Information About Layer 2 Switching; Layer 2 Ethernet Switching Overview; Switching Frames Between Segments; Building The Address Table And Address Table Changes - Cisco Nexus 7000 Series Configuration Manual

Information About Layer 2 Switching

Information About Layer 2 Switching

See the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide for information on creating
Note
interfaces.
You can configure Layer 2 switching ports as access or trunk ports. Trunks carry the traffic of multiple VLANs
over a single link and allow you to extend VLANs across an entire network. All Layer 2 switching ports
maintain MAC address tables.
See the Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide for complete information
Note
on high-availability features.

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 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. 1/10-Gigabit Ethernet operates in full duplex only.

Switching Frames Between Segments

Each LAN port on a device can connect to a single workstation, server, or to another device through which
workstations or servers connect to the network.
To reduce signal degradation, the device considers each LAN port to be an individual segment. When stations
connected to different LAN ports need to communicate, the device forwards frames from one LAN port to
the other at wire speed to ensure that each session receives full bandwidth.
To switch frames between LAN ports efficiently, the device maintains an address table. When a frame enters
the device, it associates the media access control (MAC) address of the sending network device with the LAN
port on which it was received.

Building the Address Table and Address Table Changes

The device dynamically builds the address table by using the MAC source address of the frames received.
When the device receives a frame for a MAC destination address not listed in its address table, it floods the
frame to all LAN ports of the same VLAN except the port that received the frame. When the destination
Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x
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Configuring Layer 2 Switching