Overview - Cisco Nexus 9000 Series Configuration Manual

Overview

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Layer 2 Ethernet Switching Overview
The device supports simultaneous, parallel connections between Layer 2 Ethernet segments. Switched
connections between Ethernet segments last only for the duration of the packet. New connections can be made
between different segments for the next packet.
The device solves congestion problems caused by high-bandwidth devices and a large number of users by
assigning each device (for example, a server) to its own collision domain. Because each LAN port connects
to a separate Ethernet collision domain, servers in a switched environment achieve full access to the bandwidth.
Because collisions cause significant congestion in Ethernet networks, an effective solution is full-duplex
communication. Typically, 10/100-Mbps Ethernet operates in half-duplex mode, which means that stations
can either receive or transmit. In full-duplex mode, which is configurable on these interfaces, two stations
can transmit and receive at the same time. When packets can flow in both directions simultaneously, the
effective Ethernet bandwidth doubles.
VLANs
A VLAN is a switched network that is logically segmented by function, project team, or application, without
regard to the physical locations of the users. VLANs have the same attributes as physical LANs, but you can
group end stations even if they are not physically located on the same LAN segment.
Any switch port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and
flooded only to end stations in that VLAN. Each VLAN is considered as a logical network, and packets
destined for stations that do not belong to the VLAN must be forwarded through a bridge or a router.
All ports are assigned to the default VLAN (VLAN1) when the device first comes up. A VLAN interface, or
switched virtual interface (SVI), is a Layer 3 interface that is created to provide communication between
VLANs.
Layer 2 Ethernet Switching Overview, page 3
VLANs, page 3
Spanning Tree , page 4
Related Topics, page 5
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
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