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    Odd MTU / fragmented packet issue on web GUI and haproxy

    Scheduled Pinned Locked Moved L2/Switching/VLANs
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    • S
      shewless @johnpoz
      last edited by shewless

      @johnpoz absolutely. It's a S3900-24T4S-R (which seems to operate differently than the S3900-24T4S).

      I could not find any newer firmware available for this switch nor could I find much documentation regarding this specific issue.

      From what I have read different switches consider MTU differently (Ethernet framesize vs IP MTU, etc)

      Fiberstore Co., Limited Internetwork Operating System Software
      S3900-24T4S-R Series Software, Version 2.2.0E Build 88393, RELEASE SOFTWARE
      Copyright (c) 2021 by FS.COM All Rights Reserved
      

      I'd be happy to submit a bug report for this issue if I could understand it more :)

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

        @shewless do you happen to have an example of the error?

        What is odd, is here it shows that 1522 is normal size, and anything larger would be jumbo

        https://img-en.fs.com/file/user_manual/s3900-series-configuration-guide.pdf
        2.21 Jumbo frames
        2.21.1 Introduction
        Jumbo frames are Ethernet frames with a frame length greater than 1522 bytes.

        Could you show status of one of the interfaces your seeing the errors on?

        show interfaces status ethernet

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        • S
          shewless @johnpoz
          last edited by

          @johnpoz yeah. The switch seems to be a slightly newer model with a bit different syntax:

          switch#show interface tg0/25
          TGigaEthernet0/25 is up, line protocol is up
            protocolstatus upTimes 1, downTimes 0, last transition 2000-1-1 0:0:21
            Ifindex is 189, unique port number is 49
            Hardware is 10Giga-FX, address is 649d.9928.4a3d (bia 649d.9928.4a3d)
            MTU 1550 bytes, BW 10000000 kbit, DLY 10 usec
            Encapsulation ARPA
            Full-duplex,  10000Mb/s,  Flow-Control Off
            5 minutes input rate 778815 bits/sec, 117 packets/sec
            5 minutes output rate 119461 bits/sec, 88 packets/sec
            Real time input rate 0%, 327494 bits/sec, 100 packets/sec
            Real time output rate 0%, 145816 bits/sec, 95 packets/sec
               Received 10549650 packets, 9541356381 bytes
               2110 broadcasts, 12068 multicasts, 10535472 ucasts
               0 discard, 0 error, 0 PAUSE
               0 align, 0 FCS, 0 symbol
               0 jabber, 318071 oversize, 0 undersize
               0 carriersense, 0 collision, 0 fragment
               0 L3 packets, 0 discards, 0 Header errors
               Transmitted 7473138 packets, 1683821836 bytes
               313229 broadcasts, 112992 multicasts, 7046917 ucasts
               0 discard, 0 error, 0 PAUSE
               0 sqettest, 0 deferred, 277106 oversize
               0 single, 0 multiple, 0 excessive, 0 late
               0 L3 forwards
          

          I tried it on a lesser used port and verify that as soon as I access the web interface the oversize counter goes up.

          Here is the config:

          interface TGigaEthernet0/25
           switchport mode trunk
           switchport pvid 100
          
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          • johnpozJ
            johnpoz LAYER 8 Global Moderator @shewless
            last edited by johnpoz

            @shewless that is not showing the status.

            show interfaces status ethernet tg0/25

            You have the mtu on that port set to 1550..

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            • S
              shewless @johnpoz
              last edited by

              @johnpoz that command doesn't work on my switch unless I'm in the wrong mode or something? My switch is the "newer" model: The https://www.fs.com/products/134655.html?attribute=8032&id=289447

              switch#show interfaces status ethernet tg0/25
              show interfaces status ethernet tg0/25
                   ^
              Too many parameters
              
              switch#show interface ?
                GigaEthernet      -- GigaEthernet interface
                TGigaEthernet     -- Ten GigaEthernet interface
                Vlan              -- VLAN interface
                Null              -- Null interface
                brief             -- brief information of the interface
                range             -- show interface range
                ifindex           -- show interface based on ifindex
                  |         -- Output modifiers
                  <cr>
              
              switch#show ethernet ?
                cfm  -- Configure Connection Fault Management protocol(CFM)
                oam  -- Operations, Administration and Maintenance
              

              The MTU was set globally. When I look at the manual I only see a way to do it globally for this switch (the -R version):

              switch#show system mtu
              System MTU size is 1550 bytes
              

              What am I missing?

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

                @shewless I would set it back to 1500, 1550 mtu is not standard by any means.

                did you look over that link to the manual - isn't that your switch?

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                • S
                  shewless @johnpoz
                  last edited by shewless

                  @johnpoz I can do that (set the MTU to 1500). I think when it was at 1500 I was seeing both "error" counter increases and "oversize" packet increases... I will change it now and see if that is the case.
                  I totally have been pouring over the manual. As I mentioned the -R version seems to have a different CLI unfortunately.

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                  • S
                    shewless @johnpoz
                    last edited by shewless

                    @johnpoz yeah as soon as I set the system mtu to 1500 I see both "error" and "oversize" increasing.. though I haven't noticed any functionality problems.. I'd love to get to the bottom of this.

