RE: Netmasks: Was New AS/400 Update - TCP/IP Problems

"255.255.255.255" IS usable. It defines an IP address that's the same as
the network address i.e. a single host - usually found in dial up
connections. As for the "reserved" host names, a host id of -1 defines a
broadcast but I'm not aware of any other "reserved" names.  

TrailBlazer Systems, Inc.
http://www.as400ftp.com
AS/400 Communications & E-Commerce Solutions

The early bird may get the worm, but the second mouse gets the cheese.


> -----Original Message-----
> From: Jim Langston [SMTP:jlangston@conexfreight.com]
> Sent: Thursday, December 23, 1999 2:46 AM
> To:   MIDRANGE-L@midrange.com
> Subject:      Netmasks: Was New AS/400 Update - TCP/IP Problems
> 
> Booth,
> 
> You are right, 255.255.255.255 is not usable.  Was a
> typo on my part.  I meant to say 255.255.255.0.  The
> reason 255.255.255.255 is not  usuable is becaue it
> means only your IP is in the sub net.  But each sub-net
> has 2 addresses that can not be used.  The lowest which
> is .., er, something I forget, the router maybe, and the
> highest which is the broadcast.
> 
> Which would leave -1 usuable addresses.
> 
> And you got caught by the same thing I did.  The
> netmask does not tell your what your allowable
> ip addresses are.  Your IP address and the net-mask
> states what the allowable IP range is for the netmask.
> 
> Consider this.  I have an IP address of, say, 10.0.0.3.
> My netmask is 255.255.255.240.  My sub-net goes
> from 10.0.0.1 to 10.0.0.15 with 1 being the one I
> forget and 15 being broadcast.  The reason is: the bits
> of 3 are: 0 0 0 0 0 0 1 1
> The bits of the 240 in my netmask is: 1 1 1 1 0 0 0 0
> The one's in the netmask says that for the same bit
> position in my IP, they can not change.  Since my 4
> high bits are 0's, any IP in my sub net must also have
> 0's in the 4 high bits in the last byte..  Which gives us:
> 0 0 0 0 0 0 0 1 through 0 0 0 0 1 1 1 1
> 
> On the other hand, if my IP address is 10.0.0.19 and
> my netmask is 255.255.255.240 my sub-net goes
> from 10.0.0.17 to 10.0.0.31 with 17 being the one
> I just can't remember and 31 being broadcast.
> Bitmask of 19 is 0 0 0 1 0 0 1 1.  Again, 240 is
> 1 1 1 1 0 0 0 0.  The 4 high bits in my IP can not
> change, which are 0 0 0 1.  So the last byte of
> my subnet goes from 0 0 0 1 0 0 0 1 though
> 0 0 0 1 1 1 1 1.
> 
> This goes for all the bytes in the subnet.
> 
> Regards,
> 
> Jim Langston
> 
> boothm@earth.goddard.edu wrote:
> 
> > "255.255.255.255"? is that a usable mask?  That  seems to me to mean
> there
> > is only 1 valid address for the whole network. and that address is
> > xxx.xxx.xxx.0?
> 
> <SNIP>
> 
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