In modern enterprise networks, the move towards software-defined wide area networking is not just a trend but a strategic necessity. Cisco SD-WAN with cEdge devices has emerged as a powerful solution to streamline WAN architectures, enabling flexibility, improved security, and operational efficiency. However, integrating cEdge routers into an existing network environment is not always straightforward. The success of such integration depends on several variables including site design, WAN transports, LAN topology, and high availability needs.
The Importance Of Planning Before Integration
Before any cEdge router is physically connected to a network, there are critical questions that must be answered. These questions shape the overall design and integration approach. First, you must determine whether the site demands high availability. This directly influences whether a single cEdge or a pair of cEdges will be deployed. Next, you need to assess the available WAN transports at the site, including how much IPv4 address space is allocated for each link. The LAN topology is another key consideration. Whether the LAN operates at layer 2 or layer 3 affects how routing will be handled post-deployment. Finally, it is essential to identify if WAN-bound traffic needs to pass through third-party appliances such as firewalls or WAN optimizers. Each of these factors will determine which deployment model is most suitable for the environment.
Single cEdge Deployment With Layer 2 LAN
For small branch sites or greenfield deployments, a single cEdge acting as a complete customer edge router is often the most practical design. In this setup, the cEdge terminates both WAN links directly, managing all routing responsibilities for the site. This method simplifies the architecture by eliminating the need for an upstream CE router. The cEdge becomes the focal point for both WAN and LAN traffic flows.
In this design, the WAN handoffs from service providers are often delivered with a /30 IPv4 prefix for each transport. These subnets are assigned to the cEdge interfaces, and default static routes are configured pointing to the provider edge devices. These default routes facilitate the building of IPsec tunnels across each transport to the SD-WAN overlay. The cEdge uses overlay management protocols to advertise connected LAN subnets and to learn remote prefixes dynamically from other sites.
On the LAN side, the cEdge assumes the role of the default gateway for client devices. This is typically achieved by assigning the cEdge’s LAN interface an IP address that client devices reference as their next hop for outbound traffic. Additional VLANs can be supported using sub-interfaces on the cEdge, allowing for scalable segmentation within the branch. All connected routes from the LAN are redistributed into the SD-WAN overlay using the overlay management protocol, ensuring end-to-end reachability.
WAN Transport Considerations In Single cEdge Deployments
WAN transport diversity is a major advantage in SD-WAN architectures. Having both a private MPLS circuit and an internet broadband link provides redundancy and performance optimization. The cEdge is responsible for managing path selection based on defined policies. Factors like latency, packet loss, and jitter can be monitored continuously, with traffic being dynamically steered over the most optimal path.
In a single cEdge design, WAN transport handoffs are directly terminated on the router, simplifying the physical topology. However, care must be taken to ensure sufficient address space is available on each WAN link. If public IP addresses are limited, NAT strategies must be employed to accommodate all necessary traffic flows.
Handling Internet-Bound Traffic In A Single cEdge Design
One of the decisions that must be made during integration is how to handle internet-bound traffic. In the absence of a local firewall at the branch, internet traffic can either be backhauled to a central data center for inspection or sent directly to a cloud-based security service. Backhauling adds latency and consumes bandwidth but provides centralized control. Alternatively, leveraging a cloud-delivered firewall service allows direct internet access while still ensuring security policies are enforced. This approach reduces latency and is particularly beneficial for applications like SaaS platforms.
Dual cEdge Deployment With Layer 2 LAN For High Availability
For branch sites that require hardware redundancy, deploying a pair of cEdge routers is a common design choice. Dual cEdge deployments offer resiliency against hardware failures and WAN transport outages. In this architecture, WAN links are distributed across the two cEdges, providing physical path diversity. For example, the private WAN transport can terminate on cEdge 1 while the public WAN transport terminates on cEdge 2.
However, each cEdge still needs to establish tunnels over both WAN transports. This is achieved using TLOC extensions, where WAN interfaces from one cEdge are logically extended to the other using Ethernet cross-connects. This setup enables both routers to have access to all available WAN transports, thus supporting dynamic routing decisions based on link performance.
