Network security

Types of IP addressing

Comparing transmission media

Packet switching

Static and dynamic routing

IP addressing identifies network interfaces so packets can reach their destinations. When describing an address, make three separate distinctions: which version it uses, whether it is public or private, and whether it is assigned statically or dynamically.

### IPv4 and IPv6

**IPv4** uses 32-bit addresses, usually written as four decimal numbers separated by full stops. With **IPv6**, addresses are 128 bits long and are usually written as groups of hexadecimal digits separated by colons.

| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Written representation | Four decimal groups, each from 0 to 255 | Eight hexadecimal groups in full notation; shortened forms are possible |
| Example | `192.168.10.4` | `2001:db8:0:0:0:0:0:4` |
| Address capacity | Smaller address space, with limited availability of public addresses | Vastly larger address space, supporting many more uniquely addressed interfaces |

The difference goes beyond how the addresses look. IPv6 provides many more possible addresses, easing the pressure caused by IPv4 address shortages.

### Public and private addresses

A **public IP address** is globally unique and can be routed across the public internet. Within a private network, a **private IP address** is used instead; it is not routed directly across the public internet.

Private addresses must be unique within their own network. Separate private networks, though, can reuse the same addresses. Two unrelated studios could each have a device addressed `192.168.10.4` without a conflict, because those devices belong to different private networks.

A public address doesn't automatically give anyone permission to access a device. The address makes routing possible; access controls decide which communications are permitted.

### Static and dynamic addresses

A **static IP address** stays assigned to an interface until its configuration is changed. By contrast, a **dynamic IP address** is assigned automatically for a period of use and may change when reassigned.

| Assignment | Main benefit | Main limitation |
|---|---|---|
| Static | A stable address makes a device consistently reachable at a known location | Assignments must be managed carefully to avoid conflicts and incorrect settings |
| Dynamic | Automatic assignment reduces manual configuration and allows addresses to be reused | The address is not guaranteed to remain unchanged |

These distinctions are independent. A private address, for example, can be static or dynamic. So can a public address.

### Network address translation

**Network address translation (NAT)** changes address information in packets as they pass between networks. A common IPv4 arrangement lets many devices with private addresses share one public address for internet communication.

Consider a studio with a laptop at `192.168.10.4` and a tablet at `192.168.10.5`. Both reach an internet server through a NAT router whose public address is `198.51.100.20`. The figure follows their outgoing traffic and the replies that return.
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When a packet goes out, the router replaces its private source address with the router's public address. The router records a translation entry to distinguish the devices' communications. When a reply arrives, it uses that entry to translate the destination information and forward the packet to the correct private device.

The laptop and tablet therefore don't each need their own public address, reducing the number of public IPv4 addresses required. NAT also lets devices with private addresses communicate with the public internet, where their original private addresses cannot be routed directly.

**Key terms:** IPv4, IPv6, public IP addresses, private IP addresses, static IP addresses, dynamic IP addresses, network address translation (NAT).

A bidirectional NAT schematic: laptop labelled 192.168.10.4 and tablet labelled 192.168.10.5 on the left inside a private network, NAT router labelled public address 198.51.100.20 in the centre, and public internet leading to internet server on the right. Show outgoing packets having their private source address replaced and returning replies being forwarded to the correct device using a translation entry.

Compare transmission media using the same requirements. Fibre optic cables, twisted pair cables and wireless transmission differ in performance, installation demands and risk. No single medium is best for every connection.

### How the media carry data

**Fibre optic cables** carry data as pulses of light through thin glass or plastic fibres. In **Twisted pair cables**, electrical signals carry data through pairs of insulated copper wires. The wires are twisted together to reduce electromagnetic interference. **Wireless transmission** uses electromagnetic waves to carry data through space rather than through a cable.

The figure shows how the signal paths differ: light travels through fibre, electrical signals pass through twisted copper pairs, and radio waves travel between wireless devices.
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### Comparing the required factors

**Bandwidth** describes a connection's data-carrying capacity, normally expressed in bits per second. As a signal travels through a medium, it weakens; this is **Attenuation**.

