Overlay Network

What is an overlay network?

A virtual or logical network built on top of an already-existing physical network is called an overlay network. An example of an overlay network is the Internet, which uses circuit switching to link numerous nodes. Any virtual layer above a physical network infrastructure is called an overlay network. This could be as basic as a virtual local area network (VLAN), but it usually refers to software-defined wide area networks (SD-WAN) or more complex virtual layers from SDN.

By creating a new layer, the overlay eliminates the need for physical links and allows traffic to be programmed and steered over new virtual network paths or routes. Administrators can specify and control traffic flows with overlays regardless of the physical infrastructure that underpins them.

SDN makes virtual networking more adaptable, allowing for a more detached approach without requiring modifications to the physical infrastructure. In contrast to client-server computing, where those routes were hard coded, SDN is an example of distributed computing, where the actual processing is dispersed among numerous nodes.

Overlay protocols and network architecture

Virtual Extensible LAN (VXLAN), Generic Routing Encapsulation, Stateless Transport Tunnelling, Network Virtualization utilizing GRE, and Network Virtualization Overlays are examples of overlay network technologies.

In the Open Systems Interconnection (OSI) paradigm, Layer 3 is where most network overlays operate, managing all traffic via the IP address. However, if a VLAN is made as an overlay, media access control (MAC) addresses would be used to establish the overlay at Layer 2.

The most widely used communication protocol in SDN is OpenFlow, an open standard protocol that facilitates interoperability and is utilized in some capacity by the majority of SDN products.

Advantages of Overlay networks

Some important advantages of network overlays include the following:

• By eliminating the hardcoded limitations of a physical network, the overlay offers a more flexible networking architecture and allows for usage- or function-based setup.
• As an alternative to physically managing these components, overlays provide superior access management by logically segmenting and connecting devices.
• Layer-overlay networks improve security by dividing traffic and limiting access for individuals, organizations, and devices. When SDN is used as an overlay, it becomes easier to identify and halt an attacker's traffic in the event of a network compromise.
• Efficiency and redundancy. When there is an overlay, traffic can change routes more quickly in response to network outages or traffic saturation.

Disadvantages of overlay networks

• Even with overlay networks' benefits, businesses should be aware of any potential drawbacks or difficulties, such as the following:
• There would be more managerial tiers. Every day, IT would have to oversee two distinct network layers. Above all, the layers have to work together to ensure that the underlay appropriately represents the topology that the overlay expects.
• Fixing issues. Once more, both the overlay and the underlay need to go through this.
• Possible breach of security. Misconfiguration can have detrimental repercussions on a larger group of people or devices.

Overlay network applications examples

Voice-over IP services, and non-native software-defined networks are a few instances of overlay network deployments. Here are some more overlay network applications and examples:

• VLAN or VXLAN. In order to generate logical segments for traffic routing, these networks are either created at Layer 2 or encapsulated with Layer 2.
• Virtual servers and hypervisors. In order to establish an overlay for communication, virtual networking generates virtual switches and virtual network cards.
• SD-WAN. To avoid hardcoding every communication to the connection, SD-WAN builds an overlay that controls a communication tunnel between two networks.
• By building a virtual overlay on top of network switches using protocols like OpenFlow, SDN allows the switches to undertake additional data routing tasks and improves data flow.

What distinguishes overlay networks from underlay networks?

An overlay network is constructed on top of another and uses that other network's infrastructure for support. By encasing one network packet inside another, an overlay network isolates network services from the supporting infrastructure. The encapsulated packet is de-encapsulated once it has been sent to the destination.

An underlay network: what is it?

The physical switches, routers, and other equipment that link nodes and route data between them make up an underlay network. For the physical conveyance of data, an underlay network uses a physical network media, such as fiber optic, copper wire, or even wireless.

An underlay is needed for any overlay to function. When it comes to traffic on roadways, the underlay is the actual street, while the overlay is the traffic signs, lights, and markings that guide vehicles. The road surface itself stays the same. However, one might alter the direction of traffic by altering the signs.

Routing Overlays:

The most basic type of overlay is one that doesn't carry out any extra application-level processing at the overlay nodes; instead, it exists only to support an alternative routing method. An example of a routing overlay but one that provides different routing table entries for the common IP forwarding algorithm to process rather than explicitly defining an alternate strategy or technique. In this instance, the overlay is referred to as using "IP tunnels," and many commercial routers support the use of these VPNs.