TLOC Extensions And Addressing Challenges
When implementing TLOC extensions, careful consideration must be given to IP addressing. The extension links between the cEdges require private IP addressing, and these subnets must be advertised across the WAN to ensure remote SD-WAN sites can build tunnels to both cEdges. For private WAN circuits, this typically involves enabling BGP on the cEdge connected to the provider edge router and advertising the TLOC extension subnet.
On the public WAN side, if only a single public IP address is available, NAT must be employed on the cEdge terminating the public circuit to allow both cEdges to share the public IP for outbound traffic. This introduces complexity but maintains redundancy. If additional public IPs are available, a more straightforward design without NAT can be implemented, as we will explore in a later part.
LAN Redundancy With First Hop Redundancy Protocols
High availability is not limited to WAN connectivity. The LAN side must also be resilient to cEdge failures. This is accomplished by configuring a first hop redundancy protocol such as VRRP on the cEdge LAN interfaces. VRRP allows both routers to share a virtual IP address that client devices use as their default gateway. If the active cEdge fails, the standby cEdge assumes responsibility for forwarding LAN traffic without disrupting client connectivity.
The implementation of VRRP also simplifies LAN design by abstracting the physical router IP addresses from the clients. This abstraction ensures that failovers are seamless and do not require any changes to client configurations.
Simplifying Routing Policies In Dual cEdge Deployments
With dual cEdge deployments, routing policies play a crucial role in ensuring traffic is forwarded efficiently and resiliently. Both cEdges participate in the SD-WAN overlay and advertise the same LAN prefixes. This allows the SD-WAN fabric to load balance or failover traffic based on real-time path metrics. It is essential to define clear data policies that specify how applications utilize available transports. For example, critical applications can be configured to prefer the private WAN circuit, while bulk internet traffic is directed over broadband.
Additionally, control policies can be applied to influence route advertisements and ensure consistent network behavior across the SD-WAN fabric. These policies enable network administrators to maintain control over routing decisions while still benefiting from the dynamic capabilities of SD-WAN.
Operational Considerations During Deployment
When integrating cEdge routers into an existing branch environment, it is important to consider the operational impact. Migrating from legacy CE routers to SD-WAN cEdge devices often requires a planned cutover window, especially if hardware reimaging is involved. Testing configurations in a lab environment prior to production deployment is highly recommended. Furthermore, ongoing monitoring of WAN links and application performance is essential to validate that the SD-WAN policies are achieving the desired outcomes.
Automation tools provided by SD-WAN orchestrators simplify initial deployments and ongoing management. Templates allow for standardized configurations across multiple sites, reducing human error and ensuring consistency. However, site-specific nuances such as local IP addressing and unique WAN characteristics must still be addressed carefully.
Preparing For Future Expansion And Scalability
One of the key benefits of SD-WAN is its scalability. A well-designed cEdge integration allows organizations to expand their WAN footprint without significant architectural changes. Additional WAN transports can be added to a site with minimal disruption, and new branch locations can be brought online quickly by leveraging SD-WAN templates and centralized management tools.
As network demands evolve, the flexibility of SD-WAN enables businesses to adapt rapidly. Whether it involves integrating new cloud services, deploying advanced security features, or expanding global reach, the foundation laid by a solid cEdge integration design ensures the network can meet future requirements effectively.
Key Considerations For Local Firewall Integration
Before selecting a specific integration design, it is essential to understand how the firewall will interact with both the WAN and LAN sides of the network. One of the first decisions is whether the firewall will be placed in a routed or transparent mode. In routed mode, the firewall actively participates in layer 3 routing, requiring IP addressing and dynamic routing configurations. In transparent mode, the firewall acts as a bump-in-the-wire, filtering traffic without influencing the routing table.
Another consideration is whether the firewall will inspect both inbound and outbound WAN traffic or if it will be limited to only one direction. Additionally, redundancy requirements for the firewall must be evaluated. Deploying a single firewall introduces a single point of failure, whereas dual firewalls configured in a high-availability pair provide resilience against hardware outages.
Single cEdge With External Firewall In Routed Mode
A common design for branch sites that require a local firewall involves deploying a single cEdge router with an external firewall placed in routed mode. In this architecture, the cEdge is responsible for WAN transport termination and SD-WAN overlay participation. The firewall sits between the cEdge and the LAN, acting as the gateway for client devices.
