Why does an Ethernet sub-interface fail to forward packets

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The arp broadcast enable command is not executed on this subinterface.

Other related questions:
Why do I fail to configure a sub-interface on an AR router
Before configuring a sub-interface, confirm that: - The physical interface corresponding to the sub-interface is connected properly. - The physical interface is switched to a Layer-3 interface. A sub-interface can be configured only on a Layer-3 interface that can be allocated with an IP address.

How do I configure an Ethernet sub-interface to implement inter-VLAN communication
Generally, only one primary IP address can be configured for a physical interface. When a Layer 3 device connects to a Layer 2 network device through a Layer 3 Ethernet interface and interfaces on the Layer 2 network device are assigned to different VLANs, one primary IP address of the Layer 3 physical interface cannot implement inter-VLAN communication. You can configure secondary IP addresses or sub-interfaces for the Layer 3 Ethernet interface to solve this problem. The secondary IP addresses depend on the primary IP address. When the primary IP address becomes invalid, the secondary IP addresses also become invalid. The sub-interfaces and main interface are independent. Sub-interfaces share physical layer parameters of their main interface, and are configured with their respective link layer parameters and network layer parameters. The IP address of the main interface and IP addresses of sub-interfaces are independent. You can create sub-interfaces on the Ethernet interface connecting the Layer 3 device to the Layer 2 device so that users in different VLANs can communicate.

After configuring the IP address on a sub-Interface, why can I not ping the sub-interface
You have to run arp broadcast enable on the sub-interface to be able to ping the sub-interface.

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
Description:
Route Port,The Maximum Frame Length is 9216
Internet Address is 10.1.1.1/24
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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