stretch network

Network Stretch

Network Stretch

Network stretch refers to the capability of a network to extend its reach, connecting users and devices across geographical boundaries. This can be achieved through various technologies such as virtual private networks (VPNs), wide-area networks (WANs), or cloud-based networking solutions.

Network stretch goes beyond the traditional limitations of physical infrastructure and geographical boundaries. It refers to the ability of a network to expand, adapt, and connect diverse devices and systems across various locations. This flexibility allows for enhanced communication, collaboration, and access to resources.

Table of Contents

Highlights: Network Stretch

One of the critical advantages of network stretch is enhanced connectivity. By extending the network to different locations, businesses can seamlessly connect their employees, customers, and partners, regardless of location. This improves collaboration and communication and enables organizations to tap into new markets and expand their customer base.

End users perception

Defining and engineering the most optimal network path is critical to network architecture. The value of the network is most evident in the end users’ perception of application quality. Application quality and the perception of quality will vary from user to user. For example, one user may view a 5-second interrupt to a voice call as acceptable, while another could classify this as unacceptable. To maintain a high-quality perception for all users, you must engineer a packet to reach its destination as quickly as possible. This is where the concept of “network stretch” comes into play. 

Software-defined networking (SDN)

Software-defined networking (SDN) is a crucial technology driving network stretch. SDN enables centralized control and management of network infrastructure, making it easier to scale and extend networks across multiple locations. By decoupling the network control plane from the underlying hardware, SDN offers greater flexibility, agility, and scalability, making it an ideal solution for network stretch.

Virtual private network (VPN)

Another critical technology is virtual private networks (VPNs), which provide secure and encrypted connections over public networks. VPNs play a crucial role in network stretch by enabling organizations to connect their various locations and remote workers securely. By utilizing VPNs, businesses can ensure that their data remains protected while allowing employees to access company resources anywhere in the world.

Related: For pre-information, you may find the following useful:

  1. Observability vs Monitoring
  2. Virtual Device Context
  3. Redundant Links
  4. SDN Data Center
  5. LISP Hybrid Cloud
  6. Ansible Architecture

 

Back to Basics: Network Stretch

Deploying Stretched VLANs/LAN Extensions

Migration of virtual machines to another data center is critical for virtual workload mobility. Conversely, virtual machines and their applications can still communicate and be identified on the network, and services can continue to run.

Stretched VLANs are typically required for this to work. VLANs that span multiple physical data centers are called stretched VLANs. A Layer 3 WAN SDN connects locations in multisite data center topologies. This is the most straightforward configuration that removes a lot of complex considerations from the environment.

A native Layer 3 environment requires migrated devices to change their IP addresses to match the addressing scheme at the other site, or all resources on the VLAN subnet must be moved at once. This approach severely restricts the ability to move resources from one site to another and does not provide flexibility.

It is, therefore, necessary to implement stretched VLANs to facilitate live migration over distance since they can extend beyond a single site and enable resources to communicate as if they were local.

Stretched VLAN
Diagram: Stretch VLAN. The source is VMware.

Network modularity. Different designs and approaches.

Layered hub-and-spoke topologies are more widely used because they provide better network convergence than ring topologies. What about building a full mesh of modules?

Although a full mesh design might work well for a network with a small set of modules, it does not have stellar scaling characteristics because it requires an additional (and increasingly more extensive) set of ports and links for each module added to the network. 

Additionally, full mesh designs don’t lend themselves to efficient policy implementation; each link between every pair of modules must have policy configured and managed, a job that can become demanding as the network expands.

network modularity
Diagram: Network modularity. Source is Networkdirection

The Value of Network Modularity

Modular network design is an approach to architecture that divides the entire network into small, independent units or modules. These modules can be connected to form a larger network, enabling organizations to create a custom network tailored to their specific needs. Organizations can customize their network using modular network design to meet performance and scalability requirements while providing a cost-effective solution.

