Low Latency E-Tile 40G Ethernet Intel® FPGA IP User Guide

ID 683486
Date 8/31/2021
Public
Document Table of Contents

4.1.2.3. Length/Type Field Processing

This two-byte header represents either the length of the payload or the type of MAC frame.
  • Length/type <= 0x5DC (1500) —The field represents the payload length of a basic Ethernet frame. The MAC TX/RX continues to check the frame and payload lengths.

  • 0x5DC (1500) < Length/type < 0x600 (1536) — The frames with payloads size in this range are not standard basic Ethernet frames, nor they are legal control packets. The payload length is not checked for this kind of packets.
  • Length/type >= 0x600—The field represents the frame type. The following frame types are possible:
    • Length/type = 0x8100—VLAN or stacked VLAN tagged frames. The MAC RX continues to check the frame and payload lengths.
    • Length/type = 0x8808—Control frames. The next two bytes are the Opcode field that indicates the type of control frame. For pause frames (Opcode = 0x0001) and PFC frames (Opcode = 0x0101), the MAC RX proceeds with pause frame processing.
    • For other field values, the MAC RX forwards the receive frame to the client.

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