I want to know the difference between destination host unreachable and request time out when we ping some host from our pc.

thnkx.

this explains it best for destination host unreachable

http://www.freesoft.org/CIE/RFC/1812/105.htm

as far as request time out is concerned ."The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time"