有类路由协议与无类路由协议

有类路由协议与无类路由协议
(一)有类路由协议
代表：RIPv1、IGRP              <=== RIPv1和IGRP都是距离矢量有类别的路由选择协议

特点：   

1、在发送的update包中不携带子网掩码信息
2、在主类边界路由器执行自动汇总，并且该自动汇总无法人工关闭
3、不支持VLSM，即同一个主网络下的子网若掩码长度不一致则会出现子网丢弃的

情况

主类边界路由器：如果某台Router上配置了多个网段，其中某些网段的信息必段通过某一个特定的网段向其它Router进行通告，而这个特定的网段与其它网段分属于不同的主类网络，那么这台Router就是主类边界路由器

实验：
 
                                                                             图 1-13
分析：
R1#debug ip rip
*Jul 29 20:25:54.239: RIP: sending v1 update to 255.255.255.255 via Serial1/0 (10.0.0.1)
*Jul 29 20:25:54.239: RIP: build update entries
*Jul 29 20:25:54.239:   subnet 10.0.1.0 metric 1
*Jul 29 20:25:54.239:   network 11.0.0.0 metric 1

当RIP把R1的路由表中的条目封装到update包中，并且从S1/0接口发出去时
RIP要对路由表中的条目进行筛选汇总，此筛选汇总的规则如下：
检查条目是否与发送端口属于同一主网
 1）.若否，则该条目自动被汇总成主类网络，然后封装到update包中（不带掩码）
 2）.若是，继续检查条目是否与发送接口的掩码长度一致
         a.是，发送该条目（不汇总，不带掩码）
         b.否，直接忽略

R2# debug ip rip
*Jul 29 20:27:31.151: RIP: received v1 update from 10.0.0.1 on Serial1/1
*Jul 29 20:27:31.151:      10.0.1.0 in 1 hops
*Jul 29 20:27:31.155:      11.0.0.0 in 1 hops

R2#sh ip route
Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.0.0 is directly connected, Serial1/0
     10.0.0.0/24 is subnetted, 2 subnets
C       10.0.0.0 is directly connected, Serial1/1
R       10.0.1.0 [120/1] via 10.0.0.1, 00:00:08, Serial1/1
R    11.0.0.0/8 [120/1] via 10.0.0.1, 00:00:08, Serial1/1

可以看到R2己经通过RIPv1从R1哪里学习到了两条路由条目，并且还有掩码，该掩码信息是如何产生的？当R2接受到从R1哪里传来的两条路由更新（这两条路由更新是不携带子网掩码这点已经毋庸置疑）并把它放到路由表中之前要做一些处理，该处理的规则如下：
将接收到的路由条目和接收接口的网络地址进行比较，判断是否处于同一主网络
 1）.处于同一主网络，直接将接收接口的掩码赋予该条目
 2）.不处于同一主类网络，首先查看路由表中是否存在该主网络的任一子网
        a .不存在，赋予该条目一个有类掩码，同时写入路由表
        b.存在，忽略该路由条目，直接丢弃

R2#debug ip rip
*Jul 29 21:21:53.771: RIP: sending v1 update to 255.255.255.255 via Serial1/0 (172.16.0.1)
*Jul 29 21:21:53.771: RIP: build update entries
*Jul 29 21:21:53.771:   network 10.0.0.0 metric 1
*Jul 29 21:21:53.775:   network 11.0.0.0 metric 2

R3#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.0.0 is directly connected, Serial1/1
R    10.0.0.0/8 [120/1] via 172.16.0.1, 00:00:25, Serial1/1
R    11.0.0.0/8 [120/2] via 172.16.0.1, 00:00:25, Serial1/1

R2#ping 10.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.2.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

R3#ping 10.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.2.1, timeout is 2 seconds:
U.U.U              R2给R3返回的目标不可达消息
Success rate is 0 percent (0/5)

现在我们在R2增加一个LOOPBACK 0：11.11.11.11/24

R2#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.0.0 is directly connected, Serial1/0
     10.0.0.0/24 is subnetted, 2 subnets
C       10.0.0.0 is directly connected, Serial1/1
R       10.0.1.0 [120/1] via 10.0.0.1, 00:00:01, Serial1/1
     11.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       11.11.11.0/24 is directly connected, Loopback0
R       11.0.0.0/8 [120/1] via 10.0.0.1, 00:00:44, Serial1/1

当R2从R1哪里接受到该路由条目时会直接丢弃，原因关于接受条目更新规则中有阐述
当我们等到00：03：05时
R       11.0.0.0/8 is possibly down,
          routing via 10.0.0.1, Serial1/1
当我们等到00：04：00时直接从路由表中被删除

0-30s:更新计时器
31-180s:无效计时器
180s-240s:保持失效计时器
240s之后:刷新计时器

当然我们可以直接用
R2#clear ip route *   会让RIP产生触发式的更新 重新计算路由表

R3#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.0.0 is directly connected, Serial1/1
R    10.0.0.0/8 [120/1] via 172.16.0.1, 00:00:00, Serial1/1

R2(config)#router rip
R2(config-router)#net 11.0.0.0
R3#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.0.0 is directly connected, Serial1/1
R    10.0.0.0/8 [120/1] via 172.16.0.1, 00:00:12, Serial1/1
R    11.0.0.0/8 [120/1] via 172.16.0.1, 00:00:03, Serial1/1

(二)无类路由协议
代表：RIPV2 EIGRP OSPF ISIS BGPV4
特点：

1、在发送的update包中携带子网掩码信息
2、部分无类协议（如：RIPV2 EIGRP）在主类边界路由器执行自动汇总功能是打开 的，并且该自动汇总可以人工关闭                                   

3、支持VLSM，即同一个主网络下的子网若掩码长度不一致不会出现子网丢弃

实验：
 
                                                         图 1-14

先shut掉R2的lo0，全局配置RIPV1，R2路由表显示如下：
R2#sh ip route
Gateway of last resort is not set
C    192.168.12.0/24 is directly connected, Serial1/1
R    172.16.0.0/16 [120/1] via 192.168.23.2, 00:00:26, Serial1/0
               [120/1] via 192.168.12.1, 00:00:15, Serial1/1  <==此时R2对左右两边“ 半信半疑”
C    192.168.23.0/24 is directly connected, Serial1/0

然后，激活R2的lo0，R2路由表如下：
R2#sh ip route
Gateway of last resort is not set
C    192.168.12.0/24 is directly connected, Serial1/1
     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.20.0 is directly connected, Loopback0  <===此时R2“ 只信自己”
C    192.168.23.0/24 is directly connected, Serial1/0

接着，把RIPV1升级到V2
R2#sh ip route
Gateway of last resort is not set

C    192.168.12.0/24 is directly connected, Serial1/1
     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.20.0/24 is directly connected, Loopback0
R       172.16.0.0/16 [120/1] via 192.168.23.2, 00:00:02, Serial1/0
                      [120/1] via 192.168.12.1, 00:00:02, Serial1/1      <===此时R2“ 集思广益”
C    192.168.23.0/24 is directly connected, Serial1/0

最后，no auto-summary
R2#clear ip route *
R2#sh ip route
Gateway of last resort is not set
C    192.168.12.0/24 is directly connected, Serial1/1
     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.30.0 [120/1] via 192.168.23.2, 00:00:01, Serial1/0
C       172.16.20.0 is directly connected, Loopback0
R       172.16.10.0 [120/1] via 192.168.12.1, 00:00:01, Serial1/1
C    192.168.23.0/24 is directly connected, Serial1/0
此时R2“ 拨云见日”