1.LNS device is USG2130 V1R5 .LAC device is USG50 V1R1
2. After configuration is complete, the LAC side VT port can not have IP
Cancel the “ppp ipcp dns configuration” in the LNS VT port, the LAC VT port can have IP normal normally, L2TPVPN is normal.
View LNS and LAC packet filtering rules configuration is normal
View VT port join the regional is normal
View LNS configuration found there is a command that use to assign DNS
ppp ipcp dns 18.104.22.168
By analyzing, the USG50 software version is too low. Docking with V1R5 version , if config assign DNS under LNS VT port ,this problem occurs.
If have same problems , as far as possible with a minimum configuration to test when troubleshooting.