OSPF数据包（抓包分析）：

OSPF协议是跨层封装的协议，跨四层封装，直接将应用层的数据封装在网络层协议后面的。OSPF数据包的中协议号字段为89。

分析实验图：

OSPF数据包基本结构:头部信息+相应功能数据报文

OSPF的头部数据：

hello包:

DBD包:

LSR包:

LSU包:

LSAck:

OSPF的接口网络类型：

1.BMA网络：

接口类型为Broadcast，需要进行DR/BDR选举，hello 10S，dead time 40S

此时打开R4的ospf的G0/0/0的接口表和邻居表

[r4]display  ospf interface  g0/0/0

	 OSPF Process 1 with Router ID 1.1.1.1
		 Interfaces 


 Interface: 192.168.1.1 (GigabitEthernet0/0/0)
 Cost: 1       State: DR        Type: Broadcast    MTU: 1500  
 Priority: 1
 Designated Router: 192.168.1.1
 Backup Designated Router: 192.168.1.2
 Timers: Hello 10 , Dead 40 , Poll  120 , Retransmit 5 , Transmit Delay 1

[r5]display ospf peer 

	 OSPF Process 1 with Router ID 2.2.2.2
		 Neighbors 

 Area 0.0.0.0 interface 192.168.1.2(GigabitEthernet0/0/0)'s neighbors
 Router ID: 1.1.1.1          Address: 192.168.1.1     
   State: Full  Mode:Nbr is  Slave  Priority: 1
   DR: 192.168.1.1  BDR: 192.168.1.2  MTU: 0    
   Dead timer due in 36  sec 
   Retrans timer interval: 5 
   Neighbor is up for 00:02:16     
   Authentication Sequence: [ 0 ] 

		 Neighbors 

 Area 0.0.0.0 interface 192.168.2.1(GigabitEthernet0/0/1)'s neighbors
 Router ID: 3.3.3.3          Address: 192.168.2.2     
   State: Full  Mode:Nbr is  Master  Priority: 1
   DR: 192.168.2.1  BDR: 192.168.2.2  MTU: 0    
   Dead timer due in 35  sec 
   Retrans timer interval: 5 
   Neighbor is up for 00:00:35     
   Authentication Sequence: [ 0 ]

此时会发现MA网络下，网络类型状态为Broadcast，能建立多个邻居关系，有DR和BDR，

2.P2P网络：

P2P网络，只能建立一个邻居关系，不需要进行DR/BDR的选举， hello 10S，dead time 40S

查看R对应的接口的网络类型：

[R1]display ospf interface  Serial  4/0/0

	 OSPF Process 1 with Router ID 1.1.1.1
		 Interfaces 


 Interface: 1.0.0.1 (Serial4/0/0) --> 1.0.0.2
 Cost: 48      State: P-2-P     Type: P2P       MTU: 1500  
 Timers: Hello 10 , Dead 40 , Poll  120 , Retransmit 5 , Transmit Delay 1

此时会发现P2P网络下，PPP的网络类型状态为P-2-P，接口类型也为P2P类，将自己的邻居直接标注出来，并且没有DR和BDR，而cost为48的原因是因为华为设备的接口遵循的是E1标准,最大的传输速率为2.048Mbps

②HDLC网络

此时修改PPP为HDLC网络，并重新查看接口类型

[R1]display ospf interface Serial 4/0/0

	 OSPF Process 1 with Router ID 1.1.1.1
		 Interfaces 


 Interface: 1.0.0.1 (Serial4/0/0) --> 1.0.0.2
 Cost: 48      State: P-2-P     Type: P2P       MTU: 1500  
 Timers: Hello 10 , Dead 40 , Poll  120 , Retransmit 5 , Transmit Delay 1

此时在P2P网络下，HDCL的网络类型状态依旧为P-2-P，接口类型也为P2P类，将自己的邻居直接标注出来，并且没有DR和BDR，而cost为48的原因是因为华为设备的接口遵循的是E1标准,最大的传输速率为2.048Mbps

③此时再次添加一个路由器，使用P2P进行连接（重启R1,R2,R3的ospf进程）

此时在R2上查看邻居表

[R2]display  ospf peer 

	 OSPF Process 1 with Router ID 2.2.2.2
		 Neighbors 

 Area 0.0.0.0 interface 1.0.0.2(Serial4/0/0)'s neighbors
 Router ID: 1.1.1.1          Address: 1.0.0.1         
   State: Full  Mode:Nbr is  Slave  Priority: 1
   DR: None   BDR: None   MTU: 0    
   Dead timer due in 31  sec 
   Retrans timer interval: 5 
   Neighbor is up for 00:21:29     
   Authentication Sequence: [ 0 ] 

		 Neighbors 

 Area 0.0.0.0 interface 2.0.0.1(Serial4/0/1)'s neighbors
 Router ID: 3.3.3.3          Address: 2.0.0.2         
   State: Full  Mode:Nbr is  Master  Priority: 1
   DR: None   BDR: None   MTU: 0    
   Dead timer due in 32  sec 
   Retrans timer interval: 5 
   Neighbor is up for 00:17:08     
   Authentication Sequence: [ 0 ]

证明：P2P网络，只能建立一个邻居关系，并且没有DR和BDR选举

3.环回接口：

实际无数据收发，学习到是32 位主机路由

查看环回接口的网络类型

<r4>display  ospf  interface  LoopBack  0

	 OSPF Process 1 with Router ID 1.1.1.1
		 Interfaces 


 Interface: 1.1.1.1 (LoopBack0)
 Cost: 0       State: P-2-P     Type: P2P       MTU: 1500  
 Timers: Hello 10 , Dead 40 , Poll  120 , Retransmit 5 , Transmit Delay 1

华为设备环回接口的开销值默认为0,这个值不受外界干扰(修改参考带宽不会影响环回接口的开销)

[r4-LoopBack0]ospf network-type broadcast --- 修改接口默认的网络类型
如果将环回接口的默认网络类型从P2P修改为Broadcast，则将还原环回接口真实的网络掩码

//此时去R5上查看，此时R4的环回已经修改为/24，而r6仍然为/32
<r5>display  ip routing-table  protocol ospf 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
         Destinations : 2        Routes : 2        

OSPF routing table status : <Active>
         Destinations : 2        Routes : 2

Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

        1.1.1.0/24  OSPF    10   1           D   192.168.1.1     GigabitEthernet
0/0/0
        3.3.3.3/32  OSPF    10   1           D   192.168.2.2     GigabitEthernet
0/0/1

OSPF routing table status : <Inactive>
         Destinations : 0        Routes : 0