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Unexpected ip header length #1266

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zhanghenan-dev opened this issue Jan 21, 2022 · 1 comment
Closed

Unexpected ip header length #1266

zhanghenan-dev opened this issue Jan 21, 2022 · 1 comment

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@zhanghenan-dev
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Using iperf3 to send udp packets. During iperf negotiation, a packet with an abnormal IP header length is generated.
ip header length = 32, but there are 46 bytes(32 bytes data 14 bytes 0x00)

picture is here error picture

Context

  • Version of iperf3:
    iperf 3.5 (cJSON 1.5.2)

  • Hardware:
    ESXI virtual machine

  • Operating system (and distribution, if any):
    Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 setting of window size should be explicit #1 SMP Tue Jun 1 16:14:33 UTC 2021 x86_64
    Optional features available: CPU affinity setting, IPv6 flow label, SCTP, TCP congestion algorithm setting, sendfile / zerocopy, socket pacing, authentication
@davidBar-On
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The extra 14 bytes of 0x00 are because of Ethernet packets padding. The minimum size of Ethernet packet is 64 bytes, including 14 bytes of MAC header and 4 bytes CRC. Therefore, the IP packet sent over Ethernet should be at least 46 bytes. Since the IP packet sent is only 32 bytes, 14 padding bytes are required. See for example this explanation.

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@zhanghenan-dev @davidBar-On