[NTLUG:Discuss] IP super/sub-netting maddness

[Kenneth Loafman]

Just a nit, but it is odd, not invalid...

255.255.255.200 == FFFFFFC8 or 1..11001000

which means you have 5 bits to play with, just not an adjacent 5 bits,
thus there are 32 possible IPs in the subnet, C8-CF, D8-DF, E8-EF, and
F8-FF.  This fits the def of a submask, but would not be compatible with
CIDR notation except as 4 distinct small subnets of 8 each.

I've seen this used for device subnets where redundant devices are
subnetted.  Not spiffy, but valid.

...Ken

joseph beasley wrote:
> 255.255.255.200 is not a valid subnet mask.  255.255.255.192 or
> 255.255.255.224.  Just follow the bits.
> 
> --- Wayne Walker <wwalker at bybent.com> wrote:
> 
>> In theory, you could use 255.255.255.200 and 192.168.1.64.
>>
>> BUT, why do you need to refer to those machines as a subnet?  For
>> firewall rules?
>>
>> If so, just treat it as two 26 bit subnets.
>>
>> 192.168.1.64/26  255.255.255.192
>> 192.168.1.128/26 255.255.255.192
>>
>> Wayne
>>
>> On Tue, Sep 19, 2006 at 02:18:06PM -0500, Richard Geoffrion wrote:
>>> Ok... I think I'm asking the impossible here because no matter how
>> I 
>>> calculate it the bits don't line up...but here goes. 
>>>
>>> Can you supernet multiple subnetted network ranges when they don't
>> fall 
>>> on bit boundaries??
>>>
>>> For instance, 
>>>
>>> Networks 192.168.0.0 mask 255.255.255.0 and 192.168.1.0 mask 
>>> 255.255.255.0 can be referred to / supernetted  by changing the
>> mask to 
>>> 255.255.254.0.  This gives 510 available hosts on the same network 
>>> instead of just 254.
>>>
>>>
>>> Now... what about a situation where I have a 125 ip address DHCP
>> scope 
>>> on a 192.168.1.0/24 segment...and (in my infinite wisdom and
>> foresight) 
>>> I started it at 60.  Yes... 60. Just pick a number...ANY number. 
>> Throw 
>>> a dart -- WHOO HOO!  Triple 20!   The DHCP scope is
>> 192.168.1.60-185.
>>> Now that the DHCP scope is set.. let's put servers and other
>> special 
>>> statics from 1-47 and printers from 224-254... YEAH!! Let's just
>> trash 
>>> both /25 subnets with 'stuff' we can't move.
>>>
>>> Now that we have all our static hosts and printers integrated...
>> .how 
>>> about we firm up these ranges (which is where I got those numbers
>> above) 
>>> and see if there is a way to reference the DHCP scope by network.  
>>> Hmmm... nope.. BUT.. if I modify the dhcp scope to 
>>> be...192.168.1.64-192....then the DHCP scope will fall on the
>> ranges of 
>>> several subnets.
>>>
>>> So...is it possible to supernet the subnets?  (I know it sounds 
>>> ridiculous...and unlikely...but if it's possible it would be a
>> great 
>>> learning experience for me...not to mention making firewall rules 
>>> easier. :) )
>>>
>>> Afterthought...  In the history of TCP/IP...has a subnet mask such 
>>> as........well...no...that'd be an invalid subnet mask.  hm...
>> still... 
>>> has something like (11111111.11111111.11111111.1101xxxx)
>> 255.255.255.200 
>>> ever been used?
>>>
>>> -- 
>>> Richard
>>> Nope...I'm not smoking anything....
>>> (not to say I'm not crazy...just not smok'n)
>>>
>>>
>>> _______________________________________________
>>> http://www.ntlug.org/mailman/listinfo/discuss
>> -- 
>>
>> Wayne Walker
>>
>> www.unwiredbuyer.com - when you just can't be by the computer
>>
>> wwalker at bybent.com                    Do you use Linux?!
>> http://www.bybent.com                 Get Counted! 
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>> IRC:     wwalker on freenode.net
>>
>> _______________________________________________
>> http://www.ntlug.org/mailman/listinfo/discuss
>>
> 
> 
> Joe Beasley
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