Neutron prerequisites for CentOS

This OpenStack tutorial describes prerequisites to prepare your servers to leverage OpenStack Neutron with CentOS Linux/KVM.

For a general description of Neutron networking concepts, refer to the tutorial Networking with OpenStack Neutron Basic Concepts.

Refer to Platform9 Managed OpenStack prerequisites for Linux/KVM for hardware requirements for Platform9 Managed OpenStack.

 Prepare Your Linux/KVM Physical Servers for Neutron

The following image represents three hypervisors connected in a Managed OpenStack Neutron network.

Figure 1. Neutron Network Configuration Example

In order to run a Managed OpenStack Neutron network, each of your physical hypervisors and the Neutron network nodes must be prepared with following steps.

Step 1: Install, Enable, & Start the NTP Daemon.

The NTP daemon is required for all components to have their time synchronized.

Run the following commands to install, enable and start the NTP daemon.

yum install -y ntp
systemctl enable ntpd
systemctl start ntpd

Step 2: Set SELinux to permissive

This is required for Open vSwitch (OVS) to be able to manage networking.

Run the following commands to set SELinux to permissive.

sed -i s/SELINUX=enforcing/SELINUX=permissive/g /etc/selinux/config
setenforce 0

Step 3: Disable Firewalld and NetworkManager

This is required for KVM and OVS to be able to create iptables rules directly without firewalld getting in the way.

Run the following commands to disable firewalld and NetworkManager.

systemctl disable firewalld
systemctl stop firewalld
systemctl disable NetworkManager
systemctl stop NetworkManager

Step 4: Enable Network

Run the following command to enable network.

systemctl enable network

Step 5: Load the modules needed for Neutron

Run the following commands to load the modules needed for Neutron.

modprobe bridge
modprobe 8021q
modprobe bonding
modprobe tun
modprobe br_netfilter
echo bridge > /etc/modules-load.d/pf9.conf
echo 8021q >> /etc/modules-load.d/pf9.conf
echo bonding >> /etc/modules-load.d/pf9.conf
echo tun >> /etc/modules-load.d/pf9.conf
echo br_netfilter >> /etc/modules-load.d/pf9.conf

Step 6: Add sysctl options

Run the following commands to add sysctl options.

echo net.ipv4.conf.all.rp_filter=0 >> /etc/sysctl.conf
echo net.ipv4.conf.default.rp_filter=0 >> /etc/sysctl.conf
echo net.bridge.bridge-nf-call-iptables=1 >> /etc/sysctl.conf
echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf
echo net.ipv4.tcp_mtu_probing=2 >> /etc/sysctl.conf
sysctl -p

Step 7: Add the Platform9 YUM Repo

Run the following command to install the Platform9 YUM repository.

yum -y install https://s3-us-west-1.amazonaws.com/platform9-neutron/noarch/platform9-neutron-repo-1-0.noarch.rpm

Step 8: Install Open vSwitch

Run the following command to install Open vSwitch.

yum -y install --disablerepo="*" --enablerepo="platform9-neutron-el7-repo" openvswitch

 Step 9: Enable and start Open vSwitch

Run the following commands to enable and start Open vSwitch.

systemctl enable openvswitch
systemctl start openvswitch

 Step 10: Install QEMU KVM EV

Run the following commands to install QEMU KVM EV.

yum install centos-release-qemu-ev
yum install qemu-kvm-ev

Step 11: Configure physical interfaces

Figure 1 in the article represents a sample Neutron network configuration. Steps 10 through 14 are based on the configuration shown in Figure 1 from the article. Steps 10 through 14 describe the configuration of physical interfaces into a Linux bond, addition of VLAN interfaces for management, VXLAN/GRE network traffic and storage.

You may or may not require one or more of these steps. The steps to follow would be based on your Neutron network configuration. For instance, if you do not plan on using VXLAN/GRE, you can skip the step to set up VXLAN/GRE tunneling interface.

We assume the interface names to be eth0 and eth1.
Substitute eth0 and eth1 with the appropriate interface names per your setup, when you run the commands given for this step.
Similarly, we are assuming an MTU of 9000 (VXLAN requires an MTU of at least 1600)
Make sure all physical switches are configured to handle the MTU of 1600 or you might have problems.

