0x01.OSPF message
1.报文：Packet
2.链路状态通告：LSA
3.OSPF是动态路由协议，需要报文来维护关系
4.IP承载OSPF报文：
| Link Layer Header | IP packet Header | OSPF Protocol Packet | Frame Checksum |
(1) IP protocol number is 89, used to identify the OSPF
(2) OSPF Protocol Packet = OSPF Protocol Header (header) + OSPF Packet Types (details of a certain type of package)
5.OSPF报文头部：8部分
(1) Version: 2 (default)
（2）Message Type：5种
（3）Packet Length
（4）Source Router ID
（5）Area ID
（6）Checksum
（7）Auth Type
（8）Auth Data
// As shown below, the OSPF packet header:
// Check capture binding OSPF packet header:
6.OSPF的认证
(1) certification purposes: to fulfill the legality (is legal for end equipment)
(2) the results of authentication: OSPF neighbors can be established, as well as updating and redness LSA, otherwise no neighbors (there will be no routing)
(3) a simple plain text authentication (password: huawei)
AR2：
int s1/0/0
ospf authentication-mode simple plain huawei
AR3：
int s1/0/0
ospf authentication-mode simple plain huawei
// combination of packet capture to view plain text authentication:
7.OSPF的报文类型和作用
(1) hello packets (discover and maintain neighbor relationships)
(2) DB Description (database description, sending link-state database summary)
(3) LS Request (LS Request message, requesting a particular link state information)
(4) LS Update (LS Update message sent detailed link state information)
(5) LS Acknowledge (LS acknowledgment message, the acknowledgment message transmitted)
0x02. Link state advertisement, LSA
1.LSA是什么？
(1) LSA, the LSA
(2) LSA is not the LS Acknowledge message
(3) LSA belongs to the LSU some entries
2.LSA的类型：（这里只简要描述两种类型的LSA）
(1) Class 1 LSA: Router-LSA, router LSA (produced by each router; description port link status, the area flooding)
(2) Class 2 LSA: Network-LSA, network LSA (DR generated; network broadcast / NBMA; described which devices belong to the network, flooding the area)
3.怎么学习LSA：
(1) Who? (Who produced the type of LSA)
(2) Where? (LSA its scope of action where)
(3) doing? (LSA This used to do)
4.查看ospf的LSA
（1）dis ospf lsdb
（2）dis ospf lsdb router
（3）dis ospf lsdb network
