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S6720-EI sub-interface ARP issue

Publication Date:  2018-01-31 Views:  271 Downloads:  0

Issue Description

The customer deploy one S6720-EI on the netwrok, the topology just as below:

The S6720 used the XGi0/0/24 to connect with the access switch, the XGi0/0/24 configure as the layer3 interface which used the command"undo portswitch".

Then the customer configure the sub-interface on the Xgi0/0/24, the configuration as below:


interface XGigabitEthernet0/0/24.3837
 dot1q termination vid 3837
 ip address x.x.x.x

After the customer finish the configuration, the sub-interface can't learn the MAC address of the client, the service is not work.


Handling Process

First we checked the configuration of the S6720-EI version and patch, it is ok.

Then we checked the configuration of the S6720, we found that the customer configure the VLAN tag termination sub-interfaces.

We checked the product document know that the VLAN tag termination sub-interfaces discard broadcast packets after receiving the packets.

To permit a VLAN tag termination sub-interface to forward broadcast packets, run the arp broadcast enable command on the sub-interface to enable ARP broadcast.

After configure the "arp broadcast enable "the sub-interface can learn the customer MAC address.

Root Cause

The customer configure the VLAN tag termination sub-interfaces but not enable the ARP broacast.


If you configure the VLAN tag termination sub-interfaces, you should configure the "arp broadcast enable" on the sub-interface.