Data Transmission Failure; L2Tp User Offline - H3C SR8800-F Configuration Manual

The LNS can accept L2TP tunneling requests from the LAC. For more information, see the
allow command.
Tunnel authentication is enabled on both the LAC and the LNS, and the tunnel
authentication keys configured on the two sides match.
2. Verify the following items to avoid PPP negotiation failures:
Usernames and passwords are correctly configured on the LAC and LNS.
IP address negotiation settings are correct on the remote system and LNS.
The authentication type is consistent. For example, the default authentication type for a
VPN connection created on Windows 2000 is MS-CHAP. If the peer does not support
MS-CHAP, change the authentication type to CHAP on Windows 2000.

Data transmission failure

Symptom
Data transmission fails. A connection is established, but data cannot be transmitted. For example,
the LAC and LNS cannot ping each other.
Solution
To resolve the problem:
1. Use the display ip routing-table command on the LAC and LNS to verify that the LAC has a
route to the private network behind the LNS, and vice versa. If no route is available, configure a
static route or a dynamic routing protocol.
2. Increase the link bandwidth to enhance the link availability.
Internet backbone congestion and high packet loss ratio might cause data transmission failures.
L2TP data transmission is based on UDP, which does not provide the packet error control
feature. If the line is unstable, the LAC and LNS might be unable to ping each other.
3. If the problem persists, contact H3C Support.

L2TP user offline

Symptom
A L2TP user goes offline when sending a large L2TP packet.
Solution
To resolve the problem:
1. Configure a large MTU for the tunnel interface and VT interface of the LAC or LNS to avoid
fragmentation.
L2TP does not support fragmentation. When the packet size exceeds the MTU of the tunnel
interface or the VT interface, the following occurs:
If an interface on CSPEX-1204 cards is used as the tunnel interface, the hardware discards
the packet because of fragmentation failure.
If an interface on CSPEX cards (except CSPEX-1204) is used as the tunnel interface, the
packet is not fragmented. The default MTU is 10240 even you modify the MTU of the tunnel
interface or the VT interface.
2. If the problem persists, contact H3C Support.
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