> -----Original Message-----
> From: Luis Angel Fernandez Escabias [mailto:[EMAIL PROTECTED]]
>
> Can I create an network object with the following format:
> 240.0.0.0/5
> instead of giving the IP and the netmask? I need do this
Sheesh! Ask a teeny question, get a slew of different answers!
/5 means a 5-bit mask. The first 5 bits of the 32-bits IP number are ones.
This means you use the first 5 bits to denote the network number, and
the last 27 bits to denote the host number.
11111/000.00000000.00000000.00000000 = 248.0.0.0
Don't confuse this with any network number now, this is just a representation
of the mask.
The first network in this 5-bit-mask subnet scheme is:
00000/000.00000000.00000000.00000000 = 0.0.0.0
The broadcast address for the first network is:
00000/111.11111111.11111111.11111111 = 7.255.255.255
The last network in this 5-bit-mask subnet scheme is:
11111/000.00000000.00000000.00000000 = 248.0.0.0
The broadcast address for the last network is:
11111/111.11111111.11111111.11111111 = 255.255.255.255
There is an RFC that prohibits the use of all zeros and all ones in
a network address. (can't find that darn RFC#, it's in Stevens also.)
I don't know if it's been amended but you can see how an all-zeros
and all-ones network screw with the numbering scheme. 0.0.0.0 is
reserved, so is 255.255.255.255, so we have to throw the previous two
networks out.
The first USABLE network in this 5-bit-mask subnet scheme is:
00001/000.00000000.00000000.00000000 = 8.0.0.0
The broadcast address for the first USABLE network is:
00001/111.11111111.11111111.11111111 = 15.255.255.255
The last USABLE network in this 5-bit-mask subnet scheme is:
11110/000.00000000.00000000.00000000 = 240.0.0.0
The broadcast address for the last USABLE network is:
11110/111.11111111.11111111.11111111 = 247.255.255.255
This happens to be the address you are asking about. 240.0.0.0/5
translates to 240.0.0.0 mask 248.0.0.0 in classical notation. Caveat
here, this is a class E address, marked as reserved for future use.
I don't know if it's routable, it depends on how the vendor of your
network equipments decides to implement this rule. You might see funky
behavior even if you use this only for your private intranet.
CT
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