The value of a stretch network is that it’s modular and can affect only certain network parts. Therefore, you can design around it its concept. A modular network separates the network into various functional modules consisting of network functions, each targeting a specific place or purpose in the network.

This brings a lot of value from a security and performance perspective. In a leaf and spine data center design, you could consider a network module, a pod, or a group of pods. So the stretched network concepts must be first addressed in the network design with a bird’s eye view.

Network Stretch and Route Path Selection

Network stretch is the difference between the best possible path and the actual path the traffic takes through the network. The concept of stretched network relates to both Layers 2 and 3.

For instance, if the shortest actual path available is 2 hops, but the traffic follows a 3-hop path, the stretch is 1. An increase in network stretch always represents sub-optimal use of available resources. To fully understand the concept of network stretch, first, consider the basics of route path selection and route aggregation.

stretch network
Diagram: The basics of routing: Destination-based routing.

The proceeding diagram illustrates the basics of routing. We have 3 routers in the network topology. Router 1 has two outbound connections—one connection to Router 2 and another to Router 3, each with different routing metrics. Routers 1 to Router 2 cost 10, and Router 1 to Router 3 cost 20. Destination-based routing for the same prefix length always prefers a path with a lower cost, resulting in traffic following the path to Router 2.

Route path selection

One of the critical aspects of a router’s functionality is its ability to determine the most efficient route for these packets. This process, known as route path selection, ensures data is transmitted optimally and reliably.

    • Factors Influencing Route Path Selection:

1. Network Topology:

The underlying network topology significantly impacts the route path selection process. Routers have a routing table containing information about the available paths to different destinations. Based on this information, a router determines the best path to forward packets. Factors such as the number of hops, link capacity, and network congestion are considered to ensure efficient data transmission.

2. Administrative Distance:

Administrative distance is a metric routers use to determine the reliability of a particular routing protocol or source. A numerical value is assigned to each forwarding routing protocols, indicating its preference level. With multiple routing protocols or sources, the router selects the one with the lowest administrative distance. For example, a router might prefer a directly connected network over a network learned through a dynamic routing protocol.

3. Routing Metrics:

Routing metrics are used to quantify the performance characteristics of a route. Different routing protocols utilize various metrics to determine the best path. Standard metrics include hop count, bandwidth, delay, reliability, and load. By analyzing these metrics, routers can select the most suitable path based on the network requirements and priorities.

    • Routing Algorithms:

1. Shortest Path First (SPF) Algorithm:

The SPF algorithm, Dijkstra’s algorithm, is widely used for route path selection. It calculates the shortest path between the source and destination based on the link costs. The algorithm maintains a routing table that stores the shortest path to each destination. By iteratively updating the routing table, routers can dynamically adapt to changes in the network topology.

2. Border Gateway Protocol (BGP):

BGP is a routing protocol used in large-scale networks like the Internet. Unlike interior routing protocols, BGP focuses on inter-domain routing. BGP routers exchange routing information to determine the best path for data transmission. BGP considers path length, AS (Autonomous System) path, and routing policies to select routes.

Video: Discussing Routing Convergence

What is Routing Convergence?

Routing convergence refers to the process by which routers in a network exchange information and update their routing tables to reflect changes in network conditions. It involves timely disseminating routing updates, recalculating optimal paths, and restoring connectivity after a topology change, such as a link failure or adding new routes.

Routing convergence is critical in ensuring efficient network communication by enabling routers to quickly adapt to network topology changes. This video will delve into routing convergence, its significance in network infrastructure, and how it affects overall performance and reliability.

Routing Convergence
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Route aggregation

Next, we have route aggregation. Route summarization — also known as route aggregation — is a method to minimize the number of routing tables in an IP network. It consolidates selected multiple routes into a single route advertisement. The route serves two purposes in the network. 

  1. Breaking the network into multiple failure domains and
  2. Reducing the amount of information the routing protocol must deal with when converging.

In our case, Router 1 must install all individual routes without route aggregation, including metrics, tags, and other information. The best path to reach a particular destination must be calculated every time there is a change in the topology.

