04/20/23 19:41 1

Updated IPv4 ID Specification

IETF 77

Joe Touch, USC/ISI

Quick review

Current hosts don’t ensure ID uniqueness within 2MSL Recognize existing practice

Explicitly limit ID to fragmentation Align IPv4 and IPv6 ID and

fragmentation

04/20/23 19:41 2

-03 / intarea mods

Issued as inarea doc Text mods

Reformatted pseudocode fragments Clarified requirements text Mathis ack’d only

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IPv4 vs. IPv6 IDs

IPv4 IPv6

Length 16 bits 32 bits

Presence All packets Only fragments

Frag. Location Anywhere “Source” only

Uses Frag/reassyDiscard dups

Frag/reassy

BW @1.5K 6.4 Mbps 19 Tbps

BW @64K 280 Mbps 820 Tbps

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ID MSL uniqueness already ignored

Summary of changes

SHOULD limit fragmentation in IPv4 Only at source (DF=1) Only where use is safe (ID unique or integrity

check)

MUST NOT fragment if ID not unique MUST NOT reuse ID if fragmented/able

MUST NOT use for duplicate detection MUST ignore overlap fragments

Now possible only by net duplication as transient

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Remaining issues

Clarify ‘maximum jitter’ “time during which reordering is expected &

tolerated.”

Clarify IPv6 examples IPv6 ID also in PTB ICMP, only for v6 talking to v4 May update RFC 2460 (?)

Clarify why overlaps are prohibited Never retransmit with same ID Now impacts only in-net replication (transient

impact)

04/20/23 19:41 6

More issues

Impact on NATs NATs act as hosts; SHOULD set DF, not

fragment

Note that there are boxes that ignore DF With predictable results ;-)

Transition plan Do we need one? – it might help with ignore-

DF case When to cease?

04/20/23 19:41 7