OSPF实验1：基本的OSPF配置

  实验步骤：

    1.首先在3台路由器上配 置物理接口，并且使用ping命令确保物理链路的畅通。

    2.在路由器上配置loopback接口：
    R1(config)#int loopback 0
    R1(config-if)#ip add 1.1.1.1 255.255.255.0
    R2(config)#int loopback 0
    R2(config-if)#ip add 2.2.2.2 255.255.255.0
    R3(config)#int loopback 0
    R3(config-if)#ip add 3.3.3.3 255.255.255.0
    路由器的RID是路由器接口的最高的IP地址，当有环回口存在是，路由器将使用环回口的最高IP地址作为起RID，从而保证RID的稳定。

    3． 在3台路由器上分别启动ospf进程，并且宣告直连接口的网络。
    R1(config)#router ospf 10
    R1(config-router)#network 192.168.1.0 0.0.0.255 area 0
    R1(config-router)#network 1.1.1.0 0.0.0.255 area 0
    R1(config-router)#network 192.168.3.0.0.0.255 area 0
    ospf的进程号只有本地意义，既在不同路由器上的进程号可以不相同。但是为了日后维护的方便，一般启用相同的进程号。
    ospf使用反向掩码。Area 0表示骨干区域，在设计ospf网络时，所有的非骨干区域都需要和骨干区域直连！
    R2，R3的配置和R1类似，这里省略。不同的是我们在R2和R3上不宣告各自的环回口。
    *Aug 13 17:58:51.411: %OSPF-5-ADJCHG: Process 10, Nbr 2.2.2.2 on Serial1/0 from LOADING to FULL, Loading Done
    配置结束后，我们可以看到邻居关系已经到达FULL状态。

    4. 在R1上查看路由表，可以看到以下信息：
        R1#show ip route
        Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route

          Gateway of last resort is not set

           1.0.0.0/24 is subnetted, 1 subnets
         C       1.1.1.0 is directly connected, Loopback0
         C    192.168.1.0/24 is directly connected, Serial1/0
         O    192.168.2.0/24 [110/65] via 192.168.1.2, 00:03:42, Serial1/0
         C    192.168.3.0/24 is directly connected, FastEthernet0/
        我们看到R1学到了192.168.2.0/24这个网段的路由。后面的数字[110/65]，分别表示OSPF的管理距离（AD）和路由的Metric 值
    OSPF的Metric值是由cost值逐跳累加的。Cost=100Mb/带宽值。

    5. 在R1上show ip ospf neighbor 、show ip ospf interface
       R1#show ip ospf neighbor

    Neighbor ID     Pri   State           Dead Time   Address         Interface
    3.3.3.3           1   FULL/BDR        00:00:34    192.168.3.3     FastEthernet0/0
    2.2.2.2           0   FULL/  -        00:00:32    192.168.1.2     Serial1/0

    我们看到R1和R3选取了DR和BDR，而R1和R2没有选取。

    在ospf的五种网络类型中。Point-to-Point,Point-to-Multipoint(广播与非广播)这三种网络类型不选取DR与 BDR; Broadcast,NBMA选取DR与BDR。

    R1#show ip ospf interface
    FastEthernet0/0 is up, line protocol is up
      Internet Address 192.168.3.1/24, Area 0
      Process ID 10, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
      Transmit Delay is 1 sec, State DR, Priority 1
      Designated Router (ID) 1.1.1.1, Interface address 192.168.3.1
      Backup Designated router (ID) 3.3.3.3, Interface address 192.168.3.3
      Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
        oob-resync timeout 40
        Hello due in 00:00:03
      Index 3/3, flood queue length 0
      Next 0x0(0)/0x0(0)
      Last flood scan length is 1, maximum is 1
      Last flood scan time is 0 msec, maximum is 0 msec
      Neighbor Count is 1, Adjacent neighbor count is 1
        Adjacent with neighbor 3.3.3.3  (Backup Designated Router)
      Suppress hello for 0 neighbor(s)
    Serial1/0 is up, line protocol is up
      Internet Address 192.168.1.1/24, Area 0
      Process ID 10, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64
      Transmit Delay is 1 sec, State POINT_TO_POINT,
      Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
        oob-resync timeout 40
        Hello due in 00:00:02
      Index 1/1, flood queue length 0
      Next 0x0(0)/0x0(0)
      Last flood scan length is 1, maximum is 1
      Last flood scan time is 4 msec, maximum is 4 msec
      Neighbor Count is 1, Adjacent neighbor count is 1
        Adjacent with neighbor 2.2.2.2
      Suppress hello for 0 neighbor(s)
    Loopback0 is up, line protocol is up
      Internet Address 1.1.1.1/24, Area 0
      Process ID 10, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
      Loopback interface is treated as a stub Host

    在这里我们看到环回口的网络网络类型是Loopback，这是一种特殊的网络类型，只针对环回口存在。我们到R2上看看路由表：

    R2#show ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route

    Gateway of last resort is not set

         1.0.0.0/32 is subnetted, 1 subnets
    O       1.1.1.1 [110/65] via 192.168.1.1, 00:12:34, Serial1/0
         2.0.0.0/24 is subnetted, 1 subnets
    C       2.2.2.0 is directly connected, Loopback0
    C    192.168.1.0/24 is directly connected, Serial1/0
    C    192.168.2.0/24 is directly connected, Serial1/1
    O    192.168.3.0/24 [110/65] via 192.168.1.1, 00:12:34, Serial1/0
                        [110/65] via 192.168.2.3, 00:12:34, Serial1/1

    R2的路由表显示来自环回口的路由，掩码为/32，既我们所说的“主机路由”。在实际应用中，环回口以32位的居多，用作ospf的管理接口。但是如果你 想让环回口模拟一个网段，我们可以通过以下配置来消除。

    R1(config)#int loopback 0
    R1(config-if)#ip ospf network point-to-point

    环回口只能配置成point-to-point这种类型，不可以配置成其它的类型。

    回到R2查看路由表：

    R2#show ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route

    Gateway of last resort is not set

         1.0.0.0/24 is subnetted, 1 subnets
    O       1.1.1.0 [110/65] via 192.168.1.1, 00:00:24, Serial1/0
         2.0.0.0/24 is subnetted, 1 subnets
    C       2.2.2.0 is directly connected, Loopback0
    C    192.168.1.0/24 is directly connected, Serial1/0
    C    192.168.2.0/24 is directly connected, Serial1/1
    O    192.168.3.0/24 [110/65] via 192.168.1.1, 00:00:24, Serial1/0
                        [110/65] via 192.168.2.3, 00:00:24, Serial1/1

    我们看到主机路由没有了，取而代之的是一个/24的网段。