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MTU Settings on LAN

Discussion in 'Other LAN and WAN' started by ddaenen1, Oct 17, 2019.

  1. ddaenen1

    ddaenen1 Regular Contributor

    Joined:
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    With my new ISP connection, i am hitting 850Mbps-920Mbps download speed on speedtest at times, but at other times between 400 and 600Mbps, all measured on a wired PC using the speedtest app for Win10.

    In my quest to understand this large variation, i bumped on the importance of the MTU settings. I understand the basic concept of MTU, but i am unsure on how this might impact my network performance.

    Checcking out the MTU setting on every device of importance on the network, many different values popped up.

    Here we go:

    RB3011 router: MTU=1500, actual MTU=1500, L2 MTU=1598, Max L2 MTU=8156
    Netgear 24p switch: Maximum Frame size=9216 (all ports)
    Readynas: MTU=9000
    Synology: MTU=9000
    Netgear GS108PE: Max MTU=9702
    Windows 10 Server: MTU=1500
    Microserver with Ubuntu: MTU=automatic


    So, this is what i have. Do i need to change anything to improve performance?

    Many thanks, Dominique
     
  2. coxhaus

    coxhaus Part of the Furniture

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    Your ISP is going to use a standard Ethernet packet. The size will depend on what your ISP loads in the frame like PPPOE. Since you are using large packets on your local LAN you are having to break down each large packet into several smaller packets to put on the WAN. I would stop using large packets local. If you need more bandwidth local then use LAG ports.
     
  3. ddaenen1

    ddaenen1 Regular Contributor

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    So, i need some clarity on that. The Synology and ReadyNAS are both configured with LACP layer 2 and occupy each 2 ports of the switch configured as LAG. However, they do not go out to WAN except for the occasional firmware update. I am assuming the max setting in the switch is just a max setting and doesn't influence any traffic coming in with smaller size, right? All other devices have their standard settings. Anything else i need to consider?
     
  4. coxhaus

    coxhaus Part of the Furniture

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    I would think some where down the line you are fragmenting packets since you are using different sized packets.

    I would just drop to an standard Ethernet frame size across the board and see if it works better.
     
    Last edited: Oct 17, 2019
  5. ColinTaylor

    ColinTaylor Part of the Furniture

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    Correct.
     
  6. Greg72

    Greg72 Regular Contributor

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    Speed Test results will vary since they are real world, the same reason why whwn driving, you can have very little traffic and be able to stay at a constant speez, other times your speed sucks and traffic sucks.