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    Adjust MSS calculation to account for VLANs

    Scheduled Pinned Locked Moved L2/Switching/VLANs
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    • JKnottJ
      JKnott @virtual-frog
      last edited by

      @virtual-frog said in Adjust MSS calculation to account for VLANs:

      there is a jumbo frame option that is set to 1518

      That's barely frame expansion, to allow things like VLAN tags. Jumbo frames are several KB, with 9000 common.

      PfSense running on Qotom mini PC
      i5 CPU, 4 GB memory, 32 GB SSD & 4 Intel Gb Ethernet ports.
      UniFi AC-Lite access point

      I haven't lost my mind. It's around here...somewhere...

      V 1 Reply Last reply Reply Quote 0
      • V
        virtual-frog @JKnott
        last edited by

        @JKnott said in Adjust MSS calculation to account for VLANs:

        Do switches even have an MTU setting? That's a layer 3 concept.

        Well, an L3 switch might.. mine is not so it just has the jumbo frame size

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        • V
          virtual-frog @JKnott
          last edited by

          @JKnott said in Adjust MSS calculation to account for VLANs:

          @virtual-frog said in Adjust MSS calculation to account for VLANs:

          there is a jumbo frame option that is set to 1518

          That's barely frame expansion, to allow things like VLAN tags. Jumbo frames are several KB, with 9000 common.

          It's the same setting; I can adjust it much higher but haven't set up jumbo frame on my devices yet. The default is 1518

          johnpozJ 1 Reply Last reply Reply Quote 0
          • johnpozJ
            johnpoz LAYER 8 Global Moderator @virtual-frog
            last edited by

            @virtual-frog said in Adjust MSS calculation to account for VLANs:

            haven't set up jumbo frame on my devices yet.

            no point to it either.. You think you having issues now - wait til you try and do that when you have devices that don't support jumbo or have different sizes, etc..

            if you had a san network running say 10ge and you had storage devices and say server all on this san network ok then it might make sense - but there is really zero point to trying to do it on a normal gig network.. To be honest I would turn that feature off on your switch..

            Not sure where you got the idea that those icmp packets saying to frag would or should go to your end device - how would it??

            You are sending those.. Not ddg..

            unreach.jpg

            An intelligent man is sometimes forced to be drunk to spend time with his fools
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            • V
              virtual-frog @johnpoz
              last edited by

              @johnpoz
              D'oh. My bad. But that makes even less sense. Why does WAN send the frag message for only packets originating on the VLAN?

              johnpozJ 1 Reply Last reply Reply Quote 0
              • johnpozJ
                johnpoz LAYER 8 Global Moderator @virtual-frog
                last edited by johnpoz

                @virtual-frog you have something all f'd up on that vlan would be my guess. So the mtu on the interface is 1500? What about your clients, are they wired or is wireless involved..

                No idea about that tp link when it comes to vlans - they don't seem to quite get it ;) A few years back they had an issue where they would not allow you to remove vlan 1 from any ports.. So if you wanted to run say vlan 10 on that port, you were also untagged in vlan 1.. Took them like 2 years to correct it..

                Why does WAN send the frag message for only packets originating on the VLAN?

                Its not it sending it because what ddg is sending back.. A full packet seems to be too big for your vlan?? Even though the client sent a mss of 1460.. you can see that from the syn you sent.

                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

                V RobbieTTR 2 Replies Last reply Reply Quote 0
                • V
                  virtual-frog @johnpoz
                  last edited by

                  @johnpoz

                  Yes, all MTUs are the default 1500.
                  Mix of wired and wireless, same effect on both.
                  TP Link seems to have matured somewhat (still not perfect) so I don't think there's some huge flaw in the switch.
                  It's strange that this only happens with one site, too.
                  I may reset and reinstall everything.

                  johnpozJ RobbieTTR 2 Replies Last reply Reply Quote 0
                  • johnpozJ
                    johnpoz LAYER 8 Global Moderator @virtual-frog
                    last edited by johnpoz

                    @virtual-frog I am not having any issues with that site, via tagged vlans.. Than again I am not running on tplink ;)

                    Did you try just turning off jumbo support?