The cEdge advertises a default route towards the firewall, and the firewall has static or dynamic routes back towards the cEdge for WAN-bound traffic. This design allows the firewall to inspect all outbound and inbound traffic while the cEdge manages SD-WAN path selection and overlay functions.
One advantage of this design is that it maintains a clear separation between security and routing responsibilities. However, it also introduces additional hops in the forwarding path, which can lead to increased latency. Care must be taken to ensure that routing loops are avoided, particularly when dynamic routing protocols are used between the cEdge and the firewall.
Dual cEdge With Single External Firewall In Routed Mode
For sites that require both WAN redundancy and security inspection, a design involving dual cEdge routers and a single external firewall can be considered. In this topology, both cEdges terminate WAN transports, and the firewall sits behind them as a single inspection point.
To achieve WAN transport sharing between the cEdges, TLOC extensions are used, similar to designs discussed earlier. The LAN side of both cEdges connects to the firewall, typically using a layer 2 switch. The firewall is configured with interfaces facing each cEdge, and routing policies ensure symmetric traffic flows.
One of the challenges in this design is ensuring high availability on the WAN side while managing the single point of failure introduced by the firewall. If firewall redundancy is a critical requirement, the next design involving dual firewalls becomes necessary. However, in environments where the firewall’s uptime is acceptable, this design offers a balance between simplicity and functionality.
Dual cEdge With Dual Firewalls In High Availability
For environments where both routing and security redundancy are non-negotiable, deploying dual cEdges in combination with dual firewalls configured in high availability mode is the optimal approach. In this design, each cEdge connects to both firewalls using a layer 2 switch or directly with physical links. The firewalls are configured as an active-standby pair, ensuring that if one firewall fails, the other seamlessly takes over.
Both cEdges participate in SD-WAN overlay operations, and WAN transport diversity is achieved through direct termination and TLOC extensions. The firewalls sit in routed mode, inspecting traffic flowing between the LAN and WAN. To provide LAN side redundancy, VRRP is implemented between the firewalls, offering a virtual gateway IP for client devices.
This design is resilient to multiple failure scenarios, including the failure of a cEdge, a firewall, or a WAN transport. It ensures continuous operation and security inspection, making it suitable for mission-critical branch sites.
Transparent Mode Firewall Integration
In some cases, it is desirable to deploy a firewall in transparent mode. This design allows the firewall to inspect traffic without participating in layer 3 routing. A transparent firewall sits inline between the cEdge and the LAN switch, bridging traffic while enforcing security policies.
The primary benefit of transparent mode is its simplicity. The firewall does not require IP addressing on routed interfaces, making the integration process less intrusive. However, transparent mode firewalls have limitations in terms of advanced routing features and may not support all inspection capabilities.
When deploying a transparent firewall with a single cEdge, the cEdge maintains full routing control, including managing overlay advertisements and path selection. For dual cEdge deployments, transparent firewalls must be placed inline on each path, or alternatively, connected through a layer 2 switch to handle traffic redundantly.
LAN Side Layer 3 Topology With cEdge Routers
Moving beyond layer 2 LAN designs, many enterprise sites operate with a layer 3 LAN topology where internal routers distribute traffic across different subnets. In these scenarios, the cEdge routers must integrate into the existing layer 3 routing domain. This often involves configuring dynamic routing protocols such as OSPF or BGP between the cEdge and internal LAN routers.
One design approach is to deploy the cEdge at the edge of the LAN routing domain, exchanging routes with core LAN routers while still handling WAN overlay responsibilities. The cEdge advertises learned WAN prefixes into the LAN, and similarly, LAN prefixes are redistributed into the SD-WAN overlay through the cEdge.
This design promotes a scalable and flexible routing architecture. It allows for granular control over route advertisements and policies, facilitating complex traffic engineering requirements. Additionally, it supports larger branch environments where multiple VLANs and subnets are managed by internal routers.
High Availability Considerations In Layer 3 LAN Designs
When deploying dual cEdges in a layer 3 LAN environment, high availability becomes an essential design criterion. First hop redundancy protocols such as VRRP or HSRP are typically used to provide a virtual gateway IP to downstream devices. Both cEdges must participate in the routing domain, advertising identical LAN prefixes into the SD-WAN overlay.
