My setup is as follows

vdsl2 modem doing pppoe itself and nat to 10.x.x.x -> lede master eth0.2 (wan static ip in modem's DMZ) eth0.1 (lan) doing nat to 192.168.1.x

Here is my current SQM config

config queue 'eth1'
option debug_logging '0'
option verbosity '5'
option qdisc 'cake'
option qdisc_advanced '1'
option ingress_ecn 'ECN'
option egress_ecn 'NOECN'
option qdisc_really_really_advanced '1'
option script 'layer_cake.qos'
option interface 'eth0.2'
option enabled '1'
option eqdisc_opts 'nat rtt 50000 bridged-ptm dual-srchost diffserv4'
option upload '2400'
option linklayer 'ethernet'
option overhead '8'
option squash_dscp '1'
option squash_ingress '1'
option iqdisc_opts 'nat rtt 50000 bridged-ptm dual-dsthost'
option download '0'

config queue
option debug_logging '0'
option verbosity '5'
option download '0'
option qdisc 'cake'
option script 'layer_cake.qos'
option qdisc_advanced '1'
option squash_dscp '0'
option squash_ingress '0'
option ingress_ecn 'ECN'
option qdisc_really_really_advanced '1'
option egress_ecn 'ECN'
option interface 'eth0.1'
option enabled '1'
option eqdisc_opts 'nat rtt 50000 bridged-ptm dual-dsthost diffserv4'
option upload '30000'
option linklayer 'ethernet'
option overhead '8'

Is the overhead correct? should i use the bridged-ptm keyword (or should i use pppoe-ptm). I tried using ATM_overhead_detector and get the following output

869001 lines parsed...
Found 144921 ping packets in /home/mark/src/ATM_overhead_detector/ping_sweep__20171217_075202.txt
Elapsed time is 972.739 seconds.
Minimum size of ping payload used: 16 bytes.
warning: division by zero
warning: called from
ATM_overhead_detector at line 201 column 15
warning: legend: ignoring extra labels
Unknown or ambiguous terminal name 'wxt'
Unknown or ambiguous terminal name 'wxt'
Saved figure (5) to: /home/mark/src/ATM_overhead_detector/ping_sweep__20171217_075202_data.png
lower bound estimate for one ATM cell RTT based of specified up and downlink is 0.052419 ms.
estimate for one ATM cell RTT based on linear fit of the ping sweep data is 0.052419 ms.
Starting brute-force search for optimal stair fit, might take a while...
Unknown or ambiguous terminal name 'wxt'
Unknown or ambiguous terminal name 'wxt'
Best staircase fit cumulative difference is: 2.6952
Best linear fit cumulative difference is: 2.7314
Quantized ATM carrier LIKELY (cummulative residual: stair fit 2.6952 linear fit 2.7314
remaining ATM cell length after ICMP header is 5 bytes.
ICMP RTT of a single ATM cell is 0.05871 ms.

Estimated overhead preceding the IP header: 48 bytes
Saved figure (6) to: /home/mark/src/ATM_overhead_detector/ping_sweep__20171217_075202_results.png

According to http://ace-host.stuart.id.au/russell/files/tc/tc-atm/
48 bytes overhead indicate
Overhead of 0 bytes is not possible so assume 1 full packet (48 bytes) overhead...
Connection: Bridged, LLC/SNAP+FCS RFC-1483/2684 + VLAN tag terminated at modem
Protocol (bytes): Ethernet Header (14), VLAN tag (4), Ethernet PAD [8] (0), Ethernet Checksum (4), ATM LLC (3), ATM SNAP (5), ATM pad (2), ATM AAL5 SAR (8) : Total 36

Add the following to both the egress root qdisc:
A) Assuming the router connects over ethernet to the DSL-modem:
stab mtu 2048 tsize 128 overhead 48 linklayer atm

Add the following to both the ingress root qdisc:

A) Assuming the router connects over ethernet to the DSL-modem:
stab mtu 2048 tsize 128 overhead 48 linklayer atm