These comparisons apply to typical installations. Actual performance depends on the equipment and cable specification, as well as the distance and environment.

| Factor | Fibre optic cables | Twisted pair cables | Wireless transmission |
|---|---|---|---|
| Bandwidth | Very high capacity; suits large volumes of traffic | High capacity over shorter cable runs, though generally less than fibre | Capacity varies; shared use, obstacles and interference can reduce the rate each device receives |
| Complexity of installation | Needs careful handling and termination, often requiring specialist skills | Usually easier to terminate and connect than fibre, though cables still need routing | No individual cable run is needed for each device, but access-point placement and coverage need planning |
| Cost | Specialist installation and connection equipment can lead to high initial costs | Usually economical for short wired connections | Can cut cabling costs, though access points and additional coverage equipment still cost money |
| Range | Suits long-distance links | Better suited to shorter connections within a building | Limited by signal strength, obstacles and the wireless technology used |
| Susceptibility to interference | Unaffected by electromagnetic interference | Twisting reduces electromagnetic interference without eliminating it | Other transmissions and electrical equipment can cause interference |
| Attenuation | Relatively low, so links can run further before the signal needs regeneration | Electrical signals weaken as cable length increases, limiting useful range | Signal strength falls with distance; walls and other obstacles reduce it too |
| Reliability | Usually stable if properly installed, but physical cable damage can interrupt service | Usually stable within its supported range, though damaged cables or interference can cause problems | More variable: movement, interference and obstacles can change the connection |
| Security | Intercepting the cable signal generally requires physical access; interception is difficult but possible | Intercepting or connecting to the cable generally requires physical access | Signals reach beyond the intended devices, making interception easier unless suitable protection is used |

### Matching the medium to the requirement

For a theatre linking buildings across its site, fibre optic cables may be the preferred choice. Range, bandwidth and resistance to electromagnetic interference matter more here than installation cost. Inside one building, fixed ticket-office computers may get sufficient bandwidth and reliable connections from twisted pair cables at lower cost.

Staff using handheld ticket scanners need to move, so wireless transmission suits this task. Mobility is its advantage. Coverage gaps and interference, however, may interrupt communication. Adding wireless access doesn't remove the need to consider reliability and security.

A wired connection isn't automatically secure. Nor does a high-bandwidth medium guarantee that every transfer will reach its maximum capacity.

**Key terms:** fibre optic cables, twisted pair cables, wireless transmission, bandwidth, complexity of installation, cost, range, susceptibility to interference, attenuation, reliability, security.

Three parallel schematic panels comparing signal paths. Label the first fibre optic cables and show light through fibre; label the second twisted pair cables and show electrical signals through twisted copper pairs; label the third wireless transmission and show radio waves between wireless devices. Emphasize guided signals in cables versus transmission through space.

**Packet switching** divides data into packets and forwards them separately across a network. When explaining the process, link each stage to its purpose. Segmentation makes the data manageable; headers support delivery. Network devices forward the packets, and the destination reassembles the data.

### From a message to packets

The sender splits the original data into smaller portions. Each portion becomes a packet's payload, with a routing header attached. This header carries control information, including source and destination addresses; sequence information lets the receiving system restore the original order.

Each packet travels separately, carrying the control information needed to handle it. The network doesn't have to send the original message as one uninterrupted block or reserve a dedicated path for the whole message.

### Forwarding through the network

A **switch** forwards traffic between devices within a local area network. It normally selects an outgoing port using destination MAC addresses. A **router** forwards packets between networks: it examines destination IP addresses and uses its routing table to choose an appropriate next hop.

For example, a design studio sends a file from a sender through a switch and Router A. From there, Router A can forward packets towards Router B or Router C before they reach the destination. In the figure, packets P, Q and R travel independently. P and R go through Router B; Q goes through Router C.
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Packets can take different routes when forwarding decisions or network conditions differ. They can also all follow the same route. Packet switching permits separate routing; it doesn't require different paths.

### Reassembly at the destination

Different delays can cause packets to arrive out of order. If the studio's packets arrive in the order Q, P, R, the receiving system uses sequence information to put their payloads back into the original order P, Q, R.

At the destination, the packet headers are removed and the payloads reassembled to recover the original data. Complete reconstruction must wait until any missing required data is obtained. Receiving some packets doesn't mean the whole message has arrived.

Because packets are forwarded independently, many communications can share network links. If one path becomes unavailable, an available alternative route may allow traffic to continue.

**Key terms:** packet switching, packets, routing header, control information, switches, routers, reassembled at the destination.

Left-to-right packet-switching schematic. Show sender segmenting a file into packets P, Q and R, each with routing header and payload, followed by a switch and Router A. Branch through Router B for P and R and through Router C for Q, then converge at destination. Show arrival order Q, P, R and reassembly into original order P, Q, R. Distinguish local forwarding by the switch from forwarding between networks by routers.

Both static and dynamic routing give routers the information they need to forward packets between connected local area networks. They differ in how routes enter the routing table and what happens to those routes when the network changes.

### Static routing: routes entered by an administrator

With **Static routing**, an administrator configures routes manually. Each route identifies a destination network and the next hop or outgoing interface needed to reach it.

