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Difficulty: EasyIPv4 Addressing and Subnetting

A network administrator is provisioning a small subnet for point-to-multipoint router interconnects using a subnet mask of 255.255.255.248255.255.255.248 (/2929). What is the maximum number of usable host IP addresses that can be assigned to devices within this subnet?

  1. 6Answer
  2. B
    8
  3. C
    14
  4. D
    4

Answer

The maximum number of usable host IP addresses in a /29 subnet is 6.
A /29 subnet mask leaves 3 bits for host addressing (32−29=332 - 29 = 3). Calculating total IP addresses gives 23=82^3 = 8. Subtracting the reserved network ID and broadcast ID (8−28 - 2) results in 6 usable host addresses.

Step-by-Step Solution

1
Determine the number of host bits in the /29 subnet mask
Host bits = 32−29=332 - 29 = 3 bits
An IPv4 address consists of 32 bits. Subtracting the CIDR prefix length yields the host portion.
2
Calculate the total number of IP addresses in the subnet
Total IP addresses = 23=82^3 = 8
The total number of addresses supported by nn host bits is given by 2n2^n.
3
Subtract network and broadcast addresses to find usable host IPs
Usable host IPs = 8−2=68 - 2 = 6
The first IP address represents the network ID and the last IP address represents the subnet broadcast ID; neither can be assigned to a host interface.

Key Concept

Usable Host Calculation for IPv4 Subnetting
Estimated Time:45s
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Topics

IPv4 Addressing and Subnetting

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