Dynamic Workload Scaling

Dynamic Workload Scaling ( DWS )



Dynamic Workload Scaling ( DWS ) 

In today’s fast-paced digital landscape, businesses strive to deliver high-quality services while minimizing costs and maximizing efficiency. To achieve this, organizations are increasingly adopting dynamic workload scaling techniques. This blog post will explore the concept of dynamic workload scaling, its benefits, and how it can help businesses optimize their operations.

  • Adjustment of resources

Dynamic workload scaling refers to the automated adjustment of computing resources to match the changing demands of a workload. This technique allows organizations to scale their infrastructure up or down in real time based on the workload requirements. By dynamically allocating resources, businesses can ensure that their systems operate optimally, regardless of varying workloads.

  • Defined Thresholds

Dynamic workload scaling is all about monitoring and distributing traffic at user-defined thresholds. Data centers are under pressure to support the ability to burst new transactions to available Virtual Machines ( VM ). In some cases, the VMs used to handle the additional load will be geographically dispersed, with both data centers connected by a Data Center Interconnect ( DCI ) link. The ability to migrate workloads within an enterprise hybrid cloud or in a hybrid cloud solution between enterprise and service provider is critical for business continuity for planned and unplanned outages.


Before you proceed, you may find the following post helpful:

  1. Network Security Components
  2. Virtual Data Center Design
  3. How To Scale Load Balancer
  4. Distributed Systems Observability
  5. Active Active Data Center Design
  6. Cisco Secure Firewall


Dynamic Workloads

Key Dynamic Workload Scaling Discussion Points:

  • Introduction to Dynamic Workload Scaling and what is involved.

  • Highlighting the details of dynamic workloads and how they can be implemented.

  • Critical points on how Cisco approaches Dynamic Workload Scaling.

  • A final note on design considerations.


Back to basics with OTV.

Overlay Transport Virtualization (OTV) is an IP-based technology to provide a Layer 2 extension between data centers. OTV is transport agnostic, indicating that the transport infrastructure between data centers can be dark fiber, MPLS, IP routed WAN, ATM, Frame Relay, etc.

The sole prerequisite is that the data centers must have IP reachability between them. OTV permits multipoint services for Layer 2 extension and separated Layer 2 domains between data centers, maintaining an IP-based interconnection’s fault-isolation, resiliency, and load-balancing benefits.

Unlike traditional Layer 2 extension technologies, OTV introduces the Layer 2 MAC routing concept. The MAC-routing concept enables a control-plane protocol to advertise the reachability of Layer 2 MAC addresses. As a result, the MAC-routing idea has enormous advantages over traditional Layer 2 extension technologies that traditionally leveraged data plane learning, flooding Layer 2 traffic across the transport infrastructure.


Cisco and Dynamic Workloads

A new technology introduced by Cisco, called Dynamic Workload Scaling ( DWS ), satisfies the requirement of dynamically bursting workloads based on user-defined thresholds to available resource pools ( VMs ). It is tightly integrated with Cisco Application Control Engine ( ACE ) and Cisco’s Dynamic MAC-in-IP encapsulation technology known as Overlay Transport Virtualization ( OTV ), enabling resource distribution across Data Center sites. OTV provides the LAN extension method that keeps the virtual machine’s state as it passes locations, and ACE delivers the load-balancing functionality.


dynamic workloads
Dynamic workload and dynamic workload scaling.


Dynamic workload scaling: How does it work?  

  • DWS monitors the VM capacity for an application and expands that application to another resource pool during periods of peak usage. We provide a perfect solution for distributed applications among geographically dispersed data centers.
  • DWS uses the ACE and OTV technologies to build a MAC table. It monitors the local MAC entries and those located via the OTV link to determine if a MAC entry is considered “Local” or “Remote.”
  • The ACE monitors the utilization of the “local” VM. From these values, the ACE can compute the average load of the local Data Center.
  • DWS uses two APIs. One is to monitor the server load information polled from VMware’s VCenter, and another API is to poll OTV information from the Nexus 7000.
  • During normal load conditions, when the data center is experiencing low utilization, the ACE can load incoming balance traffic to the local VMs.
  • However, when the data center experiences high utilization and crosses the predefined thresholds, the ACE will add the “remote” VM to its load-balancing mechanism.
workload scaling
Workload scaling and its operations.


