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    Is it possible to connect to the Fog server remotely?

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    • P
      PJB1983 @Sebastian Roth
      last edited by

      @sebastian-roth thx for your reply.
      The Meraki security appliance provide ip addresses and a gateway for that perticular site (school).

      1 Reply Last reply Reply Quote 0
      • P
        PJB1983 @george1421
        last edited by

        @george1421 thx for the reply.
        I’ll run wireshark asap and send the link to the pcap file.

        1 Reply Last reply Reply Quote 0
        • P
          PJB1983 @george1421
          last edited by

          @george1421

          I think the UDP request had a bad length?
          What can i do about it?

          reading from file -, link-type EN10MB (Ethernet)
          13:02:42.546737 ARP, Request who-has 192.168.5.121 tell 192.168.5.1, length 28
          13:02:42.547604 ARP, Reply 192.168.5.121 is-at 00:15:5d:00:fc:09, length 46
          13:02:47.831592 IP 95.0.0.85.59214 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:02:47.831592 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:02:57.548243 ARP, Request who-has 192.168.5.121 tell 192.168.5.1, length 28
          13:03:04.618441 ARP, Request who-has 192.168.5.1 tell 192.168.5.121, length 46
          13:03:04.618441 ARP, Reply 192.168.5.1 is-at e0:55:3d:8f:6e:50, length 28
          13:03:04.625881 IP 192.168.5.121.2070 > 95.0.0.85.69: 30 RRQ “undionly.kpxe” octet tsize 0
          13:03:04.650645 IP 95.0.0.85.48771 > 192.168.5.121.2070: UDP, length 14
          13:03:04.651880 IP 192.168.5.121.2070 > 95.0.0.85.48771: UDP, length 17
          13:03:04.667062 IP 192.168.5.121.2071 > 95.0.0.85.69: 35 RRQ “undionly.kpxe” octet blksize 1456
          13:03:04.692814 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, length 15
          13:03:04.693826 IP 192.168.5.121.2071 > 95.0.0.85.52966: UDP, length 4
          13:03:04.718623 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:03:04.718623 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:03:05.719924 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:03:05.719924 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:03:07.721833 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:03:07.721833 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:03:11.726666 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:03:11.726666 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:03:12.550408 ARP, Request who-has 192.168.5.121 tell 192.168.5.1, length 28
          13:03:12.551594 ARP, Reply 192.168.5.121 is-at 00:15:5d:00:fc:09, length 46
          13:03:19.731344 IP 95.0.0.85.52966 > 192.168.5.121.2071: UDP, bad length 1460 > 1400
          13:03:19.731344 IP 95.0.0.85 > 192.168.5.121: ip-proto-17
          13:03:27.552009 ARP, Request who-has 192.168.5.121 tell 192.168.5.1, length 28
          13:03:27.553072 ARP, Reply 192.168.5.121 is-at 00:15:5d:00:fc:09, length 46

          george1421G 1 Reply Last reply Reply Quote 0
          • george1421G
            george1421 Moderator @PJB1983
            last edited by

            @pjb1983 What is your MTU on your VPN link? Would it happen to be 1400?

            Please help us build the FOG community with everyone involved. It's not just about coding - way more we need people to test things, update documentation and most importantly work on uniting the community of people enjoying and working on FOG!

            P 1 Reply Last reply Reply Quote 0
            • S
              Sebastian Roth Moderator
              last edited by Sebastian Roth

              @pjb1983 said in Is it possible to connect to the Fog server remotely?:

              UDP, bad length 1460 > 1400

              To me this looks like a window size/MTU issue on first sight. You can test the window size/MTU in the VPN tunning using ping ICMP packets like this - using your FOG server IP instead of x.x.x.x:

              • Linux:
              ping -s 1300 -c 8 -M do x.x.x.x
ping -s 1500 -c 8 -M do x.x.x.x
              • Windows:
              ping -l 1300 -n 8 -f x.x.x.x
ping -l 1500 -n 8 -f x.x.x.x

              My guess is the 1300 byte pings will go through but not the 1500 byte ones. You can play with those numbers to see which MTU works.

