OSPF Basics (FAQ from a great interactive simulation 1.1)

Q1. What is OSPF?
Answer: OSPF can be a connection express routing protocol. OSPF routers exchange their Link State Advertisement (OSPF LSA) to find out interface IP address from each and every other. Each router saves its LSAs in its Link State Database (LSDB.) Neighboring nodes synchronize their particular LSDBs. With dependable LSDBs, OSPF routers are able to calculate speediest walkways to achieve destinations.

Q2. What does OSPF do?

Answer: Roughly, OSPF goes by means of this particular stages:

1) Each OSPF node generates a new Router LSA to be able to describe it's program IP addresses. This LSA could be the most rudimentry LSA.

2) Routers find neighbors by means of flooding Hello. When two friends locate every other, they are in 2-way state.

3) Neighbors synchronize their LSDBs in several steps:

i. Send DD for you to acquire LSDB list from each other.

ii. Send Request to ask for missing LSAs.

iii. Send Update to monitor LSAs requested.

When not one but two neighbors possess the exact LSDB, they're just in Full Adjacency state.
4) With identical LSDB, routers have dependable familiarity with your system topology as well as program IP addresses. They can compute routing routes at home and redesign their routing tables. The selection associated with routing tables through OSPF routers gives the least paths somewhere between destinations.

Q3. What is usually Router LSA?
Answer: Each OSPF router creates a Router LSA in order to describe it's interfaces' IP addresses. In quite a very simple OSPF network, solely Router LSAs are generally needed to calculate shortest paths.

Q4. What does Router LSA do?
Answer: In a simple OSPF network (no LAN, no area), neighboring nodes exchange his or her Router LSAs and learn how quite a few hyperlinks its neighbor has, and their interface IP addresses. After neighbors propagation, many OSPF nodes have the very same group of Router LSAs inside their LSDBs. Now they have got identical perception of community topology.

Q5. How can certainly a router apply LSDB to help assess routing paths?
Answer: From LSDB, an OSPF node discovers a full topology involving your network: the volume of routers becoming connected; Individual router's interfaces along with his or her IP addresses; Interface link fees (OSPF metric). With these fine detail information, OSPF calculates least amount driveways and walkways to realize most of areas within LSDB.

For case [a], within the OSPF simulation, R1's LSDB contains not one but two Router LSAs:

1) R1 come LSA features two IP addresses: 192.168.1.0/24,192.168.3.0/30.
2) R2 come LSA is made up of a couple of IP addresses: 192.168.2.0/24,192.168.3.0/30.
After LSDB synchronization, R1 and R2 together have these types of a pair of LSAs. And they will be aware that R1 and R2 will be attached through the link 192.168.3.0. Now R1 can easily assess routing path to reach remote computer support destination 192.11.68.2.2 in addition to provides a great entry (192.168.2.0/24, S1/0) that will their routing table.

[a]: This case comes from a companion OSPF simulation. You can play this simulation interactively in the outer website posted below.

access point vs router