Reproduction stages:
```
vyos@vyos# set interfaces pppoe pppoe0 authentication password 'test'
vyos@vyos# set interfaces pppoe pppoe0 authentication user 'test'
vyos@vyos# set interfaces pppoe pppoe0 source-interface 'eth1'
vyos@vyos# commit
[edit]
vyos@vyos# run show interfaces pppoe
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address S/L Description
--------- ---------- --- -----------
pppoe0 100.64.0.9/32 u/u
[edit]
vyos@vyos# set interfaces pppoe pppoe0 disable
[edit]
vyos@vyos# commit
[edit]
vyos@vyos# run show interfaces pppoe
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address S/L Description
--------- ---------- --- -----------
pppoe0 100.64.0.9/32 u/u
```