              Though this doesn’t solve your issue as you cannot tell iPXE to use a smaller MTU. You need to talk to you network engineers to set framenting and MTU correctly to packets won’t get truncated.

              Web GUI issue? Please check apache error (debian/ubuntu: /var/log/apache2/error.log, centos/fedora/rhel: /var/log/httpd/error_log) and php-fpm log (/var/log/php*-fpm.log)

              Please support FOG if you like it: https://wiki.fogproject.org/wiki/index.php/Support_FOG

              P 1 Reply Last reply Reply Quote 0
              • P
                PJB1983 @Sebastian Roth
                last edited by

                @sebastian-roth hi thx for your reply.
                the support on this forum is incredible.

                I’ve done a ping with 1300 packet size -> No problem
                1500 packet size -> Packet need to be fragmented but DF set.

                I’ll search on my Meraki security appliance to increase the packet size.
                Does this have some consequences for my network performance?

                george1421G 1 Reply Last reply Reply Quote 0
                • P
                  PJB1983 @george1421
                  last edited by

                  @george1421 thx for your reply.
                  the support on this forum is incredible.

                  I’ve done a ping with 1300 packet size -> No problem
                  1500 packet size -> Packet need to be fragmented but DF set.

                  I’ll search on my Meraki security appliance to increase the packet size.
                  Does this have some consequences for my network performance?

                  1 Reply Last reply Reply Quote 0
                  • george1421G
                    george1421 Moderator @PJB1983
                    last edited by george1421

                    @pjb1983 Try the same test with a packet size of 1461

                    If we find that the MTU is 1400 we can set the tftp block size just a bit smaller so the packets don’t fragment.

                    What host OS is your FOG server using?

                    Please help us build the FOG community with everyone involved. It's not just about coding - way more we need people to test things, update documentation and most importantly work on uniting the community of people enjoying and working on FOG!

                    P 1 Reply Last reply Reply Quote 0
                    • P
                      PJB1983 @PJB1983
                      last edited by

                      This post is deleted!
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                      • P
                        PJB1983 @george1421
                        last edited by

                        @george1421 the max MTU size is 1404.
                        I’ve installed the FOG server on a Linux Ubuntu.

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                        • S
                          Sebastian Roth Moderator
                          last edited by Sebastian Roth

                          @george1421 said in Is it possible to connect to the Fog server remotely?:

                          If we find that the MTU is 1400 we can set the tftp block size just a bit smaller so the packets don’t fragment.

                          That would get you past the TFTP part but it would fail downloading the kernel and init over HTTP then I suppose.

                          https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html

                          Web GUI issue? Please check apache error (debian/ubuntu: /var/log/apache2/error.log, centos/fedora/rhel: /var/log/httpd/error_log) and php-fpm log (/var/log/php*-fpm.log)

                          Please support FOG if you like it: https://wiki.fogproject.org/wiki/index.php/Support_FOG

                          george1421G 1 Reply Last reply Reply Quote 0
                          • S
                            Sebastian Roth Moderator
                            last edited by

                            @PJB1983 This might be a quick win: https://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/82444-fragmentation.html#enc-error

                            Web GUI issue? Please check apache error (debian/ubuntu: /var/log/apache2/error.log, centos/fedora/rhel: /var/log/httpd/error_log) and php-fpm log (/var/log/php*-fpm.log)

                            Please support FOG if you like it: https://wiki.fogproject.org/wiki/index.php/Support_FOG

                            P 1 Reply Last reply Reply Quote 0
                            • P
                              PJB1983 @Sebastian Roth
                              last edited by

                              @sebastian-roth thx for your reply, but i doesn’t have a CLI on the Meraki Firewall. I have to contact support i guess.

