Question

Suppose nodes A, B, and C each attach to the same broadcast LAN (through their adapters). If \(\mathrm{A}\) sends thousands of IP datagrams to \(\mathrm{B}\) with each encapsulating frame addressed to the MAC address of B, will C's adapter process these frames? If so, will \(\mathrm{C}\) 's adapter pass the IP datagrams in these frames to the network layer C? How would your answers change if A sends frames with the MAC broadcast address?

Short answer

C's adapter does not process frames addressed to B, but it does process broadcast frames and passes them to the network layer.

Step-by-step solution

Understanding the Problem

We have three nodes, A, B, and C, connected to a broadcast Local Area Network (LAN). We need to determine if node C's adapter processes frames sent from A to B and whether these frames are passed to the network layer of C.

Evaluating Frames Addressed to B

Node A is sending frames specifically addressed to the MAC address of node B. In a broadcast LAN, adapters only process frames addressed to them or meant for broadcast. Since these frames are addressed to B, C's adapter will check the destination MAC address and drop the frames, not processing them further.

Impact on the Network Layer of C

Since C's adapter does not process these frames, it will not pass any data to the network layer for node C, as it only forwards frames whose destination MAC address matches its own or is a broadcast address.

Considering Broadcast Address

If the frames from A use the MAC broadcast address, all adapters on the LAN, including C's, will process these frames because the broadcast address signals them to receive the frame. C's adapter will then pass the encapsulated IP datagrams to its network layer for further processing.

Key concepts

Broadcast LAN

A Broadcast Local Area Network (LAN) is a type of network where all devices are connected to a single shared communication medium. This setup allows any device on the network to communicate with all others. When a device transmits data, every other device receives it.

This functionality is particularly useful for scenarios where information needs to be disseminated to all nodes simultaneously. However, it requires careful handling to avoid unnecessary data congestion and to ensure that devices process only the information intended for them. In a broadcast LAN, special protocols are in place to manage how data is sent and received, ensuring efficient network operation.

• Broadcast LANs can use either Ethernet or Wi-Fi technologies.
• All connected devices share the same physical medium.
• The capacity of each device to listen to broadcasts depends on network design and settings.
• Nodes use broadcast addresses to send data to every connected device at once.

MAC address

Every network interface card (NIC) or adapter is assigned a unique identifier known as a MAC (Media Access Control) address. This address is used in the data link layer of the OSI model, specifically in Layer 2, to ensure that data packets are sent to the correct hardware on a network. Each MAC address is composed of a string of six sets of two hexadecimal digits.

MAC addresses play a crucial role in enforcing device uniqueness on a network. They ensure that data packets reach the intended node without the interference of other communications. In the context of a broadcast LAN, only devices whose MAC address matches the destination address in the packet - or the specified broadcast address - will process that packet.

• MAC addresses are typically hardcoded into a device's network card at manufacture.
• They are essential for distinguishing devices on the same local network.
• Broadcast MAC address is a special address that targets all devices on the network.

Network layer

The Network Layer is the third layer in the OSI (Open Systems Interconnection) model, playing a key role in the transmission of data across networks. It is responsible for routing packets from the source to the destination, managing logical addressing in the form of IP addresses.

In a broadcast LAN, the network layer ensures that messages are directed correctly, even if the physical transmission medium is shared by all devices. It does this by interpreting IP addresses which, unlike MAC addresses, can be configured and reassigned. This layer also determines the best path for data to travel across a network. In our original exercise scenario, non-broadcast frames are ignored by the network layer in C's system because its adapter first screens for its specific MAC address.

• Handles packet forwarding and routing through multiple networks.
• Uses logical IP addresses to identify network devices.
• Works closely with the link layer, which handles direct node-to-node communication.

IP datagrams

IP datagrams are the fundamental units of data transfer at the network layer. Each datagram carries data across the Internet or a local network in a structured format that includes metadata for routing and delivery, such as the source and destination IP addresses. This allows datagrams to find their way through complex networks over potentially non-direct paths.

Encapsulation is used to wrap the IP datagram in a frame suitable for transmission over the given LAN technology. When IP datagrams are encapsulated with a broadcast MAC address, they are delivered to all nodes on the broadcast LAN network. However, if encapsulated with a specific MAC address, as in the case of A sending to B, only the intended recipient processes it while others disregard it.

• Provide a means for large data to be split into smaller packets for easier handling.
• Facilitate communication between different subnets and networks.
• Each datagram is independent, allowing paths to be optimized on the fly.