The ACL configuration on a certain router is shown in the figure, so which of the following items are the addresses that satisfy this condition? (Multiple choice)

Question

Options

• A10.1.2.1/32
• B10.1.1.0/32
• C10.0.0.0/32
• D10.1.4.1/32

• A
  16% (6)
• B
  79% (30)
• D
  5% (2)

Explanation

Based on the referenced ACL figure, the rule is most likely permit 10.0.0.0 0.1.1.255, where the wildcard mask determines which bits must match.

Why B and C are correct: The wildcard mask 0.1.1.255 means: first octet must exactly equal 10; the second and third octets must have their upper 7 bits equal to 0 (so each can only be 0 or 1); the fourth octet is unrestricted. Both 10.1.1.0 (B) and 10.0.0.0 (C) satisfy all these constraints.

Why A and D are wrong: Option A (10.1.2.1) fails because its third octet is 2 (00000010 in binary), whose upper 7 bits are 0000001 - not 0000000 as required. Option D (10.1.4.1) similarly fails because its third octet is 4 (00000100), whose upper 7 bits are 0000010, again not matching.

Memory tip: When evaluating ACL wildcard masks, convert the "borderline" octets to binary and compare bit-by-bit - a wildcard 1 bit means "any value allowed there," a 0 bit means "must match the network address exactly." Addresses with third-octet values of 2 or higher (like 2, 4, 6…) will always fail a wildcard of 1 in that octet position because they set bits above bit 0.

No community discussion yet for this question.