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Difficulty: EasyIPv4 Addressing and Subnetting

A network engineer is configuring a point-to-point serial link between two routers and assigns the IPv4 subnet prefix /30/30. What is the maximum number of usable host IPv4 addresses available on this subnet?

  1. 2Answer
  2. B
    4
  3. C
    6
  4. D
    8

Answer

The maximum number of usable host IPv4 addresses on a /30/30 subnet is 2.
A /30/30 CIDR prefix leaves 2 bits for host addressing (32−30=232 - 30 = 2). Calculating total addresses yields 22=42^2 = 4. Subtracting 2 for the unassignable network and broadcast addresses results in exactly 2 usable host IP addresses, making /30/30 subnets standard for point-to-point links.

Step-by-Step Solution

1
Determine the number of host bits.
Host bits = 32−30=232 - 30 = 2.
An IPv4 address consists of 32 bits. Subtracting the prefix length gives the remaining bits dedicated to host addressing.
2
Calculate the total number of IP addresses in the subnet.
Total IP addresses = 22=42^2 = 4.
The total capacity of a subnet is 2h2^h, where hh is the number of host bits.
3
Calculate usable host addresses by subtracting reserved addresses.
Usable host addresses = 4−2=24 - 2 = 2.
The first address is the network identifier and the last address is the broadcast address; neither can be assigned to host interfaces.

Key Concept

Calculating usable host count for a given CIDR prefix
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Topics

IPv4 Addressing and Subnetting

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