IP Address Config

[Alan Horn]

On Fri, 14 Oct 2005, Ki Il Song wrote:

>Date: Fri, 14 Oct 2005 14:44:32 -0400
>From: Ki Il Song <ki at knifecenter.com>
>Reply-To: For users of Fedora Core releases <fedora-list at redhat.com>
>To: fedora-list at redhat.com
>Subject: IP Address Config
>
> I am trying to change my IP Settings updating my ifcfg-eth0 settings.
>
> Basically, I want to set it up using a static IP, with subnet
> 255.255.255.248, gateway 70.88.x.x and ip address 70.88.x.x (x will be
> replaced with real ip address).
>
> Here is my current ifcfg-eth0 file:
>
> +++++++++++++++++++++++++++
> DEVICE=eth0
> BOOTPRO=static
> BROADCAST=70.88.225.255
> IPADDR=70.88.225.1
> NETMASK=255.255.255.248
> NETWORK=70.88.225.0
> ONBOOT=yes
> TYPE=Ethernet
> +++++++++++++++++++++++++++
>
> Questions:
> Where do I put in my Gateway address?

GATEWAY goes in /etc/sysconfig/network generally.

> What are the BROADCAST and NETWORK addresses?

You don't provide enough information with the x.x piece to determine the 
subnet with that netmask, so theres no way for me to guarantee that this 
info is right.

However, if I assume you mean subnet 70.88.225.0 with 255.255.255.248 
netmask. Then BROADCAST would be 70.88.225.15 and NETWORK would be 
70.88.225.0.

In general a 248 netmask like that (also referred to as /28 network) 
splits a traditional 'class C' (/24) into chunks of 16, starting with .0 
in the class C as the first IP address, with the bottom address in each 
chunk being the network, and the top address in each chunk being the 
broadcast. If that makes sense ?

So the subnets you get when splitting a /24 into multiple /28 (for this 
number range) would be :

70.88.225.0-15 (1-14 useable IP addresses)
70.88.225.16-31 (17-30 useable IP addresses)
70.88.225.32-47 (33-46 useable IP addresses)
70.88.225.48-63 (49-62 useable IP addresses)
70.88.225.64-79 (65-78 useable IP addresses)
70.88.225.80-95 (81-94 useable IP addresses)
etc... up to 255.. the math is boring me and hurting my head at this point ;)
I may have got it slightly wrong.. I hate enumerating small subnets.

Hope this helps.

Cheers,

Al