多项选择题
A. Discontiguous subnets are not allowed.
B. Variable length subnet masks are allowed.
C. RIP v1 is a classless routing protocol.
D. IGRP supports classless routing within the same autonomous system.
E. RIP v2 supports classless routing.
单项选择题 Which one of the following statements best explains the split horizon rule used in distance vector routing protocols?（）
单项选择题 What kind of packets does OSPF send to keep up connectivity with its neighboring routers?（）
多项选择题 What kind of information does a router running a link-state routing protocol need to create and maintain its topological database?（）