Dynamic workload scaling: Design considerations

During congestion, the ACE adds the “remote” VM to its load-balancing algorithm. The remote VM placed in the secondary data center could add additional load on the DCI. Essentially hair-pining traffic for some time as ingress traffic for the “remote” VM continues to flow via the primary data center. DWS should be used with Locator Identity Separation Protocol ( LISP ) to enable automatic move detection and optimal ingress path selection.


Benefits of Dynamic Workload Scaling:

1. Improved Efficiency:

Dynamic workload scaling enables businesses to allocate resources precisely as needed, eliminating the inefficiencies associated with over-provisioning or under-utilization. Organizations can optimize resource utilization and reduce operational costs by automatically scaling resources up during periods of high demand and scaling them down during periods of low demand.

2. Enhanced Performance:

With dynamic workload scaling, businesses can effectively handle sudden spikes in workload without compromising performance. Organizations can maintain consistent service levels and ensure smooth operations during peak times by automatically provisioning additional resources when required. This leads to improved customer satisfaction and retention.

3. Cost Optimization:

Traditional static infrastructure requires businesses to provision resources based on anticipated peak workloads, often leading to over-provisioning and unnecessary costs. Dynamic workload scaling allows organizations to provision resources on demand, resulting in cost savings by paying only for the resources utilized. Additionally, by scaling down resources during periods of low demand, businesses can further reduce operational expenses.

4. Scalability and Flexibility:

Dynamic workload scaling allows businesses to scale their operations as needed. Whether expanding to accommodate business growth or handling seasonal fluctuations, organizations can easily adjust their resources to match the workload demands. This scalability and flexibility enable businesses to respond quickly to changing market conditions and stay competitive.

Dynamic workload scaling has emerged as a crucial technique for optimizing efficiency and performance in today’s digital landscape. By dynamically allocating computing resources based on workload requirements, businesses can improve efficiency, enhance performance, optimize costs, and achieve scalability. Implementing robust monitoring systems, automation, and leveraging cloud computing services are critical steps toward successful dynamic workload scaling. Organizations can stay agile and competitive and deliver exceptional customer service by adopting this approach.

Key Features of Cisco Dynamic Workload Scaling:

Intelligent Automation:

Cisco’s dynamic workload scaling solutions leverage intelligent automation capabilities to monitor real-time workload demands. By analyzing historical data and utilizing machine learning algorithms, Cisco’s automation tools can accurately predict future workload requirements and proactively scale resources accordingly.

Application-Aware Scaling:

Cisco’s dynamic workload scaling solutions are designed to understand the unique requirements of different applications. By utilizing application-aware scaling, Cisco can allocate resources based on the specific needs of each workload, ensuring optimal performance and minimizing resource wastage.

Seamless Integration:

Cisco’s dynamic workload scaling solutions seamlessly integrate with existing IT infrastructures, allowing businesses to leverage their current investments. This ensures a smooth transition to dynamic workload scaling without extensive infrastructure overhauls.


In today’s dynamic business environment, efficiently managing and scaling workloads is critical for organizational success. Cisco’s dynamic workload scaling solutions provide businesses with the flexibility, performance optimization, and cost savings necessary to thrive in an ever-changing landscape. By leveraging intelligent automation, application-aware scaling, and seamless integration, Cisco empowers organizations to adapt and scale their workloads effortlessly. Embrace Cisco’s dynamic workload scaling and unlock the full potential of your business operations.


LISP networking

LISP Protocol and VM Mobility


vm mobility


LISP Protocol and VM Mobility

The networking world is constantly evolving, with new technologies emerging to meet the demands of an increasingly connected world. One such technology that has gained significant attention is the LISP protocol. In this blog post, we will delve into the intricacies of the LISP protocol, exploring its purpose, benefits, and how it bridges the gap in modern networking and its use case with VM mobility.

  • What is LISP?

LISP, which stands for Locator/ID Separation Protocol, is a network protocol that separates the identity of a device from its location. Unlike traditional IP addressing schemes, which rely on a tightly coupled relationship between the IP address and the device’s physical location, LISP separates these two aspects, allowing for more flexibility and scalability in network design.

