Unusable IP Numbers

I may be mistaken, but aren't there a set of numbers in the fourth set
of an IP address (192.168.1.XXX) that can't be used/assigned to a
computer or network device (i.e. for broadcasting reasons or subnet
mask stuff or something)? If so, which ones are they???

TIA

On Thu, 20 Apr 2006 14:23:14 -0700, Carter wrote:

> I may be mistaken, but aren't there a set of numbers in the fourth set
> of an IP address (192.168.1.XXX) that can't be used/assigned to a
> computer or network device (i.e. for broadcasting reasons or subnet
> mask stuff or something)? If so, which ones are they???

0 and 255

"Carter" <(E-Mail Removed)> writes:

>I may be mistaken, but aren't there a set of numbers in the fourth set
>of an IP address (192.168.1.XXX) that can't be used/assigned to a
>computer or network device (i.e. for broadcasting reasons or subnet
>mask stuff or something)? If so, which ones are they???
0 and 255. (it depends on your subnet, etc)
0 might actually work.


>TIA

"Carter" <(E-Mail Removed)> wrote in news:1145568194.701967.295990
@j33g2000cwa.googlegroups.com:

> I may be mistaken, but aren't there a set of numbers in the fourth set
> of an IP address (192.168.1.XXX) that can't be used/assigned to a
> computer or network device (i.e. for broadcasting reasons or subnet
> mask stuff or something)? If so, which ones are they???
>
> TIA
>

The general rule is that the first address of a subnet is not used as a
host address as it is considered to designate the subnet itself. The last
address of the subnet is the broascast address. For example the subnet
192.168.5.32/27 (i.e the mask is 255.255.255.224) has subnet address
192.168.5.32 and broadcast address 192.168.5.63. The case you give
192.168.1.XXX implies to me that you are referring to the subnet
192.168.1.0/24 (ie mask 255.255.255.0). In this case you would not use the
subnet address 192.168.1.0 or the broadcast address 192.168.1.255 to
designate hosts.

Klazmon

Llanzlan Klazmon wrote:
> "Carter" <(E-Mail Removed)> wrote in news:1145568194.701967.295990
> @j33g2000cwa.googlegroups.com:
>
>
>>I may be mistaken, but aren't there a set of numbers in the fourth set
>>of an IP address (192.168.1.XXX) that can't be used/assigned to a
>>computer or network device (i.e. for broadcasting reasons or subnet
>>mask stuff or something)? If so, which ones are they???
>>
>>TIA
>>
>
>
> The general rule is that the first address of a subnet is not used as a
> host address as it is considered to designate the subnet itself. The last
> address of the subnet is the broascast address. For example the subnet
> 192.168.5.32/27 (i.e the mask is 255.255.255.224) has subnet address
> 192.168.5.32 and broadcast address 192.168.5.63. The case you give
> 192.168.1.XXX implies to me that you are referring to the subnet
> 192.168.1.0/24 (ie mask 255.255.255.0). In this case you would not use the
> subnet address 192.168.1.0 or the broadcast address 192.168.1.255 to
> designate hosts.
>
> Klazmon

In addition to the other explantions above, have a look at this
http://jodies.de/ipcalc

Lothar

okay. i thought x.x.x.127 was off limits too?

also if 0 designates a subnet and can't be assigned to a host, how is
the 0 in 192.168.0.33 legal/acceptable???

On 27 Apr 2006 11:26:09 -0700, "Carter" <(E-Mail Removed)> wrote:

[Where's the relevant context quote?]

>okay. i thought x.x.x.127 was off limits too?

Only if network address is x.x.x.0/25, then your x.x.x.127 is the
broadcast address.

>also if 0 designates a subnet and can't be assigned to a host, how is
>the 0 in 192.168.0.33 legal/acceptable???

Huh?? That's a legal IP address. You're confusing network and host
address. 192.168.0.0/24 is a valid network address containing the
above host address.

Grant.
--
Memory fault -- brain fried

On Thu, 27 Apr 2006 11:26:09 -0700, Carter wrote:

> okay. i thought x.x.x.127 was off limits too?
>
> also if 0 designates a subnet and can't be assigned to a host, how is the
> 0 in 192.168.0.33 legal/acceptable???

x.y.z.127 might or might not be off limit.

It all depend on the sunbet mask. And since you do not give us a subnet,
a technically correct answer is not possible..

Have a look at the following URL :


http://jodies.de/ipcalc

Hope it help.

"Carter" <(E-Mail Removed)> wrote in news:1146162369.882782.65110
@i40g2000cwc.googlegroups.com:

> okay. i thought x.x.x.127 was off limits too?

It depends on the subnet mask being used. For a /24 mask the address
x.x.x.127 is valid. It is not valid if the mask is /25.

>
> also if 0 designates a subnet and can't be assigned to a host, how is
> the 0 in 192.168.0.33 legal/acceptable??

Why should it not be?: Assuming a /24 mask the subnet address would be
192.168.0.0. There is no problem using 192.168.0.1 etc. If the mask for the
above address was /27 then the subnet address would be 192.168.0.32. In
this case you can't use 192.168.0.32 to designate a host.

In the old days there was an issue when subnetting a supernet where the
first subnet of the supernet which was called subnet zero could not be
used. When configuring a Cisco router you used to always have to specify
"ip subnet-zero" to allow the use of subnet zero. This was purely for
historical/backwards compatibility purposes. See:

http://www.ietf.org/rfc/rfc950.txt

Klazmon.



>

Llanzlan Klazmon <(E-Mail Removed)> writes:

>"Carter" <(E-Mail Removed)> wrote in news:1146162369.882782.65110
>@i40g2000cwc.googlegroups.com:

>> okay. i thought x.x.x.127 was off limits too?

Why? the only thing that is off limits are broadcast addresses, and net
addresses. Thus, you do not want to use the lowest address on a
subnet(subnet address) (of course this might only be for historical
interest as mentioned below) , nor
the highest( broadcast). then it depends on your subnet.

>It depends on the subnet mask being used. For a /24 mask the address
>x.x.x.127 is valid. It is not valid if the mask is /25.

>>
>> also if 0 designates a subnet and can't be assigned to a host, how is
>> the 0 in 192.168.0.33 legal/acceptable??

Because it is not the lowest address in the subnet.
(Well I guess it could be in a 192.168.0.33/32 subnet.)



>Why should it not be?: Assuming a /24 mask the subnet address would be
>192.168.0.0. There is no problem using 192.168.0.1 etc. If the mask for the
>above address was /27 then the subnet address would be 192.168.0.32. In
>this case you can't use 192.168.0.32 to designate a host.

>In the old days there was an issue when subnetting a supernet where the
>first subnet of the supernet which was called subnet zero could not be
>used. When configuring a Cisco router you used to always have to specify
>"ip subnet-zero" to allow the use of subnet zero. This was purely for
>historical/backwards compatibility purposes. See:

>http://www.ietf.org/rfc/rfc950.txt

>Klazmon.



>>