In this topology, failure scenarios must be thoroughly analyzed. For example, if one cEdge fails, the remaining cEdge must seamlessly continue to handle both WAN and LAN routing responsibilities. Dynamic routing protocols must be configured with appropriate timers and failover mechanisms to ensure minimal disruption.
TLOC extensions are also relevant in this design, ensuring that both cEdges have access to all WAN transports, regardless of their physical termination points. The use of routing metrics and path selection policies becomes even more critical in maintaining an optimal and resilient forwarding path.
Best Practices For Firewall And Routing Policy Integration
When combining SD-WAN cEdge routers with local firewalls, several best practices must be followed to ensure a robust deployment. First, ensure that the routing policies on both the cEdges and firewalls are aligned. Inconsistent route advertisements can lead to asymmetric routing, which is undesirable in SD-WAN environments where consistent path selection is vital.
Second, define clear security policies on the firewall that complement SD-WAN policies. For instance, allow specific applications to bypass deep inspection if they are already encrypted and monitored by SD-WAN performance policies. This ensures that security enforcement does not inadvertently degrade application performance.
Third, maintain a modular configuration approach. Use templates and profiles where possible to standardize deployments across multiple sites. This approach simplifies troubleshooting and accelerates the deployment of new branch locations.
Operational Impact And Migration Strategy
Introducing a firewall into an existing SD-WAN cEdge deployment or migrating from a legacy network to an SD-WAN environment with integrated firewalls requires a well-planned migration strategy. Pre-deployment validation in a lab environment helps to identify potential issues before impacting production traffic.
During the cutover, it is advisable to use a phased approach. Start with WAN transport terminations and SD-WAN overlay validation. Once the WAN paths are confirmed operational, introduce the firewall in monitor mode to observe traffic patterns. After ensuring that traffic flows correctly through the firewall, enforce active inspection policies.
Continuous monitoring post-deployment is critical. Utilize SD-WAN analytics and firewall logs to validate that application performance and security policies are functioning as intended. Regular audits of routing tables, path selections, and firewall policies ensure long-term operational excellence.
Preparing For Advanced Use Cases
Beyond basic integration, cEdge routers with local firewalls can support advanced network architectures. For example, sites with hybrid cloud connectivity can leverage SD-WAN overlays to establish direct secure paths to cloud environments. Firewalls can enforce policies for cloud-bound traffic, ensuring compliance and data protection.
Similarly, integration with zero trust architectures can be enhanced by deploying firewalls as segmentation gateways, while cEdges manage the dynamic path selection. This layered security and routing design aligns with modern enterprise security models.
As the SD-WAN landscape continues to evolve, having a flexible integration strategy that accommodates new technologies and business needs is essential. A well-designed cEdge and firewall integration forms the foundation for such future-ready network architectures.
The Role Of WAN Optimization And Security Appliances
WAN optimization appliances are designed to improve application performance across wide area networks by reducing latency, compressing data, caching content, and optimizing protocols. These appliances are critical in environments where bandwidth is limited, and application responsiveness is vital.
Similarly, intrusion detection and prevention systems (IDS/IPS) monitor network traffic for suspicious activities, providing deep packet inspection and threat mitigation. Integrating these appliances into SD-WAN environments allows enterprises to enhance security without compromising on SD-WAN’s agility and performance optimization.
Key Integration Considerations For WAN Edge Services
When planning the integration of WAN optimization and security appliances with cEdge routers, several factors must be evaluated. The first is the traffic flow architecture—whether the appliances will be deployed inline, in a one-arm (SPAN/TAP) configuration, or through policy-based traffic redirection.
Another critical consideration is how these appliances impact SD-WAN path selection and failover behaviors. Inline deployments can introduce single points of failure if redundancy is not carefully designed. Additionally, traffic redirection must align with SD-WAN policy configurations to ensure that performance monitoring and security enforcement are consistent.
Appliance placement must also account for the physical and logical topology of the site, particularly in scenarios involving dual cEdge routers and multiple WAN transports.
Inline Deployment Of WAN Optimization Appliances With Single cEdge
A straightforward deployment scenario involves placing a WAN optimization appliance inline between the cEdge and the LAN switch. In this design, all traffic passing between the LAN and WAN traverses the optimization appliance, ensuring comprehensive coverage.
