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Understanding Network Attributes in VIOS Configuration

In this AIXchange blog post, Technical Editor Rob McNelly explains network attributes

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This Technote—authored by Darshan Patel, Perry Smith and Saania Khanna—has some important information about VIO server configuration.

I'll start with their conclusions:

 
  • Largesend and jumbo frame does two different actions. These actions are mutually independent.
  • Largesend decides who does the segmentation
  • Jumbo frame decides the size of the segmented packet that goes on the wire

This is in response to this query: "I am configuring VIO Servers and AIX VIO Clients on Power system. There are many network attributes related to laregsend and jumbo frame such as largesend, large_send, mtu_bypass, jumbo_frame, use_jumbo_frame. I am confused about these attributes. I want to understand how largesend and jumbo_frame work and what is the difference between two."

The document includes illustrations and outlines various configuration scenarios:

  • In case 1, VIO server has largesend on, jumbo frames off, VIO client has MBP off, and MTU of 1500. In this case, messages are segmented to MTU size 1500 by TCP Kernel stack in AIX.
  • In case 2, VIO server has largesend on, jumbo frames off, VIO client has MBP on, and MTU of 1500. In this case messages are segmented to MTU size 1500 by Real Ethernet Adapter.
  • In case 3, VIO server has largesend on, jumbo frames on, VIO client has MBP off, and MTU of 9000. In this case messages are segmented to MTU size 9000 by TCP Kernel stack in AIX.
  • In case 4, VIO server has largesend on, jumbo frames on, VIO client has MBP on and MTU of 9000. In this case, messages are segmented to MTU size 9000 by Real Ethernet Adapter.

 This Technote should help you understand the different settings and give you an idea of the results you should expect to see based on 

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