| Internet-Draft | icmp-eh-len | October 2024 |
| Bonica, et al. | Expires 13 April 2025 | [Page] |
The ICMP Extension Structure does not have a length field. Therefore, unless the length of the Extension Structure can be inferred from other data in the ICMP message, the Extension Structure must be the last item in the ICMP message.¶
This document defines a length field for the ICMP Extension Structure. When length information is provided, receivers can use it to parse ICMP messages. Specifically, receivers can use length information to determine the offset at which the item after the ICMP Extension Structure begins.¶
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The ICMP Extension Structure [RFC4884] does not have a length field. Therefore, unless the length of the Extension Structure can be inferred from other data in the ICMP message, the Extension Structure must be the last item in the ICMP message.¶
This document defines a length field for the ICMP Extension Structure. When length information is provided, receivers can use it to parse ICMP messages. Specifically, receivers can use length information to determine the offset at which the item after the ICMP Extension Structure begins.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Figure 1 depicts the ICMP Extension Header.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version|Rsv| Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version: 4 bits¶
Reserved (Rsv): 2 bits¶
Length: 10 bits¶
This field represents the total length of all options contained in the ICMP Extension Structure. It does not include the length of the Extension Header. The length is measured in bytes. Legacy implementations set this field to 0.¶
Checksum: 16 bits¶
Legacy implementations set the length field to 0. When the length field is set to 0, it conveys no useful information and cannot be used to parse the ICMP packet.¶
In these cases, one of the following statements MUST be true:¶
This document requires no IANA actions.¶
This document introduces no security vulnerabilities.¶