Terms
Glossary.
Authored definitions for terms used across Architecture Atlas pages. Each entry links to architectures that teach the concept — not a certification dump.
Index
15 terms
- Anycast
Advertising the same service address from multiple locations so routing steers clients to a topologically nearby instance. Behavior depends on the routing domain and health signaling — not magic global load balancing by itself.
Anycast & global traffic steeringCloudflare (anycast edge & Unimog)
- CDN / edge cache
Content delivery network — caches and PoPs that terminate client requests closer to users. Request paths differ by operator (Open Connect, cloud CDN, etc.) and are taught from public sources only.
Edge / CDN request pathNetflix (Open Connect & control plane)
- Clos
A multi-stage non-blocking switching fabric topology (often leaf-spine in modern DCs) sized so any leaf can reach any other leaf through the spine stage without a single choke link — subject to planned oversubscription.
- Collapsed core
A campus design that merges distribution and core roles onto one redundant aggregation pair, omitting a dedicated core tier for smaller sites.
- DCI
Data Center Interconnect — linking two or more sites. Stitching method (L2 stretch, L3 handoff, EVPN multisite, etc.) is design-specific and must be cited, not assumed.
- Erasure coding
Storage redundancy that splits data into fragments with parity so the object survives a configured number of fragment losses — typically more storage-efficient than full replication at the cost of rebuild complexity.
- EVPN
Ethernet VPN — a BGP-based control plane for advertising MAC/IP reachability, commonly paired with VXLAN data-plane encapsulation in DC fabrics.
EVPN-VXLAN leaf-spine overlayMulti-site DCI and anycast gateways
- IRB
Integrated Routing and Bridging — combining L2 bridging and L3 routing on the same device. EVPN fabrics distinguish asymmetric vs symmetric IRB placement of the L3 gateway.
- Leaf (ToR)
The access stage of a Clos fabric that attaches servers or racks. Often called top-of-rack (ToR) in DC designs; role naming varies by vendor paper.
- Oversubscription
The ratio of southbound capacity to northbound (or stage-to-stage) capacity. Higher ratios save cost but can congest under load; CVDs treat targets as business-driven, not universal constants.
- SD-WAN
Software-defined WAN overlays that separate underlay transport from overlay tunnels and centralized policy. Vendor control-plane names (e.g. OMP/TLOC) are cited per product docs.
- Spine
The aggregation stage of a Clos fabric that interconnects leaf switches. Spines typically do not attach endpoints in a classic leaf-spine design.
- Token bucket
A rate-limit model that accumulates tokens at a fixed rate up to a burst capacity; each request consumes tokens. Common at API gateways and edge enforcement points.
- VXLAN
Virtual Extensible LAN — UDP-based overlay encapsulation that carries Ethernet frames over an IP underlay, identified by a VNI.
- Zero trust
A placement mindset: authenticate and authorize every session, minimize implicit trust by network location. Exact enforcement points (ZTNA, SGT, microsegmentation) vary by architecture.