Route aggregation is crucial in simplifying the routing process and optimizing network performance in networking. By consolidating multiple network routes into a single entry, route aggregation reduces the size of routing tables, improves scalability, and enhances overall network efficiency. In this blog post, we will explore the concept of route aggregation, its benefits, and its implementation in modern networking environments.

Lab guide: EIGRP Summary Address

In the following lab guide, we have a DMVPN network.  R11 is the hub, and R31 and R41 are the spokes. We are running EIGRP over the DMVPN tunnel, which is a mGRE tunnel. EIGRP has been configured to send a summary route to the spoke sites.

Notice below in the screenshot that after the configuration, we have a Null0 route on the hub where the summarization was configured, and also, the spokes now only have one route, i.e., the summary route, in their routing tables.

Remember that when you have a Hub and Spoke topology and a Distant Vector protocol, we have issues with Split Horizon at the hub site. However, as we are sending a summary route from the Hub, this is not an issue.

EIGRP Summary Address
Diagram: EIGRP Summary Address

What is Route Aggregation?

Route aggregation, also known as route summarization or supernetting, is a technique used to consolidate multiple network routes into a more concise representation. Instead of advertising individual routes, network administrators can advertise a summarized route, which encompasses several smaller routes. This consolidation allows routers to make more efficient routing decisions, reducing the complexity of routing tables.

Benefits of Route Aggregation:

1. Reduced Routing Table Size: One of the primary advantages of route aggregation is the significant reduction in routing table size. By summarizing multiple routes into a single entry, the number of entries in the routing table is significantly reduced, leading to faster routing lookups and improved scalability.

2. Enhanced Network Efficiency: With smaller routing tables, routers can process routing updates more quickly, improving network efficiency. The reduced size of routing tables also reduces memory and processing requirements, enabling routers to handle higher traffic loads without performance degradation.

3. Improved Convergence: Route aggregation helps to improve network convergence, which refers to the time it takes for routers to reach a consistent view of the network topology after a change occurs. The convergence process is expedited by consolidating routes, as routers have fewer individual routes to process and update.

4. Enhanced Security: Using route aggregation, network administrators can help protect network resources by concealing internal network details. By advertising summarized routes instead of specific routes, it becomes more challenging for potential attackers to gain insight into the network’s internal structure.

Implementation of Route Aggregation:

Route aggregation can be implemented using various routing protocols, such as Border Gateway Protocol (BGP) and Open Shortest Path First (OSPF). These protocols allow network administrators to configure route summarization at specific points within the network, optimizing routing efficiency.

Balancing summarizing routes too aggressively and maintaining the necessary network granularity level is essential when implementing route aggregation. Over-aggregation can lead to suboptimal routing decisions and potential connectivity issues. Network administrators must carefully design and configure route aggregation to ensure optimal performance.

Video: IP Routing

The following video discusses the role of IP forwarding in networking. We will start by discussing switches and VLANs and then move to the basics of IP forwarding. So, we have networks that are broken down into different VLANs. So, we will have a group of switches linked together via trunk ports that provide connectivity for VLANs across different physical distances. The routers are used to route between different subnets.

IP Forwarding
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Route Aggregation: A networking technique

Route aggregation is a networking technique that reduces the number of routes in a routing table. It is based on summarizing multiple IP addresses into a single IP address prefix. The technique reduces the size of routing tables, thereby reducing the memory and bandwidth required for network communication.

Route aggregation is also known as route summarization or supernetting. Route aggregation groups multiple IP addresses into a single IP address prefix. This is done by selecting a typical bit pattern between the IP addresses and replacing that bit pattern with a single value. This allows for a reduction in the number of routes, which reduces the total memory and bandwidth requirements for the router.

Route aggregation can be used in both interior and exterior routing protocols. In internal protocols, the router can use route aggregation to reduce the number of routes in the routing table, thus reducing the total memory and bandwidth requirements.

