“As a quick aside, the example shows a common and normal behavior with ping commands: the first ping command shows one failure to start, but then the rest of the messages work. This usually happens because some device in the end-to-end route is missing an ARP table entry. Now think about troubleshooting and what a working ping command tells us about the current behavior of this internetwork. First, focus on the big picture for a moment: R1 can send ICMP echo request messages to host B (172.16.2.101). R1 sends these messages from its outgoing interface’s IP address (by default), 172.16.4.1 in this”