200-301 · Question #817
Which subnet address is for the IP address 172.19.20.23/28?
The correct answer is E. 172.19.20.16. The subnet address for 172.19.20.23 with a /28 prefix is determined by performing a bitwise AND operation with the subnet mask 255.255.255.240, resulting in 172.19.20.16.
Question
Which subnet address is for the IP address 172.19.20.23/28?
Options
- A172.19.20.20
- B172.19.20.0
- C172.19.20.32
- D172.19.20.15
- E172.19.20.16
How the community answered
(24 responses)- A17% (4)
- B4% (1)
- D8% (2)
- E71% (17)
Why each option
The subnet address for 172.19.20.23 with a /28 prefix is determined by performing a bitwise AND operation with the subnet mask 255.255.255.240, resulting in 172.19.20.16.
172.19.20.20 is an address within the 172.19.20.16 /28 subnet, but it is not the network address itself.
172.19.20.0 would be the network address for a /24 subnet (255.255.255.0), not a /28.
172.19.20.32 would be the next network address after 172.19.20.16 /28, as the subnet block size for a /28 is 16.
172.19.20.15 is the broadcast address for the previous /28 subnet (172.19.20.0 /28), not the network address of 172.19.20.23/28.
A /28 prefix corresponds to a subnet mask of 255.255.255.240. To find the network address, you perform a bitwise AND operation between the IP address 172.19.20.23 and the subnet mask. In the last octet, 23 (00010111) AND 240 (11110000) results in 16 (00010000), making the subnet address 172.19.20.16.
Concept tested: Subnet address calculation from IP and prefix
Source: https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/13788-3.html
Topics
Community Discussion
No community discussion yet for this question.