Wild Card Mask ?????

GeeljireGeeljire Member Posts: 3 ■□□□□□□□□□
first off hi ppl, I'm new to the forum just registered today !

currently doing CCNA, whil studying Access Control List i got stumped ....

I had a hard enough time, understanding the nitty gritty of sub netting & VLSM, but wild card Mask , i'm confused

anybody can help out with this, or point me to some good material online, would appreciate it ....


  • lordylordy Member Posts: 632 ■■■■□□□□□□
    Hi and welcome to the forum !

    The wild card masks can be confusing first but in fact they are pretty easy to handle.

    Let's assume you have an ACL that should match on the network

    The subnet mask would then of course be

    Wild card masks are simply inverted subnet masks. The wild card mask for this is

    To make the inveriton a little clearer here is another example.

    If the subnet mask would be the wildcard mask would be

    Hope this helps.

    Working on CCNP: [X] SWITCH --- [ ] ROUTE --- [ ] TSHOOT
    Goal for 2014: RHCA
    Goal for 2015: CCDP
  • dmafteidmaftei Member Posts: 83 ■■□□□□□□□□
    A wildcard mask is not an inverted subnet mask. A wildcard mask is a bit pattern that indicates what bits should be compared when you try to "match" two IP addresses. With wildcard mask you would compare the first 24 bits and ignore the last 8 bits; with wildcard mask you would ignore the first 8 bits and compare the last 24 bits.

    Now consider wildcard mask The inverse of that (presumably a subnet mask) is; but is not legal as a subnet mask (you already know that).
  • pipearcepipearce Member Posts: 19 ■□□□□□□□□□
    Widcard Subnet Masks?! This is the first time I've ever heard of this. Here is a good article explaining what this is all about.


    It appears Lordy is correct with his example and the article describes it as "don't care bits" being represented by 1's, which is kind of the opposite of how things are normally done. This is used in ACLs on Cisco Routers mainly.

    There's my new thing learned today!

    Cheers, Paul
  • dmafteidmaftei Member Posts: 83 ■■□□□□□□□□
    pipearce wrote:
    There's my new thing learned today!
    You may be better off going directly to the source... Search for "contiguous" on the following page: http://www.cisco.com/en/US/products/ps6350/products_command_reference_chapter09186a0080446247.html
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