Firewall ipfw in FreeBSD

The name of the pictureThe name of the pictureThe name of the pictureClash Royale CLAN TAG#URR8PPP











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I have a doubt respect to the functionality of the IPFW firewall in FreeBSD. My scenario is the following:
enter image description here



All these machines are running FreeBSD, and all of them are virtual machines. The thing is that I don't understand one thing. If I add a rule in IPFW in the firewall machine to block pings from machine 2 to machine 1, I don't know why this block is bidirectional. I mean, I put this rule:



ipfw add 02000 deny icmp from 10.0.2.2 to 10.0.1.2


With this I understand that the firewall will block any ICMP packet coming from 10.0.2.2 (machine on the right in the picture) to 10.0.1.2 (machine on the left in the picture), but what really happens is that ok, machine 2 cannot ping to machine 1, but machine 1 cannot ping machine 2 either! Why is that? The rules of IPFW are the following:
enter image description here



Pictures of the pings:
enter image description hereenter image description here




freebsd ping ipfw




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  • 2




    What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
    – cherdt
    Apr 27 at 14:45






  • 1




    Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
    – victor26567
    Apr 27 at 14:54






  • 1




    Don't post a screenshot of text. Copy-paste the text.
    – Gilles
    Apr 29 at 15:20










  • @cherdt Since your comment is a good answer please added as one.
    – Raphael Ahrens
    May 1 at 9:07














up vote
1
down vote

favorite












I have a doubt respect to the functionality of the IPFW firewall in FreeBSD. My scenario is the following:
enter image description here



All these machines are running FreeBSD, and all of them are virtual machines. The thing is that I don't understand one thing. If I add a rule in IPFW in the firewall machine to block pings from machine 2 to machine 1, I don't know why this block is bidirectional. I mean, I put this rule:



ipfw add 02000 deny icmp from 10.0.2.2 to 10.0.1.2


With this I understand that the firewall will block any ICMP packet coming from 10.0.2.2 (machine on the right in the picture) to 10.0.1.2 (machine on the left in the picture), but what really happens is that ok, machine 2 cannot ping to machine 1, but machine 1 cannot ping machine 2 either! Why is that? The rules of IPFW are the following:
enter image description here



Pictures of the pings:
enter image description hereenter image description here




freebsd ping ipfw




share|improve this question

















  • 2




    What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
    – cherdt
    Apr 27 at 14:45






  • 1




    Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
    – victor26567
    Apr 27 at 14:54






  • 1




    Don't post a screenshot of text. Copy-paste the text.
    – Gilles
    Apr 29 at 15:20










  • @cherdt Since your comment is a good answer please added as one.
    – Raphael Ahrens
    May 1 at 9:07












up vote
1
down vote

favorite









up vote
1
down vote

favorite











I have a doubt respect to the functionality of the IPFW firewall in FreeBSD. My scenario is the following:
enter image description here



All these machines are running FreeBSD, and all of them are virtual machines. The thing is that I don't understand one thing. If I add a rule in IPFW in the firewall machine to block pings from machine 2 to machine 1, I don't know why this block is bidirectional. I mean, I put this rule:



ipfw add 02000 deny icmp from 10.0.2.2 to 10.0.1.2


With this I understand that the firewall will block any ICMP packet coming from 10.0.2.2 (machine on the right in the picture) to 10.0.1.2 (machine on the left in the picture), but what really happens is that ok, machine 2 cannot ping to machine 1, but machine 1 cannot ping machine 2 either! Why is that? The rules of IPFW are the following:
enter image description here



Pictures of the pings:
enter image description hereenter image description here




freebsd ping ipfw




share|improve this question













I have a doubt respect to the functionality of the IPFW firewall in FreeBSD. My scenario is the following:
enter image description here