                    TGigaEthernet0/25 is up, line protocol is up
                      protocolstatus upTimes 1, downTimes 0, last transition 2000-1-1 0:0:21
                      Ifindex is 189, unique port number is 49
                      Hardware is 10Giga-FX, address is 649d.9928.4a3d (bia 649d.9928.4a3d)
                      MTU 1500 bytes, BW 10000000 kbit, DLY 10 usec
                      Encapsulation ARPA
                      Full-duplex,  10000Mb/s,  Flow-Control Off
                      5 minutes input rate 202703 bits/sec, 71 packets/sec
                      5 minutes output rate 105389 bits/sec, 69 packets/sec
                      Real time input rate 0%, 133720 bits/sec, 64 packets/sec
                      Real time output rate 0%, 99284 bits/sec, 67 packets/sec
                         Received 14056231 packets, 14473843206 bytes
                         2951 broadcasts, 12725 multicasts, 14040555 ucasts
                         0 discard, 478 error, 0 PAUSE
                         0 align, 0 FCS, 0 symbol
                         0 jabber, 340230 oversize, 0 undersize
                         0 carriersense, 0 collision, 0 fragment
                         0 L3 packets, 0 discards, 0 Header errors
                         Transmitted 8803287 packets, 1840177991 bytes
                         334995 broadcasts, 121700 multicasts, 8346592 ucasts
                         0 discard, 0 error, 0 PAUSE
                         0 sqettest, 0 deferred, 287250 oversize
                         0 single, 0 multiple, 0 excessive, 0 late
                         0 L3 forwards
                    
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                    • S
                      shewless @johnpoz
                      last edited by

                      @johnpoz I submitted a ticket to the switch vendor. I'll update here if I find out anything useful.

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

                        @shewless great - that damn curiosity cat of mine is is always meowing.. Yes please let us know what comes of that.

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                        Please don't Chat/PM me for help, unless mod related
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                        • S
                          shewless @johnpoz
                          last edited by

                          @johnpoz update:

                          I verified that on my ubuntu client that this ping works:
                          ping -c 10 -M do -s 1472 192.168.120.1
                          But it results in the oversize counter increasing. wireshark shows a packet size of 1514 for both request and reply.

                          The size of 1468 is required to avoid oversize counter increasing
                          ping -c 10 -M do -s 1468 192.168.120.1
                          This results in a wireshark packet size of 1510.

                          Likely a cosmetic problem as the packets all seam to go where they are supposed to go... a support case is opened for the switch vendor.

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

                            @shewless yeah that is odd! for sure.. 1522 should be max size, even says so in the doc I linked too. I could see anything over 1522 triggering the oversize counter, if you didn't have jumbo enabled..

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                            • S
                              shewless @johnpoz
                              last edited by

                              @johnpoz Update:
                              Switch vendor believes it's okay to have to update the system MTU to a higher value (in order to remove the error counter) and to live with the "oversize" counter increases.
                              I have since set the system MTU to 9000 (which is the L2 MTU). Any IP Interface I create can have an L3 MTU applied to it of 1500.

                              Thanks for the help.

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

                                @shewless said in Odd MTU / fragmented packet issue on web GUI and haproxy:

                                it's okay to have to update the system MTU to a higher value (in order to remove the error counter)

                                Yeah that is not the correct solution.. Mismatched mtu is never a good thing..

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                                Please don't Chat/PM me for help, unless mod related
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                                • S
                                  shewless @johnpoz
                                  last edited by

                                  @johnpoz I agree that this is not the correct solution and I have let the switch vendor know. Maybe if other potential customers provide feedback they'll make changes.
                                  In my case I don't think the MTU settings will be harmful. I've already tested that my endpoint devices all have "Layer3" MTU of 1500 and having the switch system MTU set to a higher value doesn't impact the traffic being sent.

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

                                    @shewless Personally I would just live with the cosmetic errors being listed most likely vs setting a clearly mismatched mtu.

                                    As long as its not actually dropping the traffic, etc.

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                                    Please don't Chat/PM me for help, unless mod related
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                                    • S
                                      shewless @johnpoz
                                      last edited by

                                      @johnpoz In that case if there actually was an error in packet transmission it would be harder to detect.. certainly an option though. I could also return the switch :)

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

                                        @shewless said in Odd MTU / fragmented packet issue on web GUI and haproxy:

                                        I could also return the switch

                                        Another option for sure - such issues, and their "fix" is to set your mtu to something it shouldn't be doesn't instill confidence if you ask me.

                                        Now if they said, oh yeah we know about - cosmetic, will be corrected in next update.

                                        If they can not get this right, what else are they getting wrong?

                                        Reminds me of issues with entry level tplink, not letting your remove vlan 1 from ports you were putting in a different vlan.. They came back that it was meant to be like that, and normal.. Took them ever to correct it, and they never back ported it to earlier models.. Not something that instills confidence in their understanding of how vlans work ;)

                                        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
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                                        • JKnottJ
                                          JKnott @johnpoz
                                          last edited by

                                          @johnpoz

                                          I don't recall seeing an MTU size on switches I've worked on, not that I've looked though. However, as long as the switch can handle whatever size frame you throw at it, it shouldn't be a problem. So, you have to look at the largest frames that will be used on the network and allow for that. The only issue I can think of is the amount of buffer space larger frames will use. Perhaps the manufacturer is from back in the days prior to frame expansion and doesn't think frames would have more that 1500 MTU. This would, of course, cause issues with things like VLANs needing 4 bytes of the MTU.

                                          Even my cheap, crappy TP-Link 5 port switch can handle 16 KB jumbo frames.

                                          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...

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

                                            @jknott see my info from the manual, where it correctly states 1522.. its a cosmetic issue.. But you shouldn't be going about changing the actual mtu on any interface or a switch because of some cosmetic issue with the switch software.

                                            The mtu should be 1500.. Unless your running some unique network with different mtu, jumbo, etc..

                                            If he wants to enable jumbo frames that is up to him.. But he is not using jumbo, and it would do would be to remove the logging of oversized frames, that are not actually oversized.

                                            I do not have jumbo enabled.. All of my mtu's everywhere are the default 1500.. I see no oversized marked on any ports of the switch, many carry vlans..

                                            stats.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
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