Examkin

Question

Difficulty: MediumIPv4 Addressing and Subnetting

A system engineer is configuring a static IPv4 address for a database server located on a segment designated with a network ID of 172.30.100.0172.30.100.0 and a subnet mask of 255.255.254.0255.255.254.0. Company security policy requires that the configured address must be a valid usable host address within the assigned subnet and must also belong to the RFC 1918 private IPv4 address space. Which IPv4 address is a valid host address for this server?

  1. 172.30.101.250172.30.101.250Answer
  2. B
    172.30.101.255172.30.101.255
  3. C
    172.32.100.50172.32.100.50
  4. D
    172.30.102.1172.30.102.1

Answer

172.30.101.250
The subnet mask 255.255.254.0255.255.254.0 creates subnets with a block size of 22 in the third octet. For the network ID 172.30.100.0172.30.100.0, the subnet encompasses 172.30.100.0172.30.100.0 through 172.30.101.255172.30.101.255, giving a usable host range of 172.30.100.1172.30.100.1 to 172.30.101.254172.30.101.254. The IP address 172.30.101.250172.30.101.250 falls cleanly inside this usable host range and is also a valid RFC 1918 private address (within 172.16.0.0/12172.16.0.0/12).

Step-by-Step Solution

1
Determine the CIDR prefix and block size for subnet mask 255.255.254.0.
The subnet mask 255.255.254.0 corresponds to a /23 prefix length. The block size in the third octet is calculated as 256 - 254 = 2.
Calculating the block size identifies how the subnets increment across octets.
2
Calculate the network ID, broadcast address, and usable host range for the 172.30.100.0/23 subnet.
The network address is 172.30.100.0, the broadcast address is 172.30.101.255, and the range of valid usable host IPs is 172.30.100.1 through 172.30.101.254.
Host IP addresses cannot use the subnet network ID (first IP) or broadcast address (last IP).
3
Verify compliance with RFC 1918 private IPv4 address boundaries.
RFC 1918 specifies the Class B private IP range as 172.16.0.0 to 172.31.255.255 (172.16.0.0/12 block). The address 172.30.101.250 falls inside this range.
Addresses starting with 172.32.x.x fall outside RFC 1918 limits and are public addresses.

Key Concept

IPv4 Subnet Mask Calculation and RFC 1918 Private Address Boundaries
Rate this question

Topics

IPv4 Addressing and Subnetting

More questions from this topic