The cEdge maintains its role as the SD-WAN overlay participant, terminating WAN transports and performing path selection. The optimization appliance operates transparently, intercepting traffic, applying optimization techniques, and forwarding packets back to the cEdge or LAN as appropriate.
This design is simple to implement and ensures that the optimization appliance handles all traffic. However, it introduces a dependency on the appliance’s availability. If the appliance fails, traffic flow is disrupted unless bypass mechanisms, such as hardware bypass cards, are in place.
Inline Deployment With Dual cEdge And WAN Optimization Redundancy
For sites requiring high availability, deploying WAN optimization appliances in a redundant inline architecture becomes necessary. In this design, two cEdge routers and two WAN optimization appliances are deployed, creating a fully redundant path.
Each cEdge connects to its dedicated WAN optimization appliance, and the LAN side is interconnected via a layer 2 switch. First Hop Redundancy Protocols like VRRP are implemented on the LAN side interfaces to ensure a consistent gateway IP for client devices.
To allow for SD-WAN path diversity, TLOC extensions are configured between the cEdges, ensuring that both routers have access to all WAN transports. The WAN optimization appliances are configured in high availability mode if supported, or load-sharing configurations if that aligns with application traffic patterns.
This design eliminates single points of failure and ensures continuous optimization services. It also enables intelligent SD-WAN path selection while maintaining optimization transparency.
One-Arm Deployment Of Security Appliances For Passive Monitoring
In scenarios where active inline inspection is not required, deploying security appliances in a one-arm or SPAN/TAP configuration is an effective strategy. In this architecture, a cEdge router mirrors traffic towards the security appliance, allowing it to monitor and analyze packets without being in the forwarding path.
This approach is particularly beneficial for intrusion detection systems where passive monitoring suffices. The cEdge uses switch port analyzer (SPAN) sessions or network TAPs to send copies of traffic to the IDS device.
The advantage of this design is that it does not introduce any inline points of failure. However, it limits the appliance’s ability to block or modify traffic since it operates in a listen-only mode. For prevention capabilities, inline deployment remains necessary.
Policy-Based Traffic Redirection To Security Appliances
An alternative to inline deployment is to leverage policy-based traffic redirection. In this design, the cEdge identifies specific traffic flows that require inspection and forwards them to a security appliance using policy-based routing or service chaining.
For example, traffic destined for sensitive applications or originating from untrusted networks can be redirected through a firewall or IPS appliance for inspection before being forwarded to the WAN or LAN. This granular traffic steering is configured using access control lists and service insertion policies on the cEdge.
Policy-based redirection offers flexibility and allows selective enforcement of security policies without imposing inspection overhead on all traffic. It also integrates well with SD-WAN’s application-aware routing, ensuring that critical applications are prioritized while maintaining robust security.
Dual cEdge With Policy-Based Redirection And Appliance Redundancy
For high availability environments, policy-based traffic redirection can be extended to dual cEdge deployments with redundant security appliances. Each cEdge is configured with service insertion policies that forward traffic to the appropriate appliance based on traffic characteristics and appliance availability.
Redundant appliances are interconnected to allow for stateful failover, ensuring inspection continuity in the event of hardware failure. The cEdges coordinate path selection and traffic redirection to balance the load and maintain optimal performance.
This architecture supports complex security enforcement scenarios while preserving the SD-WAN fabric’s agility and failover capabilities. It is ideal for sites requiring deep inspection of specific traffic types without introducing inline dependencies for all flows.
Hybrid Deployment Models For WAN Optimization And Security Appliances
In many enterprise deployments, a combination of inline and policy-based redirection models is employed to address diverse application requirements. For example, WAN optimization appliances may be deployed inline to optimize all traffic flows, while security appliances are integrated using policy-based redirection to inspect only sensitive or high-risk traffic.
This hybrid approach maximizes optimization benefits while ensuring that security policies are enforced where necessary. The cEdge routers serve as the control point for traffic steering, leveraging SD-WAN policies to dynamically adjust traffic flows based on performance metrics and security requirements.
Dynamic Path Selection With Integrated WAN Edge Services
Integrating WAN optimization and security appliances into the SD-WAN environment introduces additional considerations for path selection. The cEdge must continuously monitor link performance, including latency, jitter, and packet loss, to determine the optimal path for each application flow.
