Typical Composition of Data Center Architecture

A data center architecture consists of three main components: the data center network, the data center security, and the data center computing architecture. In addition to these three types of architecture, there are also data center physical architectures and data center information architectures. The following are three typical compositions. Network architecture for data centers: Data center networks (DCNs) are arrangements of network devices interconnecting data center resources. They are a crucial research area for Internet companies and large cloud computing firms. The design of a data center depends on its network architecture.

It is common for routers and switches to be arranged in hierarchies of two or three levels. There are three-tier DCNs: fat tree DCNs, DCells, and others. There has always been a focus on scalability, robustness, and reliability regarding data center network architectures. Architecting data center security: Data center security refers to physical practices and virtual technologies for protecting data centers from threats, attacks, and unauthorized access. It can be divided into two components: physical security and software security. Setting up a firewall between a data center’s external and internal networks can protect it from attack.

Developing a data center network

A network serves applications’ connectivity requirements, and applications serve their organizations’ business needs. To design or operate a network in a modern data center, you must first understand the needs and topology of the data center. Here we begin our journey. My goal is for you to understand the network design of a modern data center network based on the applications’ needs and the size of the data center.

Compared to a decade ago, data centers now have much larger capacity, vastly different applications, and deployment speeds in seconds rather than days. As a result, network design and deployment change.

Border Gateway Protocol (BGP) is data centers’ most commonly used routing protocol. BGP has been used to connect Internet systems around the world for decades. It can also be used outside of a data center. The BGP protocol is a standard-based open-source software package. Its more common to find BGP peering between data centers over the WAN. However, these days we are seeing BGP often used purely inside the data center. 

Data Center Requirments

Google and Amazon, two of the world’s leading web-scale pioneers, developed a modern data center. The third wave of application architectures represents these organizations’ search and cloud applications. Towards the end of the 20th century, client-server architectures and monolithic single-machine applications dominated the landscape. This third wave of applications has three primary characteristics:

Unlike client-server architectures, modern data center applications involve a lot of communication between servers. In client-server architectures, clients communicate with monolithic servers, which either handle the request entirely themselves or communicate with fewer than a handful of other servers, such as database servers. Search (or Hadoop, its more popular variant) employs many mappers and reducers instead of search. In the cloud, virtual machines can reside on different nodes but must communicate seamlessly. In some cases, VMs are deployed on servers with the least load, scaled out, or balanced loads.

A microservices architecture also increases server-to-server communication. This architecture is based on separating a single function into smaller building blocks and interacting with them. Each block can be used in several applications and enhanced, modified, and fixed independently in such an architecture. Since diagrams usually show servers next to each other, East-West traffic is often called server communication. Traffic flows north-south between local networks and external networks.

Scale and resilience

The sheer size of modern data centers is characterized by rows and rows of dark, humming, blinking machines. As opposed to the few hundred or so servers of the past, a modern data center contains between a few hundred and a hundred thousand servers. To address the connectivity requirements at such scales, as well as the need for increased server-to-server connectivity, network design must be rethought. Unlike older architectures, modern data center applications assume failures as a given. Failures should be limited to the smallest possible footprint. Failures must have a limited “blast radius.” By minimizing the impact of network or server failures on the end-user experience, we aim to provide a stable and reliable experience.

Data Center Goal: Interconnect networks

The goal of data center design and interconnection network is to transport end-user traffic from A to B without any packet drops, yet the metrics we use to achieve this goal can be very different. The data center is evolving and progressing through various topology and technology changes, resulting in multiple network designs.  The new data center control planes we see today, such as Fabric Path, LISP, THRILL, and VXLAN, are driven by a change in the end user’s requirements; the application has changed. These new technologies may address new challenges, yet the fundamental question of where to create the Layer 2/Layer three boundaries and the need for Layer 2 in the access layer remains the same. The question stays the same, yet the technologies available to address this challenge have evolved.

