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Computer Networks

04. Network Layer

Network Layer

1. Functions

  • Interconnection of heterogeneous networks
  • Routing and packet forwarding
  • Congestion control

2. Routing Algorithms

  • Static routing and dynamic routing
  • Distance-vector routing algorithm (Bellman-Ford)
  • Link-state routing algorithm (Dijkstra)
  • Hierarchical routing

3. IPv4

  • IPv4 packet structure
  • IPv4 addressing, NAT
  • Subnetting, CIDR (Classless Inter-Domain Routing)
  • ARP protocol: Address Resolution
  • DHCP protocol: Dynamic Host Configuration
  • ICMP protocol: Network control and error reporting

4. IPv6

  • Main features of IPv6: Large address space, simplified header, enhanced security
  • IPv6 address representation

5. Routing Protocols

  • Autonomous System (AS)
  • Intra-domain routing protocols: RIP (distance-vector), OSPF (link-state)
  • Inter-domain routing protocol: BGP

6. IP Multicast and Mobile IP

  • Multicast concept, multicast address
  • Basic principles and communication process of Mobile IP

7. Network Layer Devices

  • Router: Packet forwarding, routing table maintenance
  • Routing table: Destination address, next hop, interface

Exercises

  1. Briefly describe the main functions of the network layer.
  2. What are the differences between distance-vector and link-state routing algorithms?
  3. What are the differences between IPv4 and IPv6 addresses?
  4. Briefly explain the basic principles of RIP and OSPF.
  5. What is the main function of a router?
  6. What is CIDR? What are its advantages?
Reference Answers

1. Main Functions

Interconnection of heterogeneous networks, routing and forwarding, congestion control

Distance-vector: Each node only knows the distance to its neighbors, exchanges information periodically; Link-state: Each node learns the entire network topology and independently computes the shortest path

3. IPv4 vs. IPv6

IPv4 is 32 bits, IPv6 is 128 bits; IPv6 has a much larger address space, simplified header, supports more devices

4. RIP vs. OSPF

RIP: Distance-vector, uses hop count as metric, suitable for small networks; OSPF: Link-state, uses Dijkstra algorithm, suitable for large networks

5. Function of Router

Packet forwarding, maintaining routing tables, interconnecting different networks

6. CIDR

Classless Inter-Domain Routing, flexible subnetting, reduces routing table entries, improves address utilization