Administration: Diagnostics
Configuring Port and VLAN Mirroring
Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 89
7
Configuring Port and VLAN Mirroring
Port mirroring is used on a network device to send a copy of network packets
seen on one device port, multiple device ports, or an entire VLAN to a network
monitoring connection on another port on the device. This is commonly used for
network appliances that require monitoring of network traffic, such as an intrusion-
detection system. A network analyzer connected to the monitoring port processes
the data packets for diagnosing, debugging, and performance monitoring.
Up to eight sources can be mirrored. This can be any combination of eight
individual ports and/or VLANs.
A packet that is received on a network port assigned to a VLAN that is subject to
mirroring is mirrored to the analyzer port even if the packet was eventually
trapped or discarded. Packets sent by the device are mirrored when Transmit (Tx)
mirroring is activated.
Mirroring does not guarantee that all traffic from the source port(s) is received on
the analyzer (destination) port. If more data is sent to the analyzer port than it can
support, some data might be lost.
VLAN mirroring is not active on a VLAN that was not manually created. For
example, if VLAN 23 was created by GVRP, and you manually created VLAN 34,
and you create port mirroring that includes VLAN 23, VLAN 34, or both, and later
on delete VLAN 34, the status in port mirroring is set to Not Ready, because the
VLAN34 is no longer in the database and VLAN23 was not created manually.
Only one instance of mirroring is supported system-wide. The analyzer port (or
target port for VLAN mirroring or port mirroring) is the same for all the mirrored
VLANs or ports.
To enable mirroring:
STEP 1 Click Administration > Diagnostics > Port and VLAN Mirroring.
The following fields are displayed:
• Destination Port—Port to which traffic is to be copied; the analyzer port.
• Source Interface—Interface, port, or VLAN from which traffic is sent to the
analyzer port.
• Type—Type of monitoring: incoming to the port (Rx), outgoing from the port
(Tx), or both.
• Status— Displays one of the following values:
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