ICMPv4
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... addresses backwards
compatibility with certain, widely deployed, MPLS-aware ICMPv4
implementations that send the extensions defined herein without
adding the required length attribute.
...
...
An ICMP Extension Structure MAY be appended to ICMPv4 Destination
Unreachable, Time Exceeded, and Parameter Problem messages.
...
...
When the ICMP Extension Structure is appended to an ICMPv4 message
and that ICMPv4 message contains an "original datagram ...
... ICMP Extension Structure is appended to an ICMPv4 message
and that ICMPv4 message contains an "original datagram" field, the
"original datagram ...
... defined:
- ICMPv4 Destination Unreachable (type = 3)
...
... response. RFC 792std5 defines the "original datagram" field for ICMPv4
messages. In RFC 792std5, the "original datagram" field includes the IP
header ...
... In order to solve this problem, this memo introduces an 8-bit length
attribute to the following ICMPv4 messages.
- Destination ...
... octets, whose value was previously required to be zero.
For ICMPv4 messages, the length attribute represents 32-bit words.
When the length attribute is specified, the "original datagram ...
... 32-bit boundary. Because the
sixth octet of each of the impacted ICMPv4 messages was reserved for
future use, this octet was selected as the location of the length
attribute in ICMPv4 ...
... ICMPv4 messages was reserved for
future use, this octet was selected as the location of the length
attribute in ICMPv4.
For ICMPv6 messages ...
... ICMPv4 Destination Unreachable ...
...
Figure 1 depicts the ICMPv4 Destination Unreachable Message.
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ICMPv4 Destination Unreachable
...
... ICMPv4 Time Exceeded ...
...
Figure 2 depicts the ICMPv4 Time Exceeded Message.
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: ICMPv4 Time Exceeded
The syntax and semantics ...
... ICMPv4 Parameter Problem ...
...
Figure 3 depicts the ICMPv4 Parameter Problem Message.
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ICMPv4 Parameter Problem
The syntax and semantics ...
... following types:
- ICMPv4 Destination Unreachable
...
...
When a non-compliant ICMPv4 application receives a message that
contains no extensions, the application examines the total length of
the ICMPv4 ...
... ICMPv4 application receives a message that
contains no extensions, the application examines the total length of
the ICMPv4 message. If the total ICMPv4 message length is less than
...
... contains no extensions, the application examines the total length of
the ICMPv4 message. If the total ICMPv4 message length is less than
the length of its IP header ...
... The 144-octet sum is derived from 8 octets for the first two words of
the ICMPv4 Time Exceeded message, 128 octets for the "original
datagram" field, 4 octets ...
... required if extensions were present.
If the ICMPv4 payload contains 144 octets or more, the application
must examine the 137th octet to determine whether it represents a
...
... must examine the 137th octet to determine whether it represents a
valid ICMPv4 Extension Header. In order to represent a valid
...
... not contain any extensions.
Non-compliant applications assume that the ICMPv4 Extension Structure
begins on the 137th octet of the Time Exceeded message, after a
...
... original datagram" message.
It is possible that a non-compliant application will parse an ICMPv4
message incorrectly under the following conditions:
...
... ICMP message does not exceed the minimum
reassembly buffer size (576 octets for ICMPv4 or 1280 octets for
ICMPv6 ...