Editing Ping (networking utility) (section)

===ICMP packet transported with IPv4===
An ICMP packet transported with IPv4 looks like this.
{{APHD|start|title=IPv4 datagram}}
{{APHD|0|bits1=4|field1=Version|value1=4|bits2=4|field2=IHL|value2=5|bits3=6|field3=DSCP|value3=0|bits4=2|field4=ECN|value4=0|bits5=16|field5=Total length}}
{{APHD|4|bits1=16|bits2=3|bits3=13|field1=Identification|field2=Flags|field3=Fragment offset}}
{{APHD|8|bits1=8|field1=Time to live|bits2=8|field2=Protocol|value2=1|hint2=Set to 1 to indicate ICMP.|bits3=16|field3=Header checksum}}
{{APHD|12|bits1=32|field1=Source address}}
{{APHD|16|bits1=32|field1=Destination address}}
{{APHD|end}}
{{APHD|start|header=no|title=ICMP ''Echo Request'' packet}}
{{APHD|20|bits1=8|field1=Type|value1=8|background1=mistyrose|bits2=8|field2=Code|value2=0|background2=mistyrose|bits3=16|field3=Checksum|background3=mistyrose}}
{{APHD|24|bits1=16|field1=Identifier|background1=mistyrose|bits2=16|field2=Sequence number|background2=mistyrose}}
{{APHD|28|bits1=0|field1=(Payload)|background1=linen}}
{{APHD|end}}
;{{APHD|def|name=Type|length=8 bits|text=Set to 8 to indicate 'Echo Request'.{{Ref RFC|792|rp14}}}}
;{{APHD|def|name=Checksum|length=16 bits|text=Checksum is the 16-bit [[ones' complement]] of the ones' complement sum of the ICMP packet, starting with the ''Type'' field,<ref name="networksorcery">{{cite web
| title=RFC Sourcebook's page on ICMP
| url=http://www.networksorcery.com/enp/protocol/icmp.htm#ICMP%20Header%20Checksum
| access-date=20 December 2010
| archive-date=6 July 2018
| archive-url=https://web.archive.org/web/20180706090020/http://networksorcery.com/enp/protocol/icmp.htm#ICMP%20Header%20Checksum
}}</ref> including the ''Payload''. The [[IP header]] is not included.}}
;{{APHD|def|name=Identifier|length=16 bits|text=Can be used by the client to match the reply with the request that caused the reply.}}
;{{APHD|def|name=Sequence number|length=16 bits|text=Can be used by the client to match the reply with the request that caused the reply.}}
;{{APHD|def|name=Payload|length=variable length|text=Optional. Payload for the different kind of answers; can be an arbitrary length, left to implementation detail.}}

Most Linux systems use a unique ''Identifier'' for every ping process, and ''Sequence number'' is an increasing number within that process. Windows uses a fixed ''Identifier'', which varies between Windows versions, and a ''Sequence number'' that is only reset at boot time.

The ''Echo Reply'' is returned as:
{{APHD|start|header=no|title=ICMP ''Echo Reply'' packet}}
{{APHD|20|bits1=8|field1=Type|value1=0|background1=mistyrose|bits2=8|field2=Code|value2=0|background2=mistyrose|bits3=16|field3=Checksum|background3=mistyrose}}
{{APHD|24|bits1=16|field1=Identifier|background1=mistyrose|bits2=16|field2=Sequence number|background2=mistyrose}}
{{APHD|28|bits1=0|field1=(Payload)|background1=linen}}
{{APHD|end}}
;{{APHD|def|name=Type|length=8 bits|text=Set to 0 to indicate 'Echo Reply'.{{Ref RFC|792|rp14}}}}
;{{APHD|def|name=Identifier|length=16 bits|text=Copied from the ''Echo Request'' and returned.}}
;{{APHD|def|name=Sequence number|length=16 bits|text=Copied from the ''Echo Request'' and returned.}}
;{{APHD|def|name=Payload|length=variable length|text=Optional. Payload is copied from the ''Echo Request'' and returned.}}