[Bug 1427] New: can not reuse source port to a DNATed IP if it is being used by another connection

[bugzilla-daemon at netfilter.org]

https://bugzilla.netfilter.org/show_bug.cgi?id=1427

            Bug ID: 1427
           Summary: can not reuse source port to a DNATed IP if it is
                    being used by another connection
           Product: netfilter/iptables
           Version: unspecified
          Hardware: x86_64
                OS: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: NAT
          Assignee: netfilter-buglog at lists.netfilter.org
          Reporter: antonio.ojea.garcia at gmail.com

Scenario:

There is one established connection IP1:Port1 -> IP2:Port2
There is a DNAT rule like IP3:Port3 -> IP2:Port2

If a new connection is created from IP1 to IP3:Port3,
and this connection has source port Port1,
the connection can not be established,
because the incoming packet is not de-natted

The bug was originally reported in Kubernetes:
https://github.com/kubernetes/kubernetes/issues/90258

but I was able to reproduce it here:
https://gist.github.com/aojea/4ffb520db9f72de21685294d8fec7f33

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