Ubuntu 22.04 and RFC 8200 discuss the Fragment Header Exclusions. This article aims to provide a detailed context about the topic, covering key concepts, subtitles, paragraphs, and code blocks.
Fragment Header Exclusions
The Fragment Header Exclusions (FHE) in RFC 8200 specify that the first fragment should not include the Upper-Layer header, and the fragment discardable bit should be set to 0.
Upper-Layer Header
The Upper-Layer header is the header of the protocol layer above IP, such as TCP or UDP. In the case of the first fragment, it is not included in the Fragment Header.
Fragment Discardable Bit
The Fragment Discardable bit is used to indicate that the fragment can be discarded if resources are low. In the first fragment, this bit should be set to 0, indicating that the fragment should not be discarded.
Example
Let's consider an example where a packet is being fragmented. The original packet contains an Upper-Layer header and a payload.
Original Packet:
+-------------+----------------+
| Upper-Layer | Payload |
+-------------+----------------+
First Fragment:
+-------------+----------------+
| Fragment | Payload (part) |
+-------------+----------------+
Second Fragment:
+-------------+----------------+
| Fragment | Payload (part) |
+-------------+----------------+
In this example, the first fragment does not include the Upper-Layer header.
References
- RFC 8200: Internet Protocol, Version 6 (IPv6) Specification
- IPv6 Fragmentation
- IPv6 Fragmentation and Reassembly
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