[CLUE-Tech] Network Guru?

[Keith Hellman]

Many thanks, I see where I made the mistake.

--- Jim Ockers <ockers at ockers.net> wrote:
> Keith:
> 
> > Hello all, I need the input of a network guru:
> 
> That's me.  :)
> 
> > I seem to recall that some of the fundamental rules at the IP layer is
> > that:
> > *	Every node on a subnet must have all it's network bits set
> appropriately
> > in its IP address.
> > *	Node must be to the right of the LSB of the network address
> 
> > I've been told (by IT in my org) to use: 12.147.70.88/27 for a little
> > embedded device.  This doesn't make sense to me...
> > 	12.147.70.88  = 12.147.70.01011000
> > network	12.147.70.224 = 12.147.70.11100000
> > (last octets in bin, duh..)
> 
> I have no idea where you got the .224 for your network address.  That is
> the last octet of the netmask.  Your network address is .64 .
> 
> In this case, here are the four parameters for your connection to the IP
> network:
> 
> network address: 	12.147.70.64
> IP address:		12.147.70.88
> broadcast address:	12.147.70.95
> netmask:		255.255.255.224 (/27)
> 
> In a /27 network the .88 address is a valid IP address.  There is no
> reason it shouldn't work if you are properly setting your broadcast
> address (.95), and if your route contains the correct network address
> (.64).
> 
> > On my development network, I can recreate the problem, and when I
> switch
> > the IP address to include the network bits - everything works AOK.
> 
> > So, my questions are:
> > A)  Am I way off base here?  Am I thinking circa 80's IP rules and
> things
> > are different now?
> 
> Things are the same except for the class business.  The 12 address space
> is a "Class A" but you are treating it as not a Class A address space. 
> Cisco
> routers need to be told "ip classless" to work properly.  The Linux
> kernel
> (AFAIK) defaults to classless IP addressing and does not need any
> special
> configuration to work properly.
> 
> > B)  Apparently an implementation has changed in the linux kernel since
> my
> > notebook doesn't complain - is this true?
> 
> The Linux kernel now adds the network route in its routing table based
> on
> the IP address, netmask, and broadcast address supplied when
> ifconfigging
> the interface.
> 
> --
> Jim Ockers (ockers at ockers.net)
> Contact info: please see http://www.ockers.net/
> 
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=====
Keith E. Hellman
kehellman at yahoo.com

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