Network Security I
Computer Networks
Circuit and Packet Switching
Circuit Switching
- Used in the legacy phone networks.
- A dedicated path is established through a sequence of hardware devices when two nodes start communication.
- Data is sent along this established route which is maintained until the communication ends.
Packet Switching
- Primarily used in the Internet.
- Data is divided into packets that are transported independently through the network.
- Each packet is handled on a best-effort basis, meaning it may follow different routes to reach the destination.
Advantages of Packet Switching
- No Wasted Bandwidth
- Links are not reserved during idle periods.
- Multiplexing
- Multiple connections of lesser quality can be established without blocking users.
- Adaptation
- Can adapt to network congestion and failures more effectively than circuit switching.
Multiplexing Methods
- Time Division Multiplexing (TDM)
- Frequency Division Multiplexing (FDM)
- Allows multiple sender/receiver pairs to share the same physical link.
Disadvantages of Packet Switching
- No Guaranteed Bandwidth
- Overhead
- Each packet carries a header with a source/destination address.
- Complex Control
- Packets can be lost, corrupted, or delivered out of order.
- Delay and Congestion
- Lack of congestion control may lead to arbitrary delays and packet drops.
Internet Protocols vs OSI Model
| Layer | OSI Layer | Internet Protocol Stack |
|---|---|---|
| Application | Application | FTP, SMTP, HTTP |
| Presentation | Presentation | - |
| Session | Session | - |
| Transport | Transport | TCP, UDP |
| Network | Network | IP, routing protocols |
| Data Link | Data Link | PPP, Ethernet |
| Physical | Physical | - |
Protocol Layering and Routing
- Data encapsulation example:
- Each network layer encapsulates data from the layer above it into packets and frames for transport.
- What is a Protocol?
- Defined formats and actions for message exchanges between network entities.
Key Functions of Network Layer
- Forwarding
- Moves packets from router input to appropriate output.
- Routing
- Determines the path that packets will follow from source to destination.
IP Addressing
- IP Address
- A 32-bit identifier for devices on the network, which includes a network part and a host part.
- Forwarding vs. Routing
- Forwarding is a direct action at routers using a forwarding table.
- Routing involves computing paths and updating forwarding tables among routers.
Transport Layer Protocols
TCP (Transmission Control Protocol)
- Connection-oriented, provides reliable, ordered delivery of byte streams.
- Includes error detection, retransmission, flow control, and congestion control.
UDP (User Datagram Protocol)
- Connectionless, provides best-effort delivery without guarantees.
- Efficient for real-time applications like multimedia, where some loss is acceptable.
Network Attacks and Security
- ARP Spoofing
- Allows an attacker to intercept traffic by sending false ARP responses.
- Denial of Service (DoS) Attacks
- Overwhelm a service to take it offline, targeting weaknesses in the protocol stack (against TCP/UDP).
Understanding Network Components and Operations
Clients and Servers
- In the client-server model, the client requests services from an always-on server (e.g., web applications).
- In peer-to-peer models, nodes can act as both client and server.
Address Resolution Protocol (ARP)
- Used to map an IP address to a MAC address in a local area network.
Best Practices
- Network Configuration and Monitoring
- Tools like Wireshark are used for packet analysis and monitoring network security.
- Preventive Measures Against Attacks
- Use of static ARP entries, secure protocols, and regular monitoring to deter ARP spoofing and other security threats.