Arista 7800R3 User Manual
Arista 7800R3 Platform Architecture
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Figure 1: Arista 7800R3 Universal Spine platform.
Arista Networks’ award-winning Arista 7500 Series was introduced as a high density non-blocking modular 10G systems
in April 2010 and established itself as a revolutionary switching platform, which maximized data center performance,
efficiency and overall network reliability. Since 2010 the Arista 7500 Series established the benchmark for performance
and reliability delivering continuous innovations and seamless upgrades. Nearly 10 years later, Arista is introducing the
next generation of modular system, the 7800R3 Universal Spine platform, continuing the long heritage of investment
protection, scalability and industry leading density and performance. This white paper provides an introduction to the
architecture of the Arista 7800R3 Universal Spine platform.
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Arista 7800R3: Platform Overview
The Arista 7800R3 Universal Spine Platform is the evolution of the R-Series family of modular switches, with a consistent architecture
of deep buers, VoQ and non-blocking lossless forwarding. The 7800R Series are initially available in a choice of 4-slot and 8-slot
systems that support a rich range of line cards providing high density 100G and 400G with choice of forwarding table scale and
MACsec encryption options.
At a system level, the 8-slot Arista 7808R3 with a fabric that scales to 230 Tbps enables 288 x 400G or 384 x 100G (QSFP100) in a
16 RU front to rear power ecient form factor, providing industry-leading performance and density without compromising on
features and functionality. The 7808R3 provides a platform for service providers and cloud operators to deliver the next generation
of rich services. The 7804R3 4-slot system provides the same capabilities in a more compact system with support for up to 144 400G
interfaces and 115Tbps.
Table 1: Arista 7800R3 Key Port and Forwarding Metrics
Characteristic Arista 7804R3 Arista 7808R3
Chassis Height (RU) 10 RU 16 RU
Linecard Module slots 4 8
Supervisor Module slots 2 2
50G Maximum Density using 8x50G breakout 1152 2304
100G Maximum Density (QSFP100) 192 384
400G Maximum Density (OSFP or QSFP-DD) 144 288
System Usable Capacity (Tbps) 115.2 Tbps (FD) 230.4 Tbps (FD)
Max forwarding throughput per Linecard (Tbps) 14.4 Tbps (DCS-7800R3-36P - 36 x 400G per LC)
Max forwarding throughput per System (Tbps) 115.2 Tbps (FD) 230.4 Tbps (FD)
Max packet forwarding rate per Linecard (pps) 6 Billion pps (7800R3-36P)
Max packet forwarding rate per System (pps) 24 Bpps 48 Bpps
Maximum Buer memory/ System 96 GB 192 GB
Virtual Output Queues / System More than 2.2 million
The 7800R Series is consistent with the 7500R, using a common architecture. The 7800R Series provides higher density and
forwarding on a per system basis as shown below.
Table 2: Arista 7800R3 and 7500R3 System Capacity
Characteristic 7504R3 7508R3 7512R3 7804R3 7808R3
Line card Slots 4 8 12 4 8
100G Maximum Density (QSFP100) 144 288 432 192 384
400G Maximum Density (OSFP or QSFP-DD) 96 192 288 144 288
Max forwarding throughput per System (Tbps) 76.8Tbps 153Tbps 230Tbps 115Tbps 230Tbps
Max packet forwarding rate per System (pps) 16Bpps 32Bpps 48Bpps 24Bpps 48Bpps
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Designed for the Future
The Arista 7800R3 Universal Spine platform leverages the heritage of the Arista 7500 Series platform which has delivered continuous
capacity increases for cloud scale networks for 10 years and driven the industry in new directions for power and eciency.
The Arista 7800R3 platform builds on the R-Series innovations with system level capacity and environmental enhancements for the
next 10 years of data center and core networking.
• Leveraging backplane and midplane less orthogonal connections allowing greater airow and easy migration to higher
performance
• Cooling up to 2.4kW per line card slot using high eciency fans and datacenter optimized airow.
