Subject: RE: Re: Is IP Layer 2 Interworking useful?

From: "Andrew Smith" <[email-masked]>
Date: Tue, 30 Apr 2002 12:27:48 -0700

RE: [PWE3] Re: Is IP Layer 2 Interworking useful?Neil,

Just to be clear, so long as you use bridges that support independent VLAN
learning (IVL), IEEE 802.1Q VLAN-IDs can be used to disambiguate overlapping
uses of a MAC address. By "overlapping" I mean that the same MAC address can
be used on different segments (not on the same segment, obviously) so long
as they are separate by an IVL bridge. This is to get around cases where
people invented upper-layer protocols whilst they were confused over whether
a MAC address was a name or an address :-). I'd suggest that any PWE3/L2VPN
protocol solution needs to accomodate this (IVL) in order to support
obselete but still-in-use protocols.

To digress even further ... I'd also suggest (donning my arrow-proof suit)
that, if you were to limit the "L2VPN interworking" being
discussed/standardised in these WGs to IEEE802-over-XXXX technologies, i.e.
to assume a service interface as defined in ISO/IEC15802-1:1995 (this is the
IEEE MAC service definition standard), then the L2VPN work could be done in
about 1/100th of the time (summary: write a document in PWE3 describing how
to emulate a p2p Ethernet segment and write a document in PPVPN referencing
the existing interworking standards and the pseudo-Ethernet document; then
declare victory). I guess one of the implications of this would be that
you'd have to run LANE-over-ATM in order to interwork ATM and Ethernet or
TR - but a lot of ATM deployments do this already though. I would suggest
that defining the interworking of IP-over-FR, IP-over-ATM etc. are not the
sorts of things that IETF is very good at ...

Andrew Smith
  -----Original Message-----
  From: [email-masked]
[mailto:[email-masked]]On Behalf Of
[email-masked]
  Sent: Tuesday, April 30, 2002 10:43 AM
  To: [email-masked]; [email-masked]; [email-masked];
[email-masked]
  Subject: RE: [PWE3] Re: Is IP Layer 2 Interworking useful?

  Hi Khalid,

  Ethernet is based on names.  It has no strict concept of addresses (unlike
IP say).  Ethernet is therefore not even cnls...its a broadcast medium.  And
Vlan tags in such a context are a 'group of names'

  IP is truly cnls and has proper addressing..........there is no such thing
as a cnls trails so I agree with you on this.

  L1,2,3 mean nothing....see my last posting.

  regards, Neil
    -----Original Message-----
    From: Khalid Ahmad [mailto:[email-masked]]
    Sent: 30 April 2002 17:17
    To: Maarten Vissers; [email-masked]; [email-masked]
    Subject: RE: [PWE3] Re: Is IP Layer 2 Interworking useful?

    Hi Maarten,

    could you explain what means "ethernet MAC trail" or "IP trail" in your
description below ?

    I always assumed these were connectionless mechanisms and therefore do
not require the concept of a connection (or trail as the transport people
want to say).

    I also notice you classify ATM as a L1 protocol in you interesting
diagram below.  I was always assuming it was treated as a L2 mechanism.  Is
this just a typo, or did something change ?

    In any case, it is nice to see you are continuing to try to inject some
order in this chaotic protocol layering business !

    Regards,
    Khalid

    -----Original Message-----
    From: Maarten Vissers [mailto:[email-masked]]
    Sent: Tuesday, April 30, 2002 4:35 AM
    To: [email-masked]; [email-masked]
    Subject: [PWE3] Re: Is IP Layer 2 Interworking useful?

    In my understanding, a layer X VPN provides transparent transport of
layer X
    information elements. E.g. an Ethernet VPN provides transparent
transport of
    Ethernet MAC frames between between the N access points of a customer.
An IP VPN
    provides transparent transport of IP packets between the N access points
of a
    customer.

    Both Ethernet VPN as well as IP VPN use an underlying transport layer to
provide
    an access link to the first Ethernet [IP] switching element in the
network. For
    the case of IP VPN, the IP access link can be supported by an Ethernet
MAC trail
    (but it can also be an MPLS trial, SDH VC-n trail, etc.). For the case
of
    Ethernet, the access link can be supported by an Ethernet PHY trail (but
it can
    also be an MPLS trail, SDH VC-n trail, IP trail, etc.).

    Access link technology may differ; e.g. access point 1 may use
technology A,
    while access point 2 may use technology B, etc.

    So in case an Ethernet MAC technology is used to connect a customer to
an IP
    router/switch, and transparency is at IP packet layer level, then we
should
    refer to this as an IP VPN (of which one or more IP access links are
supported
    by Ethernet MAC layer trail(s)).

    And in case an Ethernet PHY technology is used to connect a customer to
an
    Ethernet MAC bridge/switch, and transparency is at the Ethernet MAC
layer level,
    then we should refer to this as an Ethernet (MAC) VPN (of which one or
more
    Ethernet (MAC) access links are supported by Ethernet PHY layer
trail(s)).

    Regards,

    Maarten
    PS. the use of L2, L2.5, L3 gets cumbersume these days as we are
carrying
    Ethernet MAC (L2) over MPLS (L2.5) or over IP (L3), and we carry MPLS
(L2.5), IP
    (L3), E1/T1 (L1), etc over Ethernet MAC (L2), and we will carry
SDH/SONET over
    MPLS, PDH over Ethernet and ...

