Let's delve into the realm of networking. Imagine you are tasked with designing a network for a growing company with three distinct departments: Engineering, Marketing, and Sales. Each department has unique needs and security requirements. The Engineering department requires high bandwidth for data transfer and code compilation, the Marketing department needs access to various social media platforms and marketing tools, and the Sales department needs secure access to customer data and CRM systems. Furthermore, the company wants to implement a guest network for visitors. The network should be designed with scalability, security, and performance in mind. Considering these requirements, address the following:

1. Describe the network topology you would choose and why. Explain the advantages and disadvantages of your chosen topology in this scenario.
2. Outline the IP addressing scheme you would implement. Include subnetting details and justification for your choices.
3. Discuss the security measures you would implement to protect each department's data and ensure network security. Elaborate on firewall rules, access control lists (ACLs), and intrusion detection/prevention systems (IDS/IPS).
4. Explain how you would segment the network to isolate the guest network from the internal network. What specific technologies or configurations would you use to achieve this?
5. Describe how you would ensure high availability and redundancy in the network design. What measures would you take to prevent single points of failure?
6. Outline the routing protocols you would use and why. How would you configure them to optimize network performance and ensure efficient data delivery?
7. Discuss how you would monitor and manage the network to ensure optimal performance and security. What tools and techniques would you employ for network monitoring and troubleshooting?

Network Design for a Growing Company

This document outlines a network design for a growing company with three departments (Engineering, Marketing, and Sales) and a guest network, focusing on scalability, security, and performance.

1. Network Topology

I would choose a hierarchical (or multi-tiered) topology, specifically a star topology within each department connected to a central core. This provides a good balance of performance, scalability, and manageability.

Explanation:

• Star Topology (within departments): Each department's devices connect to a central switch. This simplifies troubleshooting, provides centralized management, and offers good performance for departmental traffic.
• Hierarchical Topology (connecting departments): Departmental switches connect to a core switch or a layer 3 switch/router. This allows for inter-departmental communication and provides a central point for routing and security policies.

Advantages:

• Scalability: Easily add or remove devices and departments without disrupting the entire network.
• Manageability: Centralized management simplifies configuration, monitoring, and troubleshooting.
• Performance: Dedicated bandwidth for each department reduces congestion.
• Security: Easier to implement security policies and isolate departments.
• Fault Isolation: A failure in one department does not affect other departments.

Disadvantages:

• Cost: Requires more hardware (switches, routers, etc.) compared to a simpler topology.
• Complexity: More complex to configure and maintain than a flat network.
• Single Point of Failure (Core): The core switch/router is a single point of failure. Redundancy measures (discussed later) are crucial.

2. IP Addressing Scheme

I would implement a private IP addressing scheme using RFC 1918 address spaces. This allows for internal communication without public IP addresses and enhances security.

• Address Space: Use the 10.0.0.0/8 private address range.
• Subnetting: Divide the address space into subnets for each department and the guest network:
  • Engineering: 10.10.1.0/24 (254 usable addresses)
  • Marketing: 10.10.2.0/24 (254 usable addresses)
  • Sales: 10.10.3.0/24 (254 usable addresses)
  • Guest: 10.10.4.0/24 (254 usable addresses)
  • Infrastructure (Core/Routers/Firewalls): 10.10.0.0/24

Justification:

• /24 Subnets: Provide a sufficient number of addresses for each department while keeping the subnet size manageable.
• Separate Subnets: Isolates traffic between departments, enhancing security and performance.
• Infrastructure Subnet: Dedicated subnet for network devices simplifies management and security.
• DHCP: DHCP servers within each subnet will automatically assign IP addresses to devices.

3. Security Measures

Comprehensive security measures are essential to protect each department's data and ensure network security.

