Rethinking your network game plan for peak agility

To meet dynamic business needs, enterprises are putting network virtualization on the strategic IT agenda right after server and storage virtualization.

Network virtualization helps data centers optimize overall operational efficiency and scale rapidly to meet fluctuating workload demands by provisioning and managing network resources independently of the underlying hardware. This approach is vital in cloud environments where multiple tenants share system resources.

Why logical networks?

network virtualization

A virtualized data center allows you to quickly provision virtual machines to support more workloads. Credit: Getty Images

In a virtualized data center, you can quickly provision virtual machines (VMs) to support additional workloads. In contrast, it can take two to three weeks to configure a traditional network so that the new VMs can communicate across the data center. One reason is that traditional networks are pre-provisioned and difficult to change on the fly.

In particular, compute resources are tied to the layer 2 network boundary, which means that workloads cannot use resources available in different racks because they are in separate layer 2 domains. Also, administrators cannot provision a large number of isolated layer 2 networks because the virtual LAN (VLAN) specification imposes a limit of 4,094 IDs in a network.

For optimal workload mobility, the networking architecture should not tie workloads to the physical network. Network virtualization lets you provision required network services as easily and as quickly as VMs.

The role of overlays

A software-defined network (SDN) approach decouples the logical network from the physical network. One way of implementing SDN is through Network Virtualization Overlays (NVOs). NVOs allow compute resources to be pooled across noncontiguous clusters or pods. You can then segment this pool into logical networks attached to specific workloads and applications.

Unlike VLANs, the logical networks span virtual resource pools and physical boundaries — and as such, are designed to be more efficient, scalable, resilient and manageable. Because logical networks are abstracted, you can scale them without reconfiguring the underlying physical hardware. This capability helps avoid the time-consuming cycles needed for provisioning and managing VLANs.

NVOs are logical layer 2 networks that float on top of existing physical layer 2 and layer 3 technologies. This abstraction allows VMs on different networks to communicate as if they were in the same layer 2 subnet. NVOs are enabled by the Virtual Extensible LAN (VXLAN) protocol, which specifies a format for how layer 2 logical networks are encapsulated in standard layer 3 IP packets.

A 24-bit segment ID in every VXLAN frame differentiates the logical networks from each other without the need for VLAN tags, allowing large numbers of isolated layer 2 networks to coexist on a common layer 3 infrastructure. Because VXLAN uses a 24-bit ID, a single network can support up to 16 million LAN IDs, extending far beyond the limitations of the VLAN address space.

Use of VXLAN introduces an additional layer of packet processing at the hypervisor level. For each packet on the VXLAN network, the hypervisor needs to add, or encapsulate, protocol headers on the sender side and remove, or decapsulate, these headers on the receiver side. This processing adds to the host server’s CPU load. Some network interface card (NIC) offload capabilities can be used with VXLAN, but they depend on the physical NIC and the driver.

VXLAN gateways provide encapsulation and decapsulation services to allow nonvirtualized network traffic to communicate with VXLAN virtualized network traffic. The gateways can be virtual software bridges in the hypervisor or VXLAN-capable switching hardware.

Powerful cloud capabilities

Network virtualization has the potential to revolutionize cloud deployments in which multiple tenants share system resources. To provide each tenant with network isolation, you need network security and traffic segmentation. However, to meet tenant demands, you must be able to quickly move workloads to servers with available resources.

Because VXLAN abstracts data center boundaries, VMs are virtually layer 2 adjacent, regardless of physical location within the data center. The overlay on top of existing layer 3 boundaries lets you pool all compute resources together as a cloud resource.

To help reduce operational complexity, network virtualization enables flexible VM placement without reconfiguration and seamless migration of workloads to the cloud while preserving policies, VM settings and IP addresses. You can design a virtualized network to help ensure multi-tenant isolation, scalability and performance.

The logical abstraction enabled by virtualization drives network agility and streamlines network management. In turn, network virtualization delivers the flexibility, control and automation required to accelerate business response across today’s cloud deployments and data centers. To learn more, read the Dell Power Solutions article, “Continuing the transformational journey toward peak network agility.”

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