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fix(reassembly): abandon an IPv6 datagram on an overlapping fragment (#2547) - #2569
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…2547) - IP.__discard_overlap__ (False; IPv6 sets True) makes reassembly abandon a datagram once a fragment overlaps another, per RFC 8200 section 4.5; IPv4 keeps RFC 791's newest-wins overwrite. - An exact duplicate (same offset, length, M flag and data) is dropped: only its frame number is kept in index, and its header is not taken. - Completion.OVERLAP reports the abandoned datagram via IP.submit(overlap=); the overlapping fragment is not written, and the event is logged. - Buffer.extent records each merged fragment's (start, stop, mf), sorted, for IP._find_overlap; it stays empty for IPv4. - Tests: new test_ipv6_overlap_2547_unit.py; the #1566, #1585 and payload round-trip suites now expect OVERLAP for their overlapping IPv6 cases. - Docs: IPv6 datagram and buffer structures, departures list, ip.rst.
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- Added: one's-complement checksum verification and computation (#2543), and the IPX and SCTP registration wrappers (#2521). - Folded into unreleased entries: LinuxSLL/FRAD/Netlink registries (#2527), the IGMP class names (#2542), TLS record chaining and the SSLv2 trial's warnings (#2537), DTLS reassembly via Extractor and toolkit (#2528), and IP_Pseudo's walk at any depth (#2543). ICMP drops its stale checksum line. - Breaking: make() checksums, DRARP's module (#2540), IPv6 overlapping fragments (#2569), TCP_GAP_LIMIT replacing TCP.__window__ (#2579), and Extractor/extract's positional dtls (#2528). - Changed: member order (#2490), conventions (#2542, #2521, #2570), CI -n logical (#2572). Fixed: AppType.get (#2568), trial warnings (#2519, #2577). - CHANGELOG.md regenerated; util/changelog_md.py --check passes.
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Closes #2547.
Completion.OVERLAP. Exact duplicates are dropped and the other fragments kept, as the RFC allows. IPv4 keeps RFC 791's newest-wins.IP.__discard_overlap__, set onIPv6, following__isolate_atomic__(fix(reassembly): unfragmented datagram with a buffered BUFID is dropped and flushes IPv6 #2270). Overlap is checked to the octet against the declared extents in the newBuffer.extent.Buffergains a requiredextentfield, andCompletiongainsOVERLAP.