In exterior protocols, route aggregation can reduce the number of routes sent to other network routers. This reduces the overall network traffic and the time it takes for the routing information to be propagated throughout the network.

Route aggregation and performance problems

This can cause performance problems, especially if you have a high rate of state change and a large number of routes in the network. Whenever the network topology changes, the router’s control plane must go through the convergence process steps ( detect, describe, switch, find ) and recalculate the best path to the affected destinations. If the rate of change is faster than the control plane can calculate new best paths, the network will never converge. One method used to overcome this is Route Aggregation.

Route aggregation creates separate failure domains and boundaries in the network. Routing nodes on different sides of the boundary will not query each other. It is essentially slicing the network. In addition, if a specific link frequently alternates between Up and Down states, the links uninvolved in the route summarization will not be affected. This prevents route flapping and improves network stability.

Route aggregation example:

So, in summary, route aggregation lets you take several specific routes and combine them into one inclusive route. As a result, route aggregation can reduce the number of routes a given protocol advertises. This is because the aggregates are activated by contributing routes. The routing protocols will have different route aggregation methods, such as in OSPF. When an ABR sends routing information to other areas, it originates Type 3 LSAs for each network segment.

If any contiguous segments exist in this area, run the abr-summary command to summarize these segments into one. An ABR then sends just one summarized LSA to other areas and no LSAs that belong to the summarized network segment specified by this command. Therefore, the routing table size is reduced, and router performance is improved. The critical point in the diagram below is the two separate failure domains. Failure domains A and B. 

route aggregation
Diagram: Route aggregation.

State versus stretch

This has benefits and drawbacks in that packets can follow a less optimal path to reach their destination. When you summarize at the edge of the network, the receiving router loses complete network visibility, which can cause an increase in network stretch in some cases. What happens to traffic entering Router 1 and traveling to destination 192.168.1.1/24?

route summarization
Diagram: The issues of route summarization.

Loss of visibility and state results in suboptimal traffic flow

Without aggregation on Router 3, this traffic would flow to Router 1 – Router 3 – Router 6. However, with route aggregation configured on both Router 2 and Router 3, this traffic will take the path with the better cost, Router 1 – Router 2 – Router 3 – Router 6, increasing one hop. As a result, the path from Router 1 to reach the destination 192.168.1.1/24 has stretched by one hop – or the stretch of the network has increased by 1.

Understanding Suboptimal Traffic Flow:

Suboptimal traffic flow is when data packets transmitted through routers take longer than necessary to reach their destination. This issue arises due to the complex nature of router operations, congestion, and routing protocols. Simply put, the path the data packets take is inefficient, resulting in delays, packet loss, and even degraded network performance.

    • Causes of Suboptimal Traffic Flow:

Several factors contribute to the suboptimal traffic flow in routers. One significant factor is the inefficient routing algorithms employed by routers. These algorithms determine the best path for data packets to travel through a network. However, due to limitations in these algorithms, they may choose suboptimal paths, such as congested or longer routes, resulting in delays.

Another cause of suboptimal traffic flow is network congestion. Conger occurs when multiple devices are connected to a router, and the data traffic exceeds capacity. This congestion leads to packet loss, increased latency, and inefficient traffic flow.

    • Impact on Online Experiences:

The suboptimal traffic flow in routers can significantly impact our online experiences. Slow-loading web pages, buffering videos, and laggy online gaming sessions are just a few examples. Beyond these inconveniences, businesses relying on efficient data transfer may suffer from decreased productivity and customer dissatisfaction. It is, therefore, crucial to address this issue to ensure a seamless online experience for all users.

    • Solutions to Improve Traffic Flow:

There are several approaches to improve the suboptimal traffic flow in routers. One solution is investing in routers with advanced algorithms that optimize the path selection process. These algorithms can consider network congestion, latency, and packet loss to choose the most efficient route for data packets.

