changing. Two weeks might be a reasonable
period, or it might be longer than necessary. You don't really need to change
the TTLs until [the current TTL of a record] plus [the Refresh value of its
zone] before you change the record. So if a record has an 86400 second TTL
(one day) and its zone has an 86400 second Refresh, you would shorten the TTL
two days before you make your change in order to be certain that all resolvers
on the 'net have picked up the shortened TTL (ignoring 'broken' resolvers that
incorrectly ignore TTLs).

> The default TTL for a domain is 86400 seconds (one day). You can reduce this
> to 14000 (four hours) a week before you move the DNS and webserver, and then
> there will be minimal interruption in your service. In my experience there's
> a lot of "bad" proxies and cache servers that ignore TTL settings take that
> long to refresh their cache.

There is no universal 'default' TTL value. Each zone has a default TTL (the
'Minimum' value in the zone's SOA record) for records that do not have
explicit TTLs, but there is no set 'default' value for it. 86400 seconds is
quite common, but TTLs and Minimums can be set to anything you think is
reasonable for a given record and/or zone.

> > P.S. What is a BIND?
>
> BIND (Berkeley Internet Name Domain) is a methodology by which domains are
> defined.

No. The 'D' stands for 'Daemon'. A daemon is a Unix program that runs in the
background, not attached to any terminal session. Daemons are typically
servers of various kinds, including name servers. BIND is not a methodology,
it is a specific name server program developed at Berkely Systems (the folks
who developed BSD Unix). It's sort of the granddaddy of name servers and it's
the most widely used name server on the 'net, so the way it does things is
more or less a de facto standard for the way that name servers are run. The
'methodology' of DNS is defined by various RFCs (Requests for Comments), as is
the case for most internet protocols. See <http://www.faqs.org/rfcs/> for a
comprehensive look at the RFCs.

> There is a BIND Server that's freely distributed but only runs on
> UNIX or NT in emulation, but QuickDNS is world's easier to configure. If you
> want to step backwards 10 years (or a millenium in internet-time) go to
> http://www.isc.org/products/BIND/ and start reading about it.

Again, that would be _the_ BIND name server.

Christopher Bort

Sales:
888/4-DPOINT

Support:
858/452-3696