netdev - Re: [PATCH 3/3] vxlan: virtual extensible lan

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Message-ID: <20121004081214.7f5a48fe@nehalam.linuxnetplumber.net>
Date:	Thu, 4 Oct 2012 08:12:14 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jesse Gross <jesse@...ira.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH 3/3] vxlan: virtual extensible lan

On Thu, 04 Oct 2012 08:34:50 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> On Wed, 2012-10-03 at 21:02 -0700, Stephen Hemminger wrote:
> 
> >
> > Since port is always a pair, there is no need to restrict range, unless
> > there was a broken firewall in the way. One bug there is that random32()
> > can return 0 which is not a valid port number.  A better fallback
> > would be a hash of the MAC header.
> 
> But using up to 65536 values for the port means that if vxlan traffic
> crosses a statefull firewall (eg netfilter with conntrack), this might
> need 65536 contexts/sessions.

This is UDP, there is no usable state to be found.
But as a practical matter it only needs to be wide enough to hit the
number of receive channels. Therefore even 64 is probably enough for
most people.

> So random32() is not needed.
> 
> What might be needed is additional parameters for a vxlan tunnel, to
> give an optional range for the source port.

It could be per vxlan without a lot of pain. or just derive it value
from existing ephermeral port range.
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