Modern Data Centers

There is a vast difference between modern data centers and what they used to be just a few years ago. Physical servers have evolved into virtual networks that support applications and workloads across pools of physical infrastructure and into a multi-cloud environment. There are multiple data centers, the edge, and public and private clouds where data exists and is connected. Both on-premises and cloud-based data centers must be able to communicate. Data centers are even part of the public cloud. Cloud-hosted applications use the cloud provider’s data center resources.

Unified Fabric

Through Cisco’s fabric-based data center infrastructure, tiered silos and inefficiencies of multiple network domains are eliminated, and a unified, flat fabric is provided instead, which allows local area networks (LANs), storage area networks (SANs), and network-attached storage (NASs) to be consolidated into one high-performance, fault-tolerant network. Creating large pools of virtualized network resources that can be easily moved and rapidly reconfigured with Cisco Unified Fabric provides massive scalability and resiliency to the data center.

This approach automatically deploys virtual machines and applications, thereby reducing complexity. Thanks to deep integration between server and network architecture, secure IT services can be delivered from any device within the data center, between data centers, or beyond. In addition to Cisco Nexus switches, Cisco Unified Fabric uses Cisco NX-OS as its operating system.

The use of Open Networking

We also have the Open Networking Foundation ( ONF ), which provides open networking. Open networking describes a network that uses open standards and commodity hardware. So, consider open networking in terms of hardware and software. Unlike a vendor approach like Cisco, this gives you much more choice with what hardware and software you use to make up and design your network.

Related: Before you proceed, you may find the following useful:

1. ACI Networks
2. IPv6 Attacks
3. SDN Data Center
4. Active Active Data Center Design
5. Virtual Switch

The Rise of Overlay Networking

What has the industry introduced to overcome these limitations and address the new challenges? – Network virtualization and overlay networking. In its simplest form, an overlay is a dynamic tunnel between two endpoints that enables Layer 2 frames to be transported between them. In addition, these overlay-based technologies provide a level of indirection that allows switching table sizes to not increase in the order of the number of supported end hosts.

Today’s overlays are Cisco FabricPath, THRILL, LISP, VXLAN, NVGRE, OTV, PBB, and Shorted Path Bridging. They are essentially virtual networks that sit on top of a physical network, and often, the physical network is unaware of the virtual layer above it.

1st Lab Guide: VXLAN

The following lab guide displays a VXLAN network. We are running VXLAN in multicast mode. Multicast VXLAN is a variant of VXLAN that utilizes multicast-based IP multicast for transmitting overlay network traffic. VXLAN is an encapsulation protocol that extends Layer 2 Ethernet networks over Layer 3 IP networks.

Linking multicast enables efficient and scalable communication within the overlay network. Notice the multicast group of 239.0.0.10 and the route of 239.0.0.10 forwarding out the tunnel interface. We have multicast enabled on all Layer 3 interfaces, including the core that consists of Spine A and Spine B.

Traditional Data Center Network Design

How do routers create a broadcast domain boundary? Firstly, using the traditional core, distribution, and access model, the access layer is layer 2, and servers served to each other in the access layer are in the same IP subnet and VLAN. The same access VLAN will span the access layer switches for east-to-west traffic, and any outbound traffic is via a First Hop Redundancy Protocol ( FHRP ) like Hot Standby Router Protocol ( HSRP ).

Servers in different VLANs are isolated from each other and cannot communicate directly; inter-VLAN communications require a Layer 3 device. Virtualization’s humble beginnings started with VLANs, which were used to segment traffic at Layer 2. It was expected to find single VLANs spanning an entire data center fabric.

VLAN and Virtualization

The virtualization side of VLANs comes from two servers physically connected to different switches. Assuming the VLAN spans both switches, the same VLAN can communicate with each server. Each VLAN can be defined as a broadcast domain in a single Ethernet switch or shared among connected switches.

Whenever a switch interface belonging to a VLAN receives a broadcast frame ( destination MAC is ffff.ffff.ffff), the device must forward this frame to all other ports defined in the same VLAN.

This approach is straightforward in design and is almost like a plug-and-play network. The first question is, why not connect everything in the data center into one large Layer 2 broadcast domain? Layer 2 is a plug-and-play network, so why not? STP also blocks links to prevent loops.

