Number of usable addresses on a subnet

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I was working through a Cisco book and came across a question asking how
many usable addresses there are in a class C subnet.

I answered 256, minus one for the network address and minus one for the
broadcast address, i.e. a total of 254.

The book gave the correct answer as 253, but no explanation of why.

I wondered if they were assuming one further address would be used for
the default gateway in any subnet, but I would tend to view the router
as just another host eligible to receive a host address.

What have I missed?

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Number of usable addresses on a subnet
Look at

http://www.cisco.com/univercd/cc/td/doc/product/software/ssr83/rpc_r/48383.htm#xtocid67064

where it says that that a class C network can have 254 hosts.

Your explanation about why they say 253 in the book is probably right.
There might have been something in the phrasing of the question that
implied that there would have to be a router involved which would need
one IP address leaving only 253 for "hosts" presumably defined as being
some class of non-networking devices like PCs and such.

Cisco da Gama
http://ciscostudy.blogspot.com


Re: Number of usable addresses on a subnet

Andrew W Young wrote:
Quoted text here. Click to load it

if so then you would be right. If the ans was 253, it should've said
that something like a router connets 2 Class C networks. So each
network has one router. How many addresses for 'PCs' on one of them.

If the book has an error it's good to have it recorded, maybe others
have it or will google the problem, so it'll be helpful to them..
what book, what edition, what page?

minor point- you mean Class C network not Class C subnet.


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