spanning-tree and monitor session

Answered Question
Jun 12th, 2009
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I need to setup a port for monitoring both my vlans. I think I have the commands right but I was hoping to get feedback before doing so.

monitor session 1 destintation interface fa5/3


Correct Answer by Alvaro Garcia about 8 years 1 month ago

Yes, that would be enough. :o)

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Overall Rating: 5 (1 ratings)
mahmoodmkl Fri, 06/12/2009 - 09:01
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Are the source ports on the same switch or different switch in this case u need to use RSPAN or else the above command it correct.



Alvaro Garcia Fri, 06/12/2009 - 10:51
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I don't think that is all the configuration; it only states the destination port, the source ports are missing. Please send the entire SPAN configuration and specify what exactly you are looking to monitor; so we can check it.



flagshipcreditcorp Fri, 06/12/2009 - 10:56
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''''here is the current session configured

switch#show monitor session 1

Session 1


Type : Local Session

Source VLANs :

Both : 1-2


''''I thought if I add the destination port it would then pick up all the monitoring to that that port

Alvaro Garcia Fri, 06/12/2009 - 11:05
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The configuration looks correct. All the traffic coming in and out of VLANs 1 and 2 is going to be mirrored to the destination port.

Since you are monitoring VLANs, the monitored traffic will include the trunk ports on your switch. The packets passing through trunk ports includes a VLAN tag; that VLAN tag is removed when the SPAN session sends the packets to the destination port. You may like to add the "encapsulation replicate" feature to the destination port so you cam see the packets with the VLAN tag in the monitoring device. The command is:

monitor session 1 destination port Gi x/y encapsulation replicate


flagshipcreditcorp Fri, 06/12/2009 - 11:24
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okay. I will try that. If that does not work and I want to remove it by running:

no monitor session 1

Will that remove the entire session containing the vlans? The current session was put into place before I started administratoring this switch, so I want to make sure that I can roll back.


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