>>on a slightly different note...does anyone have any clue why ciscos
>>refuse to allow you to use an "all zeros" subnet mask (ie, the
>>interface address 206.223.36.7/25 is illegal since the subnet mask is
>>a single zero bit) unless you explicitly say "ip subnet-zero"?
>
>Just leftover classful cruft.  The IOS documentation says:
>
>    Subnetting with a subnet address of zero is discouraged because
>    of the confusion inherent in having a network and a subnet with
>    indistinguishable addresses.
>
>(i.e. if you're not very smart, you can't tell the difference between
>13.0.0.0 referring to the class A network 13/8 and 13.0.0.0 referring
>to the subnet 13.0.0/22.)

that's really lame.  it sort of "implies" that i *can* tell the
difference between

  13.1.0.0/16
  13.1.0.0/20
  13.1.0.0/24

simply by looking.  after all, those don't have "all-zeroes" subnet
mask.

if they really meant what they were trying to do by that, then you'd
(a) be required to use only subnet masks that had the least
significant bit set (so you can see how long it is) and (b) you would
still be disallowed from using the "all-ones" subnet (to prevent
different types of broadcast confusion).  which could probably be
extended to mean that you can't have the most significant bit set in a
subnet mask.  or am i just being pedantic again?

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