After receiving an ICMP Request packet, a switch does not send it to the ICMP protocol stack but directly returns an ICMP Reply message. This process is called fast ICMPM reply. Switches cannot accurately calculate the delay or jitter of ping packets that require high real-time performance. The protocol stack adds the sending and receiving timestamps to ping packets. The packets need to enqueue frequently between the protocol stack and hardware. This task switching cannot ensure real-time performance of timestamps. In versions earlier than V100R006, fast ICMP reply is a common task. When a switch processes a large volume of service traffic, the reply delay is long due to task switching. In V100R006 and later versions, fast ICMP reply is a super task with a high priority. In most cases, the reply delay is about 1 ms. The actual delay depends on the CPU usage and is shorter than 100 ms. NOTE: By default, box switches have fast ICMP reply enabled in all versions.

The default aging time of ARP entries is 20 minutes. You can run the arp expire-time command to change the aging time.
You can also change the number of ARP probes by running the arp detect-times command. The default number of ARP probes is 3.
When the aging time of an ARP entry expires, the device sends a probe packet to the corresponding IP address every 5 seconds. If the device does not receive any response after the specified number of probes, it deletes the ARP entry.
For example, the aging time of ARP entries is set to 60s and the number of ARP probes is set to 6.
After 60s since an ARP entry is generated, the device sends an ARP probe every 5s. If the device does not receive any response after sending six probes, it deletes the ARP entry. Therefore, the actual aging time of the ARP entry is (60 + 6 x 5) = 90s.

NOTE:

For V100R002 version, the S2700/S3700/S5700/S6700 supports the 1/2 probe time and 3/4 probe time. The numbers of probes on the two time points are both 3 and cannot be changed. For example, if the aging time is 20 minutes (1200s) and the number of ARP probes is 6, the SS2700/S3700/S5700/S6700 sends three ARP probes at an interval of 5s after 10 minutes. After 15 minutes, the S2700/S3700/S5700/S6700 also sends three ARP probes at an interval of 5s. After 20 minutes, the S2700/S3700/S5700/S6700 sends six ARP probes at an interval of 5s. If the S2700/S3700/S5700/S6700 does not receive any response, it deletes the ARP entry.


More blog:

Why Automatical configuration backup cannot work on S5700

How to Change the Link Type of an Interface?

10G Card Issue in Quidway S5300