Actually, you can have more than just the 255 or 1 in a wildcard mask.
Try to remember that the wildcard mask bits are the exact opposite of the
subnet mask bits.
For example: In order to block a particular subnet in an access list,
131.111.8.0/21 for instance, would require a wildcard mask of 0.0.7.255.
That would block out the subnet 131.111.8.0
Make sense? Well, you can get the 7 in the wildcard mask 1 of 2 ways (that
I know of)
First, lets type out the subnet mask to make things a little easier.
255.255.248.0
The 3rd octect is only using 5 bits for the subnet mask (counting down from
128 i.e. 128+64+32+16+8=248). That leaves 3 bits in the octect; now, count
3 from THE OPPOSITE END (i.e. 1+2+4=7) and you've got the appropriate
wildcard mask #.
Another, possibly easier way of doing this is to take 255-248(the subnet
mask's 3rd octect) and that will also =7.
I hope this helps!!!!
Scott
Verizon ENOC
From: "Montgomery, Robert WARCOM Contractor" <[EMAIL PROTECTED]>
Reply-To: "Montgomery, Robert WARCOM Contractor"
<[EMAIL PROTECTED]>
To: Cisco <[EMAIL PROTECTED]>
Subject: WildCard Masks
Date: Fri, 12 May 2000 10:45:04 -0700
While reviewing a client's access lists, I noticed they have some entries
where there are other numbers in the wildcard mask (e.g., 180.12.0.0
0.15.255.255). I understand you can only have 0 or 255 but am noticing
several entries like this one. Is there something I don't know or is this
possibly a mark of a bad typist?
Thanks,
Rob Montgomery CCNA MCP
IA Systems Analyst
Sytex, Inc./ Naval Special Warfare Command
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