      --------  ------------
      |  IP  |  | SDH VC-n |
      | (L3) |  |   (L1)   |
      -----------------------  --------  ----------------
      |        MPLS         |  |  IP  |  | PDH E1/T1/.. |
      |       (L2.5)        |  | (L3) |  |   (L1)       |
      ----------------------------------------------------------------------
--------
      |                            ETH MAC
|
      |                             (L2)
|
      ----------------------------------------------------------------------
--------
      | ETH PHY |  | MPLS |  |  IP  |  | SDH VC-n |  | OTN ODUk |  | ATM VC
|
      |  (L1)   |  |(L2.5)|  | (L3) |  |  (L1)    |  |   (L1)   |  |  (L1)
|
      -----------  --------  --------  ------------  ------------  ---------
-
           |       | XXX  |  | XXX  |  |   XXX    |  |   XXX    |  |  XXX
|

    Similar figures can be made with MPLS as focus layer, or IP as focus
layer, or
    SDH VC-n as focus layer, etc.

    What we see is that what traditionally is referred to as L3 and L2.5 is
being
    used as L1. Also what is traditionally referred to as L1 is becoming
transported
    over L3, L2.5 and L2 technologies. I.e. the numbering is getting very
arbitrary
    and as such I would prefer to simply use the layer names (instead of
some
    arbitrary numbers representing those layers).

    "Joel M. Halpern" wrote:
    >
    > I would disagree.
    > What is being discussed is a VPN with two properties that are relevant
to
    > this part of the debate:
    > 1) It has dissimilar access media at different points
    > 2) At the IP routing layer, it is transparent to the customer.  He
sees a
    > set of connections among his sites.
    > This is something customer want and find useful.
    > It is most similar in behavior o a L2 VPN.  But sure, call it
something
    > different if you want.  Call it an L2+ or L2.5 or L3- or anything else
that
    > makes you happy.  Sure, it is a hybrid.  But it meets a real need.
    >
    > Yours,
    > Joel M. Halpern
    >
    > At 09:58 AM 4/29/2002 -0700, Joe Touch wrote:
    > >An L2VPN with different endpoint protocols is, IMO, NOT an L2VPN
    > >(marketing alone does not make it so). It's an L3VPN that tries to
get
    > >around looking at the L3 header by translating L2 headers.
    >
    > _______________________________________________
    > pwe3 mailing list
    > [email-masked]
    > https://www1.ietf.org/mailman/listinfo/pwe3

---

From: Keith Knightson <[email-masked]>
Date: Wed, 1 May 2002 10:10:02 -0400

At 6:42 PM +0100 4/30/02, [email-masked] wrote:
Hi Khalid,

Ethernet is based on names.  It has no strict concept of addresses 
(unlike IP say).  Ethernet is therefore not even cnls...its a 
broadcast medium.  And Vlan tags in such a context are a 'group of 
names'

IP is truly cnls and has proper addressing..........there is no such 
thing as a cnls trails so I agree with you on this.

regards, Neil

Dear PWE3'ers,

Please please do not muddy up the concepts of naming and addressing, 
CO and CLNS, as well as everything else.  What on earth is meant by 
"proper addressing"? or  strict concept of addresses?

Most quantities called "addresses" are in fact labels and nothing 
more. These labels may take the form of names, or numbers of some 
kind.  The fact that certain kinds of name or numbers  are structured 
does not, semantically,  make them addresses.

An address is a location, and as such NEVER moves. (Major cosmic 
seismic shifts excepted).

If the identifier under consideration, ie MAC address, IP address, 
can be moved around, semantically it ain't an address, even if the 
IEEE/IETF/ITU "labels" it as such.

Addresses represent the co-ordinates for a particular physical 
location.  Addresses themselves cannot be moved around. The postal 
system would never work if this was the case. Longitude  latitude and 
altitude is an addressing scheme also.

Whilst an identifier of some sort (i.e name or number) might be bound 
to a particular location for a while, it can be ported to another 
physical location, as in number portability or mobile. I.e. it gets 
bound temporarily (short or long term) to another address.

There have been several IETF documents on this subject in the context 
the semantics of IP "addresses" but I do not remember the references. 
They clearly distinguish and discuss the various uses of IP 
"addresses" , e.g. both as identifiers and locators. I also recall 
that ENUM and ITU have agreed a set of terms along these lines.

Thus, MAC addresses are simply identifiers, which by virtue of the 
medium are reachable irrespective of their physical location 
(address) within the universe of their applicability (usually global, 
but...sigh).  In reality, and more precisely all they identify is a 
particular chip.

BTW, the Ethernet flavor under consideration is connectionless. IEEE 
802 has several flavors, connectionless, connection-oriented (yes 
really) and something else (the three-legged confirmation model or 
something equally ugly), known as LLC types 1-3 as I recall.

Broadcast is another label meaning 1:N, and another attribute of 
communication. The term broadcast can be applied to connectionless 
and connection-oriented modes of communication. To say something is 
not connectionless simply because it uses a broadcast medium makes no 
sense. Please do not confuse the scope and extent of a communication 
with its type.

Regards

Keith

---

From: [email-masked]
Date: Wed, 1 May 2002 18:36:14 +0300

Keith Knightson writes:

 > IP is truly cnls and has proper addressing...

yes, an IPs problem is that it doesn't have proper naming.

-- juha