Hi Guys.
I configured the L2TP VPN as below using the RV340 Router.
IPSec Profile is as follows.
1.Default (IKEv1)
Phase I Options: Group 5, AES-128, SHA1
Phase II Options: ESP, AES-128, SHA1, Group5
The log found in RV40 is as follows.
2020-03-26T10:04:01+09:00 <info>charon: 08[IKE] nothing to initiate
2020-03-26T10:04:01+09:00 <info>charon: 08[IKE] activating new tasks
2020-03-26T10:04:01+09:00 <info>charon: 08[NET] sending packet: from 211.34.60.247[4500] to 211.36.149.154[42030] (92 bytes)
2020-03-26T10:04:01+09:00 <info>charon: 08[ENC] generating INFORMATIONAL_V1 request 1039630429 [ HASH N(DPD_ACK) ]
2020-03-26T10:04:01+09:00 <info>charon: 08[IKE] activating ISAKMP_DPD task
2020-03-26T10:04:01+09:00 <info>charon: 08[IKE] activating new tasks
2020-03-26T10:04:01+09:00 <info>charon: 08[IKE] queueing ISAKMP_DPD task
2020-03-26T10:04:01+09:00 <info>charon: 08[ENC] parsed INFORMATIONAL_V1 request 4247162276 [ HASH N(DPD) ]
2020-03-26T10:04:01+09:00 <info>charon: 08[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (108 bytes)
2020-03-26T10:03:56+09:00 <info>charon: 07[IKE] nothing to initiate
2020-03-26T10:03:56+09:00 <info>charon: 07[IKE] activating new tasks
2020-03-26T10:03:56+09:00 <info>charon: 07[NET] sending packet: from 211.34.60.247[4500] to 211.36.149.154[42030] (92 bytes)
2020-03-26T10:03:56+09:00 <info>charon: 07[ENC] generating INFORMATIONAL_V1 request 3548883819 [ HASH N(DPD_ACK) ]
2020-03-26T10:03:56+09:00 <info>charon: 07[IKE] activating ISAKMP_DPD task
2020-03-26T10:03:56+09:00 <info>charon: 07[IKE] activating new tasks
2020-03-26T10:03:56+09:00 <info>charon: 07[IKE] queueing ISAKMP_DPD task
2020-03-26T10:03:56+09:00 <info>charon: 07[ENC] parsed INFORMATIONAL_V1 request 3770949866 [ HASH N(DPD) ]
2020-03-26T10:03:56+09:00 <info>charon: 07[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (108 bytes)
2020-03-26T10:03:51+09:00 <info>charon: 15[IKE] nothing to initiate
2020-03-26T10:03:51+09:00 <info>charon: 15[IKE] activating new tasks
2020-03-26T10:03:51+09:00 <info>charon: 15[NET] sending packet: from 211.34.60.247[4500] to 211.36.149.154[42030] (92 bytes)
2020-03-26T10:03:51+09:00 <info>charon: 15[ENC] generating INFORMATIONAL_V1 request 3545216459 [ HASH N(DPD_ACK) ]
2020-03-26T10:03:51+09:00 <info>charon: 15[IKE] activating ISAKMP_DPD task
2020-03-26T10:03:51+09:00 <info>charon: 15[IKE] activating new tasks
2020-03-26T10:03:51+09:00 <info>charon: 15[IKE] queueing ISAKMP_DPD task
2020-03-26T10:03:51+09:00 <info>charon: 15[ENC] parsed INFORMATIONAL_V1 request 3081719705 [ HASH N(DPD) ]
2020-03-26T10:03:51+09:00 <info>charon: 15[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (108 bytes)
2020-03-26T10:03:46+09:00 <info>charon: 05[IKE] nothing to initiate
2020-03-26T10:03:46+09:00 <info>charon: 05[IKE] activating new tasks
2020-03-26T10:03:46+09:00 <info>charon: 05[NET] sending packet: from 211.34.60.247[4500] to 211.36.149.154[42030] (92 bytes)
2020-03-26T10:03:46+09:00 <info>charon: 05[ENC] generating INFORMATIONAL_V1 request 2260787752 [ HASH N(DPD_ACK) ]
2020-03-26T10:03:46+09:00 <info>charon: 05[IKE] activating ISAKMP_DPD task
2020-03-26T10:03:46+09:00 <info>charon: 05[IKE] activating new tasks
2020-03-26T10:03:46+09:00 <info>charon: 05[IKE] queueing ISAKMP_DPD task
2020-03-26T10:03:46+09:00 <info>charon: 05[ENC] parsed INFORMATIONAL_V1 request 4126973971 [ HASH N(DPD) ]
2020-03-26T10:03:46+09:00 <info>charon: 05[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (108 bytes)
2020-03-26T10:03:41+09:00 <info>charon: 13[ENC] parsed INFORMATIONAL_V1 request 3752504203 [ HASH N(INITIAL_CONTACT) ]
2020-03-26T10:03:41+09:00 <info>charon: 13[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (108 bytes)
2020-03-26T10:03:41+09:00 <info>charon: 09[NET] sending packet: from 211.34.60.247[4500] to 211.36.149.154[42030] (76 bytes)
2020-03-26T10:03:41+09:00 <info>charon: 09[ENC] generating ID_PROT response 0 [ ID HASH ]
2020-03-26T10:03:41+09:00 <info>charon: 09[IKE] maximum IKE_SA lifetime 28691s
2020-03-26T10:03:41+09:00 <info>charon: 09[IKE] scheduling reauthentication in 28511s
2020-03-26T10:03:41+09:00 <info>charon: 09[IKE] IKE_SA l2tp_l2tpOverIpsec_wan1[105] state change: CONNECTING => ESTABLISHED
2020-03-26T10:03:41+09:00 <info>charon: Last message '09[IKE] IKE_SA l2tp_' repeated 1 times, supressed by syslog-ng on router794083
2020-03-26T10:03:41+09:00 <info>charon: 09[IKE] IKE_SA l2tp_l2tpOverIpsec_wan1[105] established between 211.34.60.247[211.34.60.247]...211.36.149.154[10.146.90.210]
2020-03-26T10:03:41+09:00 <info>charon: 09[CFG] selected peer config l2tp_l2tpOverIpsec_wan1
2020-03-26T10:03:41+09:00 <info>charon: 09[CFG] looking for pre-shared key peer configs matching 211.34.60.247...211.36.149.154[10.146.90.210]
2020-03-26T10:03:41+09:00 <info>charon: 09[ENC] parsed ID_PROT request 0 [ ID HASH ]
2020-03-26T10:03:41+09:00 <info>charon: 09[NET] received packet: from 211.36.149.154[42030] to 211.34.60.247[4500] (92 bytes)
2020-03-26T10:03:41+09:00 <info>charon: 14[NET] sending packet: from 211.34.60.247[500] to 211.36.149.154[31050] (308 bytes)
2020-03-26T10:03:41+09:00 <info>charon: 14[ENC] generating ID_PROT response 0 [ KE No NAT-D NAT-D ]
2020-03-26T10:03:41+09:00 <info>charon: 14[IKE] FSLDBG: Now searching for PSK with :my_id,me,other_id,other: '211.34.60.247'[211.34.60.247] - '(null)'[211.36.149.154]
2020-03-26T10:03:41+09:00 <info>charon: 14[IKE] remote host is behind NAT
2020-03-26T10:03:41+09:00 <info>charon: 14[IKE] local host is behind NAT, sending keep alives
2020-03-26T10:03:40+09:00 <info>charon: 14[ENC] parsed ID_PROT request 0 [ KE No NAT-D NAT-D ]
2020-03-26T10:03:40+09:00 <info>charon: 14[NET] received packet: from 211.36.149.154[31050] to 211.34.60.247[500] (292 bytes)
2020-03-26T10:03:40+09:00 <info>charon: 10[NET] sending packet: from 211.34.60.247[500] to 211.36.149.154[31050] (180 bytes)
2020-03-26T10:03:40+09:00 <info>charon: 10[ENC] generating ID_PROT response 0 [ SA V V V V V ]
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] sending NAT-T (RFC 3947) vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] sending FRAGMENTATION vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] sending Cisco Unity vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] sending DPD vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] sending XAuth vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] IKE_SA (unnamed)[105] state change: CREATED => CONNECTING
2020-03-26T10:03:40+09:00 <info>charon: Last message '10[IKE] 211.36.149.1' repeated 1 times, supressed by syslog-ng on router794083
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] 211.36.149.154 is initiating a Main Mode IKE_SA
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received DPD vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received FRAGMENTATION vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[ENC] received unknown vendor ID: b4:f0:1c:a9:51:e9:da:8d:0b:af:bb:d3:4a:d3:04:4e
2020-03-26T10:03:40+09:00 <info>charon: 10[ENC] received unknown vendor ID: 4c:53:42:7b:6d:46:5d:1b:33:7b:b7:55:a3:7a:7f:ef
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received draft-ietf-ipsec-nat-t-ike-00 vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received draft-ietf-ipsec-nat-t-ike-02\n vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received draft-ietf-ipsec-nat-t-ike-02 vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[IKE] received NAT-T (RFC 3947) vendor ID
2020-03-26T10:03:40+09:00 <info>charon: 10[ENC] parsed ID_PROT request 0 [ SA V V V V V V V V ]
2020-03-26T10:03:40+09:00 <info>charon: 10[NET] received packet: from 211.36.149.154[31050] to 211.34.60.247[500] (356 bytes)
Thank you.