  • How Does LISP Work

Locator Identity Separation Protocol ( LISP ) provides a set of functions that allow Endpoint identifiers ( EID ) to be mapped to an RLOC address space. The mapping between these two endpoints offers the separation of IP addresses into two numbering schemes ( similar to the “who” and the “where” analogy ), offering many traffic engineering and IP mobility benefits for the geographic dispersion of data centers beneficial for VM mobility.

  • LISP Components

The LISP protocol operates by creating a mapping system that separates the device’s identifier, the Endpoint Identifier (EID), from its location, the Routing Locator (RLOC). This separation is achieved using a distributed database called the LISP Mapping System (LMS), which maintains the mapping between EIDs and RLOCs. When a packet is sent to a destination EID, it is encapsulated and routed based on the RLOC, allowing for efficient and scalable communication.


Before you proceed, you may find the following posts helpful:

  1. LISP Hybrid Cloud 
  2. LISP Control Plane
  3. Triangular Routing
  4. Active Active Data Center Design
  5. Application Aware Networking


VM Mobility

Key LISP Protocol Discussion Points:

  • Introduction to the LISP Protocol and what is involved.

  • Highlighting the details of the LISP traffic flow.

  • Technical details on LAN extension considerations. 

  • LISP Extended Subnet and Across Subnet.


  • A key point: Video on LISP configuration.

In this video, we will have a look at LISP configuration. This can be considered the first step before you get into the more advanced features of LISP and VM mobility. From its inception, the LISP protocol has been an open standard protocol that interoperates across various platforms and is incrementally deployable on top of any transport.

LISP’s flexibility has led to its application in every part of today’s modern network, from the data center to the enterprise WAN to the enterprise campus to the service provider edge and the core. The following will help you understand a LISP hybrid cloud implementation.



Back to basics with the Virtual Machine (VM).


Virtualization can be applied to subsystems such as disks and a whole machine. A virtual machine (VM) is implemented by adding a software layer to an actual device to sustain the desired virtual machine’s architecture. In general, a virtual machine can circumvent real compatibility and hardware resource limitations to enable a more elevated degree of software portability and flexibility.

n the dynamic world of modern computing, the ability to seamlessly move virtual machines (VMs) between different physical hosts has become a critical aspect of managing resources and ensuring optimal performance. This blog post explores VM mobility and its significance in today’s rapidly evolving computing landscape.

VM mobility refers to transferring a virtual machine from one physical host to another without disrupting operation. This capability is made possible through virtualization technologies such as hypervisors, which enable the abstraction of hardware resources and allow multiple VMs to coexist on a single physical machine.

LISP and VM Mobility

The Locator/Identifier Separation Protocol (LISP) is an innovative networking architecture that decouples the identity (Identifier) of a device or VM from its location (Locator). By separating the two, LISP provides a scalable and flexible solution for VM mobility.

How LISP Enhances VM Mobility:

1. Improved Scalability:

LISP introduces a level of indirection by assigning Endpoint Identifiers (EIDs) to VMs. These EIDs act as unique identifiers, allowing VMs to retain their identity even when they are moved to different locations. This enables enterprises to scale their VM deployments without worrying about the limitations imposed by the underlying network infrastructure.

2. Seamless VM Mobility:

LISP simplifies moving VMs by abstracting the location information using Routing Locators (RLOCs). When a VM is migrated, LISP updates the mapping between the EID and RLOC, allowing the VM to maintain uninterrupted connectivity. This eliminates the need for complex network reconfigurations, reducing downtime and improving overall agility.

3. Load Balancing and Disaster Recovery:

LISP enables efficient load balancing and disaster recovery strategies by providing the ability to distribute VMs across multiple physical hosts or data centers. With LISP, VMs can be dynamically moved to optimize resource utilization or to ensure business continuity in the event of a failure. This improves application performance and enhances the overall resilience of the IT infrastructure.

4. Interoperability and Flexibility:

LISP is designed to be interoperable with existing network infrastructure, allowing organizations to gradually adopt the protocol without disrupting their current operations. It integrates seamlessly with IPv4 and IPv6 networks, making it a future-proof solution for VM mobility.


Basic LISP Traffic flow

A device ( S1 ) initiates a connection and wants to communicate with another external device ( D1 ). D1 is located in a remote network. S1 will create a packet with the EID of S1 as the source IP address and the EID of D1 as the destination IP address. As the packets flow to the network’s edge on their way to D1, it is met by an Ingress Tunnel Router ( ITR ).

