Connected: An Internet Encyclopedia
Time Exceeded Message

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### Time Exceeded Message

Time Exceeded Message

```    0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |     Code      |          Checksum             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             unused                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Internet Header + 64 bits of Original Data Datagram      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Fields:

The source network and address from the original datagram's data.

ICMP Fields:

Type

11

Code

0 = time to live exceeded in transit;

1 = fragment reassembly time exceeded.

Checksum

The checksum is the 16-bit ones's complement of the one's
complement sum of the ICMP message starting with the ICMP Type.
For computing the checksum , the checksum field should be zero.
This checksum may be replaced in the future.

Internet Header + 64 bits of Data Datagram

The internet header plus the first 64 bits of the original
datagram's data.  This data is used by the host to match the
message to the appropriate process.  If a higher level protocol
uses port numbers, they are assumed to be in the first 64 data
bits of the original datagram's data.

Description

If the gateway processing a datagram finds the time to live field
is zero it must discard the datagram.  The gateway may also notify
the source host via the time exceeded message.

If a host reassembling a fragmented datagram cannot complete the
reassembly due to missing fragments within its time limit it
discards the datagram, and it may send a time exceeded message.

If fragment zero is not available then no time exceeded need be
sent at all.

Code 0 may be received from a gateway.  Code 1 may be received
from a host.
```

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Connected: An Internet Encyclopedia
Time Exceeded Message