Time Exceeded error messages
Time Exceeded error messages are used to indicate that a forwarding or reassembly operation took too long to complete and that the reporting device is discarding the data. In order to provide more-detailed reporting, the Time Exceeded message provides two different submessages (using the ICMP Message Code field as described later in Section 5.2.1.1). The submessages offered by Time Exceeded include:
- Time-to-Live Exceeded in Transit
This error message is used when an IP datagram’s Time-to-Live value has reached zero but the datagram has not yet been delivered to its final destination. Since the Time-to-Live field indicates the maximum number of hops that a datagram can take, the router cannot forward a datagram with a Time-to-Live value of zero, and must destroy it instead. Since most systems use Time-to-Live values of 30 or more, the presence of this message generally indicates that a routing loop is preventing the datagram from being delivered.
However, this message is also used with the traceroute program to identify the routers in between a source and destination system. For more information on how traceroute uses this message, refer to Section 5.3.3 later in this chapter.
- Fragment Reassembly Time Exceeded
This error message is used when a datagram has been fragmented but the destination system has not received all of the fragments within the allotted time (60 seconds on most Unix systems). This message generally indicates that a fragment has been lost ...
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