Arista Networks (previously Arastra) is a computer networking company headquartered in Santa Clara, California, USA. The company designs and sells multilayer network switches to deliver software-defined networking (SDN) solutions for large datacenter, cloud computing, high-performance computing and high-frequency trading environments. Arista's products include an array of 10/40/100 Gigabit Ethernet low-latency cut-through switches, including the 7124SX, which remained the fastest switch using SFP+ optics through September 2012, with its sub-500ns latency, as well as the 7500 series, Arista’s award-winning modular 10G/40G/100Gbit/s switch. Arista's own Linux-based network operating system, EOS (Extensible Operating System), runs on all Arista products.

Andy Bechtolsheim co-founded Sun Microsystems in 1982 and was its chief hardware designer. In 1995, David Cheriton co-founded Granite Systems with Bechtolsheim, a company that developed Gigabit Ethernet products, which was acquired by Cisco Systems in 1996. In 2001, Cheriton and Bechtolsheim founded another start up, Kealia, which was acquired by Sun in 2004. From 1996 to 2003, Bechtolsheim and Cheriton occupied executive positions at Cisco, leading the development of the Catalyst product line, along with Kenneth Duda who had been Granite Systems' first employee.

In 2004, the three then went on to found Arastra (later renamed Arista). Bechtolsheim and Cheriton were able to fund the company themselves. In May 2008, Jayshree Ullal left Cisco after 15 years at the company, and was appointed CEO of Arista in October 2008.

In June 2014, Arista Networks had its initial public offering on the New York Stock Exchange under the symbol ANET.

In December 2014, Cisco filed two lawsuits against Arista alleging extensive intellectual property infringement. As a result of the first lawsuit, the United States International Trade Commission issued limited exclusion and cease-and-desist orders concerning two of the features patented by Cisco and upheld an import ban on infringing products. The decision is being appealed to the United States Court of Appeals for the Federal Circuit. In 2016 the ban was reversed following product changes, two Cisco patents were overturned, and Cisco's claim of damages was ruled against.

EOS is Arista's network operating system, and comes as a single image that runs across all Arista devices or in a virtual machine. EOS runs on an unmodified Linux kernel under a Fedora-based userland. There are more than 100 independent regular processes, called agents, responsible for different aspects and features of the switch, including drivers that manage the switching ASICs, the CLI, SNMP, Spanning Tree Protocol, and various routing protocols. All the state of the switch and its various protocols is centralized in another process, called Sysdb. Separating processing (carried by the agents) from the state (in Sysdb) gives EOS two important properties. The first is software fault containment, which means that if a software fault occurs, the damage is limited to a single agent. The second is stateful restarts, since the state is stored in Sysdb, when an agent restarts it picks up where it left off. Since agents are independent processes, they can also be upgraded while the switch is running (a feature called ISSU – In-Service Software Upgrade).

The fact that EOS runs on Linux allows the usage of common Linux tools on the switch itself, such as tcpdump or usual configuration management systems. EOS provides extensive APIs to communicate with and control all aspects of the switch. To showcase EOS' extensibility, Arista developed a module dubbed CloudVision that extends the CLI to use XMPP as a shared message bus for managing and configuring switches. This was implemented simply by integrating an existing open-source XMPP Python library with the CLI.

In addition to all the standard programming and scripting capabilities traditionally available in a Linux environment, EOS can be programmed using different mechanisms:

Arista's product line can be separated in eight families:

The low-latency of Arista switches has made the platform prevalent in high-frequency trading environments, such as the Chicago Board Options Exchange (largest U.S. options exchange), Lehman Brothers or RBC Capital Markets. As of October 2009, one third of its customers were big Wall Street firms.

Arista's devices are multilayer switches, which support a range of layer 3 protocols, including IGMP, VRRP, RIP, BGP, OSPF, IS-IS, as well as OpenFlow. The switches are also capable of layer 3 or layer 4 ECMP, and applying per-port L3/L4 ACLs entirely in hardware.

All of Arista's switches are built using merchant silicon instead of custom switching ASICs. This strategy enables Arista to leverage latest advances in processor manufacturing technology at a lower price point, due to the prohibitive costs associated with the development and production of custom chips. Other major competitors such as Cisco and Juniper have also started following the same strategy, which led to multiple competing products built on top of the same chips. For instance Broadcom's Trident chip is used in some Cisco Nexus switches, Juniper QFX switches, Force10, IBM and HP switches. The integration of the chips with the rest of the system (including integration with the MAC, PHY, and device drivers on the control plane) and software are what differentiate the competing products.

In November 2013, Arista Networks introduced the Spline network, combining leaf and spine architectures into a single-tier network, which aims to cut operational costs.