So you think you understand IP fragmentation?

Posted Feb 9, 2024 13:52 UTC (Fri) by smurf (subscriber, #17840)
In reply to: So you think you understand IP fragmentation? by pizza
Parent article: So you think you understand IP fragmentation?

No, the checksum will not always fail. The checksum protects against one-bit changes and similar shenanigans. It's not safe for truncation. One in 65536 truncated packets will pass the checksum test. That's way too much for a protocol that's supposed to be reliable.

However, the UDP header also contains … surprise … a length. As long as you don't send IPv6 jumbograms (length word: zero) you're thus still safe there.

So you think you understand IP fragmentation?

Posted Feb 9, 2024 14:20 UTC (Fri) by farnz (subscriber, #17727) [Link]

Even IPv6 jumbograms have a length field, in the Jumbo Payload hop-by-hop header. This is a 32-bit number instead of a 16 bit number, but if you have the full IPv6 header, you'll get a length field to work with (either 16 bits, if not jumbo-sized, or 32 if jumbo-sized).