N3K-C3408-S Cisco Nexus 3408 1 Gigabit Ethernet 8-slot Chassis Switch

Cisco N3K-C3408-S 8-slot Chassis Switch

The Cisco N3K-C3408-S Nexus 3408 stands as a cornerstone of data center switching, engineered to deliver high-density 1 Gigabit Ethernet connectivity within a versatile modular chassis. As a 4-rack-unit (4RU) form factor, 8-slot chassis, it provides a scalable foundation for large-scale server aggregation, storage networking, and evolving data center architectures. Designed for environments requiring massive port counts and consistent low-latency performance, the 3408-S chassis is the physical infrastructure upon which a flexible and powerful network fabric is built. It operates on the robust Cisco NX-OS software, delivering carrier-class availability, comprehensive security, and streamlined operational management.

Core Chassis Specifications

The N3K-C3408-S chassis is meticulously designed for data center deployment, balancing high port density with essential serviceability features.

Form Factor

The switch occupies 4 rack units (4RU) of standard 19-inch rack space. Its physical dimensions are carefully calibrated for optimal airflow and cable management in both front-to-back and back-to-front cooling configurations typical of modern data centers. The chassis is engineered to operate within standard data center temperature and humidity ranges, with redundant, hot-swappable power supply units and fan trays ensuring consistent thermal management even under full load. The power supplies and fans are front-accessible, facilitating rapid serviceability without disrupting adjacent equipment.

Slot Architecture and Midplane

The eight slots are connected via a high-bandwidth, non-blocking midplane. This design is critical for the chassis's flexibility, allowing any combination of supervisor and line card modules to be installed in any slot. The midplane provides dedicated high-speed channels for control plane communication between the supervisors and line cards, as well as the data plane fabric for forwarding traffic. This architecture eliminates slot-dependent performance restrictions and simplifies capacity planning.

Advanced Layer 2 and Layer 3 Networking

The platform supports a comprehensive suite of IP routing and Ethernet switching protocols to fit any design.

Layer 2 Feature Set

For Ethernet switching, it supports a robust set of IEEE standards: 802.1Q VLANs, 802.1w Rapid Spanning Tree Protocol (RSTP) and 802.1s Multiple Spanning Tree (MST), 802.3ad Link Aggregation (LACP) for port-channels, and 802.1ah Bridge Protocol Data Unit (BPDU) Guard. Enhanced features like Cisco FabricPath provide scalable, loop-free Layer 2 multipathing for modern fabric architectures.

Layer 3 Routing Capabilities

The switch operates as a full-featured Layer 3 router. It supports static routing, RIPv2, OSPFv2/v3, EIGRP, and IS-IS for IPv4 and IPv6. For large-scale data center and enterprise edge routing, full BGP (Border Gateway Protocol) implementation is included. Protocol-independent features like Equal-Cost Multi-Path (ECMP) routing are supported for efficient load balancing across multiple uplinks or fabric paths.

Data Center Bridging and Storage Networking

The Nexus 3408 is designed for unified fabric deployments, converging LAN and SAN traffic.

Fibre Channel over Ethernet (FCoE)

With the appropriate line cards and licensing, the switch can operate as a FCoE Forwarder (FCF). It can receive native Fibre Channel frames encapsulated within Ethernet from Converged Network Adapters (CNAs) in servers, transport them across the Ethernet fabric, and bridge them to a native Fibre Channel SAN via an attached Fibre Channel switch. This requires support for Data Center Bridging (DCB) protocols: Priority Flow Control (802.1Qbb), Enhanced Transmission Selection (802.1Qaz), and DCB Exchange (DCBX).

Network Virtualization with VXLAN

To support large multi-tenant cloud environments, the Nexus 3408 with NX-OS supports VXLAN (Virtual Extensible LAN) overlay networking. VXLAN provides Layer 2 segment extension over an IP underlay, breaking the traditional 4094 VLAN limit by offering a 24-bit segment ID (up to 16 million segments). It is a key technology for network virtualization, enabling workload mobility across subnets and physical locations.

Deployment Use Cases and Applications

The modular design of the N3K-C3408-S makes it suitable for several critical roles in the data center network architecture.

Massive-Scale Server Aggregation Layer

The most common application is as a server aggregation or "leaf" switch in a large-scale data center. Fully populated with 48-port 1GbE line cards, a single chassis can provide up to 384 Gigabit Ethernet server ports. When combined with high-speed 40GbE uplink modules, it creates a high-density, cost-effective aggregation point for entire rows or pods of servers, connecting them to a 10GbE/40GbE spine layer.

Mainframe and IBM BladeCenter Connectivity

The chassis is often deployed in environments with IBM mainframe or BladeCenter systems that utilize high-port-count 1GbE connectivity. The density and reliability of the Nexus 3408 make it an ideal platform for aggregating these critical systems into the data center network fabric.

Storage Network Gateway

With its FCoE and DCB capabilities, the Nexus 3408 can act as a unified fabric gateway. It aggregates FCoE traffic from servers, consolidates it onto a few high-bandwidth links, and connects to a Fibre Channel SAN core. This reduces the number of adapters, switches, and cables needed at the server access layer while maintaining the performance and integrity of storage traffic.

Network Function Virtualization (NFV) Host

The ability to create multiple VDCs (Virtual Device Contexts) allows the physical chassis to host logical network functions. For example, different VDCs can be instantiated as dedicated firewalls, load balancers, or routers for specific application tiers or tenants, all running on shared hardware under a unified management framework.

Chassis Design and Scalability

The N3K-C3408-S chassis is the physical and operational core of the system, providing the power, cooling, and backplane infrastructure for all installed modules. Its design emphasizes high availability and serviceability.

Slot Architecture and Purpose

The eight slots are intelligently allocated to maximize flexibility and performance. Slots 1 and 2 are dedicated to supervisor modules, which house the control-plane intelligence, management interfaces, and system software. Slots 3 through 8 are designated for high-speed I/O (Input/Output) line cards, providing the actual Ethernet and storage connectivity for servers, storage arrays, and other network devices. This clear separation of control and data plane resources ensures that control traffic never competes with data traffic, leading to predictable performance and enhanced stability.

Scalable Switching Fabric

The performance of the Nexus 3408-S chassis is not fixed; it scales dynamically based on the installed supervisors, fabric modules, and line cards. This "pay-as-you-grow" model allows for tailored performance characteristics. The heart of the chassis's performance is its distributed switching fabric. This fabric comprises multiple, hot-swappable fabric modules that work in tandem.