The ITR maps the destination EID to a destination RLOC and then encapsulates the original packet with an additional header with the source IP address of the ITR RLOC and the destination IP address of the RLOC of an Egress Tunnel Router ( ETR ). The ETR is located on the remote site next to the destination device D1.

LISP protocol

The magic is how these mappings are defined, especially regarding VM mobility. There is no routing convergence, and any changes to the mapping systems are unknown to the source and destination hosts. We are offering complete transparency.


LISP Terminology

LISP namespaces:

LSP Name Component

LISP Protocol Description 

End-point Identifiers  ( EID ) Addresses

The EID is allocated to an end host from an EID-prefix block. The EID associates where a host is located and identifies endpoints. The remote host obtains a destination the same way it obtains a normal destination address today, for example through DNS or SIP. The procedure a host uses to send IP packets does not change. EIDs are not routable.

Route Locator ( RLOC ) Addresses

The RLOC is an address or group of prefixes that map to an Egress Tunnel Router ( ETR ). Reachability within the RLOC space is achieved by traditional routing methods. The RLOC address must be routable.


LISP site devices:

LISP Component

LISP Protocol Description 

Ingress Tunnel Router ( ITR )

An ITR is a LISP Site device that sits in a LISP site and receives packets from internal hosts. It in turn encapsulates them to remote LISP sites. To determine where to send the packet the ITR performs an EID-to-RLOC mapping lookup. The ITR should be the first-hop or default router within a site for the source hosts.

Egress Tunnel Router ( ETR )

An ETR is a LISP Site device that receives LISP-encapsulated IP packets from the Internet, decapsulates them, and forwards them to local EIDs at the site. An ETR only accepts an IP packet where the destination address is the “outer” IP header and is one of its own configured RLOCs. The ETR should be the last hop router directly connected to the destination.


LISP infrastructure devices:

LISP Component Name

LISP Protocol Description

Map-Server ( MS )

The map server contains the EID-to-RLOC mappings and the ETRs register their EIDs to the map server. The map-server advertises these, usually as an aggregate into the LISP mapping system.

Map-Resolver ( MR )

When resolving EID-to-RLOC mappings the ITRs send LISP Map-Requests to Map-Resolvers. The Map-Resolver is typically an Anycast address. This improves the mapping lookup performance by choosing the map-resolver that is topologically closest to the requesting ITR.

Proxy ITR ( PITR )

Provides connectivity to non-LISP sites. It acts like an ITR but does so on behalf of non-LISP sites.

Proxy ETR ( PETR )

Acts like an ETR but does so on behalf of LISP sites that want to communicate to destinations at non-LISP sites.


VM Mobility

LISP Host Mobility

LISP VM Mobility ( LISP Host Mobility ) functionality allows any IP address ( End host ) to move from its subnet to either a) a completely different subnet, known as “across subnet,” or b) to an extension of its subnet in a different location, known as “extended subnet” – while keeping its original IP address.

When the end host carries its own Layer 3 address to the remote site, and the prefix is the same as the remote site, it is known as an “extended subnet.” Extended subnet mode requires a Layer 2 LAN extension. On the other hand, when the end hosts carry a different network prefix to the remote site, it is known as “across subnets.” When this is the case, a Layer 2 extension is not needed between sites.


LAN extension considerations

LISP does not remove the need for a LAN extension if a VM wants to perform a “hot” migration between two dispersed sites. The LAN extension is deployed to stretch a VLAN/IP subnet between separate locations. LISP complements LAN extensions with efficient move detection methods and ingress traffic engineering.

LISP works with all LAN extensions – whether back-to-back vPC and VSS over dark fiber, VPLS, Overlay Transport Virtualization ( OTV ), or Ethernet over MPLS/IP. LAN extension best practices should still be applied to the data center edges. These include but are not limited to – End-to-end Loop Prevention and STP isolation.

A LISP site with a LAN extension extends a single site across two physical data center sites. This is because the extended subnet functionality of LISP makes two DC sites a single LISP site. On the other hand, when LISP is deployed without a LAN extension, a single LISP site is not extended between two data centers, and we end up having separate LISP sites.


