You are a system administrator and you want to deny access to a

group of computers with addresses 172.30.16.0 to
172.30.31.0. Which

wildcard mask would you use?

A. 0.0.15.255

B. 0.0.255.255

C. 0.0.31.255

D. 0.0.127.255

E. 0.0.255.255



You are a system administrator and you want to deny access to a group of computers with addresses..

Answer / guest

Answer:: A

0.0.15.255 will check the last 13 bits of an address so that
computers

172.30.16.0 to 172.30.31.0 will be denied access. 0.0.31.255
would check

the last 6 binary digits and deny access to addresses
172.30.32.0 to

172.30.63.0. 0.0.127.255 would check the last 7 binary
digits and deny

access to addresses 172.30.64.0 to 172.30.127.0. 0.0.255.255
would deny

172.30.0.0 to 172.30.254.0. If you write decimal 15 in
binary, you have

0001111, the 1's tell the router to ignore address with
these bits set;

0's tell the router to check the bits. The third octet for
172.30.16.0

is 00010000. The third octet for 172.30.31.0 would be
00011111. So,

traffic from these addresses would be denied.

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