On receiving a packet, the router checks the destination IP address against its routing table, then forwards the packet using the matching route. That route won't automatically adapt if the topology changes. If the selected link fails, an administrator may have to change the configuration before traffic can take an alternative path.

Paths are predictable with static routing, and there's no continuing exchange of routing updates. The trade-off is manual work: every affected router must be configured correctly. As the network grows, maintaining many routes takes more time.

### Dynamic routing: routes learned and updated

With **Dynamic routing**, routing processes learn network reachability information and update routes automatically. Routers exchange information, then use it to select routes according to the routing method's criteria.

If a link becomes unavailable, routers detect the change and share updated information before recalculating routes. Packets can then follow a suitable alternative, if one exists. An administrator doesn't have to replace each affected route manually.

**Convergence** is the process by which routers reach a consistent, updated view of available routes after a network change. Some routers may still use outdated information during convergence, so traffic can be delayed or lost.

### Following a route change

Consider Office LAN connected to Router A and Workshop LAN connected to Router B. Router A has a direct link to Router B, with an alternative path through Router C. The figure shows the direct link failing, making the alternative path necessary.
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If Router A has only a static route directly to Router B, traffic to Workshop LAN cannot switch automatically to Router C. Unless an alternative has already been configured, an administrator must change the route. Dynamic routing lets routers learn that the direct link is unavailable and select the path through Router C after convergence.

Neither method can create a physical alternative. If the failed link was the only connection, routing changes alone cannot restore communication.

### Comparing the required factors

| Factor | Static routing | Dynamic routing |
|---|---|---|
| Configuration | Routes are entered manually; straightforward when few routes are needed | A routing process must be configured correctly; routes can then be learned automatically |
| Maintenance | Changes usually need manual updates on affected routers | Route changes are handled automatically, though monitoring and troubleshooting are still necessary |
| Complexity | Simple for a small, stable topology; managing many interconnected routes is difficult | Routing behaviour is more complex, but a changing network needs less manual route management |
| Resource usage | Low processing and memory overhead; static routes generate no ongoing routing-update traffic | Maintaining and exchanging routing information uses processing, memory and bandwidth |
| Convergence | Static routes themselves do not automatically converge after a change; recovery may need manual intervention | Works towards updated routes automatically, but convergence takes time |
| Scalability | Scales less well as the number of networks and required manual entries increases | Better suited to growth because routers learn and update routes |
| Network size | Often suitable for small networks with few paths and infrequent changes | Often suitable for larger networks with multiple paths or frequent changes |

When simplicity and predictable paths matter most, along with low resource usage, static routing is attractive. Dynamic routing is attractive when automatic adaptation and scalability justify its extra configuration complexity and resource usage. Network size offers a useful guide to the choice, but the number of alternative paths matters too, as does how often the network changes.

**Key terms:** static routing, dynamic routing, configuration, maintenance, complexity, resource usage, convergence, scalability, network size.

Two matching network schematics labelled static routing and dynamic routing. In both, Office LAN connects to Router A, Workshop LAN connects to Router B, and Router C provides an alternative path between Router A and Router B. Mark the direct link between Router A and Router B as failed. In static routing, show the unchanged route blocked and label manual intervention. In dynamic routing, show the new path through Router C and label convergence followed by updated route.

Network architecture

State three differences between IPv4 addressing and IPv6 addressing.

Describe how network address translation (NAT) enables an editing computer to send a request to the online distribution service and receive its reply.

The editing computers transfer confidential, uncompressed recordings throughout the working day. Explain two reasons for connecting these computers using twisted pair cables rather than wireless transmission.

List three types of transmission media that could be used in the depot's network.

A parcel-record file has been divided into packets with routing headers. Describe how a switch and routers forward these packets to the online delivery platform, and how the original file is reconstructed there.

The tracking server remains connected permanently, while handheld scanners frequently join and leave the network. Explain one reason for assigning a static private IP address to the server and one reason for assigning dynamic private IP addresses to the scanners.

State the number of bits in an IPv6 address.

Outline one limitation of wireless transmission when researchers upload survey files while moving around the centre.

List three items of control information carried with packets that enable a survey file to be delivered and reconstructed.

Initially, the centre connects only two buildings, the network rarely changes, and its routers have limited processing capacity. Explain two reasons why static routing is suitable for this network.

The centre expands to several buildings and introduces dynamic routing. There are now alternative paths between buildings. Explain how dynamic routing restores delivery of survey files after a link fails, including why some packets may be lost temporarily.

Computer Science

IB Computer Science focuses on computational thinking and programming skills. Students learn about system fundamentals, network architecture, and software development, applying their knowledge to solve real-world problems through practical projects.

A2.3 Data transmissions

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