[TriLUG] OT: IP subnetting question

[Aaron Joyner]

Handy afternoon reading for you:
http://en.wikipedia.org/wiki/Broadcast_address
http://en.wikipedia.org/wiki/Default_gateway
http://en.wikipedia.org/wiki/Subnetwork#Subnetting

The last of those is a bit complicated, so I'll summarize here to get
you started:
0) The last address in any subnet is used as the "broadcast" address,
ie. to communicate with all hosts on the subnet.
1) At least one address with in the subnet usually needs to be a
gateway, ie. a way to get off the subnet to other networks.  Typically
what you think of as your ISP's router, your "default gateway".
2) Most people don't use the first address in any subnet, for
legacy/ambiguity reasons.  See the 3rd link above about Subnetting for
links to RFCs and historical explanations.

Happy Subnetting!
Aaron S. Joyner


On Tue, Aug 9, 2011 at 2:48 PM, Brian Henning <bhenning at pineinst.com> wrote:
> Hi Folks:
>
> I just worked out a contract with a service provider for internet service.
> I noticed that they offered the following static IP packages:
>
> /30, 1 useable address
> /29, 5 useable addresses
> /28, 13 useable addresses
>
> My question is: For each of those, that leaves three "unuseable" addresses.
> What are they for?  I made some guesses:
>
> - broadcast address (all ones)
> - ?????????         (all zeros) (does this have a name?)
> - Modem's own address
>
> Thanks for the input!
> ~Brian
>
> ------------------------------------------------------
>          Brian Henning, Software Engineer
>
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