Fabric Technology Overview
Data Center Network Evolution
The Data Center fabric journey evolved from a Spanning-Tree (STP) based network to more efficient ways of using the available resources of the infrastructure.
Initially, we built Spanning-Tree (STP) based networks where a single link was active for a given service (VLAN). The same was true for the demarcation between Layer 2 and Layer 3, where a First Hop Redundancy Protocol like HSRP or VRRP provided a single active point of egress per service (VLAN/subnet).
With the introduction of Cisco’s version of Multi-Chassis Link-Aggregation, virtual Port-Channels (vPC), a significant improvement has been achieved by providing a loop-free topology. In vPC-based environments, Spanning-Tree (STP) was still present to provide a failsafe mechanism without the disadvantages of a single path tree active. vPC also provided enhancements to the Layer 2 / Layer 3 demarcation, where now First Hop Redundancy Protocols (FHRP) like HSRP and VRRP start forwarding in an active/active manner, and this improved a former chokepoint. Nevertheless, even with vPC and FHRP active/active, further scale-out with regards to Layer 2 and Layer 3 forwarding became an ask.
Cisco introduced Layer 2 Multipathing (L2MP) to accommodate these asks with the introduction of Cisco FabricPath. With the MAC-in-MAC frame encapsulation and the IS-IS routing protocol, Cisco provided a Layer 2 Equal Cost Multipath (ECMP) based network, where hosts were allowed to talk to other hosts across all available links. Different to vPC, FabricPath did not require a pairing of network nodes and the configuration became simplified. A Layer 2 fabric was made available and the first scale-out network architecture was embraced; the need for a wider Layer 2 / Layer 3 demarcation became eminent. With Anycast-HSRP, Cisco implemented a way to scale-out the common chokepoint for First-Hop gateways and extended it to 4 active nodes. Further scale-out was an ask for FabricPath and enhancements have been added like Enhanced Forwarding, Distributed Anycast Gateway at the Leaf switch, and automation of connected workloads; these enhancements fell under Cisco’s Dynamic Fabric Automation (DFA) solution.
With the industry moving from Frame Encapsulation (MAC-in-MAC) to Packet Encapsulation (MAC-in-IP), Cisco embraced VXLAN within its Data Center Switching portfolio to provide a standards based encapsulation technique. Initially, VXLAN was introduced as a Layer 2 service only and since VXLAN Flood and Learn (as defined in RFC 7348) follows the similar Flood and Learn semantic as Ethernet or FabricPath, enhancements were required. VXLAN with a control plane became necessary to introduce Layer 2 and Layer 3 services, while optimizing forwarding to address the limitations of VXLAN Flood and Learn. Multiprotocol Border Gateway Protocol with Ethernet Virtual Private Network (MP-BGP EVPN) was introduced as the control plane, with VXLAN being used in the data plane. MP-BGP EVPN has been defined by IETF as the standards-based control plane for VXLAN overlays. The Programmable Fabric solution is based on VXLAN with BGP EVPN, with the programmability of the network fabric through APIs.
Data Center fabric challenges remained present and included disjoint provisioning, CLI centric box-by-box configuration, disruptive growth of applications (and other data center entities), deficient host overlay, and location dependency (rigid coupling of IP address to location). These challenges have led to operational complexity, architectural rigidness and infrastructure inefficiency.
A programmable infrastructure.
An open set of APIs.
Total host and IP mobility (decoupling the identity of a host to its location).
This results in simplifying of the underlying fabric and optimizing the overlay for north-south as well as east-west traffic flows, which eases the placement of workload as the network scales with integrated automation