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Make Qubes MTU configurable / inherit from sys-net uplink MTU #10758
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C: networkingThis issue pertains to networking in Qubes OS.This issue pertains to networking in Qubes OS.P: defaultPriority: default. Default priority for new issues, to be replaced given sufficient information.Priority: default. Default priority for new issues, to be replaced given sufficient information.good first issueThis is a recommended issue for first-time contributors.This is a recommended issue for first-time contributors.
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C: networkingThis issue pertains to networking in Qubes OS.This issue pertains to networking in Qubes OS.P: defaultPriority: default. Default priority for new issues, to be replaced given sufficient information.Priority: default. Default priority for new issues, to be replaced given sufficient information.good first issueThis is a recommended issue for first-time contributors.This is a recommended issue for first-time contributors.
The problem you're addressing (if any)
Some networks might need a different MTU than 1500. (in my case I need to setup1492). There is no clean way of configuring this MTU up to the qubes.
My PPPoE uplink has a MTU of 1492. Having 1500 in the rest of the LAN was breaking partially IPv6 connectivity.
My local DHCP server is sending the MTU option
dhcp-option=26,1492to force clients setting the correct MTU. This MTU is also set on the eth0 interface of sys-usb.But everything behind that keeps the default MTU of 1500.
I found this thread on the forum https://forum.qubes-os.org/t/changing-default-mtu-for-networking-vms/16902 which doesn't feel like a proper solution.
The solution you'd like
I guess, propagating the MTU from eth0 on sys-net to the rest of the qubes connected to it, would be a good way for working out of the box.
The value to a user and who that user might be
Avoiding situations where the MTU do not match, bringing IPv6 to drop packets on the GW, because it cannot fragment it to send over the next link with smaller MTU
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