Detailed description of practical application of OSPF Routing Technology

At present, China's OSPF routing technology has developed rapidly and is also widely used. So I have studied the characteristics and application of OSPF routing technology. I will share with you here, I hope it will be useful to you. Nowadays, many large enterprises use the OSPF Routing Technology in network planning, not only considering the compatibility of network devices, but also the advantage of OSPF over that of VPN, especially in network integration, for example: when the company merges or acquires other companies. The difference between OSPF and OSPF is not described here. Many people write a lot of good study notes when learning the OSPF routing technology. However, they basically use the experiment in the book, which is not representative in reality. Here, based on my experience, I would like to summarize the technical and engineering experience on OSPF route technical configuration. </P>

OSPF routing is a typical link-State routing protocol. It uses the COST overhead) as a measurement. Based on the topology table, the SPF algorithm is used to obtain the optimal path to the Target Based on the root node. It uses three tables: Neighbor table, topology table, and route table. Through these three tables, each vro can independently obtain the path to each target, instead of relying on neighbors to discover routes as far as vector protocols do. Ensures the authenticity and reliability of the route. The following are some of its features:

1. OSPF route technology update process

1) the router running OSPF routing technology sends Hello packets from all interfaces with OSPF routing technology enabled. If two routers share a data link and make the negotiation of some parameters defined in the Hello packet successful, the two routers can become neighbors Neighbor)

(2) adjacent Adjacency) can be imagined as a virtual point-to-point link formed between neighbors. Each router sends the link state advertisement, LSA) to its neighbors. LSA describes the link or interface information and link status information of all routers.

3) when the router receives the LSA from the neighbor, it records the LSA in its own link status database, link state database, LSDB), and then copies the LSA, send messages to other neighbors.

4) by flooding the flood throughout the region) LSA, all routers will establish consistent LSDB. When the information of all routers is synchronized, the router will use the SPF Shortest Path First, shortest Path First) algorithm calculates the Shortest Path to the target address

5) the router builds its own route table based on the SPF algorithm. The Hello packet exchanged between neighbors is called keepalive, And the LSA retransmits the packet once every 30 minutes.

2. Summary of related types

1) there are five network types:

Point-to-point network, broadcast network, NBMA network, point-to-point network, virtual link)

2) region type

There are 5 main types: Standard region, end stub) region, end-to-end totall stubby) region, half-end NSSA) region, and trunk region.

3) There are 11 types, mainly 6 types of LSA

1. Type 1: Router LSA:

Router lsa describes the links or interfaces connected to the physical interfaces of the ROUTER, and specifies the status and cost of the links. Vrouters in each OSPF route technology area generate the first LSA, which allows vrouters to know each other's link interfaces. Flood occurs only in the generated region.

2. Type 2: Network LSA:

The Network LSA is initiated by DR. It describes the routers in the OSPF routing technology area and floods only in the generated area.

3. Type 3: Network Summary LSA:

Nnetwork summary LSA is issued by the ABR. It informs other regions of the summary of a region, that is, it notifies the routers in other regions to contact me for these networks. This is a bit far away from the vector routing protocol and relies on the next hop router for routing.

4. Type 4: ASBR Summary LSA:

ASBR Summary LSA, which is also issued by the API, but it tells the routers in other regions to find the ASBR in the announcement for the network outside of a non-OSPF routing technology. it can be understood that the summary is generated by the ASBR but advertised by the API on behalf of the owner. It is a type of LSA that is specially set to E-bit by ASBR, and then forwarded to lsa4.

Run the show ip ospf database-summary command to view the type information of LSA. The types described above are the types that must be mastered. Otherwise, troubleshooting is impossible.