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Can you use 255.255.255.255 for a subnet mask?

cyberspace (TechnicalUser) (OP)
15 Nov 07 15:25
Had an interview today and did a networking test with 15 questions, was fairly straight forward.

There was one question, which asked which subnet mask you would use to make a printer the only host on a network. So I said 255.255.255.252 - 2 useable hosts, minimum address wastage.

But the guy said I was wrong, and that 255.255.255.255 would be used. Is this true? how if so? thanks

'When all else fails.......read the manual'

burtsbees (Programmer)
15 Nov 07 18:44
Yes---255.255.255.255 is a single host mask. This is used all the time in adsl.

Burt
cyberspace (TechnicalUser) (OP)
16 Nov 07 2:25
Oh well, that's something new for me.

In CCNA the furthest they say you can go is .252!

So how does it work then? What about wire and broadcast addresses?

'When all else fails.......read the manual'

burtsbees (Programmer)
16 Nov 07 14:00
There are no broadcasts in situations like this, and the address in effect is the wire address. You would not have anything else on the network, like a /30 would. There are certain situations (PPP) that allow a /31---I believe this is Cisco proprietary, though. Just two point to point addresses, no broadcast or wire.

Burt
gb0mb (IS/IT--Management)
26 Nov 07 9:59
Burt is 100% correct.  

The reason that the CCNA says you can only goto .252 is this:

256-252 = 4 ips in that subnet.  You will have your network id , then two usable ips, and finally your broadcast ip.  

I just wanted to explain that a little better for you in case you were not sure.

Gb0mb

........99.9% User Error........

burtsbees (Programmer)
26 Nov 07 10:01
Also, I remember even in CCNA that when configuring loopback addresses, you should use a /32 mask.

Burt
pansophic (MIS)
30 Nov 07 18:51
I, personally, think that you are both correct.

You can indeed assign a netmask of 255.255.255.255, but if you do that, I would argue that it is no longer a network but a standalone host.


pansophic

burtsbees (Programmer)
30 Nov 07 21:47
You are correct---I am not arguing that it is not a standalone host. It is.

Burt
Crowtalks (TechnicalUser)
1 Dec 07 15:41
Look at your routing tables and you find that the .255 masks are used if you want to specify routing to a single address only instead of a network block. This is one application for the single mask.

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