Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE) PDF Download

Link State(OSPF)
Link-state routing is the second major class of intra domain routing protocol. The starting assumptions for link-state routing are rather similar to those for distance-vector routing. Each node is assumed to be capable of finding out the state of the link to its neighbors (up or down) and the cost of each link.

Reliable Flooding
Reliable flooding is the process of making sure that all the nodes participating in the routing protocol get a copy of the link-state information from all the other nodes. As the term “flooding”suggests, the basic idea is for a node to send its link-state information out on its entire directly connected links, with each node that receives this information forwarding it out on all of its links. This process continues until the information has reached all the nodes in the network.

  • The ID of the node that created the LSP;
  • A list of directly connected neighbors of that node, with the cost of the link to
  • each one;
  • A sequence number;
  • A time to live for this packet.

One of the most widely used link-state routing protocols is OSPF. The first word, “Open,” refers to the fact that it is an open, nonproprietary standard, created under the auspices of the IETF. The “SPF” part comes from an alternative name for link-state routing.

Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE)

  • Authentication of routing messages
  • Additional hierarchy
  • Load balancing

Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE)

OSPF Header Format

There are several different types of OSPF messages, but all begin with the same header The Version field is currently set to 2, and the Type field may take the values 1 through 5. The SourceAddr identifies the sender of the message, and the AreaId is a 32-bit identifier of the area in which the node is located. The entire packet, except the authentication data, is protected by a 16-bit checksum using the same algorithm as the IP header (see Section 2.4). The Authentication type is 0 if no authentication is used; otherwise it may be 1, implying a simple password is used, or 2, which indicates that a cryptographic authentication checksum, of the sort described in Section 8.3, is used. In the latter cases the Authentication field carries the password or cryptographic checksum.Of the five OSPF message types, type 1 is the “hello” message, which a router sends to its peers to notify them that it is still alive and connected as described above.

The remaining types are used to request, send, and acknowledge the receipt of link-state messages. The basic building block of link-state messages in OSPF is known as the linkstate advertisement (LSA). One message may contain many LSAs. The LS sequence number is used exactly as described above, to detect old or duplicate LSAs. 

The document Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE) is a part of the Computer Science Engineering (CSE) Course Computer Networks.
All you need of Computer Science Engineering (CSE) at this link: Computer Science Engineering (CSE)
21 videos|107 docs|66 tests

Up next

FAQs on Link State (OSPF) - Computer Networks - Computer Science Engineering (CSE)

1. What is Link State in OSPF?
Ans. Link State in OSPF refers to the routing protocol's mechanism of exchanging information about network topology among routers. Each router in the OSPF network maintains a link state database (LSDB) that contains information about the state of all links and routers in the network. This information is used to build a complete map of the network, enabling routers to make informed routing decisions.
2. How does OSPF use Link State information?
Ans. OSPF uses Link State information to construct a complete network topology map and calculate the shortest path to each destination. Each router maintains a link state database (LSDB) that stores information about links, routers, and their states. By exchanging link state advertisements (LSAs) with other routers, OSPF routers build and update their LSDBs. This information helps routers determine the best path to reach a destination and ensures efficient and reliable routing in the network.
3. What are the advantages of using Link State routing in OSPF?
Ans. Link State routing in OSPF offers several advantages, including: - Faster convergence: Link State routing protocols, such as OSPF, have faster convergence times compared to distance vector protocols. This is because OSPF routers exchange only the state of their own links, reducing the amount of information that needs to be shared during network changes. - Scalability: OSPF's link state database (LSDB) allows routers to have a complete view of the network topology, enabling efficient routing in large networks. The LSDB contains summarized information about the entire network, reducing the size of routing tables and enhancing scalability. - Flexibility: OSPF supports hierarchical routing, enabling the network to be divided into multiple areas. Each area has its own LSDB, which reduces the complexity of routing and improves efficiency. Additionally, OSPF supports multiple routing metrics, allowing administrators to prioritize certain paths over others.
4. How does OSPF ensure the reliability of Link State information?
Ans. OSPF ensures the reliability of Link State information through mechanisms such as flooding and database synchronization. When a router receives a new link state advertisement (LSA), it floods the LSA to all other routers in the network, ensuring that every router has an up-to-date LSDB. Additionally, OSPF routers exchange database description (DBD) packets to synchronize their LSDBs. This synchronization process compares LSAs and ensures that all routers have consistent and accurate Link State information.
5. Can OSPF operate without Link State information?
Ans. No, OSPF cannot operate without Link State information. Link State routing is an essential component of OSPF and is necessary for routers to build a complete view of the network topology. Without Link State information, routers would not have the necessary knowledge of network links, their states, and the shortest paths to each destination. OSPF relies on the exchange of Link State information to provide efficient and reliable routing in the network.
21 videos|107 docs|66 tests
Download as PDF

Up next

Explore Courses for Computer Science Engineering (CSE) exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

study material

,

mock tests for examination

,

Semester Notes

,

Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE)

,

Sample Paper

,

Free

,

Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE)

,

Extra Questions

,

Previous Year Questions with Solutions

,

practice quizzes

,

video lectures

,

shortcuts and tricks

,

MCQs

,

ppt

,

Summary

,

pdf

,

past year papers

,

Important questions

,

Viva Questions

,

Objective type Questions

,

Exam

,

Link State (OSPF) | Computer Networks - Computer Science Engineering (CSE)

;