Is TPROXY compatible with conntrack?

Solution Verified - Updated -

Environment

Red Hat Enterprise Linux

Issue

I am using TPROXY. Can I use conntrack too?

Resolution

Either make use of NOTRACK features to avoid confusing conntrack, or upgrade to RHEL 7 and setup conntrack zones properly.

Root Cause

It depends on what are you going to use conntrack for. Conntrack uses the 5-tuple (src host, src port, dst host, dst port, protocol) to identify a connection. On TPROXY environments, this may be duplicated if you consider both sides of TPROXY. That's where the issue lies within: the 5-tuple is the same and cannot be duplicated, therefore you can track only one side of the system.

RHEL 7 adds support for (conntrack zones)[https://access.redhat.com/site/solutions/156413]. With it, you may duplicate the 5-tuple because it adds a 6th element to that hash: the zone number, a number you choose and give via iptables matches. You may only track all your connections when properly using conntrack zones.

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