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Cisco Systems IntelligentGigabit Ethernet Switch Modules for the IBMBladeCenter, Software Configuration Guide
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Chapter18 Configuring SPAN and RSPAN
Understanding SPAN and RSPAN
SPAN and RSPAN Interaction with Other Features
SPAN interacts with these features:
•Spanning Tree Protocol (STP)—A destination port or a reflector port doe s 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 gro up is configured as a SPAN source,
destination, or reflector port, it is removed from the group. After the port is removed from th e SPAN
session, it rejoins the EtherChannel group. Ports removed from an EtherCha nnel group remain
members of the group, but they are in the down or standalone state.
If a physical port that belongs to an EtherChannel g roup is a destination or reflector port and the
EtherChannel group is a source, the port is removed from the Et herChannel 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.