SPAN destination port

Answered Question
Apr 16th, 2009
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I have a setup in which I have 2 servers talking to each other and those ports are the SPANned source ports. The destination port used to be have a sniffer connected and now there is nothing connected to the destination port. In such case what will have to the mirrored packet, will it eventually die down or the the switch will broadcast the mirrored packet to the entire sunbet?

Correct Answer by divyapratap.singh about 8 years 2 months ago

Hi,

I was going through the SPAN Configuration Guidelines of 3550 sharing one of the guidelines,


"You can configure a disabled port to be a source or destination port, but the SPAN function does not start until the destination port and at least one source port or source VLAN are enabled."


So for the SPAN function to work properly in your case the destination port should be UP, if it is not UP the SPAN function will not work and the switch will not make a copy of the

frames.


So if you still have configuration on your switch it should not affect, but as a best practise it should not be there.


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saimbt Fri, 04/17/2009 - 06:45
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there is nothing connected to the destination port. Will the mirrored port discard the recieved packet?

It will in a sense, I am not 100% but I believe that the switch logic will still make a copy of the frames, and look to deliver....but since the port is down the frames will be discarded.


So a slight waste of cpu & memory, if you are not capturing the frames to be honest remove the config as it's a waste.


HTH>

saimbt Fri, 04/17/2009 - 07:18
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yeah i have removed the configuration.. but as this config was lying in the switch got inquisitive to undertsand how the switch and the frame would behave.

Correct Answer
divyapratap.singh Sat, 04/18/2009 - 06:30
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Hi,

I was going through the SPAN Configuration Guidelines of 3550 sharing one of the guidelines,


"You can configure a disabled port to be a source or destination port, but the SPAN function does not start until the destination port and at least one source port or source VLAN are enabled."


So for the SPAN function to work properly in your case the destination port should be UP, if it is not UP the SPAN function will not work and the switch will not make a copy of the

frames.


So if you still have configuration on your switch it should not affect, but as a best practise it should not be there.


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