Maybe this helps (taken from [1]) "Actually there is one way that the MAC address of the tap device affects proper operation of guest networking - if you happen to set the tap device's MAC identical to the MAC used by the guest, you will get errors from the kernel similar to this:
kernel: vnet9: received packet with own address as source address" [1] http://www.redhat.com/archives/libvir-list/2012-July/msg00984.html -- Andreas (irc: scheuran) On Thu, 2015-06-11 at 21:48 +0800, changzhi wrote: > Hi, I know that neutron port's mac address was generated by > neutron.conf and default value is "fa:16:3e" which from base_mac > configuration. I don't know how the tap device's mac address generates > and why tap device mac address was "fe:16:3e:xxx". I think that tap > device mac address was generated by libvirt. > > > Thx > changzhi > > > ------------------ Original ------------------ > From: "Radek Smigielski"<radek.smigiel...@ymail.com>; > Date: Thu, Jun 11, 2015 07:26 PM > To: "OpenStack Development Mailing List (not for usage > questions)"<openstack-dev@lists.openstack.org>; > > Subject: Re: [openstack-dev] How does instance's tap device > macaddress generate? > > > On Thursday, 11 June 2015, 12:00:46, Neil Jerram > <neil.jer...@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 > > __________________________________________________________________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: > openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > __________________________________________________________________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
