[c-nsp] Q and Q De-encapsulation

[Keegan Holley]

2011/8/24 Tóth András <diosbejgli at gmail.com>

> An egress tunnel port strips the 2-byte Ethertype field (0x8100)

and

the 2-byte length field and


The ethertype field is part of the ethernet header and is set to 0x8000 for
all modern ethernet.  Did you mean it rewrites the TPID field from 0x9100 to
0x8100? Did you mean it strips the outertag?  Likewise the TPID is part of a
valid vlan tag and shouldn't be stripped.  Also, what happens if the next
hop device is using TPID 0x9100?

http://en.wikipedia.org/wiki/EtherType
http://en.wikipedia.org/wiki/IEEE_802.1Q


transmits the traffic with the 802.1Q tag

> still intact to an 802.1Q trunk port on a customer device.


I guess I'd expect a port configured as access not to transmit tagged frames
and to not have to go look at the ingress port to figure out what's coming
out of it.  Still seems strange.


> The 802.1Q
> trunk port on the customer device strips the 802.1Q tag and puts the
> traffic into the appropriate customer VLAN.


>
> http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/dot1qtnl.html
>
> Andras
>
>
> On Wed, Aug 24, 2011 at 2:37 PM, Keegan Holley
> <keegan.holley at sungard.com> wrote:
> >
> >
> > On Aug 24, 2011, at 5:12 AM, "Arie Vayner (avayner)" <avayner at cisco.com>
> wrote:
> >
> >> Do you want to strip only the outer tag? If yes, then it should be
> >> easy... Just configure the port as a trunk, and the egress port as an
> >> access port of the VLAN you want to send there (it would work for 1 out
> >> tag VLAN at a time)
> >
> > I was wondering about this.  You'd essentially be egressing tagged frames
> > from an access port. (that's just weird)  Also doesn't q-in-q have a
> different tpid than regular vlan tags?  How does the box know what to do
> with the frames if the ingress port is just a normal trunk?
> >
> >>
> >> If you want more flexible QinQ support, you most likely need to look at
> >> ES+ modules.
> >>
> >> Arie
> >>
> >> -----Original Message-----
> >> From: cisco-nsp-bounces at puck.nether.net
> >> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Mike Aumand
> >> Sent: Wednesday, August 24, 2011 00:07
> >> To: cisco-nsp at puck.nether.net
> >> Subject: [c-nsp] Q and Q De-encapsulation
> >>
> >>
> >>   I was wondering if anyone knew if it was possible to have a single
> >> gigabitethernet port on a 7609 running Version 12.2(33)SRB5 take in
> >> 802.1Q tagged traffic and strip off the outer tag all on the single
> >> ingress port?
> >>
> >> Thanks in advance,
> >>                                   Mike
> >>
> >>
> >>
> >> Mike Aumand
> >> Network Engineer
> >> Cornerstone Telephone Company, LLC.
> >> Richmond Telephone Company ~ Richmond Networx
> >> 2 Third Street, Suite 303
> >> Troy, NY, 12180
> >> 518-328-0353 (w)
> >> 518-577-8705 (c)
> >> 518-860-1860 (f)
> >>
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