Troubleshooting Guide

About this task
Use port mirroring to aid in diagnostic and security operations.
Use port mirroring to make a copy of a traffic flow and send that copy to a device for analysis, for
example, for diagnostic sniffing. Use the mirror to see the packets in the flow without breaking into
the physical connection to place a packet onto the sniffer inline. You can also use port mirroring for
security. You can send flows to inspection engines for post processing.
Connect the sniffer (or other traffic analyzer) to the output port you specify in this procedure.
Procedure
1. Create a port mirroring instance:
mirror-by-port <1-479> in-port {slot/port[-slot/port][,...]}
{monitor-mlt <1-512>|out-port {slot/port[-slot/port][,...]}
2. Configure the mode:
mirror-by-port <1-479> mode <both|rx|tx>
3. Enable the mirroring instance:
mirror-by-port <1-479> enable
4. Modify existing mirroring entries as required:
mirror-by-port mirror-port <1-479> {slot/port[-slot/port][,...]}
OR
mirror-by-port monitor-mlt <1-479> <1-512>
OR
mirror-by-port monitor-port <1-479> {slot/port[-slot/port][,...]}
OR
Note:
Before you can modify an existing entry, you must disable the entry: no mirror-by-
port <1-479> enable .
5. Verify the configuration:
show mirror-by-port
Example
VSP-4850GTSPWR+:1>enable
VSP-4850GTSPWR+:1#configure terminal
Create the port mirroring instance. Traffic passing port 1/15 is mirrored to port 1/16:
VSP-4850GTSPWR+:1(config)# mirror-by-port 8 in-port 1/15 out-port 1/16
The analyzer connects to port 1/16.
Disable the entry:
Configuring port mirroring
January 2017 Troubleshooting 111
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