Using [TD-W8970] as a bridge modem

Need to turn my [TD-W8970] flashed with OpenWrt into a bridge modem since I have a better router that will replace it and at the same time I need to be able to graph the line stats which I can't do with default modem firmware.
The problem is that I can't seem to get it to work as such.
By itself it works fine as a full OpenWrt router/modem.
The new router flashed with OpenWrt also works fine with any cheap modem (tested with 3 different vendors not flashed with OpenWrt) and within seconds connection is made.
The [TD-W8970] and the new router together they give me "Timeout waiting for PADO packets" and no connection is made even if left overnight or after disconnecting the line for over an hour.
Setup should be really simple since no vlan ids are needed.
I checked these two posts and against my setup but still couldn't find a solution.
So maybe someone could help.
My config is as follows

config interface 'loopback'
	option ifname 'lo'
	option proto 'static'
	option ipaddr ''
	option netmask ''

config globals 'globals'
	option ula_prefix 'ea7d:94e6:e835::/48'

config atm-bridge 'atm'
	option vpi '1'
	option vci '38'
	option encaps 'llc'
	option payload 'bridged'
	option nameprefix 'dsl'

config dsl 'dsl'
	option annex 'a'
	option line_mode 'vdsl'
	option xfer_mode 'ptm'

config interface 'lan'
	option type 'bridge'
	option ifname 'eth0.1'
	option proto 'static'
	option ipaddr ''
	option netmask ''
	option ip6assign '60'

config device 'lan_dev'
	option ifname 'eth0.1'
	option macaddr 'xx:xx:xx:xx:xx:xx'

config interface 'modem'
	option type 'bridge'
	option proto 'none'
	option ifname 'eth0 ptm0'

config device 'ptm_dev'
	option ifname 'ptm0'
	option macaddr 'yy:yy:yy:yy:yy:yy'

config switch
	option name 'switch0'
	option reset '1'
	option enable_vlan '1'

config switch_vlan 'eth0_1'
	option device 'switch0'
	option vlan '1'
	option vid '1'
	option ports '0 2 4 5 6t'  

Since the internal switch has VLANs enabled, you cannot use plain eth0.
Instead, use eth0.X where X is the VLAN ID, and set up a matching VLAN in the switch configuration.
Also, double-check the ptm0 interface name, maybe this should be dsl0 instead.

To quickly arrive at a working configuration, use interface 'lan' and VLAN 1, which are already set up.
Add ptm0 or dsl0 to the lan bridge and remove the modem interface section.
You also might want to disable the DHCP server.

However, I find it better to separate lan (for management) from the modem bridge.
This requires a dedicated VLAN in the switch configurations of both the TD-W8970 and your new router, and VLAN tagging between them.

Which model is the new router?

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Yes you need to set up another VLAN in the switch, say VLAN 2, untagged on one of the Ethernet ports then use eth0.2 to connect that one port to your router.

Can the stock firmware do this? If all you want to use it for is a dumb modem, flash it back to stock.

The OP wrote:

so I guess this is not an option.

fwiw, the 2017 forum post referring to HomeHub5A is out of date.

Refer to section 9.8 of the guide for how to configure VDSL bridge modem. It should work for your TPlink:

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if your connection is PPOE ?
if so with adding a static route to the wan interface on the router could you access the web page of any of the cheep modems ?
if so can you just bridge the atm & eth0,1 and do the same thing with openwrt

another thing you could try is to setup then modem as a client on a vlan for access to luci

I got it working by using interface dsl0 instead of ptm0.
What I don't get is that I have a really old Paradyne 1 port ADSL router and without creating any vlans or doing any kind of configuration beside creating the bridge interface everything worked just fine, bridge and lan management on the same single Ethernet port. It even had all the bells and whistles anyone could dream of. snmp, syslogging (remote and local) on a 15 years old single port router.
If only it supported VDSL.
Today I can't find a decent VDSL router with half the features the Paradyne router have.
Wish I could find a similar VDSL router with broadcom chipset and small footprint 1port Ethernet.
Any suggestions in that regard?

I do remember a mode call "half bridge" witch did similar

No, it was Full bridge mode where pppoe authentication happened on the router not the modem.

the Half Bridge I was thinking of the modem did the authentication but the PC or Router plugged into it got the internet IP but you could still get to the modem page & see stats etc while connected

You are arware of this?

If you are still searching for a DSL router which is supported by OpenWrt, please open a new topic in the Hardware section of this forum.

Yes, I am aware.

Yes, I am looking for a broadcom one but it doesn't have to be supported by OpenWrt as long as it supports snmp and remote logging for monitoring and graphing. And I will just open a new topic just for that like you suggested.