Network architecture

A2.2.1 Network topologies

A topology is the layout of nodes and connections in a network.

• Star: all nodes connect to one central device, usually a switch.
• Mesh: every node links directly to the others. A partial mesh links only some of them.
• Hybrid: a mix, such as meshed base stations with a star around each.

links in a full mesh = n(n − 1) ÷ 2

Next: servers →

Next: networking models →

HL A2.2.2 The function of servers

A server provides a service to other devices. Here it mostly means the software. One computer can run many servers at once, each on its own port: web on 80 and 443, FTP on 20 and 21, SSH on 22 and DNS on 53.

# pip install dnspython
import dns.resolver

domain = "www.example.com"
try:
    for record in dns.resolver.resolve(domain, "A"):
        print(record.to_text())
except dns.resolver.NXDOMAIN:
    print("That domain does not exist.")

Proxy and reverse proxy

A proxy acts for clients, so a school can cache common pages and reduce traffic. A reverse proxy sits in front of servers, spreading requests across them and caching common replies.

Next: networking models →

A2.2.3 Networking models

In the client-server model, clients request services and servers provide them. In peer-to-peer, each device is both client and server.

Next: segmentation →

A2.2.4 Network segmentation

Segmentation splits a network into smaller, logically separate parts. It improves security, keeps heavy traffic contained and makes management easier.

Next: review →

Quick quiz

Exam-style questions

These are written for this site in the style of Paper 1. Answer on paper first, then open the mark points.

1. Outline three benefits of a star topology for a small office. [3]

   Mark points

   • A cable failure affects only one device [1].
   • It costs little for a small number of nodes [1].
   • Each device has its own link, so there is minimal risk of collisions [1].

2. A rescue service needs a network that keeps working after any one link fails. Justify a mesh topology. [3]

   Mark points

   • Each node has several paths [1].
   • Traffic can be rerouted if one link or node fails [1].
   • The extra cost of links is justified because communication is critical [1].

3. Explain one disadvantage of peer-to-peer for online banking. [2]

   Mark points

   • There is no central authority to keep the records consistent and secure [1].
   • So balances could be inconsistent or a peer could be unavailable when needed [1].

4. Compare client-server and peer-to-peer networking. [4]

   Mark points

   • Client-server has central control, while peers are equal [1].
   • A server is a single point of failure, while P2P spreads the risk [1].
   • Servers cost more, but P2P has no such hardware cost [1].
   • Servers are easier to secure and manage, but P2P capacity grows with each peer [1].

5. Explain how VLANs improve a school network. [3]

   Mark points

   • Staff and students are placed in separate logical networks on the same hardware [1].
   • Traffic is isolated, so students cannot reach staff servers [1].
   • Broadcast traffic stays within a VLAN, which reduces congestion [1].