All these machines are running FreeBSD, and all of them are virtual machines. The thing is that I don't understand one thing. If I add a rule in IPFW in the firewall machine to block pings from machine 2 to machine 1, I don't know why this block is bidirectional. I mean, I put this rule:



ipfw add 02000 deny icmp from 10.0.2.2 to 10.0.1.2


With this I understand that the firewall will block any ICMP packet coming from 10.0.2.2 (machine on the right in the picture) to 10.0.1.2 (machine on the left in the picture), but what really happens is that ok, machine 2 cannot ping to machine 1, but machine 1 cannot ping machine 2 either! Why is that? The rules of IPFW are the following:
enter image description here



Pictures of the pings:
enter image description hereenter image description here





freebsd ping ipfw





share|improve this question












share|improve this question




share|improve this question








edited Apr 29 at 15:19









Gilles

504k1199951522




504k1199951522









asked Apr 27 at 14:23









victor26567

63




63







  • 2




    What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
    – cherdt
    Apr 27 at 14:45






  • 1




    Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
    – victor26567
    Apr 27 at 14:54






  • 1




    Don't post a screenshot of text. Copy-paste the text.
    – Gilles
    Apr 29 at 15:20










  • @cherdt Since your comment is a good answer please added as one.
    – Raphael Ahrens
    May 1 at 9:07












  • 2




    What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
    – cherdt
    Apr 27 at 14:45






  • 1




    Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
    – victor26567
    Apr 27 at 14:54






  • 1




    Don't post a screenshot of text. Copy-paste the text.
    – Gilles
    Apr 29 at 15:20










  • @cherdt Since your comment is a good answer please added as one.
    – Raphael Ahrens
    May 1 at 9:07







2




2




What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
– cherdt
Apr 27 at 14:45




What evidence do you have that the ICMP packets from machine 1 do not make it through the firewall to machine 2? Please provide details. ping would not be successful, since the return packet from machine 2 would not make it through the firewall to machine 1.
– cherdt
Apr 27 at 14:45




1




1




Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
– victor26567
Apr 27 at 14:54




Ahh thats truee, the response of machine 2 will not arrive to machine 1 because of firewall. Thanks!!
– victor26567
Apr 27 at 14:54




1




1




Don't post a screenshot of text. Copy-paste the text.
– Gilles
Apr 29 at 15:20




Don't post a screenshot of text. Copy-paste the text.
– Gilles
Apr 29 at 15:20












@cherdt Since your comment is a good answer please added as one.
– Raphael Ahrens
May 1 at 9:07




@cherdt Since your comment is a good answer please added as one.
– Raphael Ahrens
May 1 at 9:07










1 Answer
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You can confirm whether or not machine 2 is receiving and responding to ICMP packets using tcpdump, e.g.:



sudo tcpdump -i eth0 icmp


In the case you have described, ping would not be successful because the return packet from machine 2 would be blocked by the firewall on machine 1.






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    up vote
    0
    down vote













    You can confirm whether or not machine 2 is receiving and responding to ICMP packets using tcpdump, e.g.:



    sudo tcpdump -i eth0 icmp


    In the case you have described, ping would not be successful because the return packet from machine 2 would be blocked by the firewall on machine 1.






    share|improve this answer

























      up vote
      0
      down vote













      You can confirm whether or not machine 2 is receiving and responding to ICMP packets using tcpdump, e.g.:



      sudo tcpdump -i eth0 icmp


      In the case you have described, ping would not be successful because the return packet from machine 2 would be blocked by the firewall on machine 1.






      share|improve this answer























        up vote
        0
        down vote










        up vote
        0
        down vote









        You can confirm whether or not machine 2 is receiving and responding to ICMP packets using tcpdump, e.g.:



        sudo tcpdump -i eth0 icmp


        In the case you have described, ping would not be successful because the return packet from machine 2 would be blocked by the firewall on machine 1.






        share|improve this answer













        You can confirm whether or not machine 2 is receiving and responding to ICMP packets using tcpdump, e.g.:



        sudo tcpdump -i eth0 icmp


        In the case you have described, ping would not be successful because the return packet from machine 2 would be blocked by the firewall on machine 1.







        share|improve this answer













        share|improve this answer



        share|improve this answer











        answered May 2 at 15:29









        cherdt

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