vlans and cloning

Sam Leffler sam at errno.com
Mon Jul 10 18:53:28 UTC 2006

Dmitry Pryanishnikov wrote:
> Hello!
> On Mon, 10 Jul 2006, Sam Leffler wrote:
>>> ifconfig vlan0 create
>>> ifconfig vlan0 vlan 1 vlandev em0
>>> sequence is required for now. Also, I thing it's perfectly correct to
>>> have
>>> cloned_interfaces="vlan30"
>>> while NOT having 'ifconfig_vlan30' assignment - system administrator
>>> could just reserve a spare interface w/o assigning it's parameters. So I
>>> think
>>> that possibility of the specific device cloning w/o arguments, e.g.,
>>> ifconfig vlan30 create
>>> should be preserved.
>> Clearly one would need to fix rc scripts.  The question is should the
>> old behaviour be preserved; it provides no functionality--i.e. a cloned
>> device is unusable until you set the tag+parent and you cannot set the
>> tag or parent on an existing cloned device (once setup).  So the only
>  I don't agree:
> 1) Cloned but unset device is perfectly legal for, e.g., mentioning
>    in ipfw rules (or any other context which requires interface name);
> 2) Sure, you _can_ change tag+parent afterwards:
> root at homelynx# ifconfig vlan32 create
> root at homelynx# ifconfig vlan32 vlan 32 vlandev rl0
> root at homelynx# ifconfig vlan32 -vlandev
> root at homelynx# ifconfig vlan32 vlan 33 vlandev rl0
> root at homelynx#

Hmm, that did not work yesterday in my testing.  That's the answer I've
been looking for.  Thank you.  OTOH I can easily see that plumbing a
vlan into firewall rules and then changing it's configuration might
generate very hard to find bugs; but whatever.

>> preserve existing practice.  Removing the 2 step procedure would allow
>> code to be removed and (IMO) clarify how a vlan is crafted.  In the
>> future there will be cloned devices that cannot/will-not be specified
>> with a 2-step procedure so having vlans work this way will violate POLA.
>  Please don't break well-known and useful behaviour! Remember that it
> allows
> to switch easily physical vlanXXX device assignment (e.g., migration to the
> another trunk) w/o reloading firewall rules.

I've got no plans.  You'll note I committed the new stuff as completely
separate.  I only asked now because I saw an opportunity to remove
cruft.  But given that it's used that cruft can just stay around.


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