LISP extended subnet

VM mobility
VM mobility: LISP protocol and extended subnets


The LAN extension technology must filter Hot Standby Router Protocol ( HSRP ) HELLO messages across the two data centers to avoid asymmetric traffic handling. This creates an active-active HSRP setup. HSRP localization optimizes egress traffic flows. LISP optimizes ingress traffic flows.

The default gateway and virtual MAC address must remain consistent in both data centers. This is because the moved VM will continue to send to the same gateway MAC address. This is accomplished by configuring the same HSRP gateway IP address and group in both data centers. When an active-active HSRP domain is used, re-ARP is not needed during mobility events.

The LAN extension technology must have multicast enabled to support the proper operation of LISP. Once a dynamic EID is detected, the multicast group IP addresses send a map-notify message by the xTR to all other xTRs. The multicast messages are delivered leveraging the LAN extension.


LISP across subnet 

VM mobility
VM mobility: LISP protocol across Subnets


LISP across subnets requires the mobile VM to access the same gateway IP address, even if they move across subnets. This will prevent egress traffic triangulation back to the original data center. This can be achieved by manually setting the vMAC address associated with the HSRP group to be consistent across sites.

Proxy ARP must be configured under local and remote SVIs to handle new ARP requests generated by the migrated workload correctly.
With this deployment, there is no need to deploy a LAN extension to stretch VLAN/IP between sites. This is why it is considered to address “cold” migration scenarios, such as Disaster Recovery ( DR ) or cloud bursting and workload mobility according to demands.


Benefits of LISP:

1. Scalability: By separating the identifier from the location, LISP provides a scalable solution for network design. It allows for hierarchical addressing, reducing the size of the global routing table and enabling efficient routing across large networks.

2. Mobility: LISP’s separation of identity and location mainly benefits mobile devices. As devices move between networks, their EIDs remain constant while the RLOCs are updated dynamically. This enables seamless mobility without disrupting ongoing connections.

3. Multihoming: LISP allows a device to have multiple RLOCs, enabling multihoming capabilities without complex network configurations. This ensures redundancy, load balancing, and improved network reliability.

4. Security: LISP provides enhanced security features such as cryptographic authentication and integrity checks, ensuring the integrity and authenticity of the mapping information. This helps in mitigating potential attacks, such as IP spoofing.

Applications of LISP:

1. Data Center Interconnection: LISP can interconnect geographically dispersed data centers, providing efficient and scalable communication between different locations.

2. Internet of Things (IoT): With the exponential growth of IoT devices, LISP offers an efficient solution for managing these devices’ addressing and communication needs, ensuring seamless connectivity in large-scale deployments.

3. Content Delivery Networks (CDNs): LISP can optimize content delivery by allowing CDNs to cache content closer to end-users, reducing latency and improving overall performance.


The LISP protocol is a revolutionary technology that addresses the challenges of scalability, mobility, multi-homing, and security in modern networking. Its separation of identity and location opens up new possibilities for efficient and flexible network design. With its numerous benefits and versatile applications, LISP is poised to play a pivotal role in shaping the future of networking.




lisp protocol

LISP networking

Data Center Design with Active Active design


data center design


Active Active Data Center Design

Data centers are vital in modern business operations, providing essential services such as web hosting, cloud computing, and data storage. However, many organizations have adopted redundant data centers with an active-active data center design to ensure their business operations remain uninterrupted during service outages or disruptions.

In today’s digital age, where businesses heavily rely on uninterrupted access to their applications and services, data center design plays a pivotal role in ensuring high availability. One such design approach is the active-active design, which offers redundancy and fault tolerance to mitigate the risk of downtime. In this blog post, we will explore the active-active data center design concept and its benefits.

  • Active Active data center design

Active-active data center design refers to the configuration where two or more data centers operate simultaneously, sharing the load and providing redundancy for critical systems and applications. Unlike traditional active-passive setups, where one data center operates in standby mode, the active-active design ensures that both are fully active and capable of handling the entire workload.


  • Redundant data centers

Redundant data centers are essentially two or more in different physical locations. This enables organizations to move their applications and data to another data center if they experience an outage. This also allows for load balancing and scalability, ensuring the organization’s services remain available.

