Networking Related Math. Based on the network figure, for each of the three networks — the LAN on Switch 1 (192.168.10.0/24), the LAN on Switch 2…

Networking Related Math. Based on the network figure, for each of the three networks — the LAN on Switch 1 (192.168.10.0/24), the LAN on Switch 2 (192.168.20.0/24) and the WAN link on G0/0 (10.0.0.0/30) — find:

  1. the subnet mask,
  2. the network address and the broadcast address,
  3. the range of usable host addresses, and
  4. the number of usable hosts.

The paper printed only the figure; this question is reconstructed from it.

From the BUET MSC (CSE) October 2026 – Written exam, question 14 of 14.

Answers (1)

Usable hosts in a subnet with prefix /n: \(2^{32-n} - 2\) (all host bits 0 is the network address, all host bits 1 is the broadcast).

LAN 1 — Switch 1 (192.168.10.0/24)

  • Subnet mask: 255.255.255.0
  • Network address: 192.168.10.0, broadcast: 192.168.10.255
  • Usable range: 192.168.10.1 – 192.168.10.254
  • Usable hosts: \(2^{8} - 2 = 254\)

LAN 2 — Switch 2 (192.168.20.0/24)

  • Subnet mask: 255.255.255.0
  • Network address: 192.168.20.0, broadcast: 192.168.20.255
  • Usable range: 192.168.20.1 – 192.168.20.254
  • Usable hosts: \(2^{8} - 2 = 254\)

WAN link — G0/0 (10.0.0.0/30)

  • Subnet mask: 255.255.255.252
  • Network address: 10.0.0.0, broadcast: 10.0.0.3
  • Usable range: 10.0.0.1 – 10.0.0.2
  • Usable hosts: \(2^{2} - 2 = 2\) — one for the router (10.0.0.1), one for the other end of the link

Check against the figure: every address shown fits. The gateways 192.168.10.1 and 192.168.20.1, the switch management IPs .254 and the PCs .11 and .12 are all inside their LAN ranges, and 10.0.0.1 is one of the only two usable addresses on the /30. A /30 is the usual choice for a point-to-point link because it wastes no addresses.

— rhs

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