200-301 · Question #905
Refer to the exhibit. What is the subnet mask for route 172.16.4.0?
The correct answer is C. 255.255.248.0. The subnet mask for a given route is determined by its prefix length, which specifies the number of bits used for the network portion of the IP address.
Question
Exhibits
Options
- A255.255.255.192
- B255.255.254.0
- C255.255.248.0
- D255.255.240.0
How the community answered
(28 responses)- A7% (2)
- B11% (3)
- C79% (22)
- D4% (1)
Why each option
The subnet mask for a given route is determined by its prefix length, which specifies the number of bits used for the network portion of the IP address.
A subnet mask of 255.255.255.192 corresponds to a /26 prefix, which is not what is shown for the 172.16.4.0 route.
A subnet mask of 255.255.254.0 corresponds to a /23 prefix, which is not what is shown for the 172.16.4.0 route.
The exhibit shows the route as 172.16.4.0/22. A /22 prefix length indicates that 22 bits are used for the network portion of the IP address. This translates to a subnet mask of 255.255.252.0 (11111111.11111111.11111100.00000000 in binary).
A subnet mask of 255.255.240.0 corresponds to a /20 prefix, which is not what is shown for the 172.16.4.0 route.
Concept tested: Subnet mask calculation from prefix length (CIDR)
Source: https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html
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