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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 24 Configuring SPAN and RSPAN
Understanding SPAN and RSPAN
• 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, or
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.
SPAN and RSPAN Session Limits
You can configure (and store in NVRAM) one local SPAN session or multiple RSPAN sessions on a
switch. The number of active sessions and combinations are subject to these restrictions:
• SPAN or RSPAN source (rx, tx, both): 1 active session limit. (SPAN and RSPAN are mutually
exclusive on a source switch).
• RSPAN source sessions have one destination per session with an RSPAN VLAN associated for that
session.
• Each RSPAN destination session has one or more destination interfaces for each RSPAN VLAN that
they support.
• RSPAN destination sessions are limited to two, or one if a local SPAN or a source RSPAN session
is configured on the same switch.