From: Chris Home (clarson52@comcast.net)
Date: Thu Apr 24 2003 - 14:07:38 GMT-3
The 6000/6500 Catalyst switch architecture
http://www.cisco.com/en/US/products/hw/switches/ps708/products_white_paper09
186a0080092389.shtml
This section of that document is where I got that particular info. Pretty
neat read. Catalyst 6000 Family Packet Flow-"A Day in the Life of a
Packet"
----- Original Message -----
From: "Volkov, Dmitry (IDS Canada)" <dmitry_volkov@ca.ml.com>
To: "'Chris Home'" <clarson52@comcast.net>
Cc: "David Buechner" <dbuechn@attglobal.net>; <ccielab@groupstudy.com>
Sent: Thursday, April 24, 2003 11:24 AM
Subject: RE: 3550 - RSPAN - Reflector Port
> Chris,
> What is the document You refer to ?
>
>
> Dmitry Volkov
> CCIE # 10292
>
> > -----Original Message-----
> > From: Chris Home [mailto:clarson52@comcast.net]
> > Sent: Wednesday, April 23, 2003 6:53 PM
> > To: David Buechner; ccielab@groupstudy.com
> > Subject: Re: 3550 - RSPAN - Reflector Port
> >
> >
> > In fact when a cat switch receives ANY frame it is copied to
> > every port.
> > When a switch receives a frame, as soon as it gets access to
> > the backplane
> > the frame is copied to every port as it travels. When a
> > forwarding decision
> > is made the interfaces that should not forward are told to flush their
> > buffer of the frame or ignore it (I am not exactly sure
> > which. I have heard
> > both ignore and flush). The forwarding ports are left to
> > forward. So a span
> > port simply never gets told to flush or ignore any packets.
> > Little to no
> > performance loss. There is also an excellent document on this
> > and the 6500
> > architecture that covers more of this kind of stuff. Very
> > informative and
> > interesting doc.
> >
> > I am not sure how this applies on dCEF cards. Since the
> > forwarding decision
> > is made at the module. I think it might be the same, the
> > forwarding decision
> > is just made sooner. I dunno really.
> >
> >
> > ----- Original Message -----
> > From: "David Buechner" <dbuechn@attglobal.net>
> > To: <ccielab@groupstudy.com>
> > Sent: Wednesday, April 23, 2003 2:53 PM
> > Subject: RE: 3550 - RSPAN - Reflector Port
> >
> >
> > > 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/product
> s_configuratio
> n_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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