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I want to increase the Ethernet Maximum Transmission Unit (MTU) for some hosts on a local network. Is there a known sequence of steps to follow? Or, can I just tweak each host's MTU as needed and it will "just work"?

One condition is only some hosts will have MTU increased. All hosts must be able to communicate with all other hosts. Secondly, assume all switches and routers can support up to 9000 byte Ethernet frames.

I could probably guess most of the steps. However, I have a feeling there is some corner-case "gotcha"s that could cause difficult problems. Or perhaps there is some definitive test to do afterward that will demonstrate everything is working well.

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  • Do you know if all of your networking equipment (switches, routers, etc.) support jumbo frames and have them turned on? What is the MTU currently set at for the hosts in question? Sep 27 '19 at 6:24
  • @RobPearson assume the switches and routers support 9000 byte frames. Currently, all configurable hosts are set to default 1500 bytes. One condition here is not all hosts can have their MTU increased. I updated the question. Thanks. Sep 27 '19 at 6:36
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It shall just work. Seamlessly in the LAN if you’re sure all devices have same limits and you’re not exceeding them. For hosts in other networks, say, in Internet you’d be relying on PMTU Discovery working properly. OTOH, some systems, say, Linux, allow to set routes with specified MTU, and this way you can enforce conventional MTU value for default and other routes — if needed, fixing any related issues beforehand.

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  • "if you’re sure all devices have same limits". Some hosts on the LAN will remain at 1500 MTU. Sep 27 '19 at 7:39
  • I've explained about hosts — you would rely on PMTU or you can make use of other workarounds, such as route's MTU. By devices I meant switches and LAN cards. If some has maximum 4k, of course you should stick to this value.
    – poige
    Sep 27 '19 at 10:14

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