Redundant data centers are generally located in geographically dispersed locations. This ensures that if one of the data centers experiences an issue, the other can take over, thus minimizing downtime. These data centers should also be connected via a high-speed network connection, such as a dedicated line or virtual private network, to allow seamless data transfers between the locations.


Before you proceed, you may find the following useful:

  1. Data Center Topologies
  2. LISP Protocol
  3. Data Center Network Design
  4. ASA Failover
  5. LISP Hybrid Cloud
  6. LISP Control Plane


Active active data center

Increased dependence on East-West traffic

Clustered Applications


Business Continuity

Workload Mobility


  • A key point: Video on LISP.

The following video gives you an overview of LISP and its functionality. We will discuss the Map Server and Map Resolver and the communication process on a LISP design network. A use case of LISP can be used to direct traffic for a functional, active active data center design enabling more efficient dynamic workload scaling.



Back to basics: Active-active Data Center Design Cisco.

At its core, an active active data center is based on fault tolerance, redundancy, and scalability principles. This means that the active data center should be designed to withstand any hardware or software failure, have multiple levels of data storage redundancy, and scale up or down as needed.

The data center also provides an additional layer of security. It is designed to protect data from unauthorized access and malicious attacks. It should also be able to detect and respond to any threats quickly and in a coordinated manner.

To ensure that the data center is functioning correctly, it is essential to have a comprehensive monitoring and management system in place. This system should be designed to track the performance of the data center, detect any problems, and provide the necessary alerting mechanisms. It should also provide insights into how the data center operates so that any necessary changes can be made.


Cisco validated design: Cisco active active data center design

Cisco has validated this design, which is freely available on the Cisco site. In summary, they have tested a variety of combinations such as VSS-VSS, VSS-vPV, and vPC-vPC and validated the design with 200 Layer 2 VLANs and 100 SVIs or 1000 VLANs and 1000 SVI with static routing.

At the time of writing, the M series for the Nexus 7000 supports native encryption of Ethernet frames through the IEEE 802.1AE standard. This implementation uses Advanced Encryption Standard ( AES ) cipher and a 128-bit shared key.


  • A key point: Lab guide on Cisco ACI

In the following lab guide, we demonstrate Cisco ACI. To extend Cisco ACI, we have different designs, for example, multi-site and multi-pod. This type of design overcomes many challenges of extending a data center that we will discuss in this post, such as the challenges of extending layer 2 networks.

One crucial value of the Cisco ACI is the COOP database that maps endpoints in the network. The following screenshots show the synchronized COOP database across spines, even in different data centers. Notice that the bridge domain VNID is mapped to the MAC address. The COOP database is unique to the Cisco ACI.


COOP database
Diagram: COOP database


The challenge: Layer 2 is weak.

The challenge of data center design is “Layer 2 is weak & IP is not mobile.” In the past, best practices recommended that networks from distinct data centers be connected through Layer 3 ( routing ), isolating the know Layer 2 turmoil. However, the business is driving the application requirements, changing the connectivity requirements between data centers. The need for active active data center has been driven by the following. It is generally recommended to have Layer 3 connections with path separation through Multi-VRF, P2P VLANs, or MPLS/VPN, along with a modular building block data center design.

Yet, some applications cannot function over a Layer 3 environment. For example, most geo clusters require Layer 2 adjacency between their nodes, whether for heartbeat and connection ( status and control synchronization ) state information or the requirement to share virtual IP.

MAC addresses to facilitate traffic handling in case of failure. However, some clustering products ( Veritas, Oracle RAC ) support communication over Layer 3 but are a minority and don’t represent the general case.


  • Defining active active data centers

The term active-active refers to using at least two data centers where both can service an application at any time, so each functions as an active application site. The demand for active-active data center architecture is to accomplish seamless workload mobility and enable distributed applications along with the ability to pool and maximize resources.  

We must first have active-active data center infrastructure for an active/active application setup. Remember that the network is just one key component of active/active data centers). An active-active DC can be divided into two halves from a pure network perspective:-

  1. Ingress Traffic – inbound traffic
  2. Egress Traffic – outbound traffic
active active data center
Diagram: Active active data center. Scenario. Source is twoearsonemouth


Active Active Data Center and VM Migration

Migrating applications and data to virtual machines (VMs) are becoming increasingly popular as organizations seek to reduce their IT costs and increase the efficiency of their services. VM migration moves existing applications, data, and other components from a physical server to a virtualized environment. This process is becoming increasingly more cost-effective and efficient for organizations, eliminating the need for additional hardware, software, and maintenance costs.

