I'm sorry to reopen this bug, but a bug report I replied in T421 has now been re generated. I have inquired the relevant service file and found that the file has been passive, and an invalid setting has been generated. The content of file `/lib/systemd/system/dhcp6c@.service` is as follows:
```
[Unit]
Description=WIDE DHCPv6 client on %i
Documentation=man:dhcp6c(8) man:dhcp6c.conf(5)
ConditionPathExists=/run/dhcp6c/dhcp6c.%i.conf
After=vyos-router.service
StartLimitIntervalSec=0
[Service]
WorkingDirectory=/run/dhcp6c
Type=forking
PIDFile=/run/dhcp6c/dhcp6c.%i.pid
ExecStart=/usr/sbin/dhcp6c -D -k /run/dhcp6c/dhcp6c.%i.sock -c /run/dhcp6c/dhcp6c.%i.conf -p /run/dhcp6c/dhcp6c.%i.pid %i
Restart=on-failure
RestartSec=20
[Install]
WantedBy=multi-user.target
```
It appears that the following settings exist for automatic recovery:
```
StartLimitIntervalSec=0
Restart=on-failure
RestartSec=20
```
But the directive:
```
StartLimitIntervalSec=0
```
I don't know why PPPoE seems to be invalid when dialing and dhcpv6-pd is used after the router is started. When dhcp6c is started, the PPPoE link has not been established. I've been waiting for at least half a minute, but it doesn't work until I manually restart by typing the following command:
```
sudo systemctl restart dhcp6c@pppoe0
```
The following is a reference to the original modified file of @c-po:
https://github.com/vyos/vyos-1x/commit/992d3560369608085eaed41c385d17cbc4566fa5