When inline appliances are part of the forwarding path, their processing delays must be factored into path selection decisions. This requires precise measurement of end-to-end path metrics, including appliance-induced latency.
Dynamic path selection policies on the cEdge should also account for the availability of appliances. For example, if a primary WAN optimization appliance becomes unavailable, the cEdge must reroute traffic through an alternative path that bypasses the failed appliance or directs traffic through a backup device.
Best Practices For Appliance Integration With cEdge Routers
To ensure successful integration of WAN optimization and security appliances with cEdge routers, several best practices should be followed. First, align appliance configurations with SD-WAN policies to avoid conflicts in traffic classification and enforcement. Consistent application identification across the SD-WAN fabric and appliances ensures coherent traffic handling.
Second, establish robust monitoring and visibility into appliance performance and health. Use SNMP, Syslog, or API-based integrations to collect telemetry from appliances, enabling proactive fault detection and resolution.
Third, design appliance failover scenarios meticulously. Inline appliances should have bypass mechanisms, while one-arm and policy-based deployments should incorporate failover paths in case of appliance failure. Ensure that cEdge routing policies dynamically adapt to these failure scenarios.
Fourth, document and standardize deployment architectures across sites. Create templates and design guides that detail appliance placement, routing policies, and redundancy configurations. This streamlines deployment processes and simplifies troubleshooting.
Operationalizing WAN Edge Service Integration
Post-deployment, continuous operational practices are essential to maintain the effectiveness of integrated WAN edge services. Regular audits of traffic flows, appliance utilization, and SD-WAN path selections ensure that optimization and security goals are consistently met.
Performance baselines should be established, and deviations should trigger investigations into appliance configurations, network conditions, or policy misalignments. Periodic updates to appliance firmware and software, coordinated with SD-WAN upgrades, ensure compatibility and security posture.
Additionally, operational playbooks should be developed for managing appliance maintenance windows, failover scenarios, and troubleshooting workflows. These playbooks provide network operations teams with clear procedures to address incidents efficiently.
Preparing For Evolving WAN Edge Requirements
The integration of WAN optimization and security appliances with cEdge routers forms the foundation for more advanced SD-WAN architectures. As enterprises adopt cloud-based security services and migrate towards Secure Access Service Edge (SASE) models, the principles of appliance integration remain relevant.
Future-proof designs should accommodate hybrid deployments where certain services are delivered on-premises, while others are consumed from the cloud. The cEdge’s ability to steer traffic dynamically and enforce policies across diverse service endpoints will remain central to these evolving architectures.
By embracing flexible and resilient integration strategies, enterprises can ensure that their WAN edge services continue to deliver performance, security, and agility in an ever-changing digital landscape.
Understanding The Fundamentals Of Multihoming In SD-WAN
Multihoming in traditional routing environments often involves BGP peering with multiple ISPs, managing inbound and outbound route advertisements, and relying on AS-path manipulations for path preferences. However, in an SD-WAN architecture, multihoming is abstracted and simplified through centralized control policies managed by vSmart controllers.
The cEdge routers build secure DTLS or TLS tunnels over each WAN transport to the SD-WAN fabric. The vSmart orchestrates control plane policies, while data plane traffic is intelligently steered across the available transports based on performance metrics and business intent.
Multihoming in SD-WAN is not limited to internet circuits. It also applies to private MPLS links, LTE/5G wireless connections, and satellite transports. The cEdge supports up to seven WAN transport interfaces, allowing enterprises to craft diverse and resilient multihoming topologies.
Active-Active Multihoming Design For Internet And MPLS
One of the most common multihoming scenarios involves connecting a site to both an MPLS network and an internet broadband circuit. In an active-active design, both transports are utilized simultaneously, enabling dynamic load balancing and seamless failover.
In this architecture, the cEdge terminates both WAN transports, creating IPsec tunnels across each transport to the SD-WAN fabric. The vSmart controller monitors transport performance, including latency, jitter, and packet loss, and dynamically steers traffic based on defined application-aware routing policies.
For example, critical business applications like voice and video can be prioritized over the MPLS circuit due to its guaranteed SLAs, while less sensitive traffic, such as software updates or cloud backups, can be directed through the broadband internet link. Should the MPLS circuit experience degradation or failure, the SD-WAN fabric automatically reroutes prioritized traffic through the internet path, maintaining application availability.