• Firewall: A next-generation firewall (NGFW) at the network perimeter is crucial.
  • Rules:
    • Default Deny: Deny all traffic unless explicitly allowed.
    • Departmental Access: Allow traffic between departments based on specific needs (e.g., Sales accessing a shared database on the Engineering subnet).
    • Internet Access: Control internet access for each department based on policies.
    • Guest Network: Restrict guest network access to the internet only, blocking access to internal resources.
• Access Control Lists (ACLs): Implemented on switches and routers to filter traffic based on source/destination IP addresses, ports, and protocols.
  • Departmental Isolation: Prevent unauthorized access between departments.
  • Internal Resource Access: Control access to specific servers and resources based on user roles and departments.
• Intrusion Detection/Prevention System (IDS/IPS): Monitors network traffic for malicious activity and automatically blocks or alerts administrators.
  • Signature-Based Detection: Identifies known threats based on predefined signatures.
  • Anomaly-Based Detection: Detects unusual network behavior that may indicate an attack.
• Network Segmentation: Separating the network into distinct segments (departments and guest network) limits the impact of a security breach.
• VPN (Virtual Private Network): Secure remote access for employees.
• Multi-Factor Authentication (MFA): Enforces stronger authentication for accessing sensitive resources.
• Regular Security Audits: Identify and address vulnerabilities in the network.

4. Guest Network Isolation

Isolating the guest network is crucial to prevent unauthorized access to internal resources.

• VLAN (Virtual LAN): Create a separate VLAN for the guest network.
• Firewall Rules:
  • Deny all traffic from the guest VLAN to internal subnets.
  • Allow traffic from the guest VLAN to the internet (through NAT).
• Captive Portal: Require guests to authenticate or accept terms of service before accessing the internet.
• DHCP Isolation: A separate DHCP server for the guest network prevents IP address conflicts.
• Content Filtering: Block access to malicious or inappropriate websites on the guest network.

5. High Availability and Redundancy

Preventing single points of failure is essential to ensure high availability.

• Redundant Core Switches/Routers: Implement two or more core switches/routers in a high-availability configuration (e.g., VRRP, HSRP).
• Link Aggregation (LAG): Combine multiple physical links into a single logical link to increase bandwidth and provide redundancy.
• Redundant Power Supplies: Use redundant power supplies for critical network devices.
• Uninterruptible Power Supplies (UPS): Protect network devices from power outages.
• Backup Internet Connection: Have a secondary internet connection in case the primary connection fails.
• Regular Backups: Regularly back up network configurations to facilitate quick recovery in case of a failure.

6. Routing Protocols

The choice of routing protocol depends on the network size and complexity. For a growing company, OSPF (Open Shortest Path First) is a good choice.

• OSPF: A link-state routing protocol that offers fast convergence, scalability, and support for VLSM (Variable Length Subnet Masking).
  • Configuration:
    • Area Design: Divide the network into areas to improve scalability and reduce routing overhead.
    • Authentication: Configure authentication to prevent unauthorized routing updates.
    • Route Summarization: Summarize routes between areas to reduce the size of the routing table.
• Static Routing (for specific cases): Static routes can be used for specific destinations or as a backup route.

Why OSPF?

• Scalability: Handles a large number of routers and networks.
• Fast Convergence: Quickly adapts to network changes.
• VLSM Support: Efficiently uses IP address space.
• Open Standard: Widely supported and interoperable.

7. Network Monitoring and Management

Proactive monitoring and management are crucial for optimal performance and security.

• SNMP (Simple Network Management Protocol): Collect network device information (CPU utilization, memory usage, interface status, etc.).
• Network Monitoring Tools: Use tools like Nagios, Zabbix, or SolarWinds to monitor network performance and security.
  • Alerting: Configure alerts for critical events (e.g., high CPU utilization, interface down, security threats).
• Log Management: Centralize and analyze network logs to identify security incidents and troubleshoot problems.
• NetFlow/sFlow: Collect network traffic flow data to identify bandwidth bottlenecks and security threats.
• Packet Capture: Use tools like Wireshark to capture and analyze network traffic for troubleshooting and security analysis.
• Regular Performance Testing: Conduct regular performance tests to identify and address performance issues.
• Configuration Management: Use a configuration management tool to automate network device configuration and ensure consistency.