Re: [PATCH] TCP: add option for silent port knocking with integrity protection

On Wed, 11 Dec 2013 21:19:00 +0100
Christian Grothoff [off-list ref] wrote:

On 12/11/2013 09:01 PM, David Miller wrote:

quoted

From: Christian Grothoff <redacted>
Date: Tue, 10 Dec 2013 19:35:36 +0100

quoted

Only NAT implementations that change the SQN are not supported
(those should be rare, but we have no hard data on this).

Even Linux's netfilter can and does do this, it is absolutely necessary
for tracking SIP and FTP protocols, and it's also used in our virtual
server load balancing modules.

We're aware that Linux _can_ do this.  I was not aware it was doing this
for
SIP and FTP specifically; regardless, what implementations can do is less
important than what they are configured to do most of the time, and that's
what we'd need hard data on.  Anyway, I'd be very interested to learn how
you use this for SIP/FTP to evaluate the impact.  Do you have documentation
on this?

As for server load balancing, I suspect that those are not the kinds of
services that one would typically use port knocking for.  Still, again a
good hint as to where trouble might lurk (and we will definitively include
those points in the next revision of the documentation).

The point is that doing it outside of TCP core is safer, less error prone
and more flexible.