• SerDes lanes supporting 112G rates for the next generation of I/O
• Up to 36kW of redundant power providing sucient capacity for future needs
• 1.3RU height modules for airow, cooling and power delivery
Arista 7800R3 - Cloud Scale And Features
Arista networks has always leveraged best in class merchant silicon packet processors for leaf and spine systems. The network silicon
within the Arista 7800 Series is no exception and utilizes the latest high capacity multi-chip system packet processor, the Jericho2
from Broadcom. Clocking in at 10Tbps (12 x 400G network interfaces and 5.2Tbps fabric) per chip, it delivers the highest overall
system capacity and scale available in the market currently.
In addition to delivering port density and performance, forwarding table capacity are designed to provide operators with Internet
route scale through Arista’s innovative FlexRoute
merchant silicon natively oers. The 7800R3-series Modular Database (MDB) enables exible allocation of forwarding resources to
accommodate a wide range of network deployment roles.
The MDB provides a common database of forwarding and lookup resources to the ingress and egress stages in the 7800R3 platform.
These resources are allocated using a set of forwarding proles that ensure the optimal allocation of resources to dierent tables
for a wide range of networking use-cases. The L3 optimized prole expands the routing and next-hop tables to address large scale
networks where route table capacity is required, while the balanced prole is suited for leaf and spine datacenter applications.
TM
Engine, extending forwarding table capacity beyond the capability that
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Figure 2: MDB enables a flexible range of deployment profiles.
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The fungible nature of the resources within the MDB ensure that operators have the exibility they need to standardize on a
common platform across a wide range of roles with the condence that the specic resource requirements can be achieved
according to the needs of any given role. There is no need to have separate platforms for core network roles and edge roles in today’s
service provider networks. This enables cloud and service providers to streamline deployments, simplify sparing and consolidate
testing.
Arista 7800R3: System Components
Chassis and Mid-Plane-less system
All Arista 7800R3 systems share a common architecture with identical fabric bandwidth and forwarding capacity per slot. Line cards,
supervisor modules and power supplies are common across systems; the only dierences are the physical size, fabric/fan module
size, number of line card slots and quantity of power supplies. Airow is always front-to-rear and all data cabling is at the front of the
chassis.
Chassis design and layout are a key aspect that enables high performance per slot: the fabric modules are directly behind line card
modules and oriented orthogonally to the line card modules. This design alleviates the requirement to route high speed signal
traces on a midplane or backplane, reducing trace lengths between system elements and enabling high speed signals to operate
more eciently with high signal integrity by being shorter lengths. The 7800R system eliminates the passive midplane or backplane,
allowing the direct connection of line cards to fabric modules improving airow and providing investment protection for future
higher capacity systems.
Supervisor Modules
The Supervisor modules on the Arista 7800R Universal Spine platform are used for control-plane and management plane functions
only. There are two redundant supervisors in the chassis, each capable of managing the system. All data-plane forwarding is
performed on line card modules and forwarding between line card modules is always via the fabric modules.
Figure 3: Arista 7800 Series Supervisor Module.
The Arista 7800 Series Supervisor provides a 6-core Intel Xeon Broadwell DE CPU running at 1.9GHz with 64GB RAM and is used with
both the 7804R3 and 7808R3.
Arista’s Extensible Operating System (EOS®) makes full use of multiple cores due to its unique multi-process state sharing
architecture that separates state information and packet forwarding from protocol processing and application logic. The multi-core
CPU and large memory conguration provides headroom for running third party software within the same Linux instance as EOS,
within a guest virtual machine or within containers. An enterprise-grade SSD provides additional ash storage for logs, VM images or
third party software packages.
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Out-of-band management is available via a serial console port and/or dual 10/100/1000 Ethernet interfaces (SFP and RJ45 ports are
provided). There are two USB 2.0 interfaces that can be used for transferring images/logs or many other uses. A pulse-per-second
clock input is provided for accurate clock synchronization.
