A network administrator is planning a branch office network. The branch needs: 80 workstations, 20 VoIP phones, 5 servers, and 10 printers. They want each device type on its own VLAN for QoS and security.
Which subnet mask size is appropriate for the workstation VLAN, and how many addresses are wasted compared to exact fit?
- A./25 (128 addresses, 126 usable): fits 80 workstations; 126 - 80 = 46 addresses wasted but provides room for growth. A /26 (62 usable) would be too small for 80 devices
- B./27 (30 usable): fits 80 workstations if wireless access points share DHCP
- C./24 (254 usable): fits 80 workstations; 254 - 80 = 174 addresses wasted
- D./26 (62 usable): fits 80 workstations perfectly with only 18 unused
Why A is correct
Workstation VLAN with 80 hosts: /26 gives 62 usable (too small: 62 < 80). /25 gives 126 usable (enough: 126 >= 80, with 46 spare for growth). /24 gives 254 usable (excessive waste for only 80 devices). Best practice: size subnets for current need + ~20-30% growth buffer. /25 is the correct answer: 126 usable, 46 spare addresses for growth (reasonable). The wasted addresses question: 126 usable - 80 used = 46 wasted, but 'wasted' is a relative concept - growth capacity is valuable.
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