Network layers forwarding.docx

network layers

1. network layers-forwarding Anusua Basu Roll no - 1703 BCA 3 rd semester, midnapore college

2. content Introduction What is network layer Network layer services What is forwarding Forwarding techniques Forwarding process

3. Introduction 7 layer of OSI model Physical layer Data link layer Network layer Transport layer Session layer Presentation layer Application layer seven layer pf OSI model network layer is layer 3. Forwarding means to place the packet in it’s to it’s destination.

4. What is network layer : In the seven layer of osi model of computer networking, the network layer is 3. the network layer is responsible for packet forwarding including routing through intermediate routers. It handles the service requests from the transport layer and further forwards the service request to the data link layer. It determine the route from the source to the destination and also manages the traffic problems such as switching, routing and control the congestion of data packets. The main role of the network layer is to move the packets from sending host to the receiving host.

5. Network layer services : The services which are offered by the network layer protocol are as follows

6. What is forwarding : Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table. When a host has a packet to send or when a router has received a packet to be forward it looks at this table to find the route to the final destination These are two other services offered by the network layer. In a network these are a number of roots available from the source to the destination. The network layer specifies has some strategies which found out the best possible route. This process is referred to as routing. There are a number of routing protocols which are used in this process and they should be run to help the routes coordinate with each other and help in establishing communication throughout the network.

7. Forwarding techniques Several techniques can make the size of the routing table manageable and also handle issues such as security. We briefly discuss these methods here. Next-hop method versus route method : Network-specified method versus host-specified method : Default method:

8. Next-hop method versus route method : One technique to reduce the contents of a routing table is called the next-hop method. In this technique, the routing table holds only the address of the next hop instead of information about the complete route(route method). The entries of a routing table must be consists with one another. The below figure show how routing tables can be simplified by using this technique.

9. Network specified method versus host specified method A second technique to reduce the routing table and simplify the searching process is called the network specified method. Here, instead of having an entry for every destination host connected to the same physical network(host specified method), we have only one entry that defines the address of the destination network itself. In other words, we treat all hosts connected to the same network as one single entity. For example, if 1000 hosts are attached to the same network. Only one entry exists in the routing table instead of 1000. the given figure show the concept.

10. Default method Another technique to simplify routing is called the default method. In given fig host a is connected to a network with two routers. Router r1 routes the packets to hosts connected to network n2. however, for the rest of the internet, router r2 is used. So instead of listing all network in the entire internet, host a can just have one entry called the default(normally define as network address 0.0.0.0)

11. Forwarding process : Let us discuss the forwarding process, we assume that hosts and routes use classless addressing because classfull addressing can be treated as a special case of classless addressing. In classless addressing, the routing table need to have one row of information for each block involved. The table need to be searched based on the network address(first address in the block). Unfortunately, the destination address to solve the problem, we need to include the mask in the table, we need to have an extra coloum that includes the mask for the corresponding block. The given figure show a simple forwarding module for classless addressing.

12. Simplified forwarding module in classless address

13. Bibliography : Geeks for geeks, java point, tutorials point. Slideshare.com Data communications and networking by behrouza a. forouzan

14. any question?