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ACL help

Discussion in 'General Cisco Certifications' started by Paulcraig1979, Apr 21, 2006.

  1. Paulcraig1979

    Paulcraig1979 New Member

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    I am trying to get my head around ACL's and I am getting stuck with wildcard masking.

    I have no problems with wildcard masks until I hit a problem where a network has been subnetted and bits have been borrowed.

    For example I am trying to write an ACL to permit traffic to the following network via ports 80 & 21: 172.16.32.0/20

    If this was a /16 network I would write my ACL like this, which I think would be correct:

    access-list 101 permit any 172.16.32.0 0.0.255.255 eq 80
    access-list 101 permit any 172.16.32.0 0.0.255.255 eq 21


    The problem I’m having is working out how I would do the same for a /20 network or any other subnetted network.
     
  2. Nelix
    Honorary Member

    Nelix Gigabyte Poster

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    I believe the /20 equates to a subnet of:

    255.255.240.0

    If i'm wrong someone will be here shortly to put me right.
     
    Certifications: A+, 70-210, 70-290, 70-291
    WIP: 70-294
  3. Paulcraig1979

    Paulcraig1979 New Member

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    yeah that's right, however how do i relate this to the wildcard mask for the ACL?
     
  4. d-Faktor
    Honorary Member

    d-Faktor R.I.P - gone but never forgotten.

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  5. r.h.lee

    r.h.lee Gigabyte Poster

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    Paulcraig1979,

    Can you "think in binary" for subnetting?
     
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
    WIP: CCDA
  6. Paulcraig1979

    Paulcraig1979 New Member

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    ah think i may have cracked it. I am using 0.0.15.255
     
  7. d-Faktor
    Honorary Member

    d-Faktor R.I.P - gone but never forgotten.

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    uhm... isn't that what i said more than a week ago? :blink
    or are you saying that 0.0.15.255 isn't working?
     
  8. Paulcraig1979

    Paulcraig1979 New Member

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    yeah you did sorry, i have only just got round to replying. Thanks.
     

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