Which route summarization most efficiently reduces perceived network complexity that is composed of subnetworks ranging from 172.16.20.0/24 to 172.16.36.0/24?

Question

Options

• A172.16.8.0/21
• B172.16.8.0/19
• C172.16.20.0/20
• D172.16.0.0/18
• E172.16.20.0/19

• A
  2% (1)
• B
  15% (7)
• C
  2% (1)
• D
  74% (35)
• E
  6% (3)

Explanation

To find the best summary, convert the boundary addresses to binary and find the longest common prefix. 172.16.20.0 in the third octet is 00010100 and 172.16.36.0 is 00100100. Comparing these bit by bit: bits 7–6 are both '00' (match), but bit 5 differs (0 vs 1). Only the first 2 bits of the third octet are common. Combined with the 16 fixed bits of 172.16, the prefix length is /18, giving the summary 172.16.0.0/18 (covers 172.16.0.0–172.16.63.255). Options A and B (172.16.8.0/21 and /19) do not cover 172.16.36.0. Option C (172.16.20.0/20) only covers up to 172.16.31.255. Option E (172.16.20.0/19) also only covers up to 172.16.31.255. Only D covers the entire range 172.16.20.0–172.16.36.0.

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