Dell Networking Intermittent High ICMP Latency seen in S-series Switches running OS9 Firmware

Summary: Dell Networking Intermittent High ICMP Latency seen in S-series Switches running OS9 Firmware

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Symptoms

An intermittent issue regarding high latency is seen when attempting to perform an ICMP ping from a client device to the gateway, generally the IP of the VLAN interface. This issue can still be seen even when directly connected to a gateway switch that has little to no production traffic. There has been some customer concern that this reflects an impact on normal production traffic.
Issue seen across all S-series platforms running OS9 firmware.

Test scenario for ICMP test (No production traffic)

ICMP test topology

Topology Configuration

PC1: 192.168.10.100/24, Gateway: 192.168.10.1/24, VLAN10
PC2: 192.168.10.200/24, Gateway: 192.168.10.1/24, VLAN10
Or
PC2: 192.168.20.200/24, Gateway: 192.168.20.1/24, VLAN20

Note: Pings between client devices are not generally affected, so not all the results of testing are listed here. This issue is only seen when pinging from a client device to a gateway IP on a switch.

PC1 ping switch gateway (directly connected) Test 1-6; same result seen, regardless of topology

Pinging 192.168.10.1 with 32 bytes of data:
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time=5ms TTL=255
Reply from 192.168.10.1: bytes=32 time=47ms TTL=255  <------ high latency !
Reply from 192.168.10.1: bytes=32 time=5ms TTL=255
Reply from 192.168.10.1: bytes=32 time=5ms TTL=255
Reply from 192.168.10.1: bytes=32 time=1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time=32ms TTL=255  <------ high latency !
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time=6ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time=40ms TTL=255  <------ high latency !
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
Reply from 192.168.10.1: bytes=32 time<1ms TTL=255
……
>>> (truncated)

Ping statistics for 192.168.10.1:
    Packets: Sent = 8280，Received = 8280，Lost = 0 (0% Loss)
Approximate round trip times in milli-seconds:
    Minimum = 0ms，Maximum = 55ms，Average = 1ms

Ping between two PCs, transit traffic (Layer2, in same and different vlan's) (Test 1-3)

Pinging 192.168.10.200 with 32 bytes of data:
Reply from 192.168.10.200: bytes=32 time=1ms TTL=128
Reply from 192.168.10.200: bytes=32 time=1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time=1ms TTL=128
Reply from 192.168.10.200: bytes=32 time=1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
……
>>> (truncated),
……
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time<1ms TTL=128
Reply from 192.168.10.200: bytes=32 time=1ms TTL=128

Ping statistics for 192.168.10.200:
    Packets: Sent = 1233，Received = 1233，Lost = 0 (0% Loss)
Approximate round trip times in milli-seconds:
    Minimum = 0ms，Maximum = 2ms，Average = 0ms

Ping between two PCs, transit traffic (Layer3, in two vlans) (Tests 4-6)

Pinging 192.168.20.200 with 32 bytes of data:
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
……
>>> (truncated),
……
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127
Reply from 192.168.20.200: bytes=32 time<1ms TTL=127
Reply from 192.168.20.200: bytes=32 time=1ms TTL=127

Ping statistics for 192.168.20.200:
    Packets: Sent = 808，Received = 808，Lost = 0 (0% Loss)
Approximate round trip times in milli-seconds:
    Minimum = 0ms，Maximum = 2ms，Average = 0ms

 

Cause

Explanation of Results

It has been confirmed with Dell Engineering that this is normal and expected behavior due to CPU scheduling and queuing.

 

Resolution

ICMP testing should only be used as a means to test reachability, rather than latency or loss due to this behavior. ICMP traffic latency is not a reflection of the impact to normal production traffic. This behavior can also be exacerbated by a busy CPU - that is for a switch that is in full production, with a higher amount of traffic on it.

 

Affected Products

PowerSwitch S3048-ON, PowerSwitch S4048-ON, PowerSwitch S4810-ON, PowerSwitch S4820T, PowerSwitch S5000, Dell Networking S3100 Series, PowerSwitch S4048T-ON, PowerSwitch S4128F-ON/S4128T-ON, PowerSwitch S4148F-ON/S4148T-ON/S4148FE-ON , PowerSwitch S4148U-ON, PowerSwitch S4248FB-ON /S4248FBL-ON, PowerSwitch S5148F-ON, PowerSwitch S5212F-ON, PowerSwitch S5224F-ON, PowerSwitch S5232F-ON, PowerSwitch S5248F-ON, PowerSwitch S5296F-ON, PowerSwitch S6010-ON, PowerSwitch S6100-ON ...
Article Properties
Article Number: 000135228
Article Type: Solution
Last Modified: 13 Nov 2025
Version:  6
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