Cisco CCNA (200-301)Network FundamentalsHard
A network engineer wants to configure a single summary static route on a core router to represent the four contiguous subnets 192.168.32.0/24, 192.168.33.0/24, 192.168.34.0/24, and 192.168.35.0/24. Which summary route correctly covers exactly these four networks with no additional address space?
- A192.168.32.0/21
- B192.168.32.0/23
- C192.168.32.0/22
- D192.168.0.0/22
Show answer & explanationAnswer & explanation
Correct answer: C. 192.168.32.0/22
The third octets 32-35 in binary are 00100000 through 00100011, sharing the first six bits (001000). Combined with the first 16 bits of 192.168, this gives a 22-bit common prefix, so 192.168.32.0/22 (mask 255.255.252.0) exactly summarizes the four /24 networks 32 through 35 with no extra address space included.
Why the other options are wrong
- A. /21 would cover eight /24 networks (32-39), including extra unintended space.
- B. /23 only covers two /24 networks (32-33), not all four.
- D. 192.168.0.0/22 covers networks 0-3, not the 32-35 range.
Route Summarization (CIDR)
Route summarization combines multiple contiguous subnets into a single advertised route using the longest common prefix shared by all subnets.
- Count of /24s summarized = 2^(24-summary prefix)
- Must verify subnets are contiguous and power-of-2 aligned
- /22 summarizes exactly 4 /24 networks
Memory trick: Four /24s fold neatly into one /22 blanket.