The metric assigned to each network depends on the type of protocol. Some simple protocol, like RIP, treats each network as equals. The（1）of passing through each network is the same; it is one（2）count. So if a packet passes through 10 network to reach the destination, the total cost is 10 hop counts. Other protocols, such as OSPF, allow the administrator to assign a cost for passing through a network based on the type of service required.A（3）through a network can have different costs (metrics). For example, if maximum（4）is the desired type of service, a satellite link has a lower metric than a fiber-optic line. On the other hand, if minimum（5）is the desired type of service, a fiber-optic line has a lower metric than a satellite line. OSPF allow each router to have several routing table based on the required type of service.
3（）
A．adaptability
B．scalablity
C．route
D．security