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Date:      Mon, 26 Oct 2015 16:44:11 -0400
From:      "Chad J. Milios" <>
To:        Terje Elde <>, Matthew Seaman <>
Subject:   Re: NIC naming
Message-ID:  <>
In-Reply-To: <>
References:  <> <> <>

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On 10/26/2015 2:16 PM, Terje Elde wrote:
>> On 26 Oct 2015, at 17:30, Matthew Seaman <> wrote:
>> This probably doesn't solve your problem, which appears to be knowing
>> which of the ethernet ports on your machine is em0 -- the usual method
>> to do that is by ifconfig'ing everything else down and then testing with
>> a network cable until you find the working port.  However it might help
>> clarify the system configuration.
> ifconfig will give you the MAC of the card. I'm not sure if there's a standard tool for it, but it should be easy to do something like "rename the card with MAC address X to Y"

you can put the following one-liner (fix if your email client breaks) 
directly into /etc/rc.conf or /etc/rc.conf.local (replace 
01:23:45:67:89:ab with your "main" card's MAC address and that interface 
will always be named, in this example net0:

eval setvar `ifconfig | while read a b; do if [ "$b" != "${b#flags=}" ]; 
then c=${a%:}; fi; if [ "$a" = ether -a "$b" = 01:23:45:67:89:ab ]; then 
echo ifconfig_${c}_name net0; fi; done`

> Personally, I've started renaming along the lines of renaming em0 to em_lan0, em1 to em_wan1 and so on. Makes it a bit easier to see what's going on, both for when another admin might inherit the box, and also for myself, if I haven't touched the box in a few years.

you may replace net0 with legal names such as up0, up1, down0, down1, 
down2, down4 (or in#, out#, wan#, lan#) etc. whatever makes most sense 
to describe your use case (just not wlan#. use wifi# or wphy# for your 
wlan#'s phy interface):

name_mac () {
eval setvar `ifconfig | while read a b; do if [ "$b" != "${b#flags=}" ]; 
then c=${a%:}; fi; if [ "$a" = ether -a "$b" = $2 ]; then echo 
ifconfig_${c}_name $1; fi; done`

name_mac up0 aa:aa:aa:aa:aa:aa
name_mac down0 bb:bb:bb:bb:bb:bb
name_mac down1 cc:cc:cc:cc:cc:cc

> Sure, you could argue all of this should be documented somewhere as well - and you wouldn't be wrong - but renaming makes things obvious where the next admin will look, not just in some doc that might be somewhere he didn't.
> Terje

-Chad J. Milios
P.S. any snippets of code contained in this email are hereby placed in 
the public domain.

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