Virtual Machine migration between data centers increases application availability, Layer 2 network adjacency between ESX hosts is currently required, and a consistent LUN must be maintained for stateful migration. In other words, if the VM loses its IP address, it will lose its state, and the TCP sessions will drop, resulting in a cold migration ( VM does a reboot ) instead of a hot migration ( VM does not reboot ).

As a result of the stretched VLAN requirement, data center architects started to deploy traditional Layer 2 over the DCI and, unsurprisingly, were faced with exciting results. Although flooding and broadcasts are necessary for IP communication in Ethernet networks, they can become dangerous in a DCI environment.


  • Traffic tramboning

Traffic tromboning can also be formed between two stretched data centers, so nonoptimal internal routing happens within extended VLANs. Trombones, by their very nature, create a network traffic scalability problem. Addressing this through load balancing among multiple trombones is challenging since their services are often stateful.

Traffic tromboning can affect either ingress or egress traffic. On egress, you can have FHRP filtering to isolate the HSRP partnership and provide an active/active setup for HSRP. On ingress, you can have GSLB, Route Injection, and LISP.

Traffic Tramboning
Diagram: Traffic Tramboning. Source is Silvanogai


Cisco Active active data center design and virtualization technologies

To overcome many of these problems, virtualization technologies can be used for Layer 2 extensions between data centers. They include vPC, VSS, Cisco FabricPath, VPLS, OTV, and LISP with its Internet locator design. In summary, we have different technologies that can be used for LAN extensions, and the primary mediums in which they can be deployed are Ethernet, MPLS, and IP.

    1.  Ethernet: VSS and vPC or Fabric Path
    2. MLS: EoMPLS and A-VPLS and H-VPLS
    3.  IP: OTV
    4. LISP


Ethernet Extensions and Multi-Chassis EtherChannel ( MEC )

Requires protected DWDM or direct fibers and works between two data centers only. It cannot support multi-datacenter topology, i.e., a full mesh of data centers, but it can support hub and spoke topologies.

Previously, LAG could only terminate on one physical switch. Both VSS-MEC and vPC are port-channeling concepts extending link aggregation to two separate physical switches. This allows for creating L2 typologies based on link aggregation, eliminating the dependency on STP, thus allowing you to scale available Layer 2 bandwidth by bonding the physical links.

Because vPC and VSS create a single connection from an STP perspective, disjoint STP instances can be deployed in each data center. Such isolation can be achieved with BPDU Filtering on the DCI links or Multiple Spanning Tree ( MST ) regions on each site.

At the time of writing, vPC does not support Layer 3 peering, but if you want an L3 link, create one, as this does not need to run on dark fiber or protected DWDM, unlike the extended Layer 2 links.


Ethernet extension and Fabric path

The fabric path allows network operators to design and implement a scalable Layer 2 fabric allowing VLANs to help reduce the physical constraints on server location. It provides a high availability design with up to 16 active paths at layer 2, each path a 16-member port channel for Unicast and Multicast.

This enables the MSDC networks to have flat typologies, separating nodes by a single hop ( equidistant endpoints ). Cisco has not targeted Fabric Path as a primary DCI solution as it does not have specific DCI functions compared to OTV and VPLS.

Its primary purpose is for Clos-based architectures. But if you have the requirement to interconnect 3 or more sites, the Fabric path is a valid solution when you have short distances between your DCs via high-quality point-to-point optical transmission links.

Your WAN links must support Remote Port Shutdown and micro flapping protection. By default, OTV and VPLS should be the first solutions considered as they are Cisco-validated designs with specific DCI features, e.g., OTV can flood unknown unicast for specific VLANs.


Diagram: FabricPath. Source is Cisco


IP core with Overlay Transport Virtualization ( OTV ).

OTV provides a dynamic encapsulation with multipoint connectivity of up to 10 sites ( NX-OS 5.2 supports 6 sites, and NX-OS 6.2 supports 10 sites ). OTV, also known as Over-The-Top virtualization, is a specific DCI technology enabling Layer 2 extension across data center sites by employing a MAC in IP encapsulation with built-in loop prevention and failure boundary preservation.

