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    Change MTU not possible

    Scheduled Pinned Locked Moved IPsec
    4 Posts 3 Posters 9.1k Views
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    • M
      moc
      last edited by

      Hi there,

      I try to change the MTU setting for our ipsec - connection because the tunnel get up, I can send packages (a lot of MB without errors) but If I try to donwload something, it stop working. So could be a MTU Problem… .

      On my PF-Sence Server using the shell and after a ifconfig get this output for the tunnel:
      enc0: flags=41 <up,running>mtu 1536

      The other side (not possible to change) uses MTU = 1456.
      Ok now enter:
      ifconfig enc0 mtu 1456
      and I get that back:
      ifconfig: ioctl (set mtu): Invalid argument

      Find a lot of persons have the same problem but no answers :(
      Hope somebody can help me?

      Regards...</up,running>

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      • jimpJ
        jimp Rebel Alliance Developer Netgate
        last edited by

        Try changing the MTU of your WAN interface instead. You can set that via the WebGUI.

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        • M
          moc
          last edited by

          I already try that but it's not working. Enter some other MTU size in the GUI and do a ifconfig after that, no change happend.
          Any other ideas?

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          • dotdashD
            dotdash
            last edited by

            Even though the field is marked MTU, it doesn't really set the MTU. Read the fine print:

            If you enter a value in this field, then MSS clamping for TCP connections to the value entered above minus 40 (TCP/IP header size) will be in effect. If you leave this field blank, an MTU of 1492 bytes for PPPoE and 1500 bytes for all other connection types will be assumed.

            If you really need to set the MTU you can do it from the shell. http://www.freebsd.org/cgi/man.cgi?query=ifconfig&apropos=0&sektion=0&manpath=FreeBSD+7.2-RELEASE&format=html
            To survive a reboot, you would need to add a startup command to the xml.

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