OSPF protocol
Outline
OSPF routing protocol Overview:
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 Type:
DR BDR ABR ASBR
Five regions:
The backbone of regional standards exist peripheral region peripheral region regional non-existence of peripheral areas
Five packet types:
Six kinds of LSA
basic concepts
Autonomous System (AS)
Interior Gateway Protocol (IGP) (including RIP, OSPF, ISIS)
Exterior Gateway Protocol (EGP) (including BGP) Ali Baba, commonly known as the Flying Platform
OSPF Area
OSPF area (Area 0 is the backbone area, and only one, other areas are non-backbone area)
in order to adapt to large networks, OSPF AS divided into multiple areas within
each OSPF router maintains a complete link-state in your area information
Router ID
IP addresses that uniquely identifies the OSPF area router
Router ID selection rule
1. Select lookback router IP address of the interface on the highest value of
2. If there is no lookback interfaces, select the highest IP address in the physical port
3. Router ID may be specified (selected manually) using the router-id command
TIP: the second is not recommended for use (except for a row of routing addresses all down, otherwise the loopback address has been helpful)
DR (primary) and BDR (backup)
network topology is more reliable, and the central star structure routing problems can not occur otherwise, all routes were not working properly.
其他路由器（DRothers）只和DR及BDR形成邻接关系
DR和BDR的选举方法
1.自动选举DR和BDR
（1）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
2.手动选择DR和BDR
（1）优先级范围是0~255，数值越大，优先级别越高，默认为1
（2）如果优先级相同，则需要比较Router ID
（3）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
OSPF的组播地址
224.0.0.5：承载地址，DR和BDR将错误地址发送给其它的路由（用来发话）；
224.0.0.6：监听其它路由的反馈信息。
(RIPv2：224.0.0.9)
OSPF的度量值为COST
COST=108/BW
最短路径是基于接口指定的代价（cost）计算的
TIP：Cost值越低越好，度量值是带宽。
OSPF启动的第一个阶段是使用Hello报文建立双向通信的过程七个状态
1、down状态：没有打招呼确定邻居状态之前
2、init状态：收到hello包之后激活
3、2-Way状态：建立交互（选举DR和BDR，只选出两个最大的，但是不确定DR和BDR）
4、ExStart：准启动状态（确定DR和BDR身份）
5、Exchange状态：交换数据（DBD报文，LSAck）
6、Loading状态：加载（数据类型：LSR/LSU/LSA/LSAck）
7、Full状态：收敛
OSPF network is divided into four types
1 point network
2. broadcast multi-access network
3. The non-broadcast multi-access network
4. multipoint networks
OSPF features
1 may be adapted to large-scale network
2. routing convergence speed change
3. No routing loop
4. supports variable length subnet mask VLSM
5. The zoning support
6. Support protocol packets to multicast addresses.
Comparison of OSPF and RIP's
