Linux – Promiscuous mode in KVM

kvm-virtualizationlinuxopenstackUbuntuvirtualization

I have cloud system based on Openstack Icehouse-version. Now I want to test newer version of Openstack (Juno) inside my existing cloud. All hosts and guests use Ubuntu 14.04 as their OS. KVM is hypervisor I am using.

So I created virtual machines on my cloud and installed components of Openstack Juno on them. But I have problems with network connectivity on these virtual machines.

Openstack installation guide says:

If you are building your OpenStack nodes as virtual machines, you must configure the hypervisor to permit promiscuous mode on the external network.

But it does not tell how this is done. Neither was I able to find this information by Googling. I have tried many things such as enabling promiscuous mode on various interfaces with command: ifconfig eth0 promisc but nothing has worked. So how can I enable promiscuous mode on my hypervisor?

EDIT: When using ifconfig I see that my interfaces are in state UP BROADCAST RUNNING PROMISC. Also I have used similar installation before installed on physical hosts and it had no problems.

Best Answer

ifconfig eth0 promisc is the correct command to enable promiscuous mode for an interface. If that didn't work try adding this line to /etc/rc.local and reboot.

ifconfig eth0 up

ifconfig eth0 promisc

Related Solutions

Linux – Are there good practices for distributing/deploying linux KVM images

You might well be better off creating it as a full-stack install including the OS and all dependencies, on an OS that you know it works well under. Then let the end user decide if they want to install it standalone or as a VM guest on KVM, VMWare, Xen, or whatever. The only thing you'd gain over this with a KVM image is some amount of hardware-agnosticity, but there are still potential pitfalls there as you've pointed out, and the site would have to be willing and able to maintain a KVM host in addition to your application and its OS.

EDIT: To respond to your reformulated question, I think you've still go to leave this stuff to the sites -- VM guests, by design, cannot control how networking is set up on the host. You can certainly provide documentation and instructions for doing this in the simplest or most effective way, but that may vary from site to site. No matter what you do, if you distribute this as a VM image or appliance, the site will have to effectively set up and maintain a VM host that is specifically configured to work on their network.

Cisco – Configuring trunk interface in Cisco 3750 switch to allow multiple Vlans connected with Ubuntu servers having a single NIC (sub-interfaced)

Absolutely you can. You're looking for 802.1q tagging, which is the underpinning of multiple VLANs on a switch.

Configure your server-facing ports like this...

interface GigabitEthernet0/1
 ! tell the switch to encapsulate frames with dot1q on this trunk port
 switchport trunk encapsulation dot1q
 ! make this a trunk port unconditionally
 switchport mode trunk
 ! allow VLANs 220, 221, and 223 to be sent on this port
 switchport trunk allowed vlan 220,221,223
 ! send vlan 221 frames untagged
 ! you could omit this command, but you'll need to move your eth0 config to a subinterface as well
 switchport trunk native vlan 221
 ! this is an end-device, and doesn't need to be treated like a switch for spanning-tree
 spanning-tree portfast trunk
 ! remove the (ignored) access vlan setting, as this is now a trunk
 no switchport access vlan

On your Ubuntu server you'll need to configure the subinterfaces to be associated to each appropriate VLAN. This can be done manually like this ...

# create a new subinterface tied to dot1q vlan 221
ip link add link eth0 name eth0.221 type vlan id 221
# change the MTU to allow for the inserted dot1q tag (4 bytes)
ifconfig eth0 mtu 1504
# bring the new interface up
ifconfig eth0.221 up

Now you can associate the correct IP address to new interface eth0.221, along with the appropriate default gateway and subnet mask.

If this doesn't work for you, please include a pastebin link to your switch config as well as the output of "ip -d link show" on your Ubuntu server.

Hope this helps!

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