SPAN sources refer to the interfaces from which traffic can be monitored. The Cisco Nexus Series device supports Ethernet, port channels, and VLANs as SPAN sources. With VLANs, all supported interfaces in the specified VLAN are included as SPAN sources. You can choose the SPAN traffic in the ingress direction, the egress direction, or both directions for Ethernet source interfaces:

• Ingress source (Rx)—Traffic entering the device through this source port is copied to the SPAN destination port.

• Egress source (Tx)—Traffic exiting the device through this source port is copied to the SPAN destination port.

A source port, also called a monitored port, is a switched interface that you monitor for network traffic analysis. The switch supports any number of ingress source ports (up to the maximum number of available ports on the switch) and any number of source VLANs.

A source port has these characteristics:

• Can be of Ethernet, port channel, or VLAN port type.

• Cannot be monitored in multiple SPAN sessions.

• Cannot be a destination port.

• Each source port can be configured with a direction (ingress, egress, or both) to monitor. For VLAN sources, the monitored direction can only be ingress and applies to all physical ports in the group. The RX/TX option is not available for VLAN SPAN sessions.

• Source ports can be in the same or different VLANs.

SPAN destinations refer to the interfaces that monitors source ports. The Cisco Nexus Series device supports Ethernet interfaces as SPAN destinations.

Each local SPAN session must have a destination port (also called a monitoring port) that receives a copy of traffic from the source ports or VLANs. A destination port has these characteristics:

• Can be any physical port. Source ethernet ports cannot be destination ports.

• Cannot be a source port.

• Cannot be a port channel.

• Does not participate in spanning tree while the SPAN session is active.

• Is excluded from the source list and is not monitored if it belongs to a source VLAN of any SPAN session.

• Receives copies of sent and received traffic for all monitored source ports. If a destination port is oversubscribed, it can become congested. This congestion can affect traffic forwarding on one or more of the source ports.

SPAN has the following guidelines and limitations:

• If you install NX-OS 5.0(3)U2(2) and then downgrade to a lower version of software, the SPAN configuration is lost.

  To avoid this, you need to save the configuration before upgrading to NX-OS 5.0(3)U2(2), and then reapply the local span configurations after the downgrade.

  For information about a similar ERSPAN limitation, see Guidelines and Limitations for ERSPAN for ERSPAN.

You create a SPAN session by assigning a session number using the monitor session command. If the session already exists, any additional configuration information is added to the existing session.

You can configure an Ethernet interface as a SPAN destination port.

Note	The SPAN destination port can only be a physical port on the switch.

Source ports can only be Ethernet ports.

You can configure the source channels for a SPAN session. These ports can be port channels, and VLANs. The monitored direction can be ingress, egress, or both and applies to all physical ports in the group.

For ease of reference, you can provide a descriptive name for a SPAN session.

The default is to keep the session state shut. You can open a session that duplicates packets from sources to destinations.

By default, the session state is shut.