Active-active multihoming enhances WAN resource utilization and delivers a more resilient user experience. The cEdge ensures that path decisions are continuously optimized based on real-time network conditions.
Active-Standby Multihoming With Diverse ISP Connections
In some enterprise scenarios, active-standby multihoming is preferred, particularly when dealing with asymmetric internet service providers or cost-sensitive environments. In this design, one ISP connection serves as the primary transport, while a secondary ISP connection is configured as a failover path.
The cEdge builds tunnels across both ISPs, but the SD-WAN control policies prefer the primary ISP for all traffic unless its performance deteriorates beyond acceptable thresholds. The standby ISP remains in a ready state, capable of handling full site traffic if a failover event occurs.
Active-standby designs are often employed in locations where primary ISP links offer superior SLAs or higher bandwidth, while secondary ISP connections are provisioned as a cost-effective redundancy measure. The cEdge’s transport performance monitoring ensures that failover events are automated and rapid, minimizing downtime.
This design is also applicable in environments where certain applications must always traverse a specific ISP due to compliance or contractual obligations. The cEdge’s policy framework allows granular traffic steering to enforce such requirements.
Load Sharing Multihoming Across Multiple Internet Circuits
For sites with multiple high-bandwidth internet circuits, implementing a load-sharing multihoming design maximizes throughput and optimizes resource utilization. In this architecture, the cEdge is connected to two or more internet circuits, and traffic is distributed across all available paths based on bandwidth availability and application priorities.
Load-sharing multihoming does not require complex BGP manipulations or static route weighting. Instead, the SD-WAN overlay fabric intelligently balances traffic flows, ensuring that no single transport becomes a bottleneck. The cEdge continuously evaluates path performance and dynamically adjusts traffic distribution.
A practical use case for load-sharing multihoming is in large branch offices or regional hubs where high aggregate bandwidth is required to support hundreds of users and multiple cloud applications. By distributing traffic across multiple circuits, enterprises achieve not only redundancy but also enhanced application performance through aggregated throughput.
Additionally, load-sharing multihoming enables the use of diverse ISP providers, further increasing network resiliency against provider-specific outages or performance issues.
Dual cEdge Multihoming For High Availability Sites
In mission-critical sites where hardware redundancy is as important as transport diversity, deploying dual cEdge routers with multihoming capabilities becomes essential. This architecture involves two cEdge routers, each connected to multiple WAN transports, providing complete hardware and path redundancy.
The dual cEdge deployment is configured with TLOC extensions, allowing each router to access all available WAN transports. First Hop Redundancy Protocols like VRRP are implemented on the LAN side interfaces to maintain a consistent default gateway for connected devices.
The vSmart controller manages overlay tunnels across each cEdge and transport combination, ensuring that traffic is dynamically routed based on the health of both the hardware and the WAN links. If one cEdge fails, the other cEdge seamlessly takes over traffic forwarding duties without disrupting active sessions.
Dual cEdge multihoming is ideal for data centers, critical branch sites, and environments requiring five-nines availability. It ensures that both hardware and transport-level failures are mitigated, providing comprehensive resiliency.
Leveraging LTE/5G As A Tertiary Transport In Multihoming Designs
Wireless WAN transports such as LTE and 5G are increasingly integrated into multihoming architectures as tertiary transport options. These wireless links provide a flexible and rapid deployment alternative to wired circuits, serving as a backup path or even as a primary link in remote or temporary sites.
The cEdge routers natively support LTE/5G interfaces, enabling them to establish overlay tunnels over these wireless transports. SD-WAN policies can designate LTE/5G as a failover path for critical applications or as an active transport for specific use cases such as mobile workforces or IoT deployments.
Wireless transports are also valuable in business continuity scenarios where primary wired circuits are disrupted due to physical outages. The cEdge’s dynamic path selection mechanisms ensure that LTE/5G links are utilized only when necessary, preserving wireless bandwidth and controlling operational costs.
Hybrid Transport Multihoming With Cloud Interconnects
As enterprises adopt multi-cloud strategies, integrating cloud direct connect services into multihoming designs becomes an essential consideration. Cloud interconnects offer low-latency and high-bandwidth connectivity to major cloud providers, bypassing the public internet.
