First off let me say I know this has been a frequent question posted here regarding slow upload speeds on the UTM. I have been a UTM user for well over a decade probably closer to 15 years. I may not be a Bob expert but I know my way around the software.
I recently got an ATT symmetric 1GB fiber line and plugged it up to my UTM VM. At first, performance was normal and expected. I was getting close enough to max throughput with the understanding that I would be getting less because it was running in a VM on older hardware. All fine. Then one day, and I honestly don't know when, upload performance just took a nose dive. I would get 3-5Mbps on uploads. Sometimes spiking to 7%.
I did all the normal things, turned off IDS, turned off web filtering, confirmed 1500 MTU on all NICs, you name it. I have a small Ubiquiti FW as a backup and it was able to get full 1Gb from all my VM's and my physical boxes, so I know my internal network is fine and can handle it. I even built not 1 but 2 brand new UTMs. One I did a restore of a config and another I did unconfigured, no settings. The performance of all these UTMs is the same 5Mbps upload. Download speeds are fine and close to theoretical maximums. I am at a complete loss. I do NOT want to migrate my services to Ubiquiti. I want to keep using the UTM. What else can I do? there are no IDS or filtering logs to check since all of that is disabled. Is this an ATT thing? Is there some special setting I need to make on the ATT FW or UTM interface setting I need to make to get this to work? It doesn't have to be perfect, but symmetrical upload is all I want.