 The issues of Layer 2

The reason is that there are many scaling issues in large layer 2 networks. Layer 2 networks don’t have controlled / efficient network discovery protocols. Address Resolution Protocol ( ARP ) is used to locate end hosts and uses Broadcasts and Unicast replies. A single host might not generate much traffic, but imagine what would happen if 10,000 hosts were connected to the same broadcast domain. VLANs span an entire data center fabric, which can bring a lot of instability due to loops and broadcast storms.

 No hierarchy in MAC addresses

MAC addressing also lacks hierarchy. Unlike Layer 3 networks, which allow summarization and hierarchy addressing, MAC addresses are flat. Adding several thousand hosts to a single broadcast domain will create large forwarding information tables.

Because end hosts are potentially not static, they are likely to be attached and removed from the network at regular intervals, creating a high rate of change in the control plane. Of course, you can have a large Layer 2 data center with multiple tenants if they don’t need to communicate with each other.

The shared services requirements, such as WAAS or load balancing, can be solved by spinning up the service VM in the tenant’s Layer 2 broadcast domain. This design will hit scaling and management issues. There is a consensus to move from a Layer 2 design to a more robust and scalable Layer 3 design.

But why is Layer 2 still needed in data center topologies? One solution is Layer 2 VPN with EVPN. But first, let us look at Cisco DFA.

Data Center Design and Cisco DFA

Cisco took a giant step and recently introduced a data center fabric with Dynamic Fabric Automaton ( DFA ), similar to Juniper QFabric. This fabric offers Layer 2 switching and Layer 3 routing at the access layer / ToR. Firstly, it has a Fabric Path ( IS-IS for Layer 2 connectivity ) in the core, which gives optimal Layer 2 forwarding between all the edges.

Then they configure the same Layer 3 address on all the edges, which gives you optimal Layer 3 forwarding across the whole Fabric.

On edge, you can have Layer 3 Leaf switches, for example, the Nexus 6000 series, or integrate with Layer 2-only devices like the Nexus 5500 series or the Nexus 1000v. You can also connect external routers or USC or FEX to the Fabric. In addition to running IS-IS as the data center control plane, DFA uses MP-iBGP, with some Spine nodes being the Route Reflector to exchange IP forwarding information.

Cisco FabricPath

DFA also employs a Cisco FabricPath technique called “Conversational Learning.” The first packet triggers a full RIB lookup, and the subsequent packets are switched in the hardware-implemented switching cache.

This technology provides Layer 2 mobility throughout the data center while providing optimal traffic flow using Layer 3 routing. Cisco commented, “DFA provides a scale-out architecture without congestion points in the network while providing optimized forwarding for all applications.”

Terminating Layer 3 at the access / ToR has clear advantages and disadvantages. Other benefits include reducing the size of the broadcast domain, which comes at the cost of reducing the mobility domain across which VMs can be moved.

Terminating Layer 3 at the accesses can also result in sub-optimal routing because there will be hair pinning or traffic tromboning of across-subnet traffic, taking multiple and unnecessary hops across the data center fabric.

The role of the Cisco Fabricpath

Cisco FabricPath is a Layer 2 technology that provides Layer 3 benefits, such as multipathing the classical Layer 2 networks using IS-IS at Layer 2. This eliminates the need for spanning tree protocol, avoiding the pitfalls of having large Layer 2 networks. As a result, Fabric Path enables a massive Layer 2 network that supports multipath ( ECMP ). THRILL is an IEEE standard that, like Fabric Path, is a Layer 2 technology that provides the same Layer 3 benefits as Cisco FabricPath to the Layer 2 networks using IS-IS.

LISP is popular in Active data centers for DCI route optimization/mobility. It separates the host’s location from the identifier ( EID ), allowing VMs to move across subnet boundaries while keeping the endpoint identification. LISP is often referred to as an Internet locator. 

That can enable some designs of triangular routing. Popular encapsulation formats include VXLAN ( proposed by Cisco and VMware ) and STT (created by Nicira but will be deprecated over time as VXLAN comes to dominate ).

