what is the effect of configuring a static route to 172.16.0.0 to the null 0 interface?
a:it result in all traffic for all subnets of 172.16.0.0 being dropped.
b:it can be used to fool bgp into believing that a route for 172.16.0.0 actually exits.
c.it will have no effect it the router does not have any of the subnets of 172.16.0.0
d.it is preferable to configure the aggregate-address command
路由器判断陆由的时候，首先的原则是最长子网掩码，
这句静态路由指向的是172.16.0.0，如果，
也有这么一条路由，指向的是172.16.1.0 255.255.255.0，下一条是s0
那么，根据最长原理，172..16.1.0 的路由就会生效，
也就是说，到172.16.0.0的subnet还会工作，
a.it result in all traffic for all subnets of 172.16.0.0 being dropped
所以，a也就错了。
