1. Basic Information

2. Problem Description

Details are:
When Dell switch directly connect to S12700, most of users under Dell switch can’t ping S127000:

3. Problem Analysis

3.1 Check the ARP which IP ping timeout, there is no ARP or Incomplete ARP

3.2 There are a lot of ARP Attack alarm in log

3.3 Check STP TC statistics, there are a large number of TC packets, and increase very fast, 3 per sencond.

Eth-trunk3 is connected to Cisco switch.

3.4 After configure arp topology-change disable and mac-address update arp, ARP table of S12700 is stable now.

4. Root Cause

Since S12700 keep receiving TC packets, and we know according STP principle, if STP device receives any TC, the device should delete all ARP and learn them again. During this time, a lot of ARP-miss message sends to CPU and incomplete ARP table is created; since S12700 keep receiving TC, the above process can’t stop, it’s why S12700 always has some ARP can’t be learned , ping timeout, or intermit.

5. Solution

1. Configure arp topology-change disable to disable the function of deleting ARP by receiving TC( when device receives TC, doesn’t delete ARP anymore)
2. Configure mac-address update arp to enable MAC update ARP(when MAC table out interface changes, update ARP table)

Notice: if only arp topology-change disable, the ARP table can’t be updated by TC. So we need to configure mac-address update arp to update ARP table