Routing | Computer Networks - Computer Science Engineering (CSE) PDF Download

Routing

A switch or router needs to be able to look at the packet’s destination address and then to determine which of the output ports is the best choice to get the packet to that address.

The forwarding table is used when a packet is being forwarded and so must contain enough information to accomplish the forwarding function. This means that a row in the forwarding table contains the mapping from a network number to an outgoing interface and some MAC information, such as the Ethernet address of the next hop.

The routing table is the table that is built up by the routing algorithms as a precursor to building the forwarding table. It generally contains mappings from network numbers to next hops. It may also contain information about how this information was learned, so that the router will be able to decide when it should discard some information.

The forwarding table needs to be structured to optimize the process of looking up a network number when forwarding a packet, while the routing table needs to be optimized for the purpose of calculating changes in topology. The forwarding table may even be implemented in specialized hardware, whereas this is rarely if ever done for the routing table.

Routing | Computer Networks - Computer Science Engineering (CSE)

Network as a Graph
Routing is, in essence, a problem of graph theory. a graph representing a network. The nodes of the graph, labeled A through F, may be hosts, switches, routers, or networks. The edges of the graph correspond to the network links. Each edge has an associated cost, which gives some indication of the desirability of sending traffic over that link. The basic problem of routing is to find the lowest-cost path between any two nodes, where the cost of a path equals the sum of the costs of all the edges that make up the path.

Routing | Computer Networks - Computer Science Engineering (CSE)

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FAQs on Routing - Computer Networks - Computer Science Engineering (CSE)

1. What is routing in computer networks?
Ans. Routing in computer networks is the process of selecting the best path or route for network traffic to reach its destination. It involves determining the optimal path based on various factors such as network congestion, available bandwidth, and the shortest distance between the source and destination.
2. How does routing work in a computer network?
Ans. Routing works by using routing protocols and algorithms to analyze network conditions and make decisions on how to forward data packets. Each router in the network maintains a routing table that contains information about the available paths, and it uses this information to determine the best next hop for each packet.
3. What are the different types of routing protocols?
Ans. There are several types of routing protocols, including distance-vector protocols, link-state protocols, and hybrid protocols. Distance-vector protocols, such as RIP (Routing Information Protocol), use hop count as the metric to determine the best path. Link-state protocols, like OSPF (Open Shortest Path First), consider various factors like bandwidth, delay, and reliability. Hybrid protocols, such as EIGRP (Enhanced Interior Gateway Routing Protocol), combine features of both distance-vector and link-state protocols.
4. What is static routing?
Ans. Static routing is a type of routing where network administrators manually configure the routing table on each router. In this approach, the routing decisions are not dynamically adjusted based on network conditions. Static routing is commonly used in small networks or for specific network configurations where the path to the destination remains constant.
5. What is dynamic routing?
Ans. Dynamic routing is a routing method where routers exchange information with each other to automatically update their routing tables. This allows routers to adapt to changes in network topology or traffic conditions. Dynamic routing protocols, such as RIP, OSPF, and BGP (Border Gateway Protocol), facilitate this exchange of information and enable routers to make real-time routing decisions.
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