[openstack-dev] How does instance's tap device mac address generate?
Radek Smigielski
radek.smigielski at ymail.com
Thu Jun 11 11:26:30 UTC 2015
> On Thursday, 11 June 2015, 12:00:46, Neil Jerram <Neil.Jerram at metaswitch.com> wrote:
> > On 11/06/15 10:47, changzhi wrote:
>> Hi, all.
>> I create a vm and it's neutron port's mac address is
>> "fa:16:3e:3f:02:ff". I see "fa:16:3e:3f:02:ff" inside
> vm when I run
>> "ifconfig eth0". Why does vm's tap device's mac address
> is
>> "fe:16:3e:3f:02:ff"? Why different between neutron port's mac
> address
>> and tap device's mac address? Does libvirt create instance tap device
>> and its mac address is generated randomly?
>>
>> Thx
>> zhi
>
> There are two MAC addresses, one at each end of the link between the
> host and the VM.
>
> -------------------+
> Host | +-------------------+
> | | VM |
> tap12345-CD ------------------- eth0 |
> fa:16:3e:56:71:42 | | fa:16:3e:3f:02:ff |
> | | |
> | +-------------------+
> -------------------+
>
> I believe that both of these addresses are randomly generated, although
> I'm not sure exactly which components do that.
>
> Does that help at all?
>
> Thanks,
> Neil
In neutron.conf you've got base_mac option and "fa:16:3e" is the default value.
# Base MAC address. The first 3 octets will remain unchanged. If the
# 4h octet is not 00, it will also be used. The others will be
# randomly generated.
# 3 octet
# base_mac = fa:16:3e:00:00:00
# 4 octet
# base_mac = fa:16:3e:4f:00:00
Cheers,
Radosław Śmigielski
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