Configuring Span; Span Configuration Guidelines - Cisco Catalyst 2950 Software Configuration Manual

Chapter 20

Configuring SPAN

•
•
Configuring SPAN
This section describes how to configure SPAN on your switch and contains this information:
•
•
•
•

SPAN Configuration Guidelines

Follow these guidelines when configuring SPAN:
•
•
•
•
•
•
•
•
•
•
•
•
78-11380-04
QoS—For ingress monitoring, the packets sent to the SPAN destination port might be different from
the packets actually received at the SPAN source port because the packets are forwarded after
ingress QoS classification and policing. The packet DSCP might not be the same as the received
packet.
Multicast traffic can be monitored. For egress and ingress port monitoring, only a single unedited
packet is sent to the SPAN destination port. It does not reflect the number of times the multicast
packet is sent.
SPAN Configuration Guidelines, page 20-5
Creating a SPAN Session and Specifying Ports to Monitor, page 20-6
Removing Ports from a SPAN Session, page 20-7
Displaying SPAN Status, page 20-8
SPAN is disabled by default.
Use a network analyzer to monitor ports.
Only one SPAN sessions can be active on a switch at the same time.
The destination port cannot be a source port; a source port cannot be a destination port.
You can have only one destination port.
An EtherChannel port can be a SPAN source port; it cannot be a SPAN destination port.
For a SPAN source port, you can monitor transmitted and received traffic for a single port or for a
series or range of ports.
When you configure a switch port as a SPAN destination port, it is no longer a normal switch port;
only monitored traffic passes through the SPAN destination port.
When you specify a single source port and do not specify a traffic type (Tx, Rx, or both), both is the
default.
You can configure a disabled port to be a source or destination port, but the SPAN function does not
start until the destination port and at least one source port is enabled.
The no monitor session session_number global configuration command removes a source or
destination port from the SPAN session from the SPAN session. If you do not specify any options
following the no monitor session session_number command, the entire SPAN session is removed.
A SPAN destination port never participates in any VLAN spanning tree. SPAN does include BPDUs
in the monitored traffic, so any spanning-tree BPDUs received on the SPAN destination port for a
SPAN session were copied from the SPAN source ports.
Catalyst 2950 Desktop Switch Software Configuration Guide
Configuring SPAN
20-5