From: CCIEin2006 (ciscocciein2006@gmail.com)
Date: Tue Oct 30 2007 - 11:37:52 ART
Tarun/Simon, thanks for your responses. I already read the documentation and
I understand your points. What I don't understand is if the first hop
PE switch overwrites the destination MAC, how does the last hop PE switch
know the original destination MAC that was in the frame? How does it know
which MAC to put back in the frame when its sends it out to the customer
switch? Is it carried in one of the L2TP fields?
And finally I don't see any information about how the CAM table is used in
dot1q or L2 tunnels.
In either case, does the last hop PE switch do a lookup in the cam table
before sending the frame or is it flooded to all ports in the customers's
access VLAN?
Thanks again.
On 10/30/07, Simon Grace <SimonG@pcsystems.gr> wrote:
>
> Have a read of this, I had a few questions and it seems to cover
> everything you need:
>
> http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/relea
> se/12.2_25_sec/configuration/guide/swtunnel.html
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Tarun Pahuja
> Sent: Tuesday, October 30, 2007 3:16 PM
> To: CCIEin2006
> Cc: Cisco certification
> Subject: Re: dot1q Tunnel vs Layer 2 Tunnels
>
> Transparent Layer 2 overwrites the customer PDU-destination MAC
> address in an Ethernet packet with a well-known Cisco proprietary
> multicast address (01-00-0c-cd-cd-d0). The Ethernet packet is then
> transparently tunneled over the core network to a peer PE router. If
> Layer 2 protocol tunneling is configured on the PE router on the
> outbound side, the destination MAC address is restored in the Layer 2
> protocol information so that packets are forwarded to all ports in the
> same metro VLAN.
>
> HTH,
> Tarun
>
>
> On 10/30/07, CCIEin2006 <ciscocciein2006@gmail.com> wrote:
> > As a follow up question, if Layer 2 tunnels overwrite the destination
> mac
> > address of frames with a proprietary mac address, how does the remote
> switch
> > know what the original mac address was when it translates it back?
> >
> > On 10/29/07, CCIEin2006 <ciscocciein2006@gmail.com> wrote:
> > >
> > > Hey Folks,
> > >
> > > I am trying to how the CAM table comes into play when forwarding
> frames
> > > using dot1q tunnels or layer 2 tunnels.
> > >
> > > When using dot1q tunnels, is the cam table checked and the frame is
> sent
> > > only to the intended port or is the frame flooded to all ports in
> the
> > > customer's vlan?
> > >
> > > Does the same hold true for Layer 2 Tunnels?
> > >
> > > Thanks in advance.
> >
> >
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