There is no data plane learning. Instead, the overlay control plane ( Layer 2 IS-IS ) on the provider’s network facilitates all unicast and multicast learning between sites. OTV has been supported on the Nexus 7000 since the 5.0 NXOS Release and ASR 1000 since the 3.5 XE Release. OTV as a DCI has robust high availability, and most failures can be sub-sec convergence with only extreme and very unlikely failures such as device down resulting in <5 seconds.


Locator ID/Separator Protocol ( LISP)

Locator ID/Separator Protocol ( LISP) has a lot of applications and, as the name suggests, separates the location and the identifier of the network hosts, making it possible for VMs to move across subnet boundaries while still retaining their IP address enables advanced triangular routing designs.

LISP works well when you have to move workloads and also when you have to distribute workloads across data centers, making it a perfect complementary technology for an active-active data center design. It provides you with the following:

  • a) Global IP-Mobility across subnets for disaster recovery and cloud bursting ( without LAN extension ) and optimized routing across extended subnet sites.
  • b) Routing with Extended subnets for Active / Active data centers and distributed clusters ( with LAN extension).


LISP networking
Diagram: LISP Networking. Source is Cisco


LISP answers the problems with ingress and egress traffic tromboning. It has a location mapping table, so when a host move is detected, updates are automatically triggered, and ingress routers (ITRs or PITRs) send traffic to the new location. From an ingress path flow inbound on the WAN perspective, LISP can answer our little problems with BGP in controlling ingress flows. Without LISP, we are limited to specific route filtering, meaning if you have a PI Prefix consisting of a /16.

If you break this up and advertise into 4 x /18, you may still get poor ingress load balancing on your DC WAN links; even if you were to break this up to 8 x /19, the results might still be unfavorable.

LISP works differently than BGP because a LISP proxy provider would advertise this /16 for you ( you don’t advertise the /16 from your DC WAN links ) and send traffic at 50:50 to our DC WAN links. LISP can get a near-perfect 50:50 conversion rate at the DC edge.


Benefits of Active-Active Data Center Design:

1. Enhanced Redundancy: With active-active design, organizations can achieve higher levels of redundancy by distributing the workload across multiple data centers. This redundancy ensures that even if one data center experiences a failure or maintenance downtime, the other data center seamlessly takes over, minimizing the impact on business operations.

2. Improved Performance and Scalability: Active-active design enables organizations to scale their infrastructure horizontally by distributing the load across multiple data centers. This approach ensures that the workload is evenly distributed, preventing any single data center from becoming a performance bottleneck. It also allows businesses to accommodate increasing demands without compromising performance or user experience.

3. Reduced Downtime: The active-active design significantly reduces the risk of downtime compared to traditional architectures. In the event of a failure, the workload can be immediately shifted to the remaining active data center, ensuring continuous availability of critical services. This approach minimizes the impact on end-users and helps organizations maintain their reputation for reliability.

4. Disaster Recovery Capabilities: Active-active data center design provides a robust disaster recovery solution. By having multiple data centers geographically distributed, organizations can ensure that their critical systems and applications remain operational even in a catastrophic failure at one location. This design approach minimizes the risk of data loss and provides a seamless failover mechanism.

Implementation Considerations:

Implementing an active-active data center design requires careful planning and consideration of various factors. Here are some key considerations:

1. Network Design: A robust and resilient network infrastructure is crucial for active-active data center design. Implementing load balancers, redundant network links, and dynamic routing protocols can help ensure seamless failover and optimal traffic distribution.

2. Data Synchronization: Organizations need to implement effective data synchronization mechanisms to maintain data consistency across multiple data centers. This may involve deploying real-time replication, distributed databases, or file synchronization protocols.

3. Application Design: Applications must be designed to be aware of the active-active architecture. They should be able to distribute the workload across multiple data centers and seamlessly switch between them in case of failure. Application-level load balancing and session management become critical in this context.

Active-active data center design offers organizations a robust solution for high availability and fault tolerance. Businesses can ensure uninterrupted access to critical systems and applications by distributing the workload across multiple data centers. The enhanced redundancy, improved performance, reduced downtime, and disaster recovery capabilities make active-active design an ideal choice for organizations striving to provide seamless and reliable services in today’s digital landscape.


data center design