Cisco CCNA Routing and Switching ICND2 200-101 Official Cert Guide

Self ping over Serial Links

Yet another scenario called the self ping points out another oddity with IOS. The term self ping refers to a ping of an address on the same device. For a self ping to succeed over a point-to-point serial link, the local router will send the IP packet (holding the ICMP Echo message) out the physical interface. Additionally, the physical link must be working, the local router needs the correct configuration, and the neighboring device needs the correct configuration. When the self ping succeeds, the packet holding the ICMP Echo Request actually leaves the router, with the next device sending the packet back. As a result, the router that issued the ping command receives its own ICMP Echo Request, at which point it must ...