Page 43 of 71
2.18
Port mirroring function
Port mirroring is the function which monitors the receiving traffic or the sending traffic of the specified
source port from the specified target port. Target port for reception mirror which monitors receiving
traffic of source port and, Target Port for transmission mirror which monitors sending traffic of
source port can be specified as target port.
When port mirroring function is used, first a probe device such as LAN analyzer is connected to the target port
to monitor the traffic condition and the connected target port and the monitored source port is specified.
Multiple source ports can be specified in this device. However when multiple ports are specified,
the total traffic for the source port should not exceed the bandwidth of the target port.
Points to be noted
▪
Only 1 target port of the mirror can be set for the sending and receiving by the device.
▪
The sending port and receiving port of the target port of the mirror cannot be set in the same port.
▪
The target port of the mirror becomes dedicated port for mirror of the source port.
▪
The port specified with the target of the mirror cannot be specified as a source.
▪
When there are multiple source ports of the mirror for the target port, the packets in the part that exceeds
the bandwidth of the target port is discarded.
▪
When the port status in the STP function of the source port is other than forwarding, the packets are mirrored
at the target port. The relation between MSTP, STP, RSTP states and the
frame to be mirrored is as follows.
When multiple source mirrors are possible, traffic corresponding to each state is mirrored.
Source port status (in the VLAN targeted in case of
MSTP)
Frame Type
Send to target port
Disable
Other than BPDU
Not sent
BPDU
Not sent
Blocking, listening (discarding in RSTP/MSTP).
Other than BPDU
Not sent
BPDU
sent
Learning
Other than BPDU
Not sent
BPDU
sent
Forwarding
Other than BPDU
sent
BPDU
sent
▪
The existence and contents of the VLAN tag of the packet that is output to the target port may differ from the
packet that is actually sent or received by the source port.
analyzer
analyzer
Network
Source port
Target port
(transmission mirror)
Target port
(reception mirror)