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trunk and SPAN

if i consider as source SPAN port a trunk port, and as destination port a no-trunk port, will i see on this destination port the traffic no-tagged, right?

I suppose that only if i configure the destination port as trunk port i will be able to se the tagged copied flow ...


Cisco Employee

Re: trunk and SPAN

Very dependant on the specific switch you are using.

From my experience with the Cat 6500 running Cat OS.

If you span multiple vlans (similar to spanning a trunk) to an access port (single vlan port), then you see all of the packets from all of the vlans, but none of the packets have trunk headers so they all look like they came from the same vlan. This works well with the Cisco IDS Sensors.

If you span multiple vlans (similar to spanning a trunk) to a trunk port, then you get the same packets, but this time the packets have the trunk headers designating the vlans (except packets on the Native vlan of the trunk port).

HOWEVER, I have heard that this is not always the case with other Cisco switches. So you will need to test this on the specific switch that you are running. It can also vary depending on whether you are running Cat OS or Native IOS.

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