Joseph Haynes wrote: > I was wondering if anyone could assist me in better understanding wildcard > masks. Perhaps a website or book you came across during your studies. Any > assistance would be most appreciated. I plan to take my test in a month and > I am having problems with this aspect. >
Hi Joseph, Those test makers will try to fool you by asking you questions using that decimal dotted octet format. The best method to deal with any IP addressing problem, including subnet masks and wildcard masks, is to convert everything to binary. Both the IP address and the subnet/wildcard mask have 32 bits. In the long run, for success in this area you should try to think in binary as much as possible and always keep those 32 bits in mind. In my opinion you'd do well to steer clear of those freeware subnet calculators. You should learn to do it in your head or on a napkin in 3-4 minutes. As you know, the wildcard mask is mostly for access lists and does everything "backwards" from a subnet mask. Let's take an example. If I have a subnet 10.0.0.0 with a subnet mask of 255.0.0.0 this means I have eight (8) ones in the first octet and the "10" is the network portion and the other 24 bits (three octets of 0.0.0) can be used for hosts. This means that 10.1.234.16 and 10.168.3.53 are on the same subnet. So if we wanted to make an access list that applied only to the 10.x.x.x subnet we would use a wildcard mask of 0.255.255.255 ( 8 zeroes and 24 ones) because in wildcard masks the zeroes mark the network portion of the address. Here's a link aimed at the beginner that may be of some value: http://www.boson.com/promo/guides/ip-access-list.htm Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=25785&t=25728 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
