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Difficulty: EasyIPv4 Addressing and Subnetting

A network technician is configuring a local area network interface using the IPv4 network block 10.20.30.0/2610.20.30.0/26. Which of the following statements regarding this subnet configuration are correct? (Select TWO.)

  1. The subnet mask in dotted-decimal notation is 255.255.255.192255.255.255.192.Answer
  2. The total number of usable host IP addresses in this subnet is 6262.Answer
  3. C
    The total number of usable host IP addresses in this subnet is 6464.
  4. D
    The IP address 10.20.30.6310.20.30.63 can be assigned directly to a host workstation interface.

Answer

The correct statements are that the subnet mask in dotted-decimal notation is 255.255.255.192255.255.255.192 and the subnet contains 6262 usable host IP addresses.
A CIDR prefix of /26/26 uses 26 bits for the network portion and 6 bits for the host portion (32−26=632 - 26 = 6). In dotted-decimal notation, 26 subnet bits translate to 255.255.255.192255.255.255.192. The total number of IP addresses in a /26/26 subnet is 26=642^6 = 64. Subtracting 2 (one for the network address 10.20.30.010.20.30.0 and one for the broadcast address 10.20.30.6310.20.30.63) leaves exactly 62 usable host IP addresses.

Step-by-Step Solution

1
Calculate the subnet mask from CIDR notation /26
26 binary 1s followed by 6 binary 0s gives 11111111.11111111.11111111.11000000, which converts to 255.255.255.192255.255.255.192.
Converting CIDR prefix to dotted-decimal notation is necessary to determine the subnet boundary.
2
Determine host bits and total IP address capacity
Remaining host bits = 32−26=632 - 26 = 6. Total addresses = 26=642^6 = 64.
Host bits determine the size of the IP block.
3
Calculate usable host IP addresses
Usable host addresses = 64−2=6264 - 2 = 62. Network ID is 10.20.30.010.20.30.0 and Broadcast address is 10.20.30.6310.20.30.63.
The first address (network ID) and last address (broadcast address) are reserved and cannot be assigned to end devices.

Key Concept

IPv4 Subnet Masking and Usable Host Calculation
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Topics

IPv4 Addressing and Subnetting

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