[Discuss] selecting a subnet

[invalid at pizzashack.org (Derek Martin)]

On Wed, Sep 10, 2014 at 04:04:12PM -0400, Stephen Adler wrote:
> I'm setting up a small network at work behind my own firewall. Typically
> I would use a 192.168.1.0/24 network but I'm afraid the IT people at
> work have used that for something in my work LAN environment. 

NEVER DO THIS.

Let's be clear here.  If you do not communicate with your IT people
and get them to give you a sanctioned subnet, and ideally get them to
firewall you off, creating your test network on randomly selected CIDR
blocks based on some pings or other simplistic method risks:

 - The IPs you tried were assigned but down, because the user(s) using
   them had turned off their PC, leading to IP conflicts.
 - The IPs you selected were actually unused but will be later
   allocated to someone else, leading to IP conflicts.
 - The traffic from your test subnet could inadvertently flood the
   production network, if your testing goes awry or your firewall is
   misconfigured, even if there are NO IP conflicts.
 - When any of the above happen, fixing the situation may take far too
   long, because the people that need to do the investigation (the IT
   people) will not have a clue what you did.

I've had to deal with all of these problems in the past, and it's fun
for absolutely no one.  All of these can interfere with the work that
some, if not all, of the other people on your network are trying to
do.  If that happens, you don't want it to be your fault.  Let them
decide how to do it so it can be theirs (and so they can have a much
better shot of figuring out how to fix it--quickly--if it does happen).

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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