                    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

                    JKnottJ 1 Reply Last reply Reply Quote 0
                    • RobbieTTR
                      RobbieTT @virtual-frog
                      last edited by

                      @virtual-frog
                      Are you not going to try removing the switch from the equation by going direct to the router for fault finding purposes?

                      Ruling these things in or out takes seconds of self-help.

                      ☕️

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                      • RobbieTTR
                        RobbieTT @johnpoz
                        last edited by

                        @johnpoz said in Adjust MSS calculation to account for VLANs:

                        @virtual-frog you have something all f'd up on that vlan would be my guess.

                        I'd probably not use that phrasing but I agree that this looks to be a local network issue.

                        ☕️

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                        • RobbieTTR
                          RobbieTT @JKnott
                          last edited by

                          @JKnott said in Adjust MSS calculation to account for VLANs:

                          Do switches even have an MTU setting? That's a layer 3 concept.

                          🙌 I think you just outed yourself as a fellow greybeard. For sure that was once the case and still referenced in some documentation but many (and disparate*) changes undermined that. Indeed, we were probably looking at switches with awe back then, as we nursed our hubs along.

                          Our distinction now is that in the context of Layer 2 switches the larger MTU is referenced with specific regard to jumbo frames and these are solely at L2.

                          At Layer 3 (network layer) the larger MTU is used in the context of jumbo packets. This is before we drift-off to sleep with oversized L3 MTU jumbo packets being jumbograms.

                          A few things don't matter and most things don't matter at all.

                          👍

                          ☕️

                          *some would argue that the word 'haphazard' should be inserted here

                          JKnottJ 1 Reply Last reply Reply Quote 0
                          • JKnottJ
                            JKnott @johnpoz
                            last edited by

                            @johnpoz said in Adjust MSS calculation to account for VLANs:

                            Did you try just turning off jumbo support?

                            What would that do? It only affects the size of frame the switch will pass. It has nothing to do with MTU.

                            PfSense running on Qotom mini PC
                            i5 CPU, 4 GB memory, 32 GB SSD & 4 Intel Gb Ethernet ports.
                            UniFi AC-Lite access point

                            I haven't lost my mind. It's around here...somewhere...

                            johnpozJ 1 Reply Last reply Reply Quote 0
                            • JKnottJ
                              JKnott @RobbieTT
                              last edited by

                              @RobbieTT said in Adjust MSS calculation to account for VLANs:

                              At Layer 3 (network layer) the larger MTU is used in the context of jumbo packets

                              I am aware of that. However, did the OP mention anything about a L3 switch? Are there any consumer level L3 switches. I have a switch that can pass 16K jumbo frames and, IIRC, there's no setting for that. It's just there and will pass any frames up to that size. Of course, with 1500 MTU, it won't see many that big.

                              PfSense running on Qotom mini PC
                              i5 CPU, 4 GB memory, 32 GB SSD & 4 Intel Gb Ethernet ports.
                              UniFi AC-Lite access point

                              I haven't lost my mind. It's around here...somewhere...

                              RobbieTTR 1 Reply Last reply Reply Quote 0
                              • RobbieTTR
                                RobbieTT @JKnott
                                last edited by

                                @JKnott I specifically said at the network layer. Nobody has mentioned any L3 features being used down at the data link layer.

                                In answer, there are very few consumer/prosumer switches with any L3-like capabilities. I have a couple of them but the L3 options are so badly implemented that I don't use them in that role.

                                ☕️

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                                • johnpozJ
                                  johnpoz LAYER 8 Global Moderator @JKnott
                                  last edited by johnpoz

                                  @JKnott with a tplink have no idea sure isn’t going to hurt turning it off I mean 1518 isn’t even a valid jumbo anything 1518 is frame if you include 14 bytes of header and 4 for crc

                                  Wouldn’t be surprise at any nonsense tplink might be doing to be honest

                                  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

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