prior to IOS 12.x, the wild card mask method alowed quite a bit of flexibility. Suppose you had all of your serers on a particular subnet, but you wanted a different subset of those servers to be accessible from different subnets. It used to be that you could specify something like
access-list 101 permit ip 172.16.24.0 0.0.0.255 192.168.1.0 0.0.0.28 access-list 101 permit ip 172.16.25.0 0.0.0.255 192.168.1.0 0.0.0.32 access-list 101 permit ip 172.16.26.0 0.0.0.255 192.168.1.0 0.0.0.65 the first line would permit the dot 24 subnet to get to servers with addresses of dot 4, dot 8, dot 12, dot 16, dot 20, dot 24, and dot 28 the second line would permit the dot 25 subnet to access the server with the address of dot 32 the third line would permit the dot 26 subnet to get to servers dot 1, dot 64, and dot 65 granted, this is a convoluted example. but it allowed flexibility and creativity in design. granted too that you can still accomplish the same thing using the host switch, or being a little more creative with the network specification. With the advent of IOS 12.x wildcard bits must be contiguous from the right, so you lose this kind of power. Also takes the fun out of the network a.b.c.d x.x.x.x area command in OSPF! BTW, Mark, I see these odd/even filtering questions in your study materials and elsewhere. While I understand the goal of the exercise, it has always struck me as a pretty bizarre premise. Where exactly in the real world is there any design such that filtering by odd or even would be practical? Let alone filtering by multiples of 4 or 8 or whatever? ( and yes, after two runs through you know where, I fully appreciate that in some places, like the brokerage firm where I used to work, there is very little relationship between the requirements you are given and the real world ) Chuck ""Marc Russell"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Yes, it does make simple tasks a little more complicated. However, using > inverse masking can make complex tasks much easier. > > Take this issue. Say you are asked to filter access to all odd 192.168.x.0 > /24 routes. > > > Your method. > > 192.168.1.0 255.255.255.0 > 192.168.3.0 255.255.255.0 > 192.168.5.0 255.255.255.0 > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30482&t=30473 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
