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    PfSense not replying to UDP traceroute on WAN

    General pfSense Questions
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    • T
      travisbrackett last edited by

      Hi there

      I'm trying to configure my pfSense firewall to reply to traceroute requests on the WAN interface and I'm having a little trouble.

      When I traceroute to the LAN interface IP, it works great. A packet capture shows the UDP traffic come in on port 3343X and then a TTL expired in transit ICMP message goes out to the IP attempting the traceroute just like it's supposed to.

      On the WAN interface, I created a firewall rule allowing UDP ports 33434 to 33534 with the source of any, destination set to WAN address. I also enabled logging on this rule.

      I don't have any outbound floating rules that would prevent the ICMP message generated by the firewall from going out.

      When I do a traceroute from a random Internet location to my firewall's WAN IP, I see the UDP packets hitting the firewall in a packet capture within the port range I allowed. I know they're hitting the allow rule because I'm seeing the packets logged in the firewall logs. However, the TTL expired in transit message never goes out, like it does on LAN according to my packet capture, and the traceroute times out for the pfSense hop.

      I tried this on two different pfSense firewalls. One running 2.3, and another running 2.4. I didn't see any setting like "Don't generate ICMP control messages on the WAN interface" and my forum/kb search has been fruitless.

      If I force traceroute to use ICMP, it works great. What am I missing?

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      • H
        Harvy66 last edited by

        Probably the "destination set to WAN address" part. The destination is probably not your firewall but something behind it. You could set it to destination of your LAN network.

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        • T
          travisbrackett last edited by

          In my traceroute, I'm using the WAN IP address, and the packet capture confirms that the destination IP is the same one assigned to my WAN interface.

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          • Derelict
            Derelict LAYER 8 Netgate last edited by

            Try rejecting, not passing. This works for me:

            ![Screen Shot 2018-03-02 at 4.20.26 PM.png](/public/imported_attachments/1/Screen Shot 2018-03-02 at 4.20.26 PM.png)
            ![Screen Shot 2018-03-02 at 4.20.26 PM.png_thumb](/public/imported_attachments/1/Screen Shot 2018-03-02 at 4.20.26 PM.png_thumb)

            Chattanooga, Tennessee, USA
            The pfSense Book is free of charge!
            DO NOT set a source port in a port forward or firewall rule unless you KNOW you need it!
            Do Not Chat For Help! NO_WAN_EGRESS(TM)

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            • johnpoz
              johnpoz LAYER 8 Global Moderator last edited by

              Yup same rule here..


              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
              2440 2.4.5p1 | 2x 3100 2.4.4p3 | 2x 3100 22.01 | 4860 22.05

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              • Derelict
                Derelict LAYER 8 Netgate last edited by

                that's a lot of NTP traffic…. :)

                Chattanooga, Tennessee, USA
                The pfSense Book is free of charge!
                DO NOT set a source port in a port forward or firewall rule unless you KNOW you need it!
                Do Not Chat For Help! NO_WAN_EGRESS(TM)

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                • johnpoz
                  johnpoz LAYER 8 Global Moderator last edited by

                  Yeah have a stratum 1 in the pool..

                  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
                  2440 2.4.5p1 | 2x 3100 2.4.4p3 | 2x 3100 22.01 | 4860 22.05

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                  • T
                    travisbrackett last edited by

                    That did the trick! Thanks!

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                    • T
                      travisbrackett last edited by

                      One weird thing I'm seeing is with Windows tracert which uses ICMP, pfSense sends a TTL expired reply when the request TTL is < 6, so I get a weird result where my pfSense firewall shows up 5 times. I don't want to reject ICMP packets, and I don't see a way to configure the TTL threshold. Anyone know of a remedy?

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                      • Derelict
                        Derelict LAYER 8 Netgate last edited by

                        I would need to see a packet capture of that.

                        Chattanooga, Tennessee, USA
                        The pfSense Book is free of charge!
                        DO NOT set a source port in a port forward or firewall rule unless you KNOW you need it!
                        Do Not Chat For Help! NO_WAN_EGRESS(TM)

                        1 Reply Last reply Reply Quote 0
                        • T
                          travisbrackett last edited by

                          Here you go. I've anonymized the pcap so 1.1.1.1 is the host running the traceroute, and 2.2.2.2 is my pfSense firewall. Looks like I was wrong and it stops sending a TTL expired, and starts replying, when the TTL is greater than 4.

                          Edit: Oops, there's a 1:1 NAT and the replies are probably the routers in between and the host the packets are being NATted to.

                          Edit: Packet capture on the LAN interface confirms this theory.

                          icmptraceroute_anonymized.pcap

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                          • Derelict
                            Derelict LAYER 8 Netgate last edited by

                            OK you're kind of all over the place. You state that pfSense responds in the negative with a TTL > 4. What, exactly am I looking for?

                            What interface was that pcap taken on?

                            Anonymizing MAC addresses? Really? I can't help you.

                            Chattanooga, Tennessee, USA
                            The pfSense Book is free of charge!
                            DO NOT set a source port in a port forward or firewall rule unless you KNOW you need it!
                            Do Not Chat For Help! NO_WAN_EGRESS(TM)

                            1 Reply Last reply Reply Quote 0
                            • johnpoz
                              johnpoz LAYER 8 Global Moderator last edited by

                              "One weird thing I'm seeing is with Windows tracert which uses ICMP, pfSense sends a TTL expired reply when the request TTL is < 6"

                              From where to where?

                              I trace through pfsense to internet all the time, never seen such a thing..


                              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
                              2440 2.4.5p1 | 2x 3100 2.4.4p3 | 2x 3100 22.01 | 4860 22.05

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                              • A
                                axsense2 last edited by

                                What was the resolution? I am having the same problem as in topic. Tracing PFSense from outside PFSense seems that it is not recognizing traces at all. Ping works fine. It can't be true that PFSense does not work with Traceroute in UDP mode... can it?

                                Ax.

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                                • johnpoz
                                  johnpoz LAYER 8 Global Moderator last edited by

                                  Ah screenshot is missing - prob got lost when they updated the forum... You juts need to set a reject rule on your wan for the udp ports. When get back from lunch can post up a screenshot.

                                  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
                                  2440 2.4.5p1 | 2x 3100 2.4.4p3 | 2x 3100 22.01 | 4860 22.05

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                                  • A
                                    axsense2 last edited by

                                    Got it... I think. I created Rejected rule for UDP between ports 33434 and 33634. It actually resolves the issue.

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                                    • johnpoz
                                      johnpoz LAYER 8 Global Moderator last edited by johnpoz

                                      yup... that is all you need to do.

                                      edit: for the next guy that finds this thread... I will post up screenshot of the rule
                                      tracerouterule.png

                                      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
                                      2440 2.4.5p1 | 2x 3100 2.4.4p3 | 2x 3100 22.01 | 4860 22.05

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