EM(4), vlans & dhclient

Lee S Clark mosfet at planet.eon.net
Mon Jul 18 06:50:28 GMT 2005

----- Original Message -----
From: "Ragnar Lonn" <raglon at packetfront.com>
To: "Lee S Clark" <mosfet at planet.eon.net>
Cc: <freebsd-net at freebsd.org>
Sent: Friday, July 08, 2005 2:49 AM
Subject: Re: EM(4), vlans & dhclient

> Lee S Clark wrote:
> >- dhclient's interactions with either em(4) or some part of vlan(4) is
flakey at best.  occasionally all 3 vlan interfaces will obtain an IP, in
other instances there is no traffic placed on the wire at all.  typically
one vlan int will get an IP the other two will not.  i suppose this has
something to do with em not liking promisc.
> >
> >
> Yeah, I've had some problems with multiple vlan interfaces too. I had
> problems using multiple unique
> MAC addresses for the different vlan interfaces on 5.x. The kernel would
> drop packets destined for
> e.g. vlan interface A that had MAC address X when the underlying
> physical network interface had
> another MAC address. It seemed easy to patch but we ended up using 4.x
> instead anyhow and
> there it works fine.
> >- the vlan interfaces _must_ have the same MAC as the parent (em0)
otherwise the parent must be in promisc in order for the vlan int to recieve
frames destined for it if a unique lladdr is applied.  this may seem
obvious, but is there a way to alter this behaviour to allow "unicast" MAC
forwarding up from the parent to the vlan interfaces without enabling
promisc (this might be another request for Linux veth on FreeBSD ;)?  our
ISP requires MAC registration in order to allocate IPs, one MAC = one IP,
> >
> >
> When we tested on 5.x, I'm fairly sure it didn't work *even if* the
> physical interface was in promiscuous
> mode. Maybe the behaviour isn't the same for all 5.x versions either. Or
> maybe I'm just confused.
> Anyway, if you want to use several MAC addresses on a single physical
> interface you have to set
> the physical interface to promiscuous mode, AFAIK. Why don't you want to
> enable promiscuous
> mode?
> You also have to turn off the autosrc flag to keep the physical if from
> overwriting the MAC
> address of the vlan if on outgoing packets, but you probably knew that.
> You could try installing 4.11 and see how things work there, as a last
> resort.
>   /Ragnar

Sorry for the delayed reply; vacation.  I don't have any particular aversion
to promiscuous
mode, just personal preference to avoid it.  I certainly agree with you,
4.11 is looking very appealing.  Thanks for the input!


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