Port mirroring can mirror several source port to a destination port(mirroring port).

I have several questions about port mirroring.

  1. in the dest port, how to differentiate the different source port? will there be several channels in the destination port? or all source ports gather in one ?

  2. if the I have 2 source ports with 1 Gbps speed, but the destination port is 1 Gbps speed too, can use this way to mirroring (source: 1+1 > dest: 1) ?

3.is it possible use virtual port as the destination port?

4.use port mirroring will affect source port?


1 Answer 1


Cisco created SPAN (Switch Port ANalyzer) for its switches as an aid to troubleshooting things on a network. It is designed to be enabled while troubleshooting, then disabled. Some other switch vendors do something similar, and others do not. Even with a particular vendor, some models may be able to do it, and some not, and it may be differently configured for different models.

  1. All the frames are usually simply mirrored to the mirror interface, and the source and destination MAC addresses are how to distinguish the frames.
  2. If you have more traffic than the destination interface can handle, then frames are simply dropped. That is how things work with any interface, mirror destination or not.
  3. Cisco created RSPAN (Remote Switch Port ANalyzer) to send mirrored frames to a VLAN interface (Switch Virtual Interface). Some other vendors have something similar, and others do not. Cisco then took it further with ERSPAN (Encapsulated Remote Switch Port ANalyzer) to send mirrored traffic to a layer-3 destination.
  4. The source interfaces have no idea if the the interface has its traffic mirrored, so they are not affected at all. This is now done all in hardware.

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