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Difficulty: EasyIPv4 Addressing and Subnetting

A network technician is configuring an isolated IPv4 subnet for a small cluster of servers using the subnet mask 255.255.255.248255.255.255.248 (/29/29). What is the maximum number of usable host IP addresses available on this subnet?

  1. 66Answer
  2. B
    88
  3. C
    77
  4. D
    44

Answer

The maximum number of usable host IP addresses on a 255.255.255.248255.255.255.248 (/29/29) subnet is 66.
A subnet mask of 255.255.255.248255.255.255.248 corresponds to a /29/29 CIDR prefix. This leaves 3 host bits (32−29=332 - 29 = 3). The total number of IP addresses is 23=82^3 = 8. Subtracting 2 (one for the network address and one for the broadcast address) leaves 66 usable host IP addresses.

Step-by-Step Solution

1
Determine the number of host bits in the /29/29 subnet mask.
There are 32−29=332 - 29 = 3 host bits.
An IPv4 address has 32 total bits. Subtracting the network prefix bits leaves the bits reserved for hosts.
2
Calculate the total number of IP addresses in the subnet block.
23=82^3 = 8 total IP addresses.
The total number of IP addresses in a subnet is calculated using the formula 2host bits2^{\text{host bits}}.
3
Subtract the reserved network and broadcast addresses to find usable host IP addresses.
8−2=68 - 2 = 6 usable host IP addresses.
The first address is reserved as the network address and the last address is reserved as the broadcast address, neither of which can be assigned to host devices.

Key Concept

IPv4 Subnet Usable Host Calculation
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Topics

IPv4 Addressing and Subnetting

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