Töma Gavrichenkov Sent: Friday, March 8, 2019 5:07 PM
On Fri, Mar 8, 2019 at 7:48 PM Saku Ytti <saku@ytti.fi> wrote:
Why do you think it would be expensive? It's cheaper than how ECMP is done for L3 keys, because you just read the flow label and not calculate any hash.
The most honest answer would be: I have no idea. That's just what I've seen, rather briefly though, as we weren't going to investigate that part at the time.
It's been a while since then, and maybe there was a mistake on our side (at least within a perfectly academic context I must assume that there was, as there was no peer review — we were not in academy after all!), but I'm still inclined to, first, see the benchmarks of any proposed piece of hardware that's promising you ECMP with flow labels, second, make any statements about the latter.
We did this exact testing a while back on Juniper 2nd and 3rd gen PFEs. The results showed it doesn't matter a tiny bit whether you do 5-tuple hash or use flow label. So the bottom line is on modern NPUs it doesn't really matter. adam