General Questions

I'm having a strange issue with my m0n0wall that has occurred ever since I switched from plain ADSL to U-Verse (AT&T VDSL2). I should be getting 24 mbps down / 3 mbps up - and I do get this when I connect my machine directly to the U-Verse modem/router unit. However, when I access the internet through my m0n0wall, I only get 0.5 mbps down and almost 3 mbps up. Previously, I had a 6.0 mbps down / 768kbps up ADSL connection, and didn't have any problems. I've completely wiped and reinstalled the m0n0wall software, but this hasn't fixed the issue.

My hardware is an older Nokia IP330. Is it likely that the hardware is the issue? Possibly one of the built-in NICs?

That sounds like the symptoms of a duplex mismatch. What does Status>Interfaces look like for your WAN?

Status    up
DHCP    up    
MAC address    00:a0:8e:0e:xx:xx
IPv4 address    108.90.xxx.xxx/255.255.254.0
IPv4 gateway    108.90.xxx.xxx
ISP DNS servers    208.67.222.222
208.67.220.220
8.8.8.8
Media    100baseTX <full-duplex>
In/out packets    521/563 (256 KB/95 KB)
In/out errors    55/0
Collisions    0

It is supposed to be full duplex, that's for sure. The device attached to the WAN port is set to auto-negotiate duplex, and it says full-duplex as well.