Additionally, implementing Quality of Service (QoS) techniques can help prioritize critical traffic, ensuring that it receives higher bandwidth and lower latency. By giving priority to time-sensitive applications such as video streaming or VoIP calls, QoS can significantly improve the overall traffic flow.

Regular router maintenance and firmware updates are also crucial to maintaining optimal traffic flow. By keeping the router’s software up to date, manufacturers can address any known issues and improve the overall performance and efficiency of the device.

    • Network Performance and CDN

Moreover, network performance can be impacted when stretching the network over long distances. Latency and bandwidth limitations can affect the user experience, particularly for applications that require real-time data transmission. To overcome these challenges, businesses must carefully design their network architecture, leveraging technologies like content delivery networks (CDNs) and edge computing.

    • State reduction ( blocking links ) costs increase the stretch. 

Consider the example of Spanning Tree about state/stretch trade-offs and spanning tree works by selecting one switch as the tree’s root and selecting specific links within the tree structure to forward towards the root. This reduces the state to an absolute minimum by forcing all traffic along a single tree and blocking redundant links that don’t belong to that Tree. However, the state reduction ( blocking links ) costs increase the stretch through the network to the maximum possible.

This has led to the introduction of THRILL and Cisco’s FabricPath. These technologies allow you to have active/active paths, thereby increasing the state of the network while decreasing the stretch. When examining the data center transition, the default way to create scalable designs for Layers 2 and 3 is to have an overlay, such as VXLAN. Layer 2 and 3 traffic is differentiated with the VNI of the VXLAN header. All of these operate over a routed Layer 3 underlay.

VXLAN Benefits
VXLAN Benefits: Scale and loop-free networks.

A closing point on the stretch network

You can’t hide state information constantly, as it decreases the network’s overall efficiency by increasing the stretch. However, if all your traffic flows north/south, decreasing the state will not impact the stretch, as the traffic can only follow one direction. But if you have a combination of traffic patterns ( north/south & east/west ), reducing the state will cause traffic to take a sub-optimal path through the network – thus increasing the stretch.

 

Summary: Network Stretch

In this fast-paced digital age, the concept of network stretch has emerged as a game-changer. Network stretch refers to expanding and optimizing networks to meet the increasing demands of connectivity. This blog post explored the various aspects of network stretch and how it can revolutionize how we connect and communicate.

Section 1: Understanding Network Stretch

Network stretch is more than just expanding physical infrastructure. It involves leveraging advanced technologies, such as software-defined networking (SDN) and network function virtualization (NFV), to enhance network capabilities. Organizations can achieve scalability, flexibility, and improved performance by embracing network stretch.

Section 2: The Benefits of Network Stretch

Network stretch offers a myriad of benefits. Firstly, it enables seamless connectivity across various locations, allowing businesses to expand their reach without compromising network performance. Secondly, it enhances disaster recovery capabilities by creating redundant pathways and ensuring business continuity. Lastly, network stretch empowers organizations to adopt cloud-based services and leverage the Internet of Things (IoT) power.

Section 3: Implementing Network Stretch Strategies

Implementing network stretch requires careful planning and execution. Organizations need to assess their current network infrastructure, identify areas for improvement, and leverage technologies like SDN and NFV. Working with experienced network providers can also help design and deploy robust network stretch solutions tailored to specific business needs.

Section 4: Overcoming Challenges

While network stretch offers immense potential, it comes with its own challenges. Ensuring security across stretched networks becomes paramount, as it involves a broader attack surface. Proper encryption, authentication protocols, and network segmentation are crucial to mitigate risks. Additionally, organizations must address potential latency issues and ensure seamless integration with existing network infrastructure.

Conclusion:

In conclusion, network stretch presents a remarkable opportunity for organizations to unlock new connectivity, scalability, and performance levels. By embracing advanced technologies and implementing sound strategies, businesses can revolutionize their networks and stay ahead in the digital era. Whether expanding geographical reach, improving disaster recovery capabilities, or embracing emerging technologies, network stretch is the key to a more connected future.

Matt Conran
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