How is wildcard the natural method for hardware to match on? I can't conceptualize it. I write it out in binary, and I can't figure out what operation a processor would use to match on.
""Howard C. Berkowitz"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > I asked one of the IOS developers about it, and he pointed out that > access lists were developed before subnetting. The wildcard mask is > the natural way hardware does matching. > > When subnets were defined, their documentation specified subnet > masks. With 20/20 hindsight, it might have been a good idea to go > back and change wildcard masks, but, of course, that would have > introduced compatibility problems. > > > > >I think is all originated from the principles of: > >1 = Do not Cares (Matches everything and anything) > >0 = Cares ( Matches only identical corresponding digit) > > > >Maybe it is a hang-on from the old binary digit stuff. Man you have no > >choice than to do the inverse, else your access-list would not work, except > >you are ready to develope a router IOS that will use the direct mask. > > > >Goodluck > > > >Regards. > >Oletu > > > >----- Original Message ----- > >From: > >To: > >Sent: Saturday, December 29, 2001 10:50 PM > >Subject: Why use wildcard mask [7:30473] > > > > > >> Hi All, > >> > >> I am trying to find out why we do an inverse/wildcard > >> masks while using access lists? > >> > >> For example, if I want to deny 192.168.1.0 255.255.255.0 > >> network, on the access list, we configure this > >> as 192.168.1.0 0.0.0.255, but why do we do it this > >> way instead of 255.255.255.0. > >> > >> All this seems to be is just an inverse relationship pointing back at the > >> same thing? Even if I want to get specific and deny 192.168.1.0 > >> 255.255.255.192, this translates to 192.168.1.0 0.0.0.63, which seems to > >be > >> just the standard mask and subtract 255.255.255.255. > >> > >> Is there a specific reason why we do inverse mask? It seems to be easier > >> just to configure it with normal masks. This way, we skip on an extra > >> procedure. > >> > >> thanks > >> Mike > >_________________________________________________________ > >Do You Yahoo!? > >Get your free @yahoo.com address at http://mail.yahoo.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30487&t=30473 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
