一个路由器有如下路由表
目的网络 | 子网掩码 | 度量值 | 转发端口 |
0.0.0.0 | 0.0.0.0 | 100 | F0/0 |
172.16.0.0 | 255.240.0.0 | 100 | F0/1 |
172.20.0.0 | 255.254.0.0 | 200 | F0/2 |
172.31.50.0 | 255.255.255.0 | 180 | F0/3 |
172.31.50.0 | 255.255.255.0 | 150 | F0/4 |
当路由器收到如下地址时,如何转发数据包?
172.18.234.56
172.21.201.112
172.31.50.22
172.33.151.2
解答:
分别算出各网络的IP范围依次是:
172.16.0.0 172.16.0.0->172.31.255.255
172.20.0.0 172.20.0.0->172.21.255.255
172.31.50.0 172.31.50.0->172.31.50.255
172.31.50.0 172.31.50.0->172.31.50.255
转发规则如下:
1:先找出在那个网络。
2:找其中范围最小的
3:找度量值最小的
4:均没有,则到默认路由
所以各IP的转发情况如下:
172.18.234.56 F0/1
172.21.201.112 F0/2
172.31.50.22 F0/4
172.33.151.2 F0/0
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