OSPF ROUTING

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OSPF ROUTING by Mind Map: OSPF ROUTING

1. Supernetting (used to aggregate Class C networks)

2. all router are configured for the backbone ospf area 0.0.0.0

3. OSPF neighborship is a relationship between two routers that allow them to see and understand each other

4. Quicker than RIP since routing updates are sent immediately instead of periodically.

5. OSPF is a widely used IGP in large enterprise networks

6. ospf hello packet is used to establish neighbour adjancies

7. OSPFv3 for IPv6 & OSPFv2 for IPv4

8. Both routers must have the same hello and dead intervals configured

9. OSPF is specifically designed to operate with larger networks.

10. OSPF uses small hello packets to verify link operation with out transferring large tables

11. Updates via Link State Advertisements (LSAs)

12. loop-free

12.1. maximum hop metric is 65,535

13. It uses the SPF algorithm, developed by Dijkstra.

14. Supports authentication using passwords and other methods.

15. Use a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs)

15.1. OSPF establishes and maintains neighbor relationships for exchanging routing updates with other routers.

16. Load balance network traffic between multiple paths of the same metric value.

17. OSPF will then construct three tables Neighbor Table, Topology Table and Routing Table.

17.1. Neighbor Table: Contains all discovered OSPF neighbors with whom routing information will be interchanged

17.1.1. Topology Table: Contains the entire road map of the network with all available OSPF routers and calculated best and alternative paths.

17.1.1.1. Routing Table: Contain the current working best paths that will be used to forward data traffic between neighbors

18. Each OSPF router passes along information about the routes and costs they’ve heard about to all of their adjacent OSPF routers, called neighbors.

19. Is a public (non-proprietary) routing protocol.

19.1. used to find the best path for packets as they pass through a set of connected networks

19.1.1. has largely replaced the older Routing Information Protocol (RIP) in corporate networks.

19.1.1.1. The OSPF (Open Shortest Path First) protocol is one of a family of IP Routing protocols, and is an Interior Gateway Protocol (IGP) for the Internet, used to distribute IP routing information throughout a single Autonomous System (AS) in an IP network.

19.1.1.1.1. The OSPF protocol is a link-state routing protocol, which means that the routers exchange topology information with their nearest neighbors.

19.1.1.1.2. It implements Dijkstra's algorithm, also known as the shortest path first (SPF) algorithm

19.1.2. OSPF has RIP support built in both for router-to-host communication and for compatibility with older networks using RIP as their primary protocol.

19.1.2.1. Each router uses the received messages to build up an identical database that describes the topology of the AS.

19.1.2.1.1. Open Shortest Path First (OSPF) is a standard routing protocol that’s been used the world over for many years

20. The OSPF routing protocol has largely replaced the older Routing Information Protocol (RIP) in corporate networks

21. OSPF sends only the part that has changed and only when a change has taken place

22. When routes change, the time it takes OSPF routers to find a new path between endpoints with no loops (which is called "open") and that minimizes the length of the path is called the convergence time.

23. OSPF routers rely on cost to compute the shortest path through the network between themselves.

24. OSPF is a widely used IGP in large enterprise networks.

25. OSPF announces subnet masks.

25.1. supports:

25.1.1. CIDR (Classless Inter Domain Routing)

25.1.2. VLSM (Variable Length Subnet Mask)

25.1.3. Non-contiguous network segments

26. Allow extensive control of routing updates

27. Uses less bandwidth.

27.1. since transmission take place only when routing changes occur.

28. Uses hello packets to discover neighbor routers

29. Two routers speaking OSPF to each other exchange information about the routes they know about and the cost for them to get there

30. OSPF was developed as a replacement for the distance vector routing protocol RIP.

31. Both routers must use the same OSPF area.

32. OSPF routers rely on cost to compute the shortest path through the network between themselves and a remote router or network destination

33. A stub area is an area with a single path in to and out of the area

34. PACKET TYPES

34.1. HELLO

34.2. DATABASES DESCRIPTION (DBD)

34.3. LINK-STATE REQUEST (LSR)

34.4. LINK-STATE ACK(LSAck)

34.5. LINK-STATE UPDATE (LSU)

35. OSPF router have to become neighbors first before exchanging LSA

36. ospf routing used to find the best path for packets

37. OSPF has better convergence than RIP. This is because routing changes are propagated instantaneously and not periodically.

37.1. Supported by practically every routing vendor

38. OSPF uses a metric called COST

38.1. The lower the cost,the better is the metric thus it is considered as the Best Path

39. OSPF allows for linking discontinuous parts of the backbone using a virtual link.

40. Is a public (non-proprietary) routing protocol.

41. OSPF is a routing protocol used to determine the best route for delivering the packets within an IP networks.

42. There is no limitation on the hop count.

42.1. OSPF uses IP multicast to send link-state updates.