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Date: Tue, 18 Mar 2014 09:05:45 -0400
From: Adam McDougall <mcdouga9@egr.msu.edu>
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To: freebsd-net@freebsd.org
Subject: Re: vlanXXX vs ifXX.YY notation
References: <20140318074246.8519@smtp.new-ukraine.org>
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On 03/18/2014 01:42, Zeus Panchenko wrote:
> hi,
> 
> is there any advantage of using vlanXXX vs ifXX.YY notation?
> 
> I mean
> 
>> ifconfig em0
> vlan777: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>        ether 00:1b:b9:8b:ca:33
> ...
>        vlan: 777 parent interface: em0
> 
> vs
> 
> em0.555: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>        ether 00:1b:b9:8b:ca:33
> ...
>        vlan: 555 parent interface: em0
> 
> - -- 
> Zeus V. Panchenko				jid:zeus@im.ibs.dn.ua
> IT Dpt., I.B.S. LLC					  GMT+2 (EET)

It would seem to have an advantage on a bridge where you are passing a
vlan through multiple interfaces since 'vlan777' cannot represent both
the incoming and outgoing vlan interfaces, but em0.555 and em1.555 seem
quite logical.  It gives an easy way to differentiate the same vlan on
more than one parent interface.  Additionally the native names are
shorter which often helps in status reporting utilities that truncate
the name for display.