Re: [openstack-dev] How does instance's tap device macaddress generate?
On 11.06.2015 18:52, Andreas Scheuring wrote: 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 I was wondering the same question myself one day and found this explanation from the same mail list: vnet0 is the backend of the guest NIC, and its MAC addr is more or less irrelevant to functioning of the guest itself, since traffic does not originate on this NIC. The only important thing is that this TAP device must have a high value MAC address, to avoid the bridge device using the TAP device's MAC as its own. Hence when creating the TAP Device libvirt takes the guest MAC addr and simply sets the top byte to 0xFE http://www.redhat.com/archives/libvir-list/2012-June/msg01330.html __ 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
Re: [openstack-dev] How does instance's tap device macaddress generate?
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 Smigielskiradek.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
Re: [openstack-dev] How does instance's tap device macaddress generate?
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 Smigielskiradek.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
