PING: (Packet
Inter-Net Groper)
What is
PING?
ICMP
message
What is
PING?
- Ping is a program that tests
the connectivity between two systems running TCP/IP.
- Ping sends an ICMP echo request message to a host and
expects an ICMP echo reply message to be returned.
- The Ping program is referred
to as the client, and the host that is being
"pinged" is referred to as the server.
- The server must echo the
identifier field, and sequence number field, and also any
optional data sent by the client. This ensures that
- Ping measures the round trip
time of the host.
- And also the time to live
(TTL).
Format of ICMP message for echo request and echo reply.
| type (0 or
8 ) |
code
(0) |
checksum |
| identifier |
sequence
number |
| optional data |
- Type - is
either '0' for echo reply or '8' for echo request.
- Code -
specifies the condition. For ping it is '0' for both
request and reply.
- Identifier field
- is set to the sending process ID. This allows ping to
identify the return response, especially when there is
multiple instances of ping running at the same time on
the same host.
- Sequence number
- starts at 0 and increments every time a new echo
request is sent. Missing, reordered or duplicated packets
can be identified.
- Each request returns the
following information:
- The number of bytes
sent
- The source IP address
(xxx.xxx.xxx.xxx)
- The ICMP_sequence
number
- The TTL - time to live in
milliseconds
- Round trip in
milliseconds
There are many Ping programs
available, each with their own set of options and format for
display of the information received.
Refer to the Tutorial for an example of one of these programs
and options.