The last implementation-method-specific reply code received.
If the ICMP Echo capability is being used, then a successful
probe ends when an ICMP response is received that contains
the code ICMP_ECHOREPLY(0). The ICMP codes are maintained
by IANA. Standardized ICMP codes are listed at
http://www.iana.org/assignments/icmp-parameters.
The ICMPv6 codes are listed at
http://www.iana.org/assignments/icmpv6-parameters.