Massive speed drop, Kernel logs oversized packet/DMA issue


I installed OpenWrt on Netgear WNR3500Lv1. It's used for a primitive homelab, so it is double NAT'ed behind another router.

My download speeds through OpenWrt (wired connections only at the moment) drops by more than 80%. The system log generates a lot of entries like this:

Tue Mar 30 13:22:14 2021 kern.err kernel: [58205.370433] bgmac_bcma bcma0:2 eth0: Found oversized packet at slot 81, DMA issue!

The realtime traffic graph shows a brief peak with ~50% loss, but shows a consistent 80% loss at all times. I know having double NAT is not best, but wasn't expecting 80% or more loss with download speeds. Also concerned about the system log error about "oversized packet... DMA issue". Figured OpenWrt defaults to MTU of 1500.

Anyone have suggestions?