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Troubleshooting Of ARP not Update For S12708(V200R006C00)

Publication Date:  2015-12-08 Views:  202 Downloads:  0
Issue Description
After replacing the connected switch under the S12708. The communication is not available between S12708 and end user.
Alarm Information
After replacing the connected switch under the S12708. The communication is not available between S12708 and end user.
Handling Process

1. The topology is just as below:


2. When replace the ME3600 with S5700. ARP could not communicate and not updated.
3. When the Link2 and Link XGi7/0/4~XGi0/0/1 become up, TC received. S12708 will learn the MAC address of S5700.And also, the User(Router) & S5700 will learn the MAC address of S12708. So, the MAC table will be updated.
4. But for the ARP table, since Link XGi7/0/0~Te0/1 is still up, the ARP table is still by path ME3600 to Router(202.Y.Y.Y). Until the ARP table aging or the ARP of ME3600 is not available .and then S12708 will relearn the ARP table. But if there is continued traffic from 202.Y.Y.Y by path S5700 to S12708, the ARP table~ path ME3600 to Router(202.Y.Y.Y), won’t become aging. And at the same time the Link XGi7/0/0~Te0/1 is still up and ARP is available the next hop is ME3600. Although the L1 is down, the S12708 thought the ARP is available. So, the ARP can’t be updated.
5. Clear the ARP table, the S1208 will relearn the ARP table and this will been updated. And then the communication resolved.
6. Advise apply use the command “mac-address update arp” in S12708. Enables the MAC address-triggered ARP entry update function. That is, the Switch is enabled to update outbound interfaces in ARP entries when outbound interfaces in MAC address entries change.

Root Cause
1. XGi7/0/0~Te0/1 is not down.
2. Continued traffic from 202.Y.Y.Y to S12708, make the ARP table won’t become aging --> ARP table can’t be updated.
Suggestions
During the Troubleshooting, using different way to reduce the scope of  possible root cause. That will be helpful for the work.

END