本文出自Simmy的个人blog：西米在线
http://simmyonline.com/archives/288.html
EIGRP advertises a
prefix length for each destination network.
Prefix Length:前缀长度，mask长度，即子网掩码为1的位数。
Sample：
ip address 172.16.1.1 255.255.255.0
it will advertise 172.16.1.0 with a prefix length of 24.
it will advertise 172.16.1.0 with a prefix length of 24.
Likewise, if the router is configured as follows:
ip address 172.16.250.1 255.255.255.252
it will advertise 172.16.250.0 with a prefix length of 30.
ip address 172.16.250.1 255.255.255.252
it will advertise 172.16.250.0 with a prefix length of 30.
本文转simmy51CTO博客，原文链接：http://blog.51cto.com/helpdesk/161851
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