So you think you understand IP fragmentation?

Posted Feb 8, 2024 13:20 UTC (Thu) by paulj (subscriber, #341)
In reply to: So you think you understand IP fragmentation? by Cyberax
Parent article: So you think you understand IP fragmentation?

Flow label is used in IPv6. Particularly in data-centre environments.

So you think you understand IP fragmentation?

Posted Feb 8, 2024 21:33 UTC (Thu) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

I'm honestly not familiar with that. I know that a lot of use-cases were proposed throughout the years (QoS, routing hints, etc.) but I'm not aware of any real uptake. Load balancers can't depend on it, because it's controlled by clients.

So you think you understand IP fragmentation?

Posted Feb 9, 2024 11:09 UTC (Fri) by paulj (subscriber, #341) [Link]

Some of the most popular L3 switching/routing ASICs by default now use the flow-label for IPv6 ECMP flow grouping, *not* the (address,port) 4-tuple (which is the flow-ID for v4). E.g. more modern Broadcom Tridents. Anything that cares about ECMP is going to have to set the flow-label. I'm sure popular TCP stacks must do already - given ASICs using it by default. I can't double-check or find an authoritative reference right now, but I'm pretty sure Linux assigns a random flow-label to a TCP connection if the app hasn't set one. So apps generally don't need to care - the kernel has it covered.