Span And Rspan Interaction With Other Features - Cisco ME 3400 Software Configuration Manual

Understanding SPAN and RSPAN
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It is normal to have multiple RSPAN VLANs in a network at the same time with each RSPAN VLAN
defining a network-wide RSPAN session. That is, multiple RSPAN source sessions anywhere in the
network can contribute packets to the RSPAN session. It is also possible to have multiple RSPAN
destination sessions throughout the network, monitoring the same RSPAN VLAN and presenting traffic
to the user. The RSPAN VLAN ID separates the sessions.

SPAN and RSPAN Interaction with Other Features

SPAN interacts with these features:
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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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RSPAN VLANs must be configured in VLAN configuration mode by using the remote-span VLAN
configuration mode command.
– To change a VLAN from a UNI-ENI isolated VLAN (the default) to an RSPAN VLAN, enter
the rspan-vlan VLAN configuration command.
– To change a UNI-ENI community VLAN to an RSPAN VLAN, you must first remove the
community VLAN type by entering the no uni-vlan VLAN configuration command.
STP can run on RSPAN VLAN trunks but not on SPAN destination ports.
Note NNIs support STP by default and you can enable STP on ENIs. UNIs do not support STP.
An RSPAN VLAN cannot be a private-VLAN primary or secondary VLAN.
Routing—For switches that are running the metro IP access image, SPAN does not monitor routed
traffic. RSPAN only monitors traffic that enters or exits the switch, not traffic that is routed between
VLANs. For example, if a VLAN is being receive-monitored and the switch routes traffic from
another VLAN to the monitored VLAN, that traffic is not monitored and is not received on the SPAN
destination port.
STP—A destination port does not participate in STP while its SPAN or RSPAN session is active.
The destination 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. However, only NNIs or ENIs can support STP; UNIs do not participate in STP.
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. NNIs have CDP enabled by default
and you can enable it on ENIs; UNIs do not participate in CDP.
VLAN and trunking—You can modify VLAN membership or trunk settings for source or
destination ports at any time. However, changes in VLAN membership or trunk settings for a
destination port do not take effect until you remove the SPAN destination configuration. 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. When a group is configured as a SPAN source, the entire group is monitored.
If a physical 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.
A physical port that belongs to an EtherChannel group can be configured as a SPAN source port and
still be a part of the EtherChannel. In this case, data from the physical port is monitored as it
participates in the EtherChannel. However, if a physical port that belongs to an EtherChannel group
Chapter 26 Configuring SPAN and RSPAN
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