Remember that with ACL masks, 1s = don't care.
so, for a mask of 0.7.255.255 you have -
00000000.00000111.11111111.11111111
so, when used with 10.0.0.0 -
You have to have 10 in the first octet (no ones)
It doesn't care what is in the 3rd and 4th octet (all ones)
The second octet is the one to watch.
because the mask is 00000111 the first five bits have to remain as they
are in the ip address - 00000
the last three bits can be either one or zero, doesn't matter
so, they can be anything from 000 to 111
so, your IP address can be 00000 000 to 00000 111
which gives you 0 - 7 in decimal
so the mask fits 10.0.0.0 to 10.7.255.255
hope that helps
Mike
>
>I need help in understanding inverse masks that are used in network &
>access
>list commands. I understabd what 0 and 255 do but I get confused when
>there
>is any number other than these two. For example...
>
>network 10.0.0.0 0.7.255.255 area 0
>
>what does the 7 represent or specifiy for the mask.
>
>Thanks
>
>Keith
>
>
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