Re: [Sheflug] Re: My First Post - Connecting Linux to the Internet

["Chris J/#6" <nospam [at] nccnet.co.uk>]

> I doesn't necessarily have to be the
> DNS of your ISP, anyone will do. You just need to find a DNS out there on
> the internet that can resolve names into machine addresses for you; once
> you've found one if it can't resolve a name for you it passes it on to the
> next one.
> 
> In Windows if you open up a DOS Prompt (while connected to the internet) and
> type ping www.yahoo.com you'll get something like this back:
> 
> Pinging www.yahoo.akadns.net [216.32.74.51] with 32
> 
> Reply from 216.32.74.51: bytes=32 time=266ms TTL=240
> Reply from 216.32.74.51: bytes=32 time=275ms TTL=240
> Reply from 216.32.74.51: bytes=32 time=255ms TTL=240
> Reply from 216.32.74.51: bytes=32 time=255ms TTL=240
> 
> It's a good chance that 216.32.74.51 will act a DNS for your configuration.
> 

This is actaully a bad thing to do in general, though it may work, it 
shouldn't really be used.

1. The owner of www.yahoo.akadns.net may, depending on what the machine is, 
bar you from connecting to the machine and moan at your ISP (reason: abuse of 
remote machine due to unauthorised use).

2. Unless its advertised as a DNS box, then the owner of the machine is free 
to disable DNS, or access to DNS on the box, leaving you helpless until you 
find a new server to hook into.

3. Do you really want a small DNS query to bounce all the way over the 
atlantic? Wastes traffic and bandwidth. It also means responses will be slow 
and subject to remote network status (ie, is the router down) outside control 
of your ISP.

4. Can you gurantee the remote server's data is accurate? If its not a 
designated name server, then data could be old, have a poisoned cache, or 
contain data pertaining to the remote network which may or may not cause a 
conflict with an internet host, yet is perfectly valid for the remote network 
(due to design of that network).

What you should really do is phone your ISP and use their DNS servers...if 
the customer support bods can't provide you with that basic information, then 
move ISP. The alternative is to run a local caching name server, either with 
bind or tinydns, that will do the querying for you...if you do this, remember 
to keep root cache up to date (not that it changes much...one every couple of 
years or so).

So unless you know better, don't rely on picking an arbitry DNS.

Just to make a point, www.yahoo.akadns.net has five different IP addresses, 
and isn't responding to name requests. :) *One* of those five *may* have a 
DNS accessible DNS server, but if a host is aliased to five IP's, do you 
really want to use it as a server? That spread of IP range allows for crude 
load balancing, so what if .51 goes down? It won't affect the service Yahoo 
is providing (portal and web search), but it'll knacker up your ability to 
use the web.

Chris...

-- 
Chris Johnson            \  "If not for me then, do it for yourself. If not
sixie@nccnet.co.uk        \  for then do it for the world." -- Stevie Nicks
www.nccnet.co.uk/~sixie/   ~---------------------------------------+
Redclaw chat - http://redclaw.org.uk - telnet redclaw.org.uk 2000   \______


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