Switching & Bridging | Computer Networks - Computer Science Engineering (CSE) PDF Download

Switching and Briding

Networking and internet working devices are classified into four cate gories: repeaters, bridges, routers, and gateways.

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

 

BRIDGES AND LAN SWITC HES:

 

It is a node that forward frames from one Ethernet to the other. This n ode would be in promiscuous mode, accepting all frames transmitted on either of the Ether nets, so it could forward them to the other. A bridge is connected between two LANs with port. By using the port number the LANs are addressed. Connected LANs are known as extended LAN

LEARNING BRIDGES:

Bridges maintains a forwwarding table which contains each host with th eir port number.

Having a human maintain this table is quite a burden, so a bridge can learn this information for itself. The idea is for each bridge to inspect the source address in all the frames it receives. When a bridge first boots, this table is empty; entries are added over time. Also a timeout is associated with each entry and the bridge is cards the entry after a specified period of time.

 

 

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

SPANNING TREE ALGORITHM

 

If the extended LAN is having loops then the frames potentially loop through the extended LAN forever. There are two reasons to an extended LAN to have a loop in it. One possibility is that the network is managed by more than one administrator; no single person knows the entire configuration of the network. Second, loops are built in to network on purpose to provide redundancy in case of failure. Bridges must be able to correctly handle loops. This problem is addressed by having the bridges run a distributed spanning tree algorithm.

 

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

The spanning tree algorithm wad developed by Digital Equipment Corporation. The main idea is for the bridges to select the ports over which they will forward frames. The algorithm selects as

follows. Each bridge has a unique identifier. In the above example they are labeled as B1, B2, B3

… the algorithm first elects the bridge with smallest ID as the root of the spanning tree. The root bridge always forwards frames out over all of its ports. Then each bridge computes the shortest path to root and notes which of its ports is on this path. This port is also elected as the bridge‟s preferred path to the root. Finally, all the bridges connected to a given LAN elect a single designated bridge that will be responsible for forwarding frames toward the root bridge. Each LANs designated bridge is the one that is closest to the root, and if two or more bridges are equally close to the root, then the bridge which having smallest ID wins.

 

In the above example, B1 is the root bridge since it having the smallest ID. Both B3 and

 

B5 are connected to LAN A, but B5 is the designated bridge since it is closer to the root.

 

Similarly B5 and B7 are connected to LAN B, but B5 is the designated bridge even they are

 

equally closer to the root since B5 having smallest ID.

 

Switching & Bridging | Computer Networks - Computer Science Engineering (CSE)

 

The bridges have to exchange configuration messages with each other and then decide whether or not they are the root or a designated bridge based on this message. The configuration contains three pieces of information.

 

1.     The ID for the bridge that is sending the message

 

2.     The ID for what the sending bridge believes to be the root bridge

 

3.     The distance, measured in hops, from the sending bridge to the root bridge. Initially each bridge thinks it is the root bridge, so the configuration message will contain the sending and root same ID. By receiving the configuration message from other bridges they select the root bridge. The selection will be by,

  •  It identifies a root with a smaller ID
  • It identifies a root with an equal ID but with a shorter distance
  • The root ID and distance are equal, but the sending bridge has a smaller ID

 

BROADCAST AND MULTICAST

Most LANs support both broadcast and multicast; then bridges must also support these two features.

Broadcast is simple, each bridge forward a frame with a destination broadcast address out on each active port other that the one on which the frame was received. In multicasting, each host deciding for itself whether or not to accept the message.

 

The document Switching & Bridging | Computer Networks - Computer Science Engineering (CSE) is a part of the Computer Science Engineering (CSE) Course Computer Networks.
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FAQs on Switching & Bridging - Computer Networks - Computer Science Engineering (CSE)

1. What is the difference between switching and bridging in Computer Science Engineering (CSE)?
Ans. Switching and bridging are both techniques used in computer networks to connect devices. Switching refers to the process of forwarding data packets between different network segments based on the destination address. On the other hand, bridging involves connecting two or more network segments to form a single network. While both techniques serve the same purpose of connecting devices, switching is typically used in larger networks, while bridging is commonly used in smaller networks or to extend network coverage.
2. What are the advantages of switching in Computer Science Engineering (CSE)?
Ans. Switching offers several advantages in computer networks. Firstly, it allows for faster data transmission as it establishes a dedicated path between the source and destination devices. Secondly, switching enables simultaneous communication between multiple devices by creating separate channels for each connection. Additionally, switching enhances network security by isolating network traffic and preventing unauthorized access to data. Lastly, switching provides scalability, allowing networks to easily expand by adding more switches to accommodate additional devices.
3. Can switching and bridging be combined in Computer Science Engineering (CSE)?
Ans. Yes, switching and bridging can be combined in computer networks. This is commonly known as bridged switching or switch bridging. In this approach, switches are used to connect multiple network segments, similar to bridging. However, the switches also incorporate switching capabilities to improve performance and efficiency. Bridged switching offers the benefits of both techniques, allowing for the extension of network coverage while maintaining fast and reliable data transmission.
4. What are some common protocols used in switching and bridging in Computer Science Engineering (CSE)?
Ans. There are several protocols commonly used in switching and bridging. Some examples include: 1. Ethernet: Ethernet is a widely used protocol for local area networks (LANs) that defines how data is transmitted over a network using switches or bridges. 2. Spanning Tree Protocol (STP): STP is a network protocol that prevents loops in bridged or switched networks by dynamically creating a loop-free logical topology. 3. Rapid Spanning Tree Protocol (RSTP): RSTP is an updated version of STP that provides faster convergence and improved network performance. 4. VLAN Trunking Protocol (VTP): VTP is used to manage the addition, deletion, and renaming of VLANs on a network-wide basis. 5. Virtual Router Redundancy Protocol (VRRP): VRRP is a protocol that provides automatic default gateway selections for routers participating in a LAN.
5. How do switching and bridging improve network performance in Computer Science Engineering (CSE)?
Ans. Switching and bridging improve network performance in several ways. By creating dedicated paths for data transmission, switching minimizes collisions and improves overall network efficiency. Switches also have the ability to filter and forward packets only to the intended destination, reducing unnecessary network traffic. Bridging extends network coverage by connecting multiple network segments, allowing devices to communicate seamlessly. This eliminates the need for long network cables and enhances network scalability. Overall, both techniques contribute to faster data transmission, reduced latency, and improved network reliability.
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