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What I should be looking for when trying to enable Jumbo Frames in networks that relies on PXE for server booting?

As far as I know I must have:

  • Network switch capable of MTU >= 9000
  • The ability to enable Jumbo Frames not only on the network interface on the switch but also on the Port Channels and VLANs
  • A compatible SO to deal with the higher MTU after the boot process with network bonding and VLANs if needed.

What I don't know exactly is how the network card on a given server would know that the connection is not using the default MTU = 1500 value during the PXE phase. Is it supported? Varies by vendor? It should work out of the box? There's something that should be added to the DHCP server the handles the addresses during boot?

Thanks

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There's a DHCP parameter for that, option 26:

5.1. Interface MTU Option

This option specifies the MTU to use on this interface. The MTU is specified as a 16-bit unsigned integer. The minimum legal value for the MTU is 68.

If this is not supported, an alternative would be to make the PXE server use a MTU of 1500b, so that frames from this is transmitted correctly to a client that works with MTU of 1500b, and house file systems to be mounted on a different server with a higher MTU.

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if you want to speed up PXE's TFTP you should consider using windowsize instead of bigger blocksize

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  • That wasn't the case, but thanks for the reply. It just the network that already runs with MTU 9000 and I need to PXE on it. – Vinícius Ferrão Jul 12 at 3:15

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