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How does MTU actually function GUI->real???

Scheduled Pinned Locked Moved General pfSense Questions
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  • M
    mer @johnpoz
    last edited by Mar 30, 2022, 9:25 AM

    @johnpoz said in How does MTU actually function GUI->real???:

    POLA violation.

    Dude ;) You dating yourself with pulling out that term.. heheheh Or maybe dating myself knowing what that means - hehehe

    Maybe dating a lot of us. It's fun using it and then explaining it to people that have never seen a 6502 cpu.

    Now how about bikesheds?

    S 1 Reply Last reply Mar 30, 2022, 11:41 AM Reply Quote 1
    • S
      stephenw10 Netgate Administrator @mer
      last edited by Mar 30, 2022, 11:41 AM

      @mer said in How does MTU actually function GUI->real???:

      Now how about bikesheds?

      😁

      M 1 Reply Last reply Mar 30, 2022, 1:40 PM Reply Quote 1
      • M
        MrPete @stephenw10
        last edited by Mar 30, 2022, 1:40 PM

        @stephenw10 I knew I'd found friends here LOL

        Y'all are youngsters though.

        How many have loved JFFO? 🚀

        (POLA is in the eyes of the beholder, BTW... at least we can document the "normal" use of the form field to make life easy.)

        And yes, @johnpoz, this is all about tunnels... Not positive I need it yet, but I'm running HE tunnel over PPPoE...

        J 1 Reply Last reply Mar 30, 2022, 1:54 PM Reply Quote 0
        • S
          stephenw10 Netgate Administrator
          last edited by stephenw10 Mar 30, 2022, 2:41 PM Mar 30, 2022, 1:45 PM

          Yeah you would need to set that lower, see:
          https://docs.netgate.com/pfsense/en/latest/recipes/ipv6-tunnel-broker.html

          If the WAN used for terminating the GIF tunnel is PPPoE or another WAN type with a low MTU, move the slider down as needed. For example, a common MTU for PPPoE lines with a tunnel broker is 1452.

          Steve

          M 1 Reply Last reply Mar 30, 2022, 3:01 PM Reply Quote 0
          • J
            johnpoz LAYER 8 Global Moderator @MrPete
            last edited by Mar 30, 2022, 1:54 PM

            @mrpete said in How does MTU actually function GUI->real???:

            Not positive I need it yet, but I'm running HE tunnel over PPPoE...

            Yeah mss clamping is not your issue with that.. I saw your other HE thread..

            An intelligent man is sometimes forced to be drunk to spend time with his fools
            If you get confused: Listen to the Music Play
            Please don't Chat/PM me for help, unless mod related
            SG-4860 24.11 | Lab VMs 2.8, 24.11

            1 Reply Last reply Reply Quote 0
            • M
              MrPete @stephenw10
              last edited by MrPete Mar 30, 2022, 3:31 PM Mar 30, 2022, 3:01 PM

              @stephenw10 said in How does MTU actually function GUI->real???:

              Yeah you would need to set that lower...

              ...a common MTU for PPPoE lines with a tunnel broker is 1452.

              OK, this is quite wierd.... I'm testing to discover the actual limit. From inside pfSense...

              ping6 -nms 1232 google.com
              PING6(1280=40+8+1232 bytes) 2001:470:39:3c7::2 --> 2607:f8b0:400f:803::200e
              76 bytes from 2607:f8b0:400f:803::200e, icmp_seq=0 hlim=119 time=6.014 ms
              

              Anything larger fails.

              I can reach both ends of the HE tunnel with 1452.

              UPDATE: looks like a pfSense bug. Why oh why would it set the gif interface MTU to 1280 as a default?!!!
              93e58ac7-dfa7-41c9-9279-e621d3d55916-image.png

              M J 2 Replies Last reply Mar 30, 2022, 3:36 PM Reply Quote 0
              • M
                MrPete @MrPete
                last edited by MrPete Mar 30, 2022, 3:37 PM Mar 30, 2022, 3:36 PM

                @stephenw10
                OK, and with my gif-based WANv6 interface manually set to MTU = 1492... I still have a minor question:

                • I can ping6 to either end of the HE tunnel with -nms 1452
                • But to go beyond requires -nms 1444

                Is there some kind of extra packet overhead involved?

                I'd really rather not chalk it up to "ipv6 is just strange that way" ;)

                1 Reply Last reply Reply Quote 0
                • S
                  stephenw10 Netgate Administrator
                  last edited by Mar 30, 2022, 3:51 PM

                  Hmm, yet you can ping the remote side of it with 1452?

                  1 Reply Last reply Reply Quote 0
                  • J
                    johnpoz LAYER 8 Global Moderator @MrPete
                    last edited by Mar 30, 2022, 5:50 PM

                    @mrpete said in How does MTU actually function GUI->real???:

                    Why oh why would it set the gif interface MTU to 1280 as a default?!!!

                    You can change it on the HE site..

                    he.jpg

                    1280 is a common MTU for IPv6, since it like a requirement that IPv6 support this min size.

                    And you can change it on your interface..

                    interface.jpg

                    An intelligent man is sometimes forced to be drunk to spend time with his fools
                    If you get confused: Listen to the Music Play
                    Please don't Chat/PM me for help, unless mod related
                    SG-4860 24.11 | Lab VMs 2.8, 24.11

                    M 1 Reply Last reply Mar 30, 2022, 7:14 PM Reply Quote 0
                    • M
                      MrPete @johnpoz
                      last edited by MrPete Mar 30, 2022, 7:24 PM Mar 30, 2022, 7:14 PM

                      @johnpoz 'twas not an issue on the HE site. Just had to set 1492 there since I am using PPPoE.

                      and yes, I can and now have forced it on my end.

                      Just more than a little surprised to see a default of 1280?!!!

                      And YES @stephenw10 , I could ping the far end of the tunnel way beyond the MTU. Crazy.

                      And now, I can ping the far end of the tunnel with 8 bytes more than the outside world.

                      Here: Near, Far, GoogleBad, GoogleGood ;)

                      [2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 2001:470:39:3c7::2
                      PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2001:470:39:3c7::2
                      1460 bytes from 2001:470:39:3c7::2, icmp_seq=0 hlim=64 time=0.180 ms
                      ^C
                      --- 2001:470:39:3c7::2 ping6 statistics ---
                      3 packets transmitted, 3 packets received, 0.0% packet loss
                      round-trip min/avg/max/std-dev = 0.148/0.163/0.180/0.013 ms
                      [2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 2001:470:39:3c7::1
                      PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2001:470:39:3c7::1
                      1460 bytes from 2001:470:39:3c7::1, icmp_seq=0 hlim=64 time=5.750 ms
                      ^C
                      
                      [2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 google.com
                      PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2607:f8b0:400f:802::200e
                      ^C
                      --- google.com ping6 statistics ---
                      5 packets transmitted, 0 packets received, 100.0% packet loss
                      [2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1444 google.com
                      PING6(1492=40+8+1444 bytes) 2001:470:39:3c7::2 --> 2607:f8b0:400f:802::200e
                      76 bytes from 2607:f8b0:400f:802::200e, icmp_seq=0 hlim=119 time=6.146 ms
                      
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