15-6
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter15 Configuring SPAN
Configuring SPAN
•VLAN and trunking—You can modify VLAN membership or trunk settings for source and
destination ports at any time. However, changes in VLAN membership or trunk settings for a
destination port do not take effect until you disable the SPAN session. Changes in VLAN
membership or trunk settings for a source port immediately take effect, and the respective SPAN
sessions automatically adjust accordingly.
•EtherChannel—You can configure an EtherChannel group as a source port but not as a SPAN
destination port. SPAN configuration fails if the destination port is part of an EtherChannel gro up.
When a channel 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 EtherCha nnel group, i t is au t omat ica ll y rem ove d fr om
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 c onfi gu red a s a SPAN source or
destination port, it is removed from the EtherChannel group . Af ter t he p ort is re m oved fro m the
SPAN session, it rejoins the EtherChannel group.
•QoS—For ingress monitoring, the packets sent to the SPAN destination port might be different fr om
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.
For egress monitoring, the packets sent out the SPAN destination port might not be the same as the
packets sent out of SPAN source ports because the egress QoS policing at the SPAN source port
might change the packet classification. QoS policing is no t a pplie d at SPAN destination ports.
•Multicast traffic can be monitored. For egress and ingress port monitori n g, onl y a sing l e une dite d
packet is sent to the SPAN destination port. It does not reflect the number of times the multicast
packet is sent.
•A secure port cannot be a SPAN destination port.
•You can enable 802.1X on a port that is a SPAN d est inatio n port ; howe ver, 802.1X is disabled until
the port is removed as a SPAN destination. You can enable 802.1X on a SPAN source port.
Configuring SPAN
This section describes how to configure SPAN on your switch. It contains this configur ation
information:
•Default SPAN Configuration, page 15-7
•SPAN Configuration Guidelines, page 15-7
•Creating a SPAN Session and Specifying Ports to Monitor, page 15-8
•Removing Ports from a SPAN Session, page 15-10
•Specifying VLANs to Monitor, page 15-11
•Specifying VLANs to Filter, page 15-12