Run the following commands to configure physical interfaces.

/etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
ONBOOT=yes
BOOTPROTO=none
MTU=9000
MASTER=bond0
SLAVE=yes

/etc/sysconfig/network-scripts/ifcfg-eth1

DEVICE=eth1
ONBOOT=yes
BOOTPROTO=none
MTU=9000
MASTER=bond0
SLAVE=yes

Step 12: Set up the Bond interface

Run the following commands to set up the bond interface.

/etc/sysconfig/network-scripts/ifcfg-bond0

DEVICE=bond0
ONBOOT=yes
BONDING_MASTER=yes
BONDING_OPTS="mode=4"
MTU=9000

Step 13: Setup the Management interface

/etc/sysconfig/network-scripts/ifcfg-bond0.101

DEVICE=bond0.101
ONBOOT=yes
BOOTPROTO=none
TYPE=Vlan
VLAN=yes
IPADDR=192.0.2.10
NETMASK=255.255.255.0
GATEWAY=192.0.2.1
DNS1=192.0.2.100
DNS2=192.0.2.200

Step 14: Setup the VXLAN/GRE tunneling interface (Optional)

Run the following commands to VXLAN/GRE tunneling interface.

/etc/sysconfig/network-scripts/ifcfg-bond0.102

DEVICE=bond0.102
ONBOOT=yes
BOOTPROTO=none
TYPE=Vlan
VLAN=yes
IPADDR=198.51.100.10
NETMASK=255.255.255.0

 Step 15: Setup the Storage interface (Optional)

Run the following commands to set up the storage interface.

/etc/sysconfig/network-scripts/ifcfg-bond0.103

DEVICE=bond0.103
ONBOOT=yes
BOOTPROTO=none
TYPE=Vlan
VLAN=yes
IPADDR=203.0.113.10
NETMASK=255.255.255.0

Step 16: Restart Networking

Run the following command to restart the network service.

systemctl restart network.service

Step 17: Create OVS Bridges

The number of OVS bridges you need will determine on how many physical networks your hosts connect to, and what types of networks you will be creating.

Let us look at some basic networking terminology before creating the bridges.

Each physical network corresponds to a trunk or access port (an individual NIC, or a pair of NICs bonded together) on the host. An Open vSwitch bridge must be created for each physical network.

When configuring Platform9 OpenStack’s Networking Config, each physical network is given a Label as a name, and that label mapped to a particular OVS bridge on the host during host authorization.

Let us look at two different examples of common host networking setups.

Example 1: Non-DVR setup with one external flat network, and trunk port for VLAN traffic

The following figure represents a non-DVR network setup with an external flat network, and a trunk port for VLAN traffic.

Figure 2. Non-DVR Network Setup

In Figure 2 above, the network has a trunk port consisting of eth0 and eth1 in a bond that will carry our VLAN based networks(tenant, provider), as well as a dedicated port (eth2) that connects to a separate external network. This is a legacy, non-DVR setup where external connectivity and L3 capability is only on network nodes. Nodes that are hypervisors only carry the tenant network traffic, and need just 1 OVS bridge.

Run the following commands to add OVS bridges on the hypervisors. The steps below assume eth0/eth1 have already been configured in a Linux bond called "bond0". Please refer to steps 10-15 to set up your physical interfaces.

ovs-vsctl add-br br-vlan
ovs-vsctl add-port br-vlan bond0

On our network node, we have a separate NIC that connects to a different physical network. For this, we need a separate OVS bridge.

Run the following commands to add an OVS bridge.

ovs-vsctl add-br br-ext
ovs-vsctl add-port br-ext eth2

Example 2: DVR setup with a pair of NICs in a bond

The following figure represents a DVR network setup with a pair of NICs in a bond.

legacy1extnet-2
Figure 3. DVR Network Setup

In the DVR setup seen in figure 3 above, every host has external L3 connectivity. Here, we only have a pair of NICs in a bond. Therefore this OVS Bridge can only support one Flat (untagged) network, and as many VLAN-tagged networks as your networking infrastructure allows. There are multiple external networks that are VLAN-based, in addition to our tenant networks.

Run the following commands to add an OVS bridge on all hosts.

ovs-vsctl add-br br-vlan
ovs-vsctl add-port br-vlan bond0


April 03, 2017