Subject: MPLS and Ethernet

From: Eric Ng <[email-masked]>
Date: Wed, 06 Oct 1999 11:54:59 -0700

Hi All,

I need clarification on the following subjects. Thanks in advance.

1)
For IEEE802.3 and Ethertype pakcets, which field in the 
layer 2 header will indicate that a packet contains the
label stack?  Is there any document(s) that specify all 
the possible layer 2 headers carrying MPLS label stack?

2)
Is it possible to have a LAN switch sits between two LSR's?  

WAN enviroment     LSR(in) 0---- SWITCH ----4 LSR(out) 
                                /  |  \
LAN enviroment                 1   2   3

Will the LSP end at LSR(in), port 0?   Then packet will be 
forward to port 4 connecting LSR(out) as a regular ethernet 
packet, i.e. no label stack, and LSR(out) will then initiate 
a new LSP.  
Or the LSP is transparent to the SWITCH and MPLS labeled packet 
will forward as a normal packet to port 4.  In this case LSR(out) 
will have to deal with packets from both MPLS domain and non-MPLS 
domain entering it from the same port. 
Is this possible and permitted? 

3)
The SWITCH in question supports VALN tagging.  Packets from port
1, 2, 3 are VLAN tagged and from a non MPLS domain.  Will LSR(out)
remove the VLAN tag and insert the "label" before it transmit?

regards,
-- 
This email has been forwarded by Allayer's RoX Switch
roxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxr
o  Eric Ng                                               o	
x  Allayer Technologies Corporation                      x
r  107 Bonaventura Drive, 	Tel : (408)570-0888 x103 r
o  San Jose, CA 95134		Fax : (408)570-0880      o
xroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxroxrox

---

From: Eric Rosen <[email-masked]>
Date: Wed, 06 Oct 1999 16:31:57 -0400

> 1) For IEEE802.3 and Ethertype  pakcets, which field in the layer 2 header
>    will indicate that a packet contains the label stack?  

See  draft-ietf-mpls-label-encaps-07.txt  section  5, "Transporting  Labeled
Packets over LAN Media".

>    Is there any document(s) that  specify all the possible layer 2 headers
>    carrying MPLS label stack?

The top of the label stack is carried in the layer 2 header ONLY in the case
of ATM  and Frame Relay  (draft-ietf-mpls-atm-02.txt and draft-ietf-mpls-fr-
03.txt respectively).  In  the case of ethernet/802.3 and  PPP, as specified
in draft-ietf-mpls-label-encaps-07.txt, the  layer 2 header merely indicates
whether a label stack is present AFTER the layer 2 header.  Nothing has been
defined for other layer 2 protocols.

> 2) Is it possible to have a LAN switch sits between two LSR's?  

This  is  completely transparent  to  the  LSRs.  As  far  as  the LSRs  are
concerned, they  are on the  same LAN.  The  switch operates on the  layer 2
header, and the LSRs operate on what follows the layer 2 header.

> 3) The SWITCH in question  supports VLAN tagging.  Packets from port 1, 2,
>    3 are VLAN tagged and from a non MPLS domain.  Will LSR(out) remove the
>    VLAN tag and insert the "label" before it transmit? 

Conceptually, the layer  2 header is removed before  the packet is processed
by the  MPLS forwarding  layer.  The result  of the MPLS  forwarding process
will be to  operate on the label stack, and then  to encapsulate the labeled
packet in a new layer 2 header for output.