common error messages in internet

INTERNET CONTROL MESSAGE PROTOCOL (ICMP):

Works at the Network layer and is used by IP for different
services. It is a management protocol and messaging service
provider for IP.Listed below are some common events and
messages that ICMP relates to:-

DESTINATION UNREACHABLE - If a router can't send an IP
datagram any further, it uses ICMP to send a message back
to the sender, advising it of the situation. For example,
if a router receives a packet destined for a network that
the router doesn't know about, it will send an ICMP
Destination unreachable message back to the sending station.

BUFFER FULL - If a routers buffer for receiving incoming data
is full, it will use ICMP to send out this message.

HOPS - Each IP datatgram is allotted a certain number of routers,
called hops, that it may go through. If it reaches it's limit of hops
before arriving at it's destination the last router to receive that
datagram deletes it. That router then uses ICMP to send an obituary
message, informing the sending machine of the demise of its datagram.

PING - Packet internet groper uses ICMP echo messages to check the
physical connectivity of machines on an internetwork.

TRACEROUTE - Using ICMP timeouts, traceroute is used to find a path
a packet takes as it traverses an internetwork.