A.A value of 4 represents the "Implicit NULL Label."
B.A value of 0 represents the "IPv4 Explicit NULL Label."
C.A value of 1 represents the "Router Alert Label". The use of this label is analogous to the use of the"Router Alert Option" in IP packets （for example， ping with record route option）
D.A value of 2 represents the "IPv6 Explicit NULL Label"
E.A value of 1 represents the "IPv1 Explicit NULL Label"
F.A value of 3 represents the "Implicit NULL Label"

A.it uses multicast address 224.0.0.10，instead of broadcast
B.it uses multicast address 224.0.0.9，instead of broadcast
C.it can use either multicast or broadcast addresses，instead of just broadcast
D.it sends incremental updates，instead of periodic updates
E.it is classless，instead of classful
F.it supports authentication，and RIPv1 does not