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43-4
Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 43 Configuring Switched Port Analyzer
Configuring SPAN
Destination Interface
A destination interface (also called a monitoring interface) is a switched interface to which SPAN sends
packets for analysis. You can have only one SPAN destination interface.
A destination interface has these restrictions:
• It needs to be a single physical port.
• It cannot be used as an ingress interface.
• When an interface is configured as a destination interface, it cannot be configured as a source
interface.
Traffic Types
Ingress SPAN (Rx) copies network traffic received by the source interfaces for analysis at the destination
interface. Egress SPAN (Tx) copies network traffic transmitted from the source interfaces. Specifying
the configuration option both copies network traffic received and transmitted by the source interfaces to
the destination interface.
SPAN Traffic
Network traffic, including multicast, can be monitored using local SPAN. Multicast packet monitoring
is enabled by default. In some local SPAN configurations, multiple copies of the same source packet are
sent to the local SPAN destination interface. For example, a bidirectional (both ingress and egress) local
SPAN session is configured for sources a1 and a2 to a destination interface d1. If a packet enters the
switch through a1 and gets switched to a2, both incoming and outgoing packets are sent to destination
interface d1; both packets would be the same (unless a Layer-3 rewrite had occurred, in which case the
packets would be different).
Configuring SPAN
The following sections describe how to configure SPAN:
• Creating a SPAN Session, page 43-4
• Removing Sources or Destination from a SPAN Session, page 43-5
Creating a SPAN Session
To create a SPAN session:
SUMMARY STEPS
1. enable
2. configure terminal
3. monitor session {session_number} type local