Subnetting and Wireless Contention at a Small School
Northfield Community School has one 192.168.10.0/24 network serving 60 devices: 25 staff laptops, 30 student tablets, and 5 servers, plus a networked printer. All devices use one wireless router that also acts as the DHCP server, with a pool from 192.168.10.100 to 192.168.10.200. The printer was configured manually with address 192.168.10.150. Users report intermittent loss of connectivity, especially when many tablets connect; sometimes a device reports 'address already in use'. The router's 2.4 GHz radio is set to channel 6, and a neighbouring school's access point is also on channel 6. The school wants separate logical networks for staff, students, guests, and servers, and expects the guest network to grow to 20 devices. The business manager asks whether to buy a second access point or a more expensive router.
1. Produce a subnet plan using 192.168.10.0/24 that gives separate subnets for staff, students, guests, and servers. Give the network address, usable range, and broadcast address for each, and justify the prefix length.
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Use /26 subnets. Each /26 has 64 addresses and 62 usable host addresses, which fits 25 staff, 30 students, 20 guests, and 5 servers with room to grow. The plan is:
| Subnet | Network | Usable range | Broadcast |
|---|---|---|---|
| Staff | 192.168.10.0/26 | 192.168.10.1 to .62 | 192.168.10.63 |
| Students | 192.168.10.64/26 | 192.168.10.65 to .126 | 192.168.10.127 |
| Guests | 192.168.10.128/26 | 192.168.10.129 to .190 | 192.168.10.191 |
| Servers | 192.168.10.192/26 | 192.168.10.193 to .254 | 192.168.10.255 |
Each subnet needs its own gateway and DHCP scope. The printer should be moved to a static address outside the DHCP pool, for example 192.168.10.10, or given a DHCP reservation. Traffic between subnets should pass through a router or Layer 3 switch with ACLs so guests cannot reach staff or servers. The benefit is not just organisation: it limits broadcast domains and provides a place to enforce policy.
2. Diagnose the 'address already in use' symptom and recommend changes to the DHCP and addressing configuration.
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'Address already in use' is a duplicate-IP symptom. The printer has static address 192.168.10.150, but the DHCP pool is 192.168.10.100 to 192.168.10.200, so the server can lease .150 to a tablet or laptop. When both are online, ARP replies conflict and connectivity becomes intermittent for one or both devices. The fact that it worsens when many tablets connect fits this explanation: more leases mean a higher chance of collision.
Confirm with the DHCP lease table, the ARP cache, and the affected device's logs. Fix it by moving static devices outside the pool, for example the printer to 192.168.10.10, and excluding that address range from DHCP. Alternatively, reserve .150 for the printer's MAC address. Shorten the lease time during the change and renew clients. The printer should also sit in the staff or server subnet with an ACL. This is a configuration fault, not a radio fault, so a new access point or router would not fix it.
3. The school can buy either a second access point or a more expensive router. Recommend one option and explain the wireless configuration changes that should accompany it.
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Buying a more expensive router alone is unlikely to fix the problem. The symptoms point to airtime contention and co-channel interference: one access point, 60 devices, a 2.4 GHz radio on channel 6, and a neighbouring access point also on channel 6. A better router may route faster, but it does not create more wireless capacity or reduce interference.
A second access point with a wired Ethernet backhaul adds capacity and coverage. Place it to reduce the number of clients per radio. Prefer 5 GHz for tablets and laptops, use non-overlapping 2.4 GHz channels (1, 6, and 11), lower transmit power to reduce overlap, and disable legacy data rates. The router still needs to support VLANs, DHCP, and ACLs; if it cannot, a Layer 3 switch may be required. Recommended plan: second access point plus a channel plan and VLANs, keeping the existing router only if it supports the required features. Measure signal strength, retry rate, and throughput per client before and after.