You are a network administrator at Pcjob. You are troubleshooting a router problem. You issue the show ip route command on one of the routers. The output from the command is shown in the following exhibit:

What does [120/3] represent?

A. 120 is the bandwidth allocation and 3 is the routing process number.
B. 120 is the administrative distance and 3 is the metric for that route.
C. 120 is the value of the update timer and 3 is the number of updates received.
D. 120 is the UDP port for forwarding traffic and 3 is the number of bridges.

　　作为Pcjob的网络管理员，你正在为路由器排错，你在其中的一台路由器使用show ip route命令，输出的结果如上图，[120/3]描述的是什么意思？

正确答案：B

解释：

　　路由器的IOS使用一个名为Administrative Distance(管理距离)的概念来决定使用哪一个路由。Admininstrative distance表示的是一个单独路由器中所有路由协议的可信度的这样一个数值，数值越低越好，也就是说，数值越低，路由协议可信度越高。

Route Type Administrative Distance

• Connected 0
• IGRP 100
• RIP 120

参考资料：

CCNA Self-Study CCNA ICND exam certification Guide (Cisco press, ISBN 1-58720-083-X) Page 177