When performing troubleshooting for a routing issue, which method should be used first to isolate the problem?

A. Pinging the destination IP back to the originating IP
B. Pinging the originating IP to the destination IP
C. Traceroute from the originating IP to the destination IP
D. Traceroute from the destination IP to the originating IP

C. Traceroute should be used from the originating IP when the problem is to the destination IP. When the traceroute times out is most likely where the problem is located.

"Traceroute sends messages with low TTL values to make the routers send back a TTL Exceeded message. Specifically, a traceroute command begins by sending several packets (usually three), each with the header TTL field equal to 1. When that packet arrives at the next router—host A’s default Router R1 in the example of Figure 18-12—the router decrements TTL to 0 and discards the packet. The router then sends host A the TTL."
- CCNA 200-301 Official Cert Guide, Volume 1