[Bug 444] New: REDIRECT not working in kernel 2.6.16-rc[12] as before (<= 2.6.15.x)

bugzilla-daemon at bugzilla.netfilter.org bugzilla-daemon at bugzilla.netfilter.org
Wed Feb 8 19:17:36 CET 2006


           Summary: REDIRECT not working in kernel 2.6.16-rc[12] as before
                    (<= 2.6.15.x)
           Product: netfilter/iptables
           Version: linux-2.6.x
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: NAT
        AssignedTo: laforge at netfilter.org
        ReportedBy: spiney at spiney.org


I used the following two lines on my notebook for a long time to get to an
external mailserver at a place where outbound tcp port 25 connections are
blocked but SSH is allowed: (using REDIRECT so no change of mail client
configuration was necessary)

  iptables -t nat -I OUTPUT -p tcp -d $MAILSERVER --dport 25 \
             -j REDIRECT --to 10025
  ssh -L 10025:localhost:25 $MAILSERVER

Telnetting to localhost port 10025 still redirects to the mailserver port 25, so
the SSH is working as usual, but when telnetting to $MAILSERVER port 25 the
connection hangs.

This used to work fine until 2.6.15.x, but with 2.6.16-rc[12] this is broken. I
couldn't see anything in the kernel changelog about this, so I'm reporting this
here as a bug. 

Attached are 4 pcap-files captured with tcpdump from the loopback, 2 for kernel
2.6.15, 2 for 2.6.16-rc2, one showing the working telnet to localhost 10025 and
one showing the attempted(2.6.16-rc2) and successful(2.6.15) attempt to telnet
to mailserver port 25. BTW, the SSH versions in between tries were the same, as
is the kernel version and configuration of the remote mailserver. If any more
information is needed I'll be happy to provide it.

Kind regards,

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