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Re: [Qemu-discuss] any restriction on the guest mac addr when using tap
Re: [Qemu-discuss] any restriction on the guest mac addr when using tap networking?
Mon, 29 Apr 2013 02:26:14 +0200
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On 28-04-2013 07:49, Xeslaro wrote:
when using tap networking, everything works perfectly when i don't specify a
specific mac addr for the guest, but when i choose a mac addr for the
guest(just 6 random bytes), strange things happen. sometimes it works,
sometimes it don't.
when i dump the traffic on the tap device, the host obviously could receive
the packets sent by the guest because it answers all the arp requests, but the
guest seems couldn't receive anything at all as it still send arp request and
the packets it received is zero from the status of the connection(it's running
so i guess there's some limitation about the mac addr i could assign to the
guest? i googled but didn't find anything related.
p.s. the host is running linux 3.9.0-rc6+ and qemu-1.4.1
I have not seen your particular situation before, but there are 3 rules that
I know about for MAC addresses:
- In the first byte, the least significant bit should be 0 for addresses
can be assigned to an adapter.
- In the first byte, the second-to-least significant bit (the 2's bit)
be 1 for made up addresses.
- If the first byte second-to-least significant bit is not set, then the
3 bytes should be a vendor prefix assigned to someone who will let you
misuse their prefix for virtual machines, there are very few of those.
So the second hex digit should be 2, 6, A or E and odd values are extra bad.
Very bad: 13:34:56:78:9a:bc
Jakob Bohm, CIO, partner, WiseMo A/S. http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark. direct: +45 31 13 16 10
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