[thelist] DNS caching? Tips to override, refresh DNS?

genghis at members.evolt.org genghis at members.evolt.org
Thu Feb 22 06:15:14 CST 2001


> -----Original Message-----
> From: thelist-admin at lists.evolt.org
> [mailto:thelist-admin at lists.evolt.org]On Behalf Of Daniel J. Cody
> Sent: 21 February 2001 21:45
> To: thelist at lists.evolt.org
> Subject: Re: [thelist] DNS caching? Tips to override, refresh DNS?
> 
> 
> Hey Joe -
> 
> Welcome to one of the most frustrating and common problems on the 
> internet today :)
> 

Well, that knocks my tip from last week into a cocked
hat (all hail Dan), but there's a couple more things 
to add here...

1	ISPs use DNS caching too.  Whilst that's OK
	most of the time (web sites in particular
	usually move at the right speed), the real
	bastard with caching is the domain's MX records.
	Despite the record (and the cached copy thereof)
	holding a specific TTL (time to live) value,
	it can take forever for ISPs to flush their
	caches for mail routing.

	Example: we changed the name servers for 
	a client of ours in January, and altered none
	of the values in any of the records.  The
	UK's biggest ISP and Hotmail *still* won't
	route mail to them.

2	Actually i'm going to put this one in as a tip.

<tip type="DNS">
Some DNS servers will let you use some of
the more advanced switches available to
nslookup, and some deny non-local use.
If you know that a DNS server is reporting
incorrectly, and if the server will let
you do it, type

ls -d mydomain.com

at the prompt.  This command lists _all_ data
attached to a domain, including things like
SOA and NS records.  It's useful because
the chances are that the server doesn't have
*every* record for your domain in the cache.
Therefore in order to fulfil the request,
the server has to retrieve your details anew,
flushing out its incorrect elderly information
in the process.
</tip>

------------------------------------------
John Handelaar

T +44 20 7209 4117       M +44 7930 681789
F +44 870 169 7657   E john at userfrenzy.com
------------------------------------------




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