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unable to create multiple interfaces from one VM attached to the same network

asked 2015-10-26 09:44:16 -0600

abhinav gravatar image

I am using HEAT orchestrator to create a deployment. one of configuration requires creating 2 ports on single VM connecting to same network. 1. creating network net1 2. Create VM with 2ports. VM.port0 = Net1 VM.port1= Net1


type: OS::Nova::Server
  name: Server1
  image: { get_param: image }
  flavor: { get_param: flavor }
  key_name: { get_param: key_name }
    - port: { get_resource: server1_port0 }
    - port: { get_resource: server1_port1}


type: OS::Neutron::Port
  network_id: { get_resource: private_net }
    - subnet_id: { get_resource: private_subnet }


type: OS::Neutron::Port
  network_id: { get_resource: private_net }
    - subnet_id: { get_resource: private_subnet }

I get an error saying : Duplicate Port/Network, VM creation failed.

My question is: why nova doesn't allow creating multiple ports attached to same network. same problem is described in ( fix is also propsed :

Work around is to hot plug the port after VM creation. But I want the deployment to be created using HEAT without manually adding the port from cmd line.

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Any reason, why you are trying to achieve this?

fgorbat gravatar imagefgorbat ( 2015-10-26 13:07:42 -0600 )edit

I am trying to do a LTE-EPC deployment on openstack . LTE-MMe nodes have various interfaces.. so need multiple ips/nics some of them connected to same network.

abhinav gravatar imageabhinav ( 2015-10-29 07:47:47 -0600 )edit

2 answers

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answered 2015-11-03 05:56:01 -0600

capsali gravatar image

Is a bad practice to have multiple eth on the same subnet on linux from routing point of view. It can be done with some dirty workarounds but it is not recommanded. Instead of issuing nova attach-interface, you should be adding another ip to the first port with nova add-fixed-ip. This way you will have only one interface on the subnet and can create multiple veth on it for multiple IP's (eg eth0:1, eth0:2 and so on).

Alternativly you can create the port using neutron prior to booting and set as many ip's on the port as necessary and then boot up the instance with the created port!

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answered 2015-10-29 08:03:20 -0600

abhinav gravatar image

updated 2015-10-30 02:08:35 -0600

I am able to create multiple Nics connected to same network.

neutron.conf --> allow_duplicate_networks = True

nova.conf -->allow _duplicate_networks =True

nova/network/neutronv2/ : allow_duplicate_networks = True.

We are able to create VM with 2 nics attached to the same network. BUT

unable to ping all the ips in the same subnet.

only one interface is pingable.

say VM has



I am able to ping but unable to ping

when pinging 102 and doing tcpdump -i eth1 : no pkts but tcpdump -i eth0 : icmp req and reply both are going.

Also i did ifconfig eth0 down then after some time ping is going to eth1( then quickly if you ping it is un pingable!!!!!

any explanation for this behaviour.

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solved** multiple vEThs are created as discussed above and traffic issue can be resolved in two ways. 1. iptables --flush on compute nodes. 2. add iptable rules on each vm .

abhinav gravatar imageabhinav ( 2015-11-16 04:55:07 -0600 )edit

Hi, i would like to know how you did it to solve the problem adding the iptables rules on each Vm. Exactly wich Iptable rules you need to add?

Thank you.

filatan gravatar imagefilatan ( 2018-12-04 07:32:11 -0600 )edit

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Asked: 2015-10-26 09:44:16 -0600

Seen: 2,505 times

Last updated: Nov 03 '15