HN829: EVPN/VXLAN Vs. TradCore

The episode opens by framing the central question: when should a network engineer choose TradCore (traditional core-aggregation-access layer designs using SVIs, VLANs, spanning tree, and MLag) versus EVPN/VXLAN fabric designs for data center or campus networks? Tony Burke, a seasoned network instructor, pitched the topic after observing the question arise repeatedly among students and in network design discussions.

Tony begins by defining TradCore as the legacy networking stack using Layer 2 constructs like 802.1Q trunks, VLANs, and MLag/VPC for redundancy at the aggregation layer — a model familiar to anyone trained on Cisco's CCNA/CCNP curriculum. He contrasts this with EVPN/VXLAN, which uses an underlay routing protocol, an MPBGP overlay, VXLAN encapsulation, and constructs like VNIs, route targets, and route distinguishers to create a scalable, distributed fabric.

A common misconception Tony addresses is the VLAN scale argument: while VXLAN theoretically supports over 16 million segments, in practice each VXLAN segment still maps to a local VLAN, so most deployments remain constrained to the 4,000 VLAN limit unless significant complexity is added (as Cisco ACI does internally). Multi-vendor EVPN/VXLAN is technically possible but Tony strongly discourages it due to differing vendor interpretations, inconsistent show commands, and the operational burden of cross-vendor troubleshooting — even between Cisco and Arista, which have similar CLI styles but very different EVPN implementations.

The three primary decision factors Tony identifies are: (1) Scale — EVPN/VXLAN scales far better, supporting hundreds of leaf switches via spine layers and super-spine (five-stage Clos) topologies, while TradCore is limited by the number of chassis line cards and the constraint of only two aggregation devices in an MLag pair; (2) Redundancy — EVPN/VXLAN allows three or four spines, preserving 66-75% capacity after a failure, whereas TradCore's two-device aggregation layer loses all redundancy if one device fails; and (3) Operational overhead — EVPN/VXLAN is significantly more complex to configure and operate, involving underlays, overlays, VLAN-to-VNI mappings, multiple BGP EVPN route types, and distributed forwarding tables.

Tony is emphatic that EVPN/VXLAN should never be deployed manually in production — only in labs for learning purposes. He argues automation is essentially mandatory for EVPN/VXLAN environments, whether through vendor tools like Arista Cloud Vision/AVD, Cisco Nexus Dashboard/Catalyst Center, Juniper Apstra (now Apstra Data Center Director), or Nokia's Event-Driven Automation, or through homegrown solutions using Ansible, Jinja, Python, and YAML. TradCore, by contrast, can be managed effectively without automation, which matters for smaller teams with broad responsibilities.

On the topic of workload mobility — the requirement that any subnet be reachable from any rack, enabling vMotion and flexible workload placement — both TradCore and EVPN/VXLAN satisfy the requirement equally within a single data center. EVPN/VXLAN has a slight edge for multi-data-center interconnect. This requirement dates to around 2006-2008 when AMD and Intel processor virtualization extensions made VM workloads practical with near-zero performance overhead.

Tony and the hosts also compare MLag versus ESI (Ethernet Segment Identifier) for multi-homing hosts to multiple switches. MLag is a mature, proprietary-between-two-devices technology that requires same-vendor hardware and matched software versions. ESI, available only in EVPN/VXLAN environments, is a distributed LAG using a 10-byte identifier, supports more than two devices, allows mixed hardware models, and does not require a dedicated peer link between switches — though Tony notes these advantages are rarely decisive in practice given typical rack-and-stack patterns.

The conversation concludes with a caution against industry fashion: VARs and vendors are often pushing EVPN/VXLAN as a default recommendation, but Tony and the hosts argue that TradCore remains a fully legitimate, often preferable choice for smaller organizations, teams without automation skills, or networks that will never reach the scale where EVPN/VXLAN's advantages materialize. Tony summarizes: small shops with limited teams should lean TradCore; very large fabrics should use EVPN/VXLAN; and many mid-size environments could go either way depending on specific organizational factors.