Lec-14: Routers in Computer Networks | Physical, data link and network layer device

Summary

This video explains the essential role of routers in networking, specifically in Wide Area Networks (WANs) and the Internet. It covers the router's function of forwarding packets using IP addresses, its use of routing tables, and its ability to filter and flood packets. The video also explores concepts like collision domains, store-and-forward methods, and the difference between MAC and IP addresses. Key topics include the router's operation at the network layer, routing protocols like RIP, and the assignment of IP addresses to router interfaces. This is a fundamental guide for understanding routers in the context of UGC NET and GATE exams.

Takeaways

• 😀 Routers are essential devices used to connect different networks, specifically in the context of the Internet (WAN).
• 🌐 The Internet is a collection of networks, and routers are responsible for facilitating this interconnection.
• 📶 Routers work on three layers: Physical, Data Link, and Network, while other devices like switches primarily function on two layers.
• 🔄 Routers use **IP addresses** for forwarding packets between different networks, unlike MAC addresses used within local networks.
• 🗺️ Routers maintain a **Routing Table** that helps decide the best direction for sending packets.
• 🌊 When routers can't determine the best direction, they use **Flooding** to broadcast packets in all directions.
• 🚫 Routers can **Filter** packets by deciding whether to forward or stop them, for instance, using ARP requests to resolve IP addresses to MAC addresses.
• 💡 Routers use the **Store and Forward method** to prevent packet collisions by temporarily storing and processing them in memory.
• 📡 Routers can be assigned an IP address from the network they are connected to, enabling communication between networks.
• 💬 **Routing Protocols** like **RIP** and **Distance Vector Routing** are used to manage the routing process and enhance network efficiency.
• 🔌 The distinction between LANs and WANs is crucial, with routers playing a key role in facilitating communication across the larger scale of the Internet.

Q & A

What is the primary purpose of a router?

A router is used to connect two different networks, enabling communication between them, typically within the context of the Internet or Wide Area Networks (WAN).

What layers of the OSI model do routers operate on?

Routers operate on three layers: the Physical Layer, the Data Link Layer, and the Network Layer. This distinguishes them from devices like bridges and switches, which generally operate on two layers.

What is the difference between MAC addresses and IP addresses in networking?

MAC addresses are used within Local Area Networks (LANs) to identify devices on a local network, while IP addresses are used in Wide Area Networks (WANs) and the Internet to identify devices across different networks.

What role does a router play in packet forwarding?

A router forwards packets between different networks by using a routing table. It determines the best path for each packet to reach its destination based on the network's topology.

What happens when a router cannot determine the direction for packet forwarding?

If a router cannot determine the forwarding direction from its routing table, it may flood the packet, sending it in all directions as a form of broadcast, attempting to reach the correct destination.

Can routers filter packets, and how do they do so?

Yes, routers can filter packets. They use the routing table to decide whether to forward or block a packet, based on its destination and other criteria. For instance, routers can stop ARP requests from being forwarded beyond the local network.

What is the significance of ARP requests in router functionality?

ARP (Address Resolution Protocol) requests are used to map IP addresses to MAC addresses. Routers can handle ARP requests within a network, but they do not forward ARP requests to other networks, as ARP operates within the local network.

How does a router handle collisions between packets?

Routers use the 'Store and Forward' method to process packets. This means they temporarily store packets in memory before forwarding them, preventing collisions between packets, as the router processes them sequentially.

What is a routing table, and why is it important?

A routing table is a data structure stored in routers that contains information about different networks and the best routes to reach them. It is essential for packet forwarding, as it helps the router determine the optimal path for packets based on their destination IP addresses.

What is the role of the router's IP address in network connectivity?

Each router interface is assigned an IP address from the network it is connected to. This IP address enables the router to facilitate communication between networks, helping to route packets between different network segments.