Span And Rspan Interaction With Other Features - Cisco Catalyst 2950 Software Configuration Manual

Understanding SPAN and RSPAN

SPAN and RSPAN Interaction with Other Features

SPAN interacts with these features:
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Spanning Tree Protocol (STP)—A destination port or a reflector port does not participate in STP
while its SPAN or RSPAN session is active. The destination or reflector port can participate in STP
after the SPAN or RSPAN session is disabled. On a source port, SPAN does not affect the STP status.
STP can be active on trunk ports carrying an RSPAN VLAN.
Cisco Discovery Protocol (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.
VLAN Trunking Protocol (VTP)—You can use VTP to prune an RSPAN VLAN between switches.
VLAN and trunking—You can modify VLAN membership or trunk settings for source, destination,
or reflector ports at any time. However, changes in VLAN membership or trunk settings for a
destination or reflector port do not take effect until you disable the SPAN or RSPAN session.
Changes in VLAN membership or trunk settings for a source port immediately take effect, and the
SPAN session automatically adjusts accordingly.
EtherChannel—You can configure an EtherChannel group as a source port but not as a SPAN
destination port. When a group is configured as a SPAN source, the entire group is monitored.
If a port is added to a monitored EtherChannel group, the new port is added to the SPAN source port
list. If a port is removed from a monitored EtherChannel group, it is automatically removed from
the source port list. If the port is the only port in the EtherChannel group, the EtherChannel group
is removed from SPAN.
If a physical port that belongs to an EtherChannel group is configured as a SPAN source, destination,
or reflector port, it is removed from the group. After the port is removed from the SPAN session, it
rejoins the EtherChannel group. Ports removed from an EtherChannel group remain members of the
group, but they are in the down or standalone state.
If a physical port that belongs to an EtherChannel group is a destination or reflector port and the
EtherChannel group is a source, the port is removed from the EtherChannel group and from the list
of monitored ports.
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.
Port security—A secure port cannot be a SPAN destination port.
Chapter 24 Configuring SPAN and RSPAN
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