Troubleshooting L2TP VPN Authentication Issue on AR2240 with Windows 8 Clients

l2tp enable<br/>aaa<br/>local-user vpn password cipher %$%$bE%\WX_E<>dY/T7UiW1KTG8x%$%$<br/>local-user vpn service-type ppp<br/>interface Virtual-Template1<br/>ppp authentication-mode chap<br/>remote address pool l2tp<br/>ppp ipcp dns 202.103.24.68 202.103.44.150<br/>ip address 10.18.0.1 255.255.255.0<br/>ip pool l2tp<br/>gateway-list 10.18.0.1<br/>network 10.18.0.0 mask 255.255.255.0<br/>l2tp-group 1<br/>undo tunnel authentication<br/>allow l2tp virtual-template 1

Process

1. Verify device links and interfaces using ping and display interface brief; no issues were found. 2. Confirm AR2240 configuration, including IPSec and routing settings, which were correct. 3. Check the PC1 workstation; no abnormalities were detected. 4. Run debugging ppp all and debugging l2tp control to capture debug logs, revealing that the username sent from the PC did not match the one configured on the AR2240.

The root cause was that Windows 8 automatically prefixes the username with the domain name unless the user manually adds a leading backslash ("\"). Without this backslash, authentication fails.

Solution

When entering the username on PC1, prepend a backslash (e.g., "\vpn"). After this adjustment, the L2TP dial‑up succeeded.

Recommendation and Summary

For Windows 8 clients establishing L2TP connections to an AR2240, always include a leading backslash before the username to prevent the OS from adding the domain automatically and causing authentication failure.