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Destination unreachable is generated by the host or its inbound gateway [2] to inform the client that the destination is unreachable for some reason. Reasons for this message may include: the physical connection to the host does not exist (distance is infinite); the indicated protocol or port is not active; the data must be fragmented but the ...
The simplest approach uses ICMP ECHO REQUEST messages to an unallocated IP address, such as 1.2.3.4. Since 1.2.3.4 is not allocated, the ICMP REQUEST will not be routed by routers without a default route; ICMP DESTINATION UNREACHABLE messages that may be created by those routers can just be ignored by the server.
MTR also has a User Datagram Protocol (UDP) mode (invoked with "-u" on the command line or pressing the "u" key in the curses interface) that sends UDP packets, with the time to live (TTL) field in the IP header increasing by one for each probe sent, toward the destination host. When the UDP mode is used, MTR relies on ICMP port unreachable ...
408 Request Timeout The server timed out waiting for the request. According to HTTP specifications: "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." 409 Conflict
Ping measures the round-trip time for messages sent from the originating host to a destination computer that are echoed back to the source. The name comes from active sonar terminology that sends a pulse of sound and listens for the echo to detect objects under water. [1] Ping operates by means of Internet Control Message Protocol (ICMP) packets.
The most common form of black hole is simply an IP address that specifies a host machine that is not running or an address to which no host has been assigned.. Even though TCP/IP provides a means of communicating the delivery failure back to the sender via ICMP, traffic destined for such addresses is often just dropped.
A specified period of time that will be allowed to elapse in a system before a specified event is to take place, unless another specified event occurs first; in either case, the period is terminated when either event takes place. Note: A timeout condition can be canceled by the receipt of an appropriate time-out cancellation signal.
The command reports the round-trip times of the packets received from each successive host (remote node) along the route to a destination. The sum of the mean times in each hop is a measure of the total time spent to establish the connection. The command aborts if all (usually three) sent packets are lost more than twice.