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Cannot ping directly connected device

Publication Date:  2014-09-12 Views:  3126 Downloads:  0
Issue Description
The two switches are connected through a eth-trunk / port channel (on cisco side). Comunication between these two devices is done through Vlan 50.
Alarm Information
Although mac-address table is completed with the addresses of the remote device the arp table is not:


  ===============display arp===============


x.x.x.x         cccc-cccc-cccc       I -  MEth0/0/1

z.z.z.z     cccc-cccc-cccc            I -  Vlanif50


Total:2         Dynamic:0       Static:0     Interface:2  
Handling Process
After concluding that this fault occured because there was no entry in the arp table we tried to update the arp table according to the maca address table using command: "mac-address update arp". It didn't solved the issue so we tried a static arp entry for the physical interface but that also didn't solve the issue.
The solution was running the command : "arp detect-mode unicast". This issue is caused by the difference in behavior of a Huawei device as opposed to a non-Huawei device (your Cisco device). The default mode for arp aging detection is broadcast. The Cisco device discards arp detection packets with broadcast destination MAC address if there already is an entry in the arp table. When our switch doesn’t receive a reply to the arp aging detection packets it deletes the entry from the arp table, thus the lack of synchronization between the arp table and the mac-address table.
Root Cause
Ping does not work because there is no entry in the arp table of the S5700  for the outbound physical interface or the eth-trunk.
As a precoution whenever you connect a Huawei switch with a non-Huawei device you should consider running command "arp detect-mode unicast" because this could occur even if the remote device is not cisco (could be any other vendor).