The role of OTV

OTV is a data center interconnect ( DCI ) technology enabling Layer 2 extension across data center sites. While Fabric Path can be a DCI technology with dark fiber over short distances, OTV has been explicitly designed for DCI. In contrast, the Fabric Path data center control plane is primarily used for intra-DC communications.

Failure boundary and site independence are preserved in OTV networks because OTV uses a data center control plane protocol to sync MAC addresses between sites and prevent unknown unicast floods. In addition, recent IOS versions can allow unknown unicast floods for certain VLANs, which are unavailable if you use Fabric Path as the DCI technology.

The Role of Software-defined Networking (SDN)

Another potential trade-off between data center control plane scaling, Layer 2 VM mobility, and optimal ingress/egress traffic flow would be software-defined networking ( SDN ). At a basic level, SDN can create direct paths through the network fabric to isolate private networks effectively.

An SDN network allows you to choose the correct forwarding information per-flow basis. This per-flow optimization eliminates VLAN separation in the data center fabric. Instead of using VLANs to enforce traffic separation, the SDN controller has a set of policies allowing traffic to be forwarded from a particular source to a destination.

The ACI Cisco borrows concepts of SDN to the data center. It operates over a leaf and spine design and traditional routing protocols such as BGP and IS-IS. However, it brings a new way to manage the data center with new constructs such as Endpoint Groups (EPGs). In addition, no more VLANs are needed in the data center as everything is routed over a Layer 3 core, with VXLAN as the overlay protocol.

Closing Points: Data Center Design

Data centers are the backbone of modern technology infrastructure, providing the foundation for storing, processing, and transmitting vast amounts of data. A critical aspect of data center design is the network architecture, which ensures efficient and reliable data transmission within and outside the facility.  1. Scalability and Flexibility

One of the primary goals of data center network design is to accommodate the ever-increasing demand for data processing and storage. Scalability ensures the network can grow seamlessly as the data center expands. This involves designing a network that supports many devices, servers, and users without compromising performance or reliability. Additionally, flexibility is essential to adapt to changing business requirements and technological advancements.

Redundancy and High Availability

Data centers must ensure uninterrupted access to data and services, making redundancy and high availability critical for network design. Redundancy involves duplicating essential components, such as switches, routers, and links, to eliminate single points of failure. This ensures that if one component fails, there are alternative paths for data transmission, minimizing downtime and maintaining uninterrupted operations. High availability further enhances reliability by providing automatic failover mechanisms and real-time monitoring to promptly detect and address network issues.

Traffic Optimization and Load Balancing

Efficient data flow within a data center is vital to prevent network congestion and bottlenecks. Traffic optimization techniques, such as Quality of Service (QoS) and traffic prioritization, can be implemented to ensure that critical applications and services receive the necessary bandwidth and resources. Load balancing is crucial in evenly distributing network traffic across multiple servers or paths, preventing overutilization of specific resources and optimizing performance.

Security and Data Protection

Data centers house sensitive information and mission-critical applications, making security a top priority. The network design should incorporate robust security measures, including firewalls, intrusion detection systems, and encryption protocols, to safeguard data from unauthorized access and cyber threats. Data protection mechanisms, such as backups, replication, and disaster recovery plans, should also be integrated into the network design to ensure data integrity and availability.

Monitoring and Management

Proactive monitoring and effective management are essential for maintaining optimal network performance and addressing potential issues promptly. The network design should include comprehensive monitoring tools and centralized management systems that provide real-time visibility into network traffic, performance metrics, and security events. This enables administrators to promptly identify and resolve network bottlenecks, security breaches, and performance degradation.

Data center network design is critical in ensuring efficient, reliable, and secure data transmission within and outside the facility. Scalability, redundancy, traffic optimization, security, and monitoring are key considerations for designing a robust, high-performance network. By implementing best practices and staying abreast of emerging technologies, data centers can build networks that meet the growing demands of the digital age while maintaining the highest levels of performance, availability, and security.