A network administrator is selecting an IPv4 subnetwork block for a new internal departmen… — Cisco CCNA

A network administrator is selecting an IPv4 subnetwork block for a new internal department segment that requires support for up to $60$ usable host interfaces. The network design policy requires using an RFC 1918 private IPv4 address block and selecting the most efficient prefix length to avoid wasting addresses. Which subnetwork address and CIDR prefix satisfies all requirements?

$10.40.16.0/26$ Answer
B
$172.32.16.0/26$
C
$10.40.16.0/27$
D
$192.168.10.0/25$

Answer

The subnetwork

10.40.16.0/26

meets all design requirements by using an RFC 1918 private IPv4 address and providing

62

usable host IP addresses, which is the most efficient subnet size for

60

hosts.

The subnetwork

10.40.16.0/26

utilizes an address within the RFC 1918 Class A private block (

10.0.0.0/8

). A

/26

prefix leaves

6

host bits (

32 - 26 = 6

), providing

2^6 - 2 = 62

usable host IP addresses. This accommodates the required

60

host interfaces with the minimum possible address waste.

Step-by-Step Solution

Determine the required number of host bits (

h

) for

60

usable hosts

Using the formula

2^h - 2 \ge 60

, we test

h = 5 \rightarrow 30

usable hosts (too small) and

h = 6 \rightarrow 62

usable hosts (sufficient). Thus,

6

host bits are needed.

Two addresses in every IPv4 subnet are reserved for the network ID and the directed broadcast address.

Calculate the CIDR prefix length

Prefix length

= 32 - 6 = /26

An IPv4 address consists of 32 total bits.

Verify RFC 1918 private IPv4 address range compliance

10.40.16.0

is inside the

10.0.0.0/8

private address block (

10.0.0.0

10.255.255.255

RFC 1918 defines private address spaces:

10.0.0.0/8

172.16.0.0/12

, and

192.168.0.0/16

Key Concept

IPv4 Subnet Sizing and RFC 1918 Private Addressing

Question

Answer

Step-by-Step Solution

Key Concept

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