Can I Span The Same Port Twice ?????

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Aug 16th, 2007
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I would just like to check can I span the same port twice?????

At the moment I have a request from a customer who has port spanned on the outside of the firewall on a 6509, that is working, but their device isn't able to cope. They have asked if I can span the port again, so they can monitor the traffic again on a new device they are going to install?

I have mentioned to them about vlan filters, but they want to span the ports twice.

I just need confirmation that this can or cannot be done

Thank you in advance.

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Jagdeep Gambhir Thu, 08/16/2007 - 04:45
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Is possible with RSPAN only.

Only one destination port is allowed per SPAN session, and the same port cannot be a destination port for multiple SPAN sessions.

Each RSPAN destination session has one or more destination interfaces for each RSPAN VLAN that they support.

?RSPAN destination sessions are limited to two, or one if a local SPAN or a source RSPAN session is configured on the same switch.

Hope that helps



tromer Thu, 08/16/2007 - 14:09
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Easy fix. Insert a TAP between the switch-span and the monitoring device.


using TAP

switchspan --------TAP -------olddevice

The TAP gives you a 3rd interface that you can plug into the new device. This way you don't have to mess with anything on the switch.



royalblues Fri, 08/17/2007 - 02:21
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Yes, the easiest way out would be to have a hub connected to the spam destination port.

I have also seen some implementations with Radware switches connected to the span destination that can intelligently load balance the traffic to multiple servers



supertoaster2 Wed, 09/05/2007 - 07:11
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I have tried this on the 6509, and it can be down? Why the customer wants don't know. But, it allows you to span the same vlan to different ports.

This can be signed off! ☺


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