Doubt about an address. Pls Help

applepieapplepie Member Posts: 2 ■□□□□□□□□□
in CCNA & CCENT
In the answer to this question if the mask to be denied is 255.255.0.0, as shown in the given info: 172.16.0.0/16, In the answer why do they use the inverse mask 0.0.255.255?
icon_confused.gif 18. Which of the following configures interface ethernet 0 to deny inbound packets originated from subnet 172.16.0.0/16?
access-list 1 deny 172.16.0.0 0.0.255.255
access-list 1 permit any
interface ethernet 0
ip access-group 1 in
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  • keenonkeenon Member Posts: 1,922 ■■■■□□□□□□
    the 0.0 requires it to check those bits when using the 255 it excludes the bits from being checked.

    so if u want to ID 172.16.x.x 0(ID this bit). 0(ID this bit). 255 (no ID). 255 (no ID)
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  • applepieapplepie Member Posts: 2 ■□□□□□□□□□
    keenon wrote:
    the 0.0 requires it to check those bits when using the 255 it excludes the bits from being checked.

    so if u want to ID 172.16.x.x 0(ID this bit). 0(ID this bit). 255 (no ID). 255 (no ID)
    :D
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