Elapsed time is 1042.06 seconds.
Done...
ans = [](0x0)

Could my VDSL2 be using ATM? so i have the wrong overhead set?

here is my tc -s qdisc output

root@OpenWrt-Mi3G:~# tc -s qdisc
qdisc noqueue 0: dev lo root refcnt 2
Sent 0 bytes 0 pkts (dropped 0, overlimits 0)
qdisc fq_codel 0: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
Sent 3460986864 bytes 3651814 pkts (dropped 0, overlimits 0)
maxpacket 17032 drop_overlimit 0 new_flow_count 29673 ecn_mark 0
new_flows_len 0 old_flows_len 0
qdisc noqueue 0: dev br-lan root refcnt 2
Sent 0 bytes 0 pkts (dropped 0, overlimits 0)
qdisc cake 8055: dev eth0.1 root refcnt 2 bandwidth 30Mbit diffserv4 dual-dsthost nat rtt 50.0ms ptm overhead 22 via-ethernet total_overhead 22 hard_header_len 14
Sent 20012069 bytes 35472 pkt (dropped 10, overlimits 7587 requeues 0)
backlog 0b 0p requeues 0
memory used: 36684b of 4Mb
capacity estimate: 30Mbit
Bulk Best Effort Video Voice
thresh 1875Kbit 30Mbit 15Mbit 7500Kbit
target 9.7ms 2.5ms 2.5ms 2.5ms
interval 57.2ms 50.0ms 50.0ms 50.0ms
pk_delay 0us 5.6ms 855us 15us
av_delay 0us 436us 28us 10us
sp_delay 0us 27us 8us 6us
pkts 0 33679 457 1346
bytes 0 19869595 80517 69940
way_inds 0 249 0 0
way_miss 0 3099 19 7
way_cols 0 0 0 0
drops 0 10 0 0
marks 0 0 0 0
ack_drop 0 0 0 0
sp_flows 0 1 1 0
bk_flows 0 1 0 0
un_flows 0 0 0 0
max_len 0 7064 2982 350

qdisc cake 8053: dev eth0.2 root refcnt 2 bandwidth 2400Kbit diffserv4 dual-srchost nat rtt 50.0ms ptm overhead 22 via-ethernet total_overhead 22 hard_header_len 14
Sent 23218772 bytes 35904 pkt (dropped 205, overlimits 27550 requeues 0)
backlog 0b 0p requeues 0
memory used: 94752b of 4Mb
capacity estimate: 2400Kbit
Bulk Best Effort Video Voice
thresh 150Kbit 2400Kbit 1200Kbit 600Kbit
target 121.1ms 7.6ms 15.1ms 30.3ms
interval 242.2ms 55.1ms 62.6ms 77.8ms
pk_delay 0us 29.5ms 19us 4.4ms
av_delay 0us 3.8ms 1us 2.3ms
sp_delay 0us 50us 1us 9us
pkts 0 34979 31 1099
bytes 0 23342354 2930 162457
way_inds 0 177 0 0
way_miss 0 2003 27 16
way_cols 0 0 0 0
drops 0 205 0 0
marks 0 0 0 0
ack_drop 0 0 0 0
sp_flows 0 1 0 0
bk_flows 0 1 0 0
un_flows 0 0 0 0
max_len 0 8342 98 598

qdisc noqueue 0: dev wlan1 root refcnt 2
Sent 0 bytes 0 pkts (dropped 0, overlimits 0)
qdisc noqueue 0: dev wlan0 root refcnt 2
Sent 0 bytes 0 pkts (dropped 0, overlimits 0)
qdisc fq_codel 0: dev tun0 root refcnt 2 limit 10240p flows 1024 quantum 1500 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
Sent 304 bytes 4 pkts (dropped 0, overlimits 0)
maxpacket 0 drop_overlimit 0 new_flow_count 0 ecn_mark 0
new_flows_len 0 old_flows_len 0

Thanks,

Mark