🛡️ Secure Network Topology with Cisco ACL Implementation

This project demonstrates a secure network infrastructure designed in Cisco Packet Tracer. It features inter-subnet traffic control and optimized security using standard Access Control Lists (ACLs).

🏗️ Topology Design

The network is logically segmented into two distinct subnets connected via a Cisco 2911 Router:

• User Subnet (Subnet A): 192.168.1.0/24 (Hosts PC0 and PC1)
• Server Subnet (Subnet B): 192.168.2.0/24 (Hosts the critical Server)

🔐 Security Policy

The configuration follows the Principle of Least Privilege:

• PC0 (Authorized): Granted full access to the Server. 192.168.1.10/24
• PC1 (Unauthorized): Access to the Server is strictly denied at the Router interface to prevent unauthorized entry. 192.168.1.20/24

Router Configuration (Cisco IOS CLI):

enable
configure terminal
# Define the ACL: Deny specific host, permit others
access-list 10 deny 192.168.1.20
access-list 10 permit any

# Apply the ACL to the inbound interface
interface GigabitEthernet 0/0
 ip access-group 10 in

✅ Verification & Testing

To ensure the network security policy is correctly implemented, several connectivity tests were performed.

1. Authorized Access Test (PC0)

Scenario: PC0 (192.168.1.10/24) attempts to reach the Server (192.168.2.100/24). Expected Result: Success (ICMP Reply). Actual Result: ✅ The connection is established successfully as PC0 is permitted by the ACL.

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2. Unauthorized Access Test (PC1)

Scenario: PC1 (192.168.1.20/24) attempts to reach the Server. Expected Result: Denied (Destination Host Unreachable). Actual Result: ❌ The connection is blocked by the Router. The Router drops the packets from this specific host, proving the ACL is active.

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3. Security Audit (Router Match Logs)

By executing the show access-lists command on the Cisco 2911 Router, we can verify the "match" count. Each match represents a packet that was successfully inspected and dropped based on our security policy.

Command: Router# show access-lists 10