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    Changing MTU doesn't work on PFSense 2.0 FINAL

    Scheduled Pinned Locked Moved General pfSense Questions
    16 Posts 3 Posters 5.7k Views
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    • A
      alexpacio
      last edited by

      Any suggestion?
      ps. if i try to use pfsense 1.2.3 mtu works correctly
      why?

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      • jimpJ
        jimp Rebel Alliance Developer Netgate
        last edited by

        In 1.2.3 the MTU box only adjusts MSS, not MTU

        on 2.0 the MTU setting actually does MTU. The MSS value is separate.

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        • A
          alexpacio
          last edited by

          I put in MTU box 1496 and in MSS box 1456 but it still doesn't work as it should. WHY?

          I have an Internet connection that need an MTU equal to 1496. how can I get this value working in PFsense???

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          • A
            alexpacio
            last edited by

            any suggestion???

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            • T
              tommyboy180
              last edited by

              Have you changed the MTU and MSS rates and applied a reboot? Sometimes the hypervisor needs the VM to be rebooted before virtual hardware changes are applied.

              -Tom Schaefer
              SuperMicro 1U 2X Intel pro/1000 Dual Core Intel 2.2 Ghz - 2 Gig RAM

              Please support pfBlocker | File Browser | Strikeback

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              • A
                alexpacio
                last edited by

                Yes, i tried to reboot vm after applying mtu but it still doesn't work. Is there anyone who have got working a diffrenet mtu in pfsense 2? I'm beginning to think that it is a pfsense bug…

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                • A
                  alexpacio
                  last edited by

                  I also tried to reboot the VM after MTU change.

                  Today I tried with a bare metal installation on a PC but I couldn't get it working neither in the PC.

                  In pfSense 1.2.3 WORKS…

                  WHY????  :'( :'(

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                  • jimpJ
                    jimp Rebel Alliance Developer Netgate
                    last edited by

                    Have you tried leaving the MTU at 1500 but changing only the MSS to 1496?

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                    • A
                      alexpacio
                      last edited by

                      Yes… i tried every possible combination :D

                      It seems that the freebsd network stack doesn't change MTU even if i do a ifconfig the new value is correctly displayed...

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                      • jimpJ
                        jimp Rebel Alliance Developer Netgate
                        last edited by

                        It wasn't changing the MTU in 1.2.3 - so your problem is probably not the MTU.

                        In 1.2.3 the MTU value only adjusted MSS, not the MTU, so if it worked on 1.2.3, then the MTU change is not to blame.

                        And yes, FreeBSD does change the MTU.

                        Try doing a packet capture on the WAN and see if it really is sending out packets larger than the MTU.

                        try this with MSS set:

                        grep -i mss /tmp/rules.debug
                        

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                        • A
                          alexpacio
                          last edited by

                          grep -i mss /tmp/rules.debug

                          output:

                          scrub in on $FORINI all max-mss 1456 fragment reassemble

                          It seems to be correct but if i vist some webpages which require correct MTU it doesn't work, while with other firewalls webpages are shown correctly!!!

                          WHY?

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