In a hybrid multihoming design, the cEdge connects to a combination of MPLS, broadband internet, LTE/5G, and cloud interconnect circuits. The SD-WAN fabric intelligently steers cloud-destined traffic through the direct connect paths, while other traffic types leverage MPLS or internet circuits based on application requirements.
This architecture enhances cloud application performance, reduces latency, and improves security posture by avoiding the public internet where possible. The cEdge’s ability to manage diverse transports under a unified policy framework simplifies operational management and ensures consistent application experience.
Implementing Path Affinity And Application SLAs In Multihoming Designs
Advanced multihoming designs often require enforcing path affinity policies to ensure that specific applications consistently utilize designated transports. For example, a financial trading application may require low-latency MPLS connectivity, while email and collaboration tools can leverage broadband internet circuits.
The cEdge enables path affinity configurations through data policies that bind specific applications or traffic types to designated TLOCs. These policies ensure that critical applications maintain their transport preferences, even in dynamic failover scenarios.
Additionally, application SLAs can be defined within the SD-WAN policy framework, specifying acceptable thresholds for latency, jitter, and packet loss. The cEdge monitors these metrics in real-time and triggers path failover if SLA violations occur, maintaining application performance standards.
Path affinity and application SLAs provide precise control over traffic steering decisions, enabling enterprises to align network behavior with business requirements.
Addressing Asymmetric Routing Challenges In Multihoming
One of the challenges in multihoming environments is managing asymmetric routing, where traffic ingress and egress paths differ, potentially impacting performance and security monitoring. Cisco SD-WAN mitigates asymmetric routing concerns through its overlay fabric, ensuring that traffic flows are encapsulated and managed consistently across diverse transports.
However, careful planning of NAT configurations, policy-based routing rules, and appliance integrations is necessary to maintain flow symmetry, especially when integrating inline security or optimization appliances. The cEdge provides flexible NAT and routing configurations to address asymmetric routing scenarios effectively.
Best Practices For Operationalizing Multihoming Designs
To ensure successful multihoming deployments, several best practices should be followed. First, perform thorough transport performance assessments during the design phase to understand the capabilities and limitations of each WAN circuit. This informs policy decisions and path preference configurations.
Second, standardize multihoming architectures across sites wherever possible. Creating design templates for single cEdge, dual cEdge, and hybrid transport scenarios streamlines deployment and simplifies operational management.
Third, establish robust monitoring and alerting mechanisms. Utilize SD-WAN telemetry data to continuously monitor transport performance, detect anomalies, and trigger proactive remediation actions.
Fourth, maintain comprehensive documentation of transport configurations, policy mappings, and failover procedures. This documentation is invaluable for troubleshooting and for onboarding new network operations personnel.
Finally, plan for future scalability. As business requirements evolve, multihoming designs should accommodate additional transports, increased bandwidth demands, and integration with emerging technologies like SASE.
Future Outlook On Multihoming In SD-WAN Architectures
Multihoming strategies will continue to evolve as enterprises adopt more complex hybrid work environments, edge computing models, and cloud-centric applications. Cisco SD-WAN’s flexible policy framework and cEdge’s transport-agnostic capabilities position them well to adapt to these future demands.
Emerging technologies like intent-based networking and AI-driven path optimization will further enhance multihoming architectures, enabling networks to self-adjust to changing conditions and application needs. Enterprises that build robust and adaptable multihoming foundations today will be better prepared to leverage these advancements in the future.
Conclusion
In conclusion, integrating Cisco SD-WAN cEdge routers into a multihomed site design provides enterprises with unmatched flexibility, resiliency, and control over their WAN environments. Whether deploying active-active, active-standby, load-sharing, or hybrid transport architectures, cEdge enables seamless connectivity across MPLS, internet, LTE/5G, and cloud interconnects. Advanced features like TLOC extensions, path affinity, and application SLAs ensure that business-critical applications consistently meet performance expectations, while centralized management through vSmart simplifies operations. As network demands continue to evolve, adopting robust multihoming strategies with Cisco SD-WAN cEdge positions organizations to deliver high availability, optimized performance, and scalable growth for the future.