To determine the number of subnets in the given enterprise network, we count each distinct Layer-3 network segment separated by routers or firewall interfaces. Each router or firewall interface connects a different subnet.
Analysis of the network components:
1. Two Ethernet segments:
Each Ethernet LAN represents a separate broadcast domain and hence a separate subnet.
So, these contribute:
→ 2 subnets
2. Web Server:
The web server is connected through a dedicated interface and resides in its own network segment (often a DMZ or server subnet).
So, this contributes:
→ 1 subnet
3. Firewall:
The firewall separates the internal enterprise network from the external network.
It has two interfaces:
- One facing the internal enterprise network
- One facing the external (Internet-facing) network
Each interface corresponds to a different subnet.
→ 2 subnets
4. Routers:
The three routers interconnect the Ethernet segments, firewall, and server network.
Their interfaces terminate the subnets already identified above and do not introduce additional independent subnets beyond those counted.
Total number of subnets:
\[
2 \text{ (Ethernet)} + 1 \text{ (Web Server)} + 2 \text{ (Firewall)} + 1 \text{ (External link)} = 6
\]