Let's say, then, that you want to utilize a routing method that the manufacturers of commercial routers were unwilling to integrate into their goods. How would you approach the task? You would have to tunnel through the Internet routers and run your algorithm on a group of end hosts. In the overlay network, these hosts would act similarly to routers: As hosts, they would likely have a single physical link connecting them to the Internet; however, as overlay nodes, they would have many tunnel connections to their neighbors.

We cannot cite any standard overlays as examples because overlays are, by definition, a means of introducing new technologies outside of the standardization process. Rather, we use a number of experimental systems constructed by network researchers to demonstrate the basic concept of routing overlays.

Experimental Versions of IP?

IP Overlays are perfect for implementing test versions of your IP that you hope will soon take over the world. For instance, many Internet routers still do not support IP multicast despite its origins as an extension of IP. Using IP multicast on top of the Internet's unicast routing, the MBone (multicast backbone) was an overlay network. Several multimedia conference technologies were created specifically for the Mbone and implemented there. For many years, for instance, the week-long IETF meetings, which drew thousands of attendees, were broadcast over the MBone. (Today, the MBone-based method has been supplanted by the widely accessible commercial conferencing solutions.)

Similar to VPNs, the MBone used IP tunnels and IP addresses, but it employed a different forwarding method, sending packets to every downstream neighbour in the multicast tree with the shortest path. In the hopes that older routers would eventually disappear, multicast-aware routers tunnel through them as an overlay.

An analogous overlay called 6-BONE was employed to roll out IPv6 gradually. Similar to the MBone, the 6-BONE routed packets across IPv4 routers via tunnels. However, 6-BONE nodes went beyond just offering an alternative interpretation of IPv4's 32-bit addresses, in contrast to the MBone. Rather, they used the 128-bit address space of IPv6 to route packets. The 6-BONE also supported IPv6 multicast. (Although commercial routers nowadays handle IPv6, overlays are still a useful strategy when a new technology is being tested and refined.)

Multicast at the End of the System

While IP multicast has widespread popularity among researchers and specific networking communities, its implementation on the global Internet has been, at most, restricted. End system multicast is an alternate tactic that multicast-based applications, such as videoconferencing, have recently adopted in response. Accepting that IP multicast will never become widely used, end-system multicast allows the end hosts to take part in a given multicast-based application to design their multicast trees.

Thus, end system multicast provides an abstract solution to the following issue: The objective is to locate the embedded multicast tree that spans all group members, starting with a fully linked graph that represents the Internet. Keep in mind that there is a more straightforward version of this issue made possible by the global accessibility of cloud-hosted virtual machines. Multiple locations may host virtual machines (VMs) that are aware of multicast. The actual end hosts can create a static multicast tree in the cloud and connect to the closest cloud location because these sites are well-known and largely fixed. However, the approach is described in its entirety in the following for thoroughness.

Overlay networks' salient features include:

Independence from the Underlying Infrastructure: Overlay networks function autonomously from the underlying physical network. This is known as independence from the underlying infrastructure. They don't need to modify the network architecture in order to be deployed on top of already existing networks.

• Virtualization: Virtualization of network resources is a common practice in overlay networks. This makes it possible to create virtual machines, virtual routers, and virtual switches inside the overlay, among other virtual network components.
• Encapsulation: Encapsulation is commonly used to facilitate communication within overlay networks. Packets or frames containing data are transmitted over the underlying network, logically separating the overlay network from the physical infrastructure.
• Security: Because overlay networks provide isolation and encryption, they can increase security.

Overlay networks are useful in many different contexts, such as:

• Cloud computing: Overlay networks are frequently used in cloud environments to facilitate communication between virtual machines and boxes.
• Content Delivery Networks (CDNs): CDNs efficiently deliver material across numerous servers or locations by utilizing overlay networks.

Overlay networks offer a strong and adaptable means of boosting network functionality, enhancing performance, and meeting particular needs in a variety of networking contexts.

Conclusion:

In Conclusion, overlay networks are essential to contemporary networking because they offer a scalable and adaptable means of addressing particular needs and enhancing network performance. These virtual networks create a logical separation between the overlay and the real network by utilising virtualization, tunnelling, and encapsulation to operate independently of the underlying infrastructure. This approach has many benefits, including enhanced scalability, flexibility, protection, and adaptability to shifting network requirements.

They play a crucial role in tackling the opportunities and difficulties brought about by new developments in the networking industry because of their agility and adaptability. Overlay networks are likely to stay an essential part of networking solutions as long as technology does, helping businesses meet the needs of a constantly evolving digital landscape and optimize their network infrastructures. Overlay networks offer a potent tool for building and administering contemporary networks, regardless of whether they are used in data centers, cloud settings, or dispersed systems.