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Why are ping accepted, but not HTTP traffic?

Scheduled Pinned Locked Moved NAT
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  • F
    Fafa24
    last edited by Apr 11, 2018, 5:55 PM

    Hello,

    My LAN is in the 192.168.1.0/24 subnet with an internet connection and a pfsense firewall. I have an other network which is 192.168.2.0/24 and has a separate internet with a pfsense too. At my pfsense which is in 192.168.1.0 I have a static route configured to network 192.168.2.0.

    From network 192.168.2.0 I can ping to network 192.168.1.0 fine the same the other way. However on network 192.168.2.0 I cannot access websites which are on network 192.168.1.0.

    See screenshot of the pfsense in network 192.168.1.0 firewall log of LAN interface - what puzzles me from a client on network 192.168.2.0 I can ping the machine 192.168.1.99, but http traffic is not allowed. The pfense has the standard rule for the LAN interface applied.

    Thanks,
    Edy

    ![firewall rule.jpg](/public/imported_attachments/1/firewall rule.jpg)
    ![firewall rule.jpg_thumb](/public/imported_attachments/1/firewall rule.jpg_thumb)

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    • V
      viragomann
      last edited by Apr 11, 2018, 6:23 PM

      You have an asymmetric routing issue.
      It seems that the request packets from 192.168.2.0/24 doesn't pass the firewall of 192.168.1.0/24, while responses try to pass, but are blocked, since pfSense is missing the SYN packet.

      @Fafa24:

      what puzzles me from a client on network 192.168.2.0 I can ping the machine 192.168.1.99, but http traffic is not allowed.

      The ICMP protocol is stateless, so response packet can pass, no matter if the request packet took the same way or another one.
      TCP is a stateful protocol.

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      • F
        Fafa24
        last edited by Apr 11, 2018, 6:35 PM

        Okay - thanks  I found the relevant docs for pfsense. I guess this is the article to refer to https://doc.pfsense.org/index.php/Asymmetric_Routing_and_Firewall_Rules

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        • V
          viragomann
          last edited by Apr 11, 2018, 6:39 PM

          For a TCP communication you need routes on both routers. Also on the pfSense in 192.168.2.0/24 you have to add a route pointing on the other router.

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          • F
            Fafa24
            last edited by Apr 12, 2018, 2:07 PM

            Thank you - I was able to resolve it

            I checked "Bypass firewall rules for traffic on the same interface"

            I have the same interface configured on both Pfsense.

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            • J
              johnpoz LAYER 8 Global Moderator
              last edited by Apr 12, 2018, 2:19 PM

              ""Bypass firewall rules for traffic on the same interface""

              That is NOT the correct way to fix asymmetrical routing… If you have 2 different routers and you want to route between them - then connect them with a transit/transfer network.

              If you have 192.168.1/24 on 1 and 192.168.2/24 on the other - connect the 2 routers with say a 172.16.0/30 transit and create the appropriate routes..

              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 2.7.2, 24.11

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              • F
                Fafa24
                last edited by Apr 12, 2018, 3:12 PM

                Thanks for your input - I really appreciate it, so I can learn how it works and what is the correct way. I unchecked the option and I had to set a default gateway on the optional interface for network 192.168.1.0. This was the problem. No gateway was set in the interface. Does this make sense?

                I can browse now from both subnet websites on the other subnet and also use UNC for file share access.

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                • J
                  johnpoz LAYER 8 Global Moderator
                  last edited by Apr 12, 2018, 3:42 PM

                  draw your network… if you do not have a transit network I can almost promise you have asymmetrical..

                  If you have this its asymmetrical!  unless you host route on each device in the 192.168.1 network.

                  2nd pic is non symmetrical

                  asym.png
                  asym.png_thumb
                  nonasym.png
                  nonasym.png_thumb

                  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 2.7.2, 24.11

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