May be silly question but...
When I check connectivity between two neighbour Cisco devices (routers and switches) using standart ping command with default parameters, I frequently see, what first ping probe is timeout and next four are successfull
I suppose what on Ethernet links this is due ARP mechanism. But default ping timeout 2s, ARP Requst/Reply roundtrip on 100 Mbit/s Ethernet is ~ 100 us (I have observed with analyzer).
The same situation on serial point-to-point links, where no ARP exists.
Any Idea, why first ping probe is timeout?
Also I have found this question in Cisco BCMSN Course LAB Guide
On some pings, there was one lost packet (.) and then four good packets. You should know why that occurred.