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Date:      Fri, 02 Aug 2019 04:54:14 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 239590] ipfw rule doesn't forward TCP connections made through the host's LAN address
Message-ID:  <bug-239590-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D239590

            Bug ID: 239590
           Summary: ipfw rule doesn't forward TCP connections made through
                    the host's LAN address
           Product: Base System
           Version: 11.2-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: yuri@freebsd.org

I need to forward incoming TCP connections made to my host 192.168.5.3 on t=
he
port 3100 to the IP address 10.0.0.101 port 3000 connected through another
interface.

These rules work when connection is made from a remote host:
> ipfw -q nat 19001 config redirect_port tcp 10.0.0.101:3000 192.168.5.3:31=
00
> ipfw -q add 19001 nat 19001 tcp from any to 192.168.5.3 3100 in recv sk0
> ipfw -q add 19001 nat 19001 tcp from 10.0.0.101 3000 to any out xmit sk0

The problem:
A similar firewall rule for connections from the host's LAN IP address (that
pass through lo0) doesn't work:
> ipfw -q add 19001 nat 19001 tcp from 192.168.5.3 to 192.168.5.3 3100 in r=
ecv lo0

Wireshark shows that the incoming connection is from 192.168.5.3 to 192.168=
.5.3
on 3100 but it gets immediately rejected instead of being forwarded.
This rule looks very similar to the second rule above, just the interface is
different. Why doesn't it work?

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