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Date: Fri, 3 Nov 2006 06:28:51 +1300
From: Andrew Thompson <thompsa@freebsd.org>
To: 'Jeremie Le Hen' <jeremie@le-hen.org>
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Cc: Raymond Wagner <wagnerrp@email.uc.edu>, freebsd-net@freebsd.org
Subject: Re: Virtual Network Interfaces
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On Thu, Nov 02, 2006 at 06:12:22PM +0100, 'Jeremie Le Hen' wrote:
> Hi Raymond,
> 
> On Tue, Oct 31, 2006 at 11:10:47AM -0500, Raymond Wagner wrote:
> > Your other method is that I keep NAT on the internal interface as normal,
> > and then create VLANs, bridged to the external interface, to each computer
> > with an external IP.  Those machines would communicate as normal on the
> > internal network, but use the VLAN interface for external access.  I've not
> > used VLANs before, so I don't know exactly how they work.  I know the
> > wrapper causes some overhead, and my switch drops packets >1500 bytes.  Do I
> > have to lower the MTU on the internal network, or just the VLANs and
> > external?  Also, will my ISP know not to send the larger packets?
> 
> 802.1q (namely VLAN) adds a 4-bytes header which means your network
> adapter must support a MTU of 1504 bytes.  AFAIK, most of network
> cards do this.  I haven't heard of problems like this so far.
> 
> I've Cc'ed Andrew Thompson which has imported if_bridge(4) from
> OpenBSD into FreeBSD.  He will likely be able to answer your question
> and tell whether it is possible to bridge two VLAN interfaces
> (attached to a physical interface) with another physical interface.

That will work fine. The area where the bridge lacks is bridging vlan
trunks but you do not appear to be doing that.


Andrew