Sent by a router when it cannot deliver an IP
datagram. A datagram is the unit of data, or packet, transmitted in
a TCP/IP network.
Source
Quench
Sent by a host or router if it is receiving data too
quickly for it to handle. The message is a request that the source
reduce its rate of datagram transmission.
Time
Exceeded
Sent by a router if the datagram has reached the
maximum limit of routers through which it can travel.
Parameter
Problem
Sent by a router if a problem occurs during the
transmission of a datagram such that it cannot complete processing.
One potential source of such a problem is invalid datagram
header.
Network troubleshooting
Echo
Request, Echo Reply
Used to test destination accessibility and status. A
host sends an Echo Request and
listens for a corresponding Echo
Reply. This is most commonly done using the ping command.
IPv4 network address and routing
configuration
Redirect
Sent by a router if it receives a datagram that
should have been sent to a different router. The message contains
the address to which the source should direct future datagrams.
This is used to optimize the routing of network traffic.
Router
Advertisement, Router
Solicitation
Allow hosts to discover the existence of routers.
Routers periodically broadcast their IP addresses via Router Advertisement messages. Hosts may also
request a router address by broadcasting a Router Solicitation message to which a router
will reply with a Router
Advertisement.
Timestamp
Request, Timestamp
Reply
Used to synchronize the clocks between hosts and to
estimate transit time.
Information
Request, Information
Reply
Obsolete. These messages were used earlier by hosts
to determine their inter-network addresses, but are now considered
outdated and should not be used.
Address Mask
Request, Address Mask
Reply
Used to find the mask of the subnet (i.e. what
address bits define the network). A host sends an Address Mask Request to a router and receives
an Address Mask Reply in
return.