Date: Thu, 29 Sep 2005 08:44:09 +0930 From: "Wilkinson, Alex" <alex.wilkinson@dsto.defence.gov.au> To: Peter Jeremy <PeterJeremy@optushome.com.au> Cc: freebsd-arch@freebsd.org, Max Laier <max@love2party.net>, Yar Tikhiy <yar@comp.chem.msu.su> Subject: Re: Bridges Message-ID: <20050928231409.GB38338@squash.dsto.defence.gov.au> In-Reply-To: <20050928184731.GA72352@cirb503493.alcatel.com.au> References: <200509241525.16173.max@love2party.net> <20050924192237.GP40237@cirb503493.alcatel.com.au> <20050928102153.GA86457@comp.chem.msu.su> <20050928032933.G16027@xorpc.icir.org> <20050928184731.GA72352@cirb503493.alcatel.com.au>
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0n Thu, Sep 29, 2005 at 04:47:32AM +1000, Peter Jeremy wrote:
>On Wed, 2005-Sep-28 03:29:33 -0700, Luigi Rizzo wrote:
>>On Wed, Sep 28, 2005 at 02:21:53PM +0400, Yar Tikhiy wrote:
>>> On Sun, Sep 25, 2005 at 05:22:38AM +1000, Peter Jeremy wrote:
>>> >
>>> > Since I've recently needed it, neither bridge.c nor if_bridge.c allow
>>> > you to bridge VLAN trunks (you can bridge individual VLANs but that
>>> > becomes unwieldly when you have dozens of VLANs). I have code to do
>>> > this in bridge.c.
>>>
>>> Couldn't you bridge across the parent, or trunk, physical interfaces
>>> carrying tagged VLAN traffic then? (Of course, hardware support for
>>> VLAN should be turned off on them in that case.)
>
>That's actually what I was trying to do.
>
>>yes in fact i was wondering what's wrong with that because
>>we have been using bridge.c like this for ages now...
>
>The problem is that the current bridge code only considers the MAC
>address for forwarding. When VLANs are in use, this is incorrect as
>both the MAC address and VLAN tag must be considered. The difference
>is crucial when you have the same MAC address appearing in multiple
>VLANs. This can occur when using DECnet Phase IV or Solaris with
>Cassini NICs - both of which have a per-host MAC address rather than a
>per-NIC MAC address.
>
>As an example, consider a system with a host-based MAC address that
>has two NICs. One NIC attaches to VLAN 123 on switch a, the other
>attaches to VLAN 124 on switch b [this is the situation we have in our
>test lab]. If I then attempt to join trunks from both switches using
>bridge(4), it sees the same MAC address on both bridged interfaces and
>shuts down. In reality, this situation is safe because the MAC
>addresses are in different VLANs.
Peter,
What is the difference between a "per-host MAC address" and a "per-NIC
MAC address" ?
- aW
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