Users Guide

Layer 2 Switching Commands 658
the implicit deny all). If configuring an egress ACL on the destination port,
care must be taken with the ACL numbering to ensure the mirrored traffic is
properly processed.
Bidirectional mirroring of multiple ports in a network may result in duplicate
packets transmitted on the probe port (one copy for the receive side and
another copy for the transmit side). Configuring the mirroring as rx only may
help to reduce this issue.
RSPAN VLANs must be configured with the remote-span command prior to
configuration in an RSPAN session. RSPAN intermediate switches may also
be configured with multiple sources feeding into an existing RSPAN VLAN.
The source configuration requires an interface parameter, so traffic mirrored
on the intermediate switch is not flooded across the entire RSPAN VLAN.
Place probe ports upstream of the intermediate switch in this case.
Configuring a second session on a source switch that mirrors RSPAN traffic
from the reflector port is not supported. Configuring a second session on a
source switch that mirrors an RSPAN source port to a local probe port is
supported.
VLAN mirroring is not recommended for RSPAN if sources on multiple
switches are members of the VLAN. This is because, as stations communicate
with each other over the mirrored VLAN, duplicate packets will be sent to the
probe, once for the source port and once for each switch over which the
packet is received in the source VLAN.
Example
This example shows how to configure a source switch using VLAN 723 as the
destination RSPAN VLAN and Gi1/0/3 as the source interface. Te1/0/1 is
configured as the reflector port. It is recommended that interface Te1/0/1 be
configured as a trunk port. Interface Te1/0/1 must be configured as a member
of VLAN 723 and may also carry traffic on other VLANs. No other interface
should be configured as a member of VLAN 723.
console(config)#vlan 723
console(config-vlan723)#remote-span
console(config-vlan723)#exit
console(config)#interface Te1/0/1
console(config-if-Te1/0/1)#switchport mode trunk
console(config-if-Te1/0/1)#exit
console(config)#monitor session 1 source interface gi1/0/3 both