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                              • george1421G
                                george1421 Moderator @Sebastian Roth
                                last edited by george1421

                                @sebastian-roth I think our only option is to handle this on the tftp server size. I think the issue is packet fragmentation over UDP. I think we can set a maximum block size for the tftp server. What we need to do is set it at -64b from the MTU. I did find an example of it here: https://askubuntu.com/questions/644031/tftpd-hpa-how-can-i-set-blksize-option but I don’t know if ubuntu uses xinetd or something else.

                                @pjb1983 What version number of ubuntu? 20.04?

                                Please help us build the FOG community with everyone involved. It's not just about coding - way more we need people to test things, update documentation and most importantly work on uniting the community of people enjoying and working on FOG!

                                P 1 Reply Last reply Reply Quote 1
                                • P
                                  PJB1983 @george1421
                                  last edited by

                                  @george1421

                                  Distributor ID: Ubuntu
                                  Description: Ubuntu 20.04.1 LTS
                                  Release: 20.04

                                  george1421G 1 Reply Last reply Reply Quote 0
                                  • george1421G
                                    george1421 Moderator @PJB1983
                                    last edited by

                                    @pjb1983 So following the link I provided did you try to reduce the maximum packet size to something below 1400 (the mtu)? Something like 1385 would be a start.

                                    Please help us build the FOG community with everyone involved. It's not just about coding - way more we need people to test things, update documentation and most importantly work on uniting the community of people enjoying and working on FOG!

                                    P 2 Replies Last reply Reply Quote 0
                                    • P
                                      PJB1983 @george1421
                                      last edited by

                                      @george1421 i’ve changed the block size and rebooted the device.
                                      But that did not solve the problem.
                                      If i ask meraki support to increase the MTU for the site-to-site VPN, will that solve it?

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                                      • P
                                        PJB1983 @george1421
                                        last edited by

                                        @george1421 the answer from Meraki Support:

                                        The two sites are using MTU 1432 size due to protocol overhead. This is the recommended value. The best option here is to adjust the MTU of the PXE. Increasing the MTU would result in an MTU greater than 1500 which may lead to fragmentation. Also, Meraki does not support Jumbo size MTU. Should you require further assistance, please do not hesitate to reach out to us asap.

                                        george1421G 1 Reply Last reply Reply Quote 0
                                        • george1421G
                                          george1421 Moderator @PJB1983
                                          last edited by

                                          @pjb1983 I could have almost predicted that. Changing the VPN MTU is not really an option.

                                          So you updated the max size from the tftp server. Lets see what the tftp server is telling the target computer.

                                          Lets use this tutorial but for the port capture just use port 69

                                          https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue

                                          With the reduced max block size the tftp server should report the size you set in the configuration. You can review the pcap with wireshark.

                                          Please help us build the FOG community with everyone involved. It's not just about coding - way more we need people to test things, update documentation and most importantly work on uniting the community of people enjoying and working on FOG!

                                          P 1 Reply Last reply Reply Quote 0
                                          • S
                                            Sebastian Roth Moderator
                                            last edited by

                                            @PJB1983 Just so we get the full picture… So you have another router or layer-3 switch between the PXE booting host and the VPN gateway?

                                            In the best case the two communication partners should adjust MTU/packet size according to response from intermediate gateways and we might find out why this isn’t working properly by looking at the packet dump.

                                            When capturing the traffic please use the filter port 69 or icmp so we get that part as well. Would be great if you could upload the PCAP and post a link here or via private message to George and me.

                                            Web GUI issue? Please check apache error (debian/ubuntu: /var/log/apache2/error.log, centos/fedora/rhel: /var/log/httpd/error_log) and php-fpm log (/var/log/php*-fpm.log)

                                            Please support FOG if you like it: https://wiki.fogproject.org/wiki/index.php/Support_FOG

                                            P 1 Reply Last reply Reply Quote 0
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