Thank you for the rapid response.
All settings were cleared before setting up the DSL connection with many, many resets to test each change, so I was sure if I found the answer exactly how I arrived at it
I attempted the migration path you suggest - and repeated it again just to be sure - and between 19 and 21 the configuration transfers, yet is modified during access of the LuCI Intefaces page.
18.06 network config relevant parts:
config dsl 'dsl' option annex 'b' option tone 'a' option ds_snr_offset '0' config interface 'wan' option proto 'dhcp' option ifname 'dsl0.101' config device 'wan_dev' option name 'dsl0' option macaddr 'xxxxxxxxxxxxxx'
Importantly the interface dsl0.101 appears to be recognised:
Upgrading to 19.07 with config:
On the Interface page the WAN network device is not recognised similar to how it is in 21.02...
However, unlike 21.02 under theInterfaces>WAN>Physical Interfaces the device is not appearing as Device Absent:
Relevant parts of network config:
config dsl 'dsl' option annex 'b' option tone 'a' option ds_snr_offset '0' config interface 'wan' option proto 'dhcp' option ifname 'dsl0.101' config device 'wan_dsl0_dev' option name 'dsl0' option macaddr 'ac:3b:77:27:d4:ef'
The WAN device name changes slightly to "wan_dsl0_dev". I checked and tested this as the previous "wan_dev", but it appeared to make no difference.
Upgrading to 21.02 testing keeping the config:
Going to interfaces:
The DSL page looks fine, yet the devices page shows the dsl0 network device as not present:
So no improvement. Running a firstboot && reboot now, to clear the config clears the configuration, but the network devices remain as not present.
To answer you question:
" ps. is dsl_control enabled as I note one of images shows eth0.2 interface?"
I understand eth0.2 is the Red WAN port alongside the 4 Yellow LAN ports and can be configured as an additional LAN port if necessary or as a WAN port for connection to a VDSL model.
I am unaware of dsl_control and have not seen reference to it in my searches, except in pages for devs - requiring a little more headspace than I can cope with at the moment.