The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a discarded datagram due to the time to live field reaching zero. A time exceeded message may also be sent by a host if it fails to reassemble a fragmented datagram within its time limit.
Time exceeded messages are used by the traceroute utility to identify gateways on the path between two hosts.
| 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Type = 11 | Code | Header Checksum | |||||||||||||||||||||||||||||
| unused | |||||||||||||||||||||||||||||||
| IP Header + First 8 Bytes of Original Datagram's Data | |||||||||||||||||||||||||||||||
Type must be set to 11. The code, which specifies the reason for the time exceeded message, include the following:
| Code | Description |
|---|---|
| 0 | Time-to-live exceeded in transit. |
| 1 | Fragment reassembly time exceeded. |
The header and first 64 bits of the original payload are used by the source host to match the time exceeded message to the discarded datagram. For higher level protocols such as UDP and TCP the 64 bit payload will include the source and destination ports of the discarded packet.
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