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I wouldn't call it an issue, but I'm curious. On our Quanta switch we have a couple of VLANs and vlan interfaces accordingly.

Let's say I'm on a computer in VLAN 10, if I do:

ping 192.168.10.1

with 192.168.10.1 being the VLAN 10 interface on the switch which is set as gateway for the devices in that VLAN, I get responses in range from 1 ms to (sometimes) 28 ms, or even 50 ms etc. If I ping any other device on the LAN I get responses in less than a millisecond.

Same goes if I go with

traceroute www.stackexchange.com

Here, from the first three hops I get highest delay from my VLAN interface:

  1. gateway (192.168.10.1) 1.601 ms 2.401 ms 2.884 ms

  2. 192.168.xx.xx (192.168.xx.xx) 0.714 ms 0.710 ms 0.749 ms

  3. xx.xx.xx.xx (xx.xx.xx.xx) 0.185 ms 0.224 ms 0.220 ms

Can you give me some ideas about that?

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    The latency measured by ping is the ICMP latency (including processing of the ICMP messages). ICMP is very low on the priority list for a network device. The primary job of a router is to route, and of a switch to switch, and they get around to processing ICMP messages as they have time. You do not want a router or switch to drop traffic while it processes ICMP messages, so routing/switching take precedence, and ICMP is handled as a very low priority, which is why you may see timeouts from network devices because the reply can take too long from the perspective of the host sending the request.
    – Ron Maupin ♦
    Commented Aug 12, 2019 at 13:14

2 Answers 2

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A "L3 switch" will perform the actual packet forwarding (both L2 and L3) using dedicated hardware, but exceptional cases like sending a ping reply or a time exceeded message are normally handled in software by the switch's CPU.

Depending on how powerful and busy the CPU is and how the switch vendor decided to prioritize it's different tasks it may take the CPU some time to get around to processing your packet.

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It could be something related to the architecture of the device keep in mind that those interfaces are logical interfaces not physical interfaces, hence, the processing may vary between physical and logical interfaces, also must of the platforms now a days use a virtualized os running as a host on some Linux distri... that May also help to create latency of pings for logical interfaces :)

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    Modern switching is performed in hardware. ICMP is at the network layer, one above the switching data-link layer, and it will be handled in software, which is much slower than hardware switching.
    – Ron Maupin ♦
    Commented Aug 15, 2019 at 16:26

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