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What is the subnet mask equivalent of the CIDR notation 10.0.0.0/20?

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Computer Networks - IP Addressing
What is the subnet mask equivalent of the CIDR notation 10.0.0.0/20?
A255.255.240.0
B255.255.255.0
C255.255.248.0
D255.255.255.240
Step-by-Step Solution
Solution:

  1. Step 1: Convert /20 prefix to subnet mask

    /20 means first 20 bits are 1s; in decimal: 255.255.240.0.

  2. Step 2: Verify mask blocks

    Third octet 240 corresponds to 11110000 in binary, matching 4 bits set after 16 bits.

  3. Final Answer:

    255.255.240.0 -> Option A

  4. Quick Check:

    /20 = 255.255.240.0 subnet mask [OK]
Quick Trick: Count bits: 8+8+4 = 20 bits for mask [OK]
Common Mistakes:
MISTAKES
  • Confusing /20 with /24
  • Wrong third octet value
  • Using too many bits in mask

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