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fedora-users: Re: doc question on private network IP allocation

Re: doc question on private network IP allocation

From: Tim <ignored_mailbox_at_nospam>
Date: Fri Oct 14 2011 - 15:02:47 GMT
To: Community support for Fedora users <users@lists.fedoraproject.org>

On Fri, 2011-10-14 at 00:59 -0700, Paul Allen Newell wrote:

> A long time ago when I first struggled and figured out how to set up a
> LAN network, I got some advice about how I should alloc the numbers. 1)
> start static address at *.*.*.10, 2) put WAPs at *.*.*.245, and 3) for a
> gateway of 192.168.1.1, assign your router that connects to the 3rd
> party (Verizon) to be 192.168.2.2.
>
> I have never really found documentation to support such, but my network
> behaves nicely so I don't argue.

Out of the various IP ranges [1] that are available for private use,
because they are not, and will not, be used as public IPs on the
internet, there are really only two addresses in each block with special
meanings: The ones that *END* with 0 or 255. You should not try to use
those addresses *for* equipment, they used for things like broadcasting
(e.g. sending traffic to that IP will be sent to all IPs on the LAN),
and wildcarding (e.g. firewall rules will be applied to all IPs in that
range).

1. 10.0.0.0 to 10.255.255.255
   169.254.0.0 to 169.254.255.255
   172.16.0.0 to 172.31.255.255
   192.168.0.0 to 192.168.255.255

   See http://en.wikipedia.org/wiki/Private_network
   and http://en.wikipedia.org/wiki/Link-local_address
   for some details about those ranges

It's common practice to use an address ending with 254 for routers and
gateway, but it's purely customary. The address is not treated
differently by any equipment, than any other address. Before home
routers became commonplace, it was customary for the first computer on
the network to be the gateway, and it's address usually ended with 1.
It's merely handy for people who might have to type addresses in, to
pick one of the ones at the end of the range, rather than try to
remember which other address was used.

As for how to allocate IPs within a LAN, that's up to you. Some people
have all IPs in the range, that they're using, available for use. Some
people just use a small section of the range. They may let IPs ending
in 1 to 100 be used for dynamic addresses (e.g. DHCP clients), and leave
the rest for static addresses (e.g. network servers). Some people put
clients into the network starting from the 1 end of the range, with
incrementing numbers, and servers into the network from the 254 end of
the range, using decrementing numbers.

If the users aren't doing machine to machine stuff, then they probably
don't care what the IPs are, at all. If they're doing file sharing
between Windows boxes, they're probably going to use machine names, with
SMB handling the IP/name resolution for them. Again, not caring what
the IPs are.

> I am helping my niece set up her network for her apartment / roommates
> and find that I don't want to give her the advice I was given as I can't
> prove its worth. Plus, she and the roommates are all living on wireless
> DCHP and I never dealt with that (translation is the one laptop I do
> have I just let it do its thing and turn a blind eye).
>
> They are all Windows-centric so I am trying to find best practice
> regardless of opSys.

Probably best to let something handle it automatically, if none of them
will be able to manage it for themselves. Which usually means having a
modem/router running all the time, and it handling address allocation.
Most home modem/router devices are set up that way, by default.

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