Windows: wintun MTU is not set

Windows: wintun MTU is not set

[kay]

Hi Everyone,

I noticed that the desired MTU is not set on the wintun interface.

I tried to set MTU after I create an interface:

        interfaces, err := winipcfg.GetIPInterfaceTable(windows.AF_UNSPEC)
        if err != nil {
                return err
        }
        for _, iface := range interfaces {
                if iface.InterfaceLUID == luid {
                        log.Printf("Iface: %+#v", iface)
                        iface.NLMTU = 1302
                        err = iface.Set()
                        if err != nil {
                                log.Printf("failed to set MTU: %s", err)
                        }
                }
        }

but it fails with "The parameter is incorrect." for AF_INET. Setting
MTU for AF_INET6 works with no issues.

Any idea how I can set MTU without netsh?

Regards,

Re: Windows: wintun MTU is not set

[Jason A. Donenfeld]

Try using the object returned by luid.IPInterface(windows.AF_INET). Or
in your example, use AF_INET instead of AF_UNSPEC.

Re: Windows: wintun MTU is not set

[kay]

Thanks. The following code worked for me:

        luid := winipcfg.LUID(tun.LUID())
        iface, err := luid.IPInterface(windows.AF_INET)
        if err != nil {
                return err
        }
        iface.NLMTU = 1302
        err = iface.Set()
        if err != nil {
                return fmt.Errorf("failed to set MTU: %s", err)
        }

On Wed, Mar 10, 2021 at 3:03 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Try using the object returned by luid.IPInterface(windows.AF_INET). Or
> in your example, use AF_INET instead of AF_UNSPEC.