The last implementation method specific reply code received. The Nokia SROS OAM Trace Route is usually implemented by transmitting a series of probe packets with increasing time-to-live values. A probe packet is a UDP datagram encapsulated into an IP packet. Each hop in a path to the target (destination) host rejects the probe packets (probe's TTL too small, ICMP reply) until either the maximum TTL is exceeded or the target host is received. For icmpTraceRoute, both icmp packet type and code are included.