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[All About Switches] PCs and the Gateway Cannot Communicate with Each Other Due to the Rate Limit of ARP Miss Packets

Latest reply: Mar 9, 2018 00:38:55 1630 1 0 0 0

Involved Products and Versions

All products and versions


As shown in Figure 1-1, the gateway SwitchA is connected to the Layer 2 device SwitchB, which is then connected to a PC.

Figure 1-1 Networking diagram for the communication failure between a PC and the gateway due to the rate limit of ARP Miss packets



Fault Symptom

The PC and SwitchA cannot communicate with each other.

Cause Analysis

The rate limit of ARP Miss packets is incorrectly configured.

Troubleshooting Procedure

                         Step 1    Run the display cpu-defend statistics allcommand. It is found that a large number of ARP Miss packets and ARP Request packets are sent to the CPU for processing while a large number of these packets are discarded.

<SwitchA> display cpu-defend statistics all
Statistics on slot 1:
Packet Type Pass(Packet/Byte) Drop(Packet/Byte) Last-dropping-time 
arp-miss           135576021           1601690  2017-03-31 05:17
                 14520988007         513234651
arp-reply             281572                 0  - 
                    18113898                 0
arp-request         39556247           2009617 2017-03-31 05:17
                  2536513490         128877696
fib-hit               229127             13806 2017-03-31 05:17
                    41911145           1577046

                         Step 2    Check the configuration on SwitchA. It is found that the rate limit of ARP Miss packets is configured.

arp-miss anti-attack rate-limit enable
arp-miss anti-attack rate-limit packet 16384 interval 84600
arp-miss speed-limit source-ip maximum 16384

According to the preceding configuration, the arp-miss anti-attack rate-limit packet 16384 interval 84600 command is improper. On average, only 0.1 ARP Miss packets can be processed per second. However, there are many ARP Miss packets on the live network. After the arp-miss anti-attack rate-limit packet 16384 interval 84600 and arp-miss speed-limit source-ip maximum 16384 commands are deleted, the fault is rectified.


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Created Mar 9, 2018 00:38:55

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