Re: Difference between vlan pseudo interfaces and physical interfaces?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> are there any differences in application between vlans and physical
> network interfaces when it comes to non-IP protocols?

You may have found one (but also may not; see below).  In my opinion
there should not be any, excepting being capable of being the
underlying interface for a vlan instance, and that much only because
(AIUI) 802.1q is broken (it doesn't do vlan-in-vlan the sensible way).

> I just rototilled my home network for a vlan capable switch, and
> found that the Netatalk 2 atalkd refuses to work with vlan
> interfaces:

>  19528      1 atalkd   CALL  ioctl(4,SIOCGIFADDR,0x7f7fffdbb950)

>  19528      1 atalkd   RET   ioctl -1 errno 49 Can't assign requested address

I don't know Appletalk.  But it does occur to me that vlans do one
thing that, while entirely permissible, is rare, and thus may not have
been correctly handled by the atalkd authors: it uses the same MAC as
its underlying interface.  It is entirely permissible for multiple
interfaces on the same host to use the same MAC (provided, of course,
they're not connected to the same Ethernet-level addressing domain -
approximately, the same broadcast domain), and indeed some OSes do that
on some Suns where the MAC a property of the machine rather than the
interface hardware.  But it is comparatively rare, especially in the
peecee world, and, depending on how AARP is implemented, it might break
the NetBSD EtherTalk implementation.

It might help debug this if you try real interfaces which support
setting the MAC, and configure two of them to use the same MAC.  If you
can, of course.

Mind you, I don't see why a failure would show up as SIOCGIFADDR
errors.  Personally, I'd treat this as a routine debugging task: is
atalkd broken, is the underlying system broken, or is atalkd doing
something that isn't necessarily expected to work (like expecting all
interfaces' MACs to be distinct)?

/~\ The ASCII				  Mouse
\ / Ribbon Campaign
 X  Against HTML		mouse%rodents-montreal.org@localhost
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B