Managing Device Diagnostics
Configuring Port and VLAN Mirroring
Cisco Small Business 300 Series Managed Switch Administration Guide 61
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• Output Power—Transmitted optical power.
• Input Power—Received optical power.
• Transmitter Fault—Remote SFP reports signal loss. Values are True, False,
and No Signal (N/S).
• Loss of Signal—Local SFP reports signal loss. Values are True and False.
• Data Ready—SFP is operational. Values are True and False
Configuring Port and VLAN Mirroring
Port Mirroring is used on a network switch to send a copy of network packets
seen on one switch port, multiple switch ports, or an entire VLAN to a network
monitoring connection on another switch port. 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 displays
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 switch 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 created. For example, if VLAN
23 was created by GVRP and later on removed from the VLAN database for any
reason 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 VLANs are no longer in the
database.
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 mirrored ports.
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