The MPLS WG Archive

["Thomas D. Nadeau" <tnadeau@cisco.com>]

         Hi Tim,

At 06:25 PM 9/27/00 -0400, Mancour, Tim wrote:
>Hi,
>
>How would one setup an LSP over an Ethernet interface using the
>MPLS-LSR-MIB? Consider the following where A, B , C, and D are all LSRs with
>Ethernet interfaces attached to an Ethernet Bridge (S):
>
>            A
>            |
>         B -- S -- C
>            |