902中104题，为什么loopback会回应，ping 224.0.0.5 的包？

枫叶瑾

902中104题，为什么loopback会回应，ping 224.0.0.5 的包？
QUESTION 104
OSPF is enabled on router A. You execute the following command on router A and receive the
accompanying output:
RouterA#ping 224.0.0.5 repeat 1
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.0.0.5, timeout is 2 seconds:
Reply to request 0 from 10.100.100.1, 4 ms
10.100.100.1 is the IP address of a loopback interface on router A. What can you conclude about router A?
Select the best response.
A. Only the router A loopback interface is participating in the OSPF routing process.
B. None of the router A interfaces are participating in the OSPF routing process.
C. Router A is using the loopback interface IP address as its OSPF router ID.
D. Router A does not have any reachable OSPF neighbors.

lim203344

A
当接口宣告进路由协议后，show ip int lo 0
会看到接口加入了组播组224.0.0.5，成为一个接收者，
224.0.0.5是OSPF的组播地址
当ping224.0.0.5时，组成员会回应，就知道哪些接口参与了OSPF

yanglei1125

是选 D吗