The MPLS WG Archive

[seenu@samsung.co.kr]

Hi Sandeep,
The frame encapsulation for ethernet over MPLS at L2 is:

| L2 header | MPLS label stack | L3 header| .....|

Yes. The way u r following is correct.

  The label stack entries MUST immediately precede the network layer
   header, and MUST follow any data link layer headers, including, e.g.,
   any VLAN headers, 802.1Q headers, etc. that may exist.

   The ethertype values can be used with either the ethernet
   encapsulation or the 802.3 SNAP/SAP encapsulation to carry labeled
   packets.

Seenu
Samsung India Software Operations
Level 7, Prestige Meridian - II
M.G.Road
Bangalore





Dear Friends,

I would highly appreciate if you could please help me out in
resolving my doubt about Position of MPLS Label in an Ethernet Lan
environment. (Especially in the case of 802.3 LLC / SNAP).

With reference to the following doc.:

    draft-ietf-mpls-label-encaps-08.txt


Section 5: (page18)  states the following:
-----------------------------------------

  The label stack entries immediately precede the network layer header,
   and follow any data link layer headers, including, e.g., any 802.1Q
   headers that may exist.
   ...........   .......
   ..........    .......

   These ethertype values can be used with either the ethernet
   encapsulation or the 802.3 LLC/SNAP encapsulation to carry labeled
   packets.

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The Doubt I have is:

Q1.:  Does it mean that mpls label   " MUST "  precede before the
         IP Network Packet ?

Q2. :  If Answer to Q1 is Yes, then in case of 802.3 LLC/SNAP,
          Does it mean that the mpls label "MUST" come after the
          SNAP type field, in the order as depicted below ?

           [ 12 bytes of  MAC Address] -->  [4 bytes of 802.1Q :
optional] -->
           [2 bytes of Length / type field] -->  [6 bytes of 802.2 LLC /
SNAP] -->
           [2 bytes of MPLS ethernet Type] --> [ MPLS  labels] --> [IP
Packet]



Appreciate your kind help becuase I want to be fully sure about it in
 802.3 LLC/SNAP case.


Thanks a lot
Sandeep

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Sandeep Relan
Senior Member Technical Staff,
INTEL (software and silicon systems),

E-mail : srelan@ieee.org
Phone : +91-80-5550888
Fax    :  +91-80-5550718

5th Floor, Prestige Meridian -I,
29, M.G. Road, Bangalore -560001,
INDIA
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