From: David Buechner (dbuechn@attglobal.net)
Date: Wed Apr 23 2003 - 15:53:47 GMT-3
Daniel,
Here's how I understand it:
First, let's start with a SPAN session. In SPAN you have some traffic that
you're monitoring which is then duplicated on a port local to the switch so
that it is visible to a locally attached device (such as a protocol
analyzer). One of the things that I suspect is important to switch
performance here is that very little processing is done on the duplicated
packet - it's just copied to the monitor port.
Now consider the RSPAN scenario. Here, instead of copying the frame to a
particular port you need to get it into a particular VLAN and then switch
it as new traffic for that VLAN, thus enabling delivery to a remote
destination port. The mechanism on the local switch to do this is the
reflector port. In essence the reflector port acts similarly to a
destination port, only instead of transmitting the packet out the physical
port it transmits it out the RSPAN VLAN. I don't know the hardware
intimately, but I would guess that maybe the ASIC in the port can handle
"reflecting" the traffic back to the RSPAN VLAN thereby keeping the switch
CPU from having to modify the packet. (I'd be happy to hear from someone
who knows the hardware better to see if my WAG is right! :-))
If I'm wrong in any of this I'd very much appreciate commentary!
David
At 07:25 am 4/23/2003 -0600, groupstudy wrote:
>http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration_guide_chapter09186a00800c6f4c.html
>Pretty good explanation
>
>-----Original Message-----
>From: Daniel Cisco Group Study [mailto:danielcgs@imc.net.au]
>Sent: Wednesday, April 23, 2003 6:19 AM
>To: ccielab@groupstudy.com
>Subject: 3550 - RSPAN - Reflector Port
>
>
>Hi all,
>
>Can someone explain the use / purpose of the reflector port when setting
>up RSPAN?
>
>The docs are a bit vague on this.
>
>Thanks in advance.
>
>Daniel
>
>
>
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