Subject: Re: Another Ethernet PW question

From: Eric Rosen <[email-masked]>
Date: Fri, 19 Sep 2003 15:35:21 -0400

> How to identify a "service-delimiting" VLAN tag? 

I think the model is the following.  A particular interface is configured to
be one of two kinds: 

- uses service delimiting tags

- doesn't use service delimiting tags

If it  is of the  first kind, then  the VLAN tag  which is seen  on ethernet
frames received over that interface  is a service delimiting tag.  Each such
tag may  be thought of  as corresponding to  a different customer.   I think
that the  only untagged  traffic received  on that port  will be  SP control
traffic. 

> Consider the scenario, when PE receives  a frame from CE which already has
> a VLAN tag (placed by CE) which is not a "service-delimiting" tag.  In
> this situation, is  PE supposed to add a  "service-delimiting" VLAN tag on
> top of the CE VLAN tag? 

Since the  frame was  received without a  service-delimiting tag,  and since
frames must carry service-delimiting tags  on tagged mode pws, the answer is
yes. I value of the tag to be put on would need to be configured, I think.

---

From: "Yongjun Im" <[email-masked]>
Date: Sat, 20 Sep 2003 11:31:56 +0900

----- Original Message ----- 
  From: [email-masked] 
  To: [email-masked]' 
  Sent: Saturday, September 20, 2003 1:31 AM
  Subject: [PWE3] Another Ethernet PW question

  Hi All,

     I have a couple of similar questions. Can somebody please answer them?

  1.  In section 3.1.2 (draft-ietf-pwe3-ethernet-encap-03.txt) it's been stated that in tagged mode every frame must have a "service-delimiting" VLAN tag. Consider the scenario, when PE receives a frame from CE which already has a VLAN tag (placed by CE) which is not a "service-delimiting" tag. In this situation, is PE supposed to add a "service-delimiting" VLAN tag on top of the CE VLAN tag?

  > I believe that a standard VLAN tagged frame is able to have a single VLAN tag, therefore even if ingress PE add a additional
     VLAN tag on the CE VLAN tag, I believe that added tag has to be stripped at egress PE. If so, I'm wondering
     what's the role of the VLAN tag added by ingress PE.

  2. How to identify a "service-delimiting" VLAN tag? Is it expected that the user will configure at PE, for ex, list of tags as  "service-delimiting" tags and based on the encapsulation mode determine whether to strip it (raw) or keep it (tagged)?

  > I believe whether an incoming VLAN tag is "service-delimiting" or "non service-delimiting" can be identified by
  only configuration at PE. By the way, do we really need a concept of "service-delimiting" and "non service-delimiting"?

  thanks
  Mari
    -----Original Message-----
    From: Shahram Davari [mailto:[email-masked]]
    Sent: Thursday, September 18, 2003 2:21 PM
    To: [email-masked]'
    Subject: [PWE3] Another Ethernet PW question

    Hi,

    Imagine the following scenario.

    A customer tells the its service provider:

    Send all my Ethernet packets with VLAN = X to Dest A
    Send all my Ethernet packets with VLAN = Y to Dest B
    Send all my Ethernet packets without any VLAN to Dest C

    Is this VLAN tag considered to be service-delimiting tag? if so then what about
    packets without VLAN tag? how should they be treated in tagged mode? should
    a configured VLAN tag be added to them before encapsulating is MPLS?

    Thanks,
    _________________________________________ 
    Shahram Davari, B.Eng., M.A.Sc. 
    Senior Product Research Engineer 
    PMC-Sierra, Inc. 
    Tel: (613)271-4018 
    Fax: (613)271-6468 
    MailTo: [email-masked] 
    __________________________________________

---

From: Ali Sajassi <[email-masked]>
Date: Mon, 22 Sep 2003 10:45:00 -0700

At 11:31 AM 9/20/2003 +0900, Yongjun Im wrote:
>From: <mailto:[email-masked]>[email-masked]
>To: <mailto:[email-masked]'>[email-masked]'
>1.  In section 3.1.2 (draft-ietf-pwe3-ethernet-encap-03.txt) it's been 
>stated that in tagged mode every frame must have a "service-delimiting" 
>VLAN tag. Consider the scenario, when PE receives a frame from CE which 
>already has a VLAN tag (placed by CE) which is not a "service-delimiting" 
>tag. In this situation, is PE supposed to add a "service-delimiting" VLAN 
>tag on top of the CE VLAN tag?
>
> > I believe that a standard VLAN tagged frame is able to have a single 
> VLAN tag, therefore even if ingress PE add a additional
>    VLAN tag on the CE VLAN tag, I believe that added tag has to be 
> stripped at egress PE. If so, I'm wondering

I think there may be a confusion here between UNI mode and PW mode. UNI can 
be configured to treat the VLAN tags as either service delimiting tag or as 
non-service delimiting tag. If the UNI is configured for service-delimiting 
mode, then you can either use raw-mode PW (one PW per service instance) or 
tagged-mode PW (one PW for all service instances over that UNI). If the UNI 
is configured for non-service-delimiting mode, then raw-mode PW should be 
used for that UNI; however, if multiple UNIs are getting muxed over the 
same PW, then tagged-mode PW can be used (since each UNI can be identified 
by service-delimiting tag imposed by the PE).

-Ali
>
>2. How to identify a "service-delimiting" VLAN tag? Is it expected that 
>the user will configure at PE, for ex, list of tags 
>as  "service-delimiting" tags and based on the encapsulation mode 
>determine whether to strip it (raw) or keep it (tagged)?
>
>only configuration at PE. By the way, do we really need a concept of 
>"service-delimiting" and "non service-delimiting"?
>
>thanks
>Mari