Wendell Odom

“For instance, consider the topology in Figure 33-6, with Router R4 on the right acting as NTP server and the other routers acting as clients. R4 has three IP addresses that the clients could put in their ntp server address commands. Now consider what happens when one interface on R4 fails, but only one. No matter which of the three interfaces fails, that IP address on that interface cannot be used to send and receive packets. In that case, for any NTP clients that had referred to that specific IP address There would likely still be a route to reach R4 itself. The NTP client would not be able to send packets to the configured address because that interface is down.”
― Wendell Odom, CCENT/CCNA ICND1 100-105 Official Cert Guide

“commands like ping. As a protocol, ICMP does not rely on TCP or UDP, and it does not use any application layer protocol. It exists as a protocol used to assist IP by helping manage the IP network functions.”
― Wendell Odom, CCENT/CCNA ICND1 100-105 Official Cert Guide