Cause of slow server access rate and discontinuous packet loss on S series switches


When a user uses an S series switch to access a server, the access rate is slow and packets are lost discontinuously. In V100R001 and V100R002, check whether there are many ARP entries on the switch. If an ARP hash collision or entry delivery failure occurs or software forwarding is slow on a fixed switch, some packets are dropped by CAR and services are affected. In V100R006 and later versions, after an ARP hash collision occurs, entries are delivered to the DEFIP table, avoiding packet loss.

Other related questions:
What causes packet loss on the port of S series switches
For S series switches (except the S1700), packets will be discarded if traffic is too heavy or burst traffic occurs.

The reason of S series switch Ping packet loss
For S-series chassis switches: The Ping packets of the local switch are processed by the switch as a fib-hit packet. For packets of type fib-hit, the switch sends to CPUs at the default CAR value to prevent this type of packets from impacting the CPU. In the case of the default CAR value, the number of ping packets per second is too large for the CAR value, so the switch will discard some packets. Increase the fib value of fib-hit, you can solve the packet loss problem.

Question about packet loss when the rate of ping packets is high on S series switches
When another device pings an S series switch (a non-S1700 switch), the device and the switch exchange ICMP packets. To protect the CPU, you can run the icmp rate-limit command to configure a rate threshold for ICMP packets. The undo icmp rate-limit command restores the default rate threshold of ICMP packets.

Reason for ping packet loss on S series switch
For S series modular switches: Ping packets sent from other devices to a switch are processed by the switch as fib-hit packets. The switch sends fib-hit packets to the CPU at the default CAR value to protect the CPU from being attacked by these packets. If the rate of ping packets sent to the CPU exceeds the CAR value, the switch discards the excess packets. To resolve the problem, set a larger CAR value for fib-hit packets.

How to check ping packet loss on S series switches
For S series switches (except the S1700), you can run the ping command to check ping packet loss directly. For example: [HUAWEI] ping -c 100 PING 56 data bytes, press CTRL_C to break Reply from bytes=56 Sequence=1 ttl=124 time=1 ms ... --- ping statistics --- 100 packet(s) transmitted //Total number of sent packets 91 packet(s) received //Total number of received packets 9.00% packet loss //Packet loss ratio round-trip min/avg/max = 1/1/19 ms You can also perform the following steps to configure traffic statistics collection to check ping packet loss: Configure traffic statistics collection for packets received by a switch. 1. Configure an ACL rule. [HUAWEI] acl number 3000 [HUAWEI-acl-adv-3000] rule permit icmp source 0 destination 0 [HUAWEI-acl-adv-3000] quit 2. Configure a traffic classifier. [HUAWEI] traffic classifier 3000 [HUAWEI-classifier-3000] if-match acl 3000 [HUAWEI-classifier-3000] quit3. Configure a traffic behavior. [HUAWEI] traffic behavior 3000 [HUAWEI-behavior-3000] statistic enable [HUAWEI-behavior-3000] quit 4. Configure a traffic policy. [HUAWEI] traffic policy 3000 [HUAWEI-trafficpolicy-3000] classifier 3000 behavior 3000 [HUAWEI-trafficpolicy-3000] quit 5. Apply the traffic policy to an interface. [HUAWEI] interface gigabitethernet 0/0/2 [HUAWEI-GigabitEthernet0/0/2] traffic-policy 3000 inbound [HUAWEI-GigabitEthernet0/0/2] quit 6. Check traffic statistics of packets received by the switch. [HUAWEI] display traffic policy statistics interface gigabitethernet 0/0/2 inbound verbose rule-base //The output is omitted. For more information about ping packet loss, see "Ping Failure Troubleshooting" or "S Series Switches packet Loss Troubleshooting" in "Maintenance Topics" in the Huawei S Series Campus Switches Maintenance Guide.

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