CCNA OSPF features and common terminology

First, the OSPF characteristics:

1.IETF Standard: Open room agreement, supported by different manufacturer's equipment

2. No loop by protocol: the implementation of SPF algorithm, will not produce loops

3. No class routing protocol: Support for VLSM and CIDR

4. Have unrestricted hop count: can be applied with large network

5. Level: Easy to expand, router burden will not increase with the size of the network increased dramatically

6. Regionalization design: Reduce the flow of routing updates, reduce the use of memory, CPU and bandwidth

7. Fast convergence: Trigger-type update

8. Support Validation: Support for validation of zones and links

Second, OSPF terminology

1. Link: Interfaces are added to the OSPF process and are considered a link to OSPF

2. Link state (link-state): Includes IP address and subnet mask, network type of interface, link cost, neighbor on link

3. Router ID (Router ID, RID): ① manually specify ② the highest IP address in the interface, ③ the highest IP address in all active home interfaces

4. Neighbour (neighbor): connected to a public network

5. Adjacency (adjacency): OSPF only shares routing information with neighbors that have established adjacency relationships but ① not all neighbors can become adjacency relations ② is not a neighboring router is a neighbor (virtual circuit)

6. Region (area): OSPF is divided into the link area to achieve tiered design. Routers within the same as (autonomous system) are divided into multiple regions, and routers across multiple regions become ABR (area boundary routers). Area 0 is the backbone

7. Designated router (designated router, DR): All Drother routers have an adjacency relationship with Dr and Bdr, and Dr represents all routers in the multiple access network, and each router sends topology changes to DR and BRD. Then the DR notifies the other routers in the Multiple access network

8. Alternate designated router (backup designated router i.e. BDR): When Dr is offline, BRD is turned into Dr to replace Dr's work

9. Cost: The only measure used by OSPF is cost. Each link has a cost that can be calculated based on the bandwidth of the link, or it can be artificially modified

Three, OSPF package type

1.hello

① establish and maintain the adjacency relationship between OSPF routers ② to select DR and DBR in multiple access networks

2.DBD (db description, Database Status description package)

Send a brief description of the LSDB, compare the receiving router with the local LSDB, and detect LADB synchronization

3.LSR (link-state request, link State requests package)

The receiving router can send LSR to request detailed information about some entries in the router's DBD

4.LSU (link-state Update, link State update package)

Update the OSPF routing information and reply to the LSR request.

LSU is divided into multiple types of LSA (link-state advertisement, link State notification), such as: Type 1--router LSA; type 2--network LSA

5.LSAck (link-state acknowledgement, link status confirmation)

When a LSU is received, the router sends Lsack to confirm

Iv. The establishment stage of the OSPF neighbor relationship

1.down: Initial state, no exchange information

2.init: Initialization phase, the neighbor's hello message received, but the neighbors have not found their

3.two-way: A two-way phase, a neighbor relationship is established, but routing information cannot be shared

4.exstart: Ready to start the swap phase, with Hello Group to negotiate the main/from the router relationship

5.exchange: Start the exchange phase, the local LSDB with the DBD message to describe, sent to the neighbors

6.loading: Loading phase, sending LSR message to the neighbor requesting the other's routing entry details

7.full: Fully contiguous, the router becomes full adjacency