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Cisco EVPN Underlay Design
Plan the IP underlay for Cisco EVPN fabrics, defining addressing, routing, reachability, MTU and the behaviour of physical-path failures.
Devices supported
across the UK
Client locations
supported
Traffic handled
at peak time
Average
response time
Average response is not a resolution time or a contractual guarantee. Support scope and response commitments are agreed for each engagement.
Cisco EVPN underlay design builds the IP paths that the overlay relies on. Those paths must reach the right tunnel endpoints and recover as planned when a link fails. We design this foundation for supported Cisco fabrics. The aim is a clear, supportable network with enough capacity for the traffic it must carry.
Workload-led design
Start with application, compute and storage dependencies rather than the switch model.
Clear failure domains
Understand which links, devices and sites can fail together.
Operational clarity
Make fabrics, external routing and management responsibilities supportable.
Define the physical topology and reachability requirements
We identify leaf, spine and border roles, the required links and the addresses that must remain reachable. The underlay design is separated from tenant routing so that each layer has a clear purpose. This helps prevent unnecessary app prefixes or policy exceptions from entering a transport network that should primarily support the fabric’s own network access.
Physical constraints are reviewed early. Rack layout, optics, cable paths, power and available ports influence the topology that can actually be delivered. The design includes capacity after a link or device failure, not just aggregate bandwidth in the normal state. Shared physical dependencies are documented so that the logical mesh is not mistaken for complete independence.
Standards & partnerships
Confidence in the team behind your network.
Cisco Partner
Cisco Meraki
Cyber Essentials
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Choose an appropriate routing approach
Supported underlay options depend on the Cisco platform, release and fabric architecture. We compare the available approaches against scale, convergence, operational familiarity and interaction with the overlay control plane. The goal is not to use the largest possible collection of protocols but to make endpoint reachability stable and diagnosable.
Routing identifiers, loopbacks and point-to-point addressing follow an allocation plan. We document neighbour relationships and expected route propagation, including what should not be advertised. Consistent naming and addressing make future expansion easier and reduce the risk of copying a setup with an identifier already used elsewhere. The plan also records any dependency on automation or a fabric-management system.
A useful starting point
Not sure where to start?
Bring the requirement. We will help you define the engineering work.
Plan MTU and encapsulation across every path
VXLAN transport introduces encapsulation that must be accommodated by the underlay. We check the required MTU against the chosen design and platform rather than assuming that a default interface value is enough. The check includes all relevant links, border paths and any external transport carrying encapsulated traffic.
Testing should use packets and endpoints that exercise the intended encapsulated path. A small unicast probe between management addresses does not prove that the fabric can carry workload traffic at the required size. We identify where fragmentation is unsupported or undesirable and establish a consistent design. MTU assumptions are recorded with the physical-link schedule so that later circuit or switch changes do not silently break the overlay.
Different environments. The same care.
Built around the work
your network supports.
Finance, banking and the wider private sector. We start with the systems and people that depend on your connections.
Finance & banking
Market-data paths, routing and provider coordination on clients’ behalf.
Financial-market services ↗Offices & multi-site teams
Reliable access between people, workplaces and business applications.
Office network design ↗Data centres & cloud
Network boundaries, workload connections and operational ownership.
Data centre networks ↗Design failure detection without unnecessary instability
The underlay must detect and recover from relevant link and node failures within the agreed service aims. We review routing behaviour, available equal-cost paths and supported detection mechanisms. Aggressive timers are not automatically better: they can increase instability when a device or path is under stress. Settings are chosen for the actual platform and observed conditions.
Recovery analysis includes the return of a failed component. A newly available node should not attract traffic before it can forward it correctly. We examine supported mechanisms and the wider startup sequence, documenting the expected behaviour. The app impact still depends on the overlay and endpoints, so underlay convergence is not presented as a complete measure of service recovery.
Protect management and control-plane functions
The transport network needs appropriate restrictions on administration and routing peers. We review management paths, authentication options and control-plane protection supported by the equipment. Tenant access to fabric infrastructure is not assumed to be acceptable simply because the addresses are private. Logging and time synchronisation are included so that incidents can be investigated coherently.
Operational access should remain available during the fault scenarios the design is intended to tolerate. Where out-of-band management is part of the plan, its independence is checked. Configuration backups and device inventory records are established before the fabric becomes a production dependency. A resilient forwarding topology does not remove the need for recoverable admin access.
Validate the foundation before enabling tenant services
Acceptance checks confirm expected neighbours, routes, endpoint reachability, MTU and physical-link health. Authorised failure tests show the behaviour of alternate paths and restoration. We record the baseline and any limitations before overlay services are added. This creates a clear separation between an underlay defect and a later tenant or control-plane issue.
MCI can design a new underlay or review a current fabric with unexplained instability. The work supports our wider VXLAN EVPN architecture service. Provide the topology, platform inventory and scale needs to begin. The deliverable will identify the routing, addressing, capacity and verification standards needed for a supportable Cisco fabric foundation.
Talk to a specialist
What does your network need next?
Tell us what you are planning, changing or trying to improve. We will help define a practical next step and the engineering scope.
+44 203 196 6566Choose option 1
sales@proxar.co.ukUK-wide service.
Most of our engineers are based in Kent, with a focus on London, Sussex, Essex and Berkshire.
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