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Re: 802.1q Was (Re: Plans for 2.5 / 2.6 ???

To: greearb@xxxxxxxxxxxxxxx
Subject: Re: 802.1q Was (Re: Plans for 2.5 / 2.6 ???
From: Rob Walker <rob@xxxxxxxxxxx>
Date: Fri, 2 Jun 2000 18:40:29 -0700 (PDT)
Cc: rob@xxxxxxxxxxx, buytenh@xxxxxxx, hadi@xxxxxxxxxx, netdev@xxxxxxxxxxx, gleb@xxxxxxxxxxxxxxxxxxxxx
In-reply-to: <3938611E.D074F254@xxxxxxxxxxxxxxx>
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Reply-to: rob@xxxxxxxxxxx
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>>>>> On Fri, 02 Jun 2000 18:36:30 -0700, Ben Greear
>>>>> <greearb@xxxxxxxxxxxxxxx> said:

Ben> Rob Walker wrote:

>> Why should VLANs not be fake devices?  How are they different from
>> aliased interfaces?

Ben> I think most of us are in violent agreement that they should be
Ben> devices, Alexey and Jamal seem to be the main dissenters, and at
Ben> least IMO, they have not offered a reason good enough to make me
Ben> consider trying to make VLANs anything other than devices...

Ben> On this account, my vlan implementation, and Lenert and Gleb's
Ben> are almost identical.  Other than some internal issues, I believe
Ben> the only user-visible difference between my imp and theirs is
Ben> that they re-write the packet header on the way up the stack so
Ben> that it looks **exactly** like an ethernet pkt, where as I just
Ben> leave the header alone and pull 4 extra bytes off of the SKB
Ben> before giving it to the higher levels.

Remember how hard *BSD keeps ragging that their stack is faster due to 
"zero copy"?  I can't evaluate whether that statement is true, or if
the speed advantage has worn off with time, but I do think that the
faster the implementation, the better.  

Ben> I like their idea, but it means they have to move the header
Ben> around for each pkt.  In mine, the packet is not modified, *BUT*,
Ben> programs such as dhcpd which expect to be reading the raw
Ben> ethernet pkt have to be modified.

Maybe a run-time switch could be added to dhcpd, or you could extend
it to automatically read both types of frames as detected.  Is this
even possible?

rob

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