Can't access VMs on public network in devstack with Neutron

asked 2013-09-19 11:46:26 -0600

gvdm gravatar image

updated 2014-01-22 15:12:36 -0600

Evgeny gravatar image

Hi to all,

I built a DevStack machine (on Ubuntu 12.04) with Neutron ( ) support. This added the bridge "br-ex" to my Devstack's machine with the IP

Now I can access Neutron's functionalities into Horizon and I can build Networks, Routers and link a VM to a network. I also see the prebuilt network called "public" into Horizon, which has the network IP range

I create a brand new VM using the cirrOS built-in image (ah, what is the cirrosOS package manager? I'd like to install apache on it cannot find both "apt-get" and "yum") and associate to it the network "public". The Neutron module gives it the IP

I also modify (by using the Horizon GUI) the "default" security group so that it allows ICMP and SSH network traffic (and, of course, associate the "default" security group to my cirrOS VM).

The problem is that I cannot even ping my VM from the Devstack node and the VM cannot ping the Devstack machine.

DevStack machine:

$ ping

PING ( 56(84) bytes of data.

From icmp_seq=1 Destination Host Unreachable

What could be the problem? Should the "br-ex" bridge allow the access to the "public" network?

Thanks Giulio

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Maybe you are trying to boot the vm directly attached to the external network? If so, you need to boot to an internal network and associate a floating ip instead.

darragh-oreilly gravatar imagedarragh-oreilly ( 2013-09-19 12:10:26 -0600 )edit

So i should build a router, associate it to che "public" network (building a new network for the router's inner one), link the vm to the router and then add a floating ip to the vm? But why cannt I just link the vm to the "public" network?

gvdm gravatar imagegvdm ( 2013-09-19 12:29:04 -0600 )edit

yep, something like that. One reason is because VM VIFs won't be created on br-ex because it is not set as the intergration bridge. I don't know why you are even allowed to try.

darragh-oreilly gravatar imagedarragh-oreilly ( 2013-09-19 12:44:37 -0600 )edit

Thank you. This solved my problem :) Only one more thing: could you please explain me why cannot I link the VM to the "public" network? Why do I have to build a network with a router and then give the VM a bridge-network's IP (using floating IPs) when I can associate the VM with a bridge-network's IP just by adding the VM to the "public" network?

gvdm gravatar imagegvdm ( 2013-09-20 03:14:01 -0600 )edit

Booting a VM directly to the "public" network does not work because devstack sets it up as an external network for floating ips. Devstack also creates an internal network "private" and a "router1" all linked together. So you should be able to boot to "private" and associate a floating ip instead.

darragh-oreilly gravatar imagedarragh-oreilly ( 2013-09-23 12:44:16 -0600 )edit

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answered 2015-03-08 23:28:20 -0600

osdiaj gravatar image


Have a look at and . If you are using provider vlan for tenant network, then it is possible to make the instance talk to external network directly. I'm not sure about devstack localrc configurations to enable the provider vlan network mode, but probably you can have a look here at and .


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Asked: 2013-09-19 11:46:26 -0600

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Last updated: Mar 08 '15