Editing Ping (networking utility) (section)

==Error indications==
In cases of no response from the target host, most implementations display either nothing or periodically print notifications about timing out. Possible ping results indicating a problem include the following:
* {{Mono|H,}} {{Mono|!N}} or {{Mono|!P}}{{snd}} host, network or protocol unreachable
* {{Mono|S}}{{snd}} source route failed
* {{Mono|F}}{{snd}} fragmentation needed
* {{Mono|U}} or {{Mono|!W}}{{snd}} destination network/host unknown
* {{Mono|I}}{{snd}} source host is isolated
* {{Mono|A}}{{snd}} communication with destination network administratively prohibited
* {{Mono|Z}}{{snd}} communication with destination host administratively prohibited
* {{Mono|Q}}{{snd}} for this [[Type of service|ToS]] the destination network is unreachable
* {{Mono|T}}{{snd}} for this ToS the destination host is unreachable
* {{Mono|X}}{{snd}} communication administratively prohibited
* {{Mono|V}}{{snd}} host precedence violation
* {{Mono|C}}{{snd}} precedence cutoff in effect

In case of error, the target host or an intermediate router sends back an ICMP error message, for example ''host unreachable'' or ''TTL exceeded in transit''.  In addition, these messages include the first eight bytes of the original message (in this case header of the ICMP echo request, including the quench value), so the ping utility can match responses to originating queries.<ref>{{Cite web
 | url = http://repo.hackerzvoice.net/depot_madchat/ebooks/TCP-IP_Illustrated/icmp_int.htm
 | title = ICMP: Internet Control Message Protocol
 | date = 13 January 2000
 | access-date = 4 December 2014
 | website = repo.hackerzvoice.net
 | archive-url = https://web.archive.org/web/20160804032607/http://repo.hackerzvoice.net/depot_madchat/ebooks/TCP-IP_Illustrated/icmp_int.htm
 | archive-date = 4 August 2016
 | url-status = dead
 }}</ref>