Error 676 Occasionally Occurs in PPPoE Dialup

How to troubleshoot the fault when error 676 occasionally occurs in Point-to-Point Protocol over Ethernet (PPPoE) dialup. Here is the solution:

Fault Description

Network topology: ONU -> optical line terminal (Huawei OLT) -> switch -> broadband remote access server (BRAS)
An ONU user occasionally encounters error 676 in PPPoE dialup. In addition, the fault duration varies.

Possible Causes

• An ONU user forges the MAC address of the BRAS.
• An OLT user forges the MAC address of the BRAS.
• The configuration of the BRAS or remote authentication dial in user service (RADIUS) is incorrect.
• A VLAN conflict occurs.

Procedure

1. Run the security mac-filter command to configure MAC address filtering on the ONU, which prevents the MAC address of the BRAS from being forged. The fault persists.
2. Run the security mac-filter command to configure MAC address filtering on the OLT. The fault persists.
3. Check the configurations of the BRAS and RADIUS. The configurations are correct. Check the VLAN configurations on the upper-layer aggregation switch and OLT. The VLAN configurations are correct.
4. When an ONU user in VLAN A encounters error 676, another user in the same VLAN is already online on the BRAS. Therefore, it is determined that a VLAN conflict occurs on the BRAS. The maximum number of concurrent online users configured on the BRAS is 1 in PPPoE dialup. Therefore, if a user is online in the VLAN with conflicts, error 676 occurs with other users of the same VLAN in PPPoE dialup.
5. Query the configurations of all ONUs connected to the OLT. It is found that VLANs have the same outer VLAN tags and the same inner VLAN tags. Modify the VLAN settings so that they have different outer tags and different inner tags. Then, the fault is rectified.

Suggestions and Summary

Properly plan VLANs for the PON ports on an OLT. It is suggested to configure an outer VLAN tag for each PON port. In such a manner, the fault location scope is minimized even when an inner VLAN conflict occurs.

The more information about technical support you can consult with our technician - Bill, and his e-mail address is as below:  

bill@huanetwork.com

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