Destination Port; Span Interaction With Other Features - Cisco Catalyst 2360 Software Configuration Manual

Chapter 20 Configuring SPAN

Destination Port

Each local SPAN session destination session must have a destination port (also called a monitoring port)
that receives a copy of traffic from the source ports or VLANs and sends the SPAN packets to the user,
usually a network analyzer.
A destination port has these characteristics:
•
•
•
•
•
•
•
•
•
•
•
•
Local SPAN destination ports behave differently regarding VLAN tagging and encapsulation:
•

SPAN Interaction with Other Features

SPAN interacts with these features:
•
•
•
OL-19808-01
For a local SPAN session, the destination port must reside on the same switch as the source port.
When a port is configured as a SPAN destination port, the configuration overwrites the original port
configuration. When the SPAN destination configuration is removed, the port reverts to its previous
configuration. If a configuration change is made to the port while it is acting as a SPAN destination
port, the change does not take effect until the SPAN destination configuration had been removed.
If the port was in an EtherChannel group, it is removed from the group while it is a destination port.
It can be any Ethernet physical port.
It cannot be a source port.
It cannot be an EtherChannel group or a VLAN.
It can participate in only one SPAN session at a time (a destination port in one SPAN session cannot
be a destination port for a second SPAN session).
When it is active, incoming traffic is disabled. The port does not transmit any traffic except that
required for the SPAN session. Incoming traffic is never learned or forwarded on a destination port.
If ingress traffic forwarding is enabled for a network security device, the destination port forwards
traffic at Layer 2.
It does not participate in any of the Layer 2 protocols (STP, VTP, CDP, DTP, PagP).
A destination port that belongs to a source VLAN of any SPAN session is excluded from the source
list and is not monitored.
The maximum number of destination ports in a switch is 64.
For local SPAN, if the encapsulation replicate keywords are specified for the destination port,
these packets appear with the original encapsulation (untagged or IEEE 802.1Q). If these keywords
are not specified, packets appear in the untagged format. Therefore, the output of a local SPAN
session with encapsulation replicate enabled can contain a mixture of untagged or IEEE
802.1Q-tagged packets.
STP—A destination port does not participate in STP while its SPAN session is active. The
destination port can participate in STP after the SPAN session is disabled. On a source port, SPAN
does not affect the STP status.
CDP—A SPAN destination port does not participate in CDP while the SPAN session is active. After
the SPAN session is disabled, the port again participates in CDP.
Catalyst 2360 Switch Software Configuration Guide
Understanding SPAN
20-5