Content structure:
OSPF routing protocol:
Open Shortest Path First (Open Shortest Path First, OSPF) is a dynamic routing protocol is widely used as a link-state routing protocol, the route change fast convergence, no routing loops, supports variable length subnet advantage (VLSM) and aggregated level zoning and so on. The OSPF protocol used in the network, most of the route calculated by the OSPF protocol and self-generating, without the network administrator manually configured, when the network topology changes, the protocol can be automatically calculated, the route correction, which greatly facilitates network management.
Routes into types : DR BDR ABR ASBR
Five regions: the backbone area, the standard area, peripheral area, the peripheral area of deposit, non-deposit peripheral region
Five Packet Type : Hello packet, the DBD packet, the LSR , the LSU (the LSA) , LSAck
Six kinds lLSA :
Seven states:
basic concept:
OSPF area
To accommodate large networks, OSPF plurality of divided regions in the AS
Each OSPF router maintains a complete link-state information in your area
Area ID
Region ID can be expressed as - a decimal number
IP can also be expressed as a
The backbone area Area 0
Responsible for routing information dissemination between regions
Non-backbone area
Router ID
IP addresses that uniquely identifies the OSPF area router
Router ID selection rule
Select router loopback interface. Numerically highest IP address
If no loopback interface, select the highest IP address in the physical port
Router ID can also be specified using the router-id command
DR and the BDR (designated router)
Other routers (DRothers) and DR and BDR only adjacency relationship
DR and BDR election method
Automatic DR and BDR election
网段上Router ID最大的路由器将被选举为DR,第二大的将被选举为BDR
手工选择DR和BDR
优先级范围是0~255,数值越大，优先级越高，默认为1
如果优先级相同，则需要比较Router ID
如果路由器的优先级被设置为0，它将不参与DR和DBR的选举
DR和BDR的选举过程
路由器的优先级可以影响-个选举过程，但是它不能强制更换已经存在的DR或BDR路由器，
Ospf的组播地址
224.0.0.5
224.0.0.6
OSPF的度量值为COST_
COST= 10的8次方/BW
最短路径是基于接口指定的代价(cost) 计算的
OSPF数据包
承载在IP数据包内，使用协议号89
OSPF的包类型
| OSPF的包类型 | 描述 |
| Hello包 | 用于发现和维持邻居关系，选举DR和BDR |
| 数据库描述包(DBD) | 用于向邻居发送摘要信息以同步链路状态数据库 |
| 链路状态请求包(LSR) | 在路由器收到包含新信息的DBD后发送，用于请求更详细的信息 |
| 链路状态更新包(LSU) | 收到LSR后发送链路状态通告(LSA) ，一个LSU数据包可能包含几个LSA |
| 链路状态确认包(LSAck） | 确认已经收到LSU, 每个LSA需要被分别确认 |
OSPF邻接关系的建立（也就是七种状态）
OSPF启动的第一个阶段是使用Hello报文建立双向通信的过程
OSPF启动的第个阶段是建立完全邻接关系
OSPF将网络划分为四种类型
点到点网络(Point-to-Point)
广播多路访问网络(Broadcast MultiAccess, BMA)
非广播多路访问网络(None Broadcast MultiAccess,NBMA)
点到多点网络(Point-to-Multipoint)
OSPF的应用环境
从以下几方面考虑OSPF的使用
网络规模
网络拓扑
其他特殊要求
路由器自身要求
OSPF的特点
可适应大规模网络
路由变化收敛速度快
无路由环
支持变长子网掩码VLSM
支持区域划分
支持以组播地址发送协议报
OSPF与RIP的比较
OSPF的配置命令
启动OSPF路由进程
Router(config)# router ospf process-id
Interface and the area where the specified OSPF protocol runs
Router(config-router）# network address inverse-mask area area-id
Priority modify the interface
Router(config-if)#ip ospf priority priority
Cost modified values interface
Router(config-if)#ip ospf cost cost
View the routing table
Router#show ip route
View a list of neighbors and their status
Router#show ip ospf neighbor
View OSPF configuration
Router#show ip ospf
View the data structure of the OSPF interface
Router#show ip ospf interface type number