I have a DIR859 with wifi disabled and configured as a NAT router between my LAN and the ISP fiber modem.
Real IP is on the ISP external interface;
Between it's internal interface and the DIR859 WAN port, a private LAN is configured (192.168.0.0/24). ISP modem is doing NAT;
DIR859 does another NAT for another private LAN (intranet 10.0.0.0/24) and it is configured as a gateway (advancec routing).
ISP rates: 200 Mbps down / 100 Mbps up.
I used this for years now with QOS enabled (HFSC, FQ_CODEL_FAST, 190/95 Mbps) and it seemed to work as it should.
Two weeks ago, I noticed a dramatic decrease in performance.
Down and up limited to 30 ~ 40 Mbps.
I upgraded from r46069 to r46259 to try to solve the issue, same results.
Disabling QOS solves the issue.
I know I am being a bit vague... not that I have the expectation to solve it with so little info, but just to ask where I should look for to understand this change in behavior.
In the QOS page, I was trying to use MAC priority and Netmask priority. After deleting those, performance went back to normal (tested from a different machine from the ones specified).