The company internetwork is subnetted using 29 bits. Which wildcard mask should be used to configure an extended access list to permit or deny access to an entire subnetwork?
A.
255.255.255.224
B.
255.255.255.248
C.
0.0.0.224
D.
0.0.0.8
E.
0.0.0.7
F.
0.0.0.3
Explanation:
29 bits subnet is 8bits + 8bits + 8bits + 5bits
255.255.255.(5bits)
11111000 = 128+64+32+16+8+0+0+0
= 248
Subnet is 255.255.255.248
Simple method to calculate the Wildcard mask from known subnet is to
Reverse 1s into 0s and 0s into 1s from the binary representation of subnet.
For above example (248 = 11111000 subnet)
11111000 (subnet) = 00000111 (wildcard mask) last octet.
= 7 (wildcard mask) for last octet.
Converting the remaining first 3 octets of subnet into wildcard mask using above method
Resulted wildcard mask is 0.0.0.7