table of Contents
- concept
- RIP disadvantages
- OSPF features
- OSPF principle
- OSPF message
- Router ID, neighbors, and adjacency
- Neighbor discovery
- Database synchronization
- DR & BDR election
- OSPF area
1. Concept
Open Shortest Path First (Open Shortest Path First) protocol is an internal gateway routing protocol based on link state defined by IETF.
2. Disadvantages of RIP
- Slow convergence
- Loops
- Poor scalability
- Does not support authentication
3. Features of OSPF
- No loop
- Fast convergence
- Good scalability
- Support authentication
4. OSPF principle
- LSA: Link State Advertisement
- LSDB: Link state database (each device will have a link state database after OSPF is enabled)
5. OSPF message
- OSPF packets are encapsulated in IP packets with a protocol number of 89.
- There are 5 types of OSPF packets:
- Hello message: maintain neighbor relationship
- DD (Database Description) message: database description message
- LSR（Link State Request）报文
- LSU（Link State Update）报文
- LSACK（Link State Acknowledgment）报文
6. Router ID, neighbors and adjacency
- Neighbor: No routing interaction
- Adjacency: routing interaction
Adjacency is based on neighbors
- Router ID: equivalent to the name of the router
In an OSPF, the router ID cannot be repeated, it is an IP address format ID.
7. Neighbor discovery
- Network Mask: Subnet mask
- Hello Interval: Hello time (about 10s)
- Router Dead Interval: timeout time (40s (hello time * 4))
- Designated Router: designated router
- Backup Designated Router: Backup router
- Neighbor: Declaring neighbor relations
Hello messages are used to discover and maintain OSPF neighbor relationships.
8. Database synchronization
- Exstart: select the master-slave relationship of the database
- Exchange: Start to exchange routing information
9. DR & BDR election
Priority: The priority
DR is elected based on the DR priority value of the port.
10. OSPF area
- Backbone area: area0
- Non-backbone area: area is non-zero
The non-backbone area must be connected to the backbone area
