If certain packets are discarded in a network that employs the QinQ function, you can solve the problem by adding bytes to short packets.
Products

OptiX OSN 1500A/1500B
OptiX OSN 2500
OptiX OSN 3500 II
OptiX OSN 3500
OptiX OSN 7500
Fault Type

Configuration fault
Symptom

The point-to-point protocol over Ethernet (PPPoE) client services enter a switch for convergence. The converged services are accessed to an OptiX NE for transmission over networks to the broadband access server at the destination end. The PPPoE active discovery session-confirmation (PADS) data packets in the downlink services returning from the broadband server to the client side are lost. As a result, the PPPoE verification fails.
Cause Analysis

The PPPoE services include the PADI, PADO, PADR and PADS data packets. Compared with the other types of data packets, the PADS data packet is only of a 64-byte length which is the minimum data packet length that the Ethernet supports.
After the QinQ function is configured, two tags are added without changing the original data packet length: C-VLAN and S-VLAN. When the downlink services travel over the OptiX NE to the client-side NE, the external S-VLAN tag is detagged. Hence, the data packet length changes from 64 bytes to 60 bytes. As a result, when the 60-byte services travel over the switch, they are regarded as abnormal and extra-short Ethernet data packets and are thus discarded. In this case, the PPPoE endpoint cannot receive the PADS data packet. As a result, the PPPoE verification fails and the services are not available.
Currently, some Ethernet boards are added with the short-packet length extension function against the problem that the extra-short data packets caused during detagging are discarded. When the length of a data packet is extra-short, it can be complemented on the Ethernet boards on the client side and system side to ensure that the data packet is transmitted at a length compliant with the Ethernet specification.