What are causes for QinQ traffic forwarding failures


Traffic forwarding on an interface configured with selective QinQ fails in the following situations:

The outer VLAN specified for selective QinQ is not created.
The interface is not added to the outer VLAN specified for selective QinQ in untagged mode.

Other related questions:
What are the causes of the L2TP dialup failure
The causes of the L2TP dialup failure are as follows: -The firewall deployed on the public network or the built-in firewall on the PC discards L2TP packets. -The corresponding L2TP port, usually UDP port 1701, is disabled or occupied. For example: ACL or NAT is configured on the port. -The user name and password configured on the LAC are incorrect, or no related user is configured on the LNS. -The configuration address, such as the static address of the VT interface, is incorrect. -The tunnel authentication modes are different. -LCP renegotiation is not configured. -The address pool cannot meet user requirement or no address pool is configured. -No gateway address is reserved in the IP address pool, so that the gateway address is allocated to users. -The LAC and LNS have no reachable routes to each other. -An incorrect remote tunnel name is specified in the L2TP group view. -The authentication domain is incorrectly configured. -The control packets sent by the PC client do not carry the SQ number, so that the L2TP negotiation fails. -When IPSec encryption is used, the IPSec parameters on both ends are different.

What are QinQ and selective QinQ
Switch QinQ is also called port QinQ or Dot1q-tunnel. The port adds the default VLAN tag to packets no matter whether the packets carry VLAN tags. Selective QinQ indicates VLAN stacking. Different from port QinQ, selective QinQ encapsulates outer VLAN tags according to different VLANs.

Why does traffic forwarding fail when an S series switch is connected to another device through Eth-Trunk
After Eth-Trunk link aggregation is configured for an S series switch (except the S1700), the Eth-Trunk works in manual load balancing mode by default. If Eth-Trunk link aggregation is also configured for the peer device, the Eth-Trunk works in LACP mode by default. The two ends of the Eth-Trunk work in different default modes, resulting in forward traffic failure. To ensure normal traffic forwarding, you must configure the same working mode for the two ends.

Possible causes for failures to forward Layer 3 traffic between directly connected interfaces on CE series switches
In V100R002 and later versions, the interface can be switched to the Layer 3 mode through the undo portswitch command. The possible causes for a Layer 3 traffic forwarding failure between interfaces are as follows:
- The interface is connected incorrectly.
- The physical layer status of the interface is Down.
- The interface is not assigned an IP address.
- The IP addresses of interfaces are on different network segments.
You can run the display interface command to check the physical layer status and IP address of an interface.
display interface 10ge 1/0/1
10GE1/0/1 current state : UP (ifindex: 16)
Line protocol current state : UP
Last line protocol up time : 2013-12-26 03:20:13
Route Port,The Maximum Frame Length is 9216
Internet Address is
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 0025-9e01-0205
Port Mode: COMMON FIBER, Port Split: -
Speed : 10000, Loopback: NONE
Duplex: FULL, Negotiation: DISABLE
Mdi : -
Last physical up time : 2013-12-26 03:20:13
Last physical down time : 2013-12-26 03:20:02
Current system time: 2013-12-27 01:58:44

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