Network Virtualization

Understanding network virtualization including VLANs, VXLAN, SDN, virtual switches, and how cloud providers implement virtual networking.

Network virtualization creates abstract versions of physical network resources, allowing multiple virtual networks to operate on a single physical infrastructure. It's essential for cloud computing, enabling multi-tenant isolation, flexible network topologies, and software-defined networking.

Network Virtualization Architecture

┌─────────────────────────────────────────────────────────────┐ │ NETWORK VIRTUALIZATION LAYERS │ │ │ │ ┌─────────────────────────────────────────────────────┐ │ │ │ VIRTUAL NETWORKS (Tenant View) │ │ │ │ ┌─────────────┐ ┌─────────────┐ │ │ │ │ │ Tenant A │ │ Tenant B │ │ │ │ │ │ 10.0.0.0/16 │ │ 10.0.0.0/16│ (same IPs, │ │ │ │ │ ┌──┐ ┌──┐ │ │ ┌──┐ ┌──┐ │ isolated!) │ │ │ │ │ │VM│ │VM│ │ │ │VM│ │VM│ │ │ │ │ │ │ └──┘ └──┘ │ │ └──┘ └──┘ │ │ │ │ │ └─────────────┘ └─────────────┘ │ │ │ └─────────────────────────────────────────────────────┘ │ │ │ │ ┌─────────────────────────────────────────────────────┐ │ │ │ SDN CONTROLLER / OVERLAY NETWORK │ │ │ │ (VXLAN / GRE / Geneve encapsulation) │ │ │ └─────────────────────────────────────────────────────┘ │ │ │ │ ┌─────────────────────────────────────────────────────┐ │ │ │ PHYSICAL NETWORK INFRASTRUCTURE │ │ │ │ Switches, Routers, NICs (shared) │ │ │ └─────────────────────────────────────────────────────┘ │ └─────────────────────────────────────────────────────────────┘

Types of Network Virtualization

1. VLAN (Virtual LAN)

Segments a physical network into logical broadcast domains.

bash example

# Create VLAN on Linux
sudo ip link add link eth0 name eth0.100 type vlan id 100
sudo ip addr add 192.168.100.1/24 dev eth0.100
sudo ip link set dev eth0.100 up

# Switch configuration (Cisco-style)
# interface GigabitEthernet0/1
#   switchport mode trunk
#   switchport trunk allowed vlan 100,200,300

2. VXLAN (Virtual Extensible LAN)

Overlay network protocol that encapsulates L2 frames in UDP packets, supporting up to 16 million virtual networks.

bash example

# Create VXLAN interface on Linux
sudo ip link add vxlan100 type vxlan \
  id 100 \
  dstport 4789 \
  local 192.168.1.10 \
  group 239.1.1.1 \
  dev eth0

sudo ip link set vxlan100 up
sudo ip addr add 10.0.0.1/24 dev vxlan100

3. Software-Defined Networking (SDN)

┌─────────────────────────────────────────────────────┐ │ SDN ARCHITECTURE │ │ │ │ ┌───────────────────────────────────────────────┐ │ │ │ APPLICATION LAYER │ │ │ │ Network apps, monitoring, security policies │ │ │ └───────────────────────┬───────────────────────┘ │ │ │ Northbound API │ │ ┌───────────────────────┴───────────────────────┐ │ │ │ CONTROL PLANE (SDN Controller) │ │ │ │ OpenFlow, ONOS, OpenDaylight │ │ │ │ Centralized network intelligence │ │ │ └───────────────────────┬───────────────────────┘ │ │ │ Southbound API │ │ ┌───────────────────────┴───────────────────────┐ │ │ │ DATA PLANE (Network Devices) │ │ │ │ Switches, routers (just forward packets) │ │ │ └───────────────────────────────────────────────┘ │ └─────────────────────────────────────────────────────┘

Virtual Switches

bash example

# Open vSwitch (OVS) - Most popular virtual switch
sudo ovs-vsctl add-br br0
sudo ovs-vsctl add-port br0 eth0
sudo ovs-vsctl add-port br0 vnet0  # VM port
sudo ovs-vsctl add-port br0 vnet1  # VM port

# Show bridge configuration
sudo ovs-vsctl show

# Add flow rules
sudo ovs-ofctl add-flow br0 \
  "priority=100,in_port=1,dl_dst=00:00:00:00:00:02,actions=output:2"

# Linux Bridge (simpler alternative)
sudo brctl addbr br0
sudo brctl addif br0 eth0
sudo brctl addif br0 vnet0

Cloud Provider Implementations

Feature	AWS	Azure	GCP
Virtual Network	VPC	VNet	VPC
Subnets	Per-AZ subnets	Per-region subnets	Per-region subnets
Overlay Tech	Proprietary	VXLAN-based	Andromeda
Virtual Switch	Nitro (custom)	Azure vSwitch	Andromeda
Network Controller	AWS SDN	Azure SDN	Andromeda SDN

bash example

# AWS VPC (virtual network)
aws ec2 create-vpc --cidr-block 10.0.0.0/16
aws ec2 create-subnet --vpc-id vpc-123 --cidr-block 10.0.1.0/24

# Azure VNet
az network vnet create --name myVNet --resource-group myRG \
  --address-prefix 10.0.0.0/16 --subnet-name default \
  --subnet-prefix 10.0.1.0/24

Network Function Virtualization (NFV)

Replaces physical network appliances with software:

Virtual firewalls
Virtual load balancers
Virtual routers
Virtual IDS/IPS

Interview Questions

What is network virtualization and why is it important for cloud computing?

Network virtualization abstracts physical network infrastructure into logical networks, enabling multi-tenant isolation on shared hardware. It's essential for cloud because it allows each customer to have isolated virtual networks with overlapping IP ranges on the same physical infrastructure.

Explain the difference between VLAN and VXLAN.

VLAN operates at Layer 2, limited to 4,096 networks (12-bit ID), and confined to a single L2 domain. VXLAN operates over Layer 3 (UDP encapsulation), supports 16 million networks (24-bit VNI), and can span across data centers — making it suitable for large-scale cloud environments.

What is SDN and how does it change traditional networking?

SDN (Software-Defined Networking) separates the control plane (decision-making) from the data plane (packet forwarding). A centralized controller programs network devices, enabling automation, dynamic configuration, and programmable network behavior — versus traditional distributed control in each device.

How do cloud providers implement network isolation between tenants?

Through overlay networks (VXLAN/Geneve), virtual switches, security groups, and network ACLs. Each tenant gets a VPC with its own IP space, routing tables, and firewall rules — all logically isolated despite sharing physical infrastructure.

What is Open vSwitch and when would you use it?

Open vSwitch is a production-quality virtual switch supporting OpenFlow for SDN integration. Use it when building cloud infrastructure, implementing network overlays, or needing programmable network forwarding — it's used in OpenStack, oVirt, and many cloud platforms.