Assuming a /24 prefix a statement to permit all odd source addresses in
the last octet would look like this:
access-list 101 permit ip 0.0.0.1 255.255.255.254 any
The mask of 255.255.255.254 indicates all bit postitions except the last
position in the last octet are "don't care" bits. Therefore it will only
try to
match the last bit against the test address of 0.0.0.1. If the last bit is
turned
on then the octet value must be odd and will be permitted to pass. If off
then it is an even value and will not match. If this is the last statement
in
your access list then the implicit (unseen) deny at the end of the ACL
will cause it to be dropped.
HTH,
Prof. Tom Lisa, CCAI
Community College of Southern Nevada
Cisco Regional Networking Academy
Chris Boyd wrote:
> A guy here has asked me a question and I have never done this so I need
some
> help....can some show me an example of how to write and extended ACL
> deny/permitting only even or odd addresses? Without permitting each
> individual address... I have never done this and don't know why you would
> but I didn't know the answer...thanks in advance
>
> Thanks,
>
> Chris Boyd, CCNA
> Network Support
> 828.323.4103
> Alex Lee, Inc.
> 120 4th St SW
> Hickory, NC 28602
> www.alexlee.com
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