RIPE 82: An Update on Fragmentation Loss Rates in IPv6
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The document reports on the improvements in handling IPv6 fragmentation, showing a significant reduction in packet drop rates from 2017 to 2021. A series of tests indicated an overall drop rate decrease by two-thirds, with smaller packets showing better success compared to larger ones. Factors such as regional differences, service provider equipment, and potential security policies may influence drop rates.
RIPE 82: An Update on Fragmentation Loss Rates in IPv6
- 1. An Update on IPv6 Fragmentation Geoff Huston Chief Scientist, APNIC
- 2. Initial Tests: 2014 (RFC 7872) • August 2014 and June 2015 • Sent fragmented IPv6 packets towards “well known” IPv6 servers (Alexa 1M and World IPv6 Launch • Drop Rate:
- 3. APNIC Test – August 2017 • Use APNIC IPv6 measurement platform to test the drop rate of IPv6 packets flowing in the opposite direction (server to client) Count % Tests 1,675,898 ACK Fragmented Packets 1,324,834 79% Fragmentation Loss 351,064 21% This is an improvement over the RFC7872 measurement
- 4. APNIC Test - 2021 Re-work of the 2017 measurement experiment – Same server-to-client TCP session fragmentation mechanism – Uses a middlebox to fragment outgoing packets - drop is detected by a hung TCP session that fails to ACK the sequence number in the fragmented packet – This time we randomly vary the initial fragmented packet size between 1,200 and 1,416 bytes – Performed as an ongoing measurement
- 5. 2021 Fragmentation Drop Rate This is a significant improvement over 2017 data Since 2017 there are 10x the number of IPv6 users and the fragmentation drop rate has come down by 2/3 – we appear to be getting better at handling IPv6 fragments!
- 6. 2021 Fragmentation Drop Rate More recent IPv6 deployments appear to be a lot better than more mature ones
- 7. Drop Rate by Size This is unexpected. At a total IPv6 packet size of 1408 bytes we did not expect to see higher packet drop rates for this packet size, as there is still an IP encapsulation budget of 92 bytes
- 8. Drop Size Profile by Region North America Europe Asia
- 9. Why? • Drop patterns vary across service providers, so there are probably contributary factors from network equipment and configurations 1% Drop 80% Drop
- 10. Why? Other potential factors that could contribute: • Local security policies • IPv6 EH may trigger “slow path” processing in network equipment that could lead to higher drop rates • IPv6 Path MTU woes!
- 12. Summary • The network is improving it’s handling of fragmented packets • In 5 years its gone from unusably bad to tolerably poor • Recent IPv6 deployments appear to show more robust handling of IPv6 packets • Smaller frags appear to be more robust than larger ones (if you are going to fragment a packet, prefer smaller fragment sizes)
- 13. That’s it!