How to do if L2TP VPN fails to be established on Reyee EG?

Issue Description

• PC/Phone can't access Reyee EG L2TP VPN
• EG devices can't access Reyee EG L2TP VPN
  

Device model and firmware

Device Type	Device Model	Device Version
Gateway	EG105G-P V2	ReyeeOS 2.248.0.2212

Possible Cause
1. Reyee EG can't access the network or the HQ EG is deployed on a layer-2 NAT environment
2. The configurations of branch EG and HQ EG are inconsistent
3. The traffic of VPN port is disabled by the uplink network
4. The terminals doesn't support L2TP VPN or L2TP VPN. The terminals settings are abnormal.
Troubleshooting Guide
1. Reyee EG can't access the network or the HQ EG is deployed on a layer-2 NAT environment;
(1) Check whether the WAN port configurations meet the requirements of uplink network. For example, whether the account and password of PPPOE are correct or not. And check whether the VLAN TAG is needed to configured. Please contact ISP to check the network situation.

(2) If the HQ EG is deployed on a layer-2 NAT environment, please DNZ the EG IP on egress device.

2. The configurations of branch EG and HQ EG are inconsistent
Please check the configurations by refering 8.2 Configuring L2TP VPN: RG-EG Web-based Configuration Guide, Release ReyeeOS 1.216(V1.2) - Ruijie Networks
3. The traffic of VPN port is disabled by the uplink network
Draw a package on EG to check whether the EG normally sends and receives packets. If packets are sent but not received, you need to contact the ISP to check whether the uplink device disable the L2TP VPN UDP 1701 port

4. The terminals don't support L2TP VPN or L2TP VPN settings are abnormal.

If the terminals don't support L2TP VPN, please use L2TP over IPsec VPN
If only the windows PC L2TP VPN is abnormal, please troubleshooting by Simple Fix: VPN Error 789 L2TP Connection Attempt Failed (windowsreport.com)