There is more than 126 Gbps of inband connectivity from data-plane to control-plane and 10G connectivity between redundant
Supervisor modules. Combined, these enable very high performance connectivity for the control-plane to manage and monitor the
data-plane as well as replicate state between redundant Supervisors.
Arista 7800R3: Distributed Packet Forwarding
Distributed Data-Plane Forwarding
All Arista 7800R3 systems share a common architecture with identical fabric bandwidth and forwarding capacity per slot. Line cards,
supervisor modules and power supplies are common across systems; the only dierences are the physical size, fabric/fan module
size, number of line card slots and quantity of power supplies. Airow is always front-to-rear and all data cabling is at the front of the
chassis.
Figure 4: Distributed Forwarding within an Arista 7500R3 Series
Arista 7800R3 Universal Spine platform line card modules utilize packet processors to provide distributed dataplane forwarding.
Forwarding between ports on the same packet processor utilizes local switching and no fabric bandwidth is used. Forwarding
across dierent packet processors uses all fabric modules in a fully active/active mode. There is always Virtual Output Queuing (VoQ)
between input and output, for both locally switched and nonlocally switched packets, ensuring there is always fairness even where
some trac is local.
Fabric Modules
Within the Arista 7800R3 up to six fabric modules are utilized in an active/active mode. Each fabric module provides up to 6 Tbps
fabric bandwidth full duplex (3 Tbps transmit and 3 Tbps receive) to each line card slot, and with six active fabric modules in a
7808R3 system 288 Tbps (144 Tbps transmit and 144 Tbps receive) of bandwidth is available. If a fabric module were to fail, the
throughput of the fabric degrades gracefully. Fabric modules support hot swap and may be inserted or removed while the system is
in operation.
Each 7808R3 fabric module contains 8 fan modules comprised of dual counter-rotating fans. Fans are connected to two
independent fan controllers to increase fault tolerance. To ensure that there is sucient cooling capacity for line cards and fabric
modules, fans are powered on before any active forwarding elements.
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Figure 5: Arista DCS-7800R3 Series Fabric/Fan modules
Packets are transmitted across fabric modules as variable sized cells of up to 256 bytes. Serialization latency of larger frames is
amortized via the parallel cell distribution that utilizes all available paths in an active/active manner, preventing hot spots or
blocking that can occur with packet-based fabrics.
Besides data-plane packets, the fabric modules are also used for a number of other functions:
• Virtual Output Queuing (VoQ): a distributed scheduling mechanism is used within the switch to ensure fairness for trac
ows contending for access to a congested output port. A credit request/grant loop is utilized and packets are queued in
physical buers on ingress packet processors within VoQs until the egress packet scheduler issues a credit grant for a given
input packet.
• Hardware-based distributed MAC learning and updates: when a new MAC address is learned, moves or is aged out, the
ingress packet processor with ownership of the MAC address will update other packet processors.
• Data-plane health tracer: all packet processors within the system send continuous health check messages to all other packet
processors, validating all data-plane connectivity paths within the system.
The 7800R3 series is designed to ensure growth for the future. As SerDes speeds increase from 50G per lane to 100G per lane, there
is sucient capacity to double the system capacity overall.
Table 3: Arista 7800R3 Fabric Bandwidth
7800R3
50G SerDes
Lanes per Line card 384 384
Fabric bandwidth per Line card
(Full Duplex)
Fabric bandwidth per 8-Slot system
(Full Duplex)
38.4T 76.8T
273.6T 614.4T
7800R3
100G SerDes
7800R3 Series Power Supplies
The 7800R3 series uses a common 3kW AC power supply across all form-factors. This power supply has dual AC inputs for
redundancy and supports integrated Auto-Transfer Switchover (ATS). The 7800R3 series platforms utilize a single internal power
domain, so there is no need to allocate specic power supply units to individual power zones. This enables operators to achieve N+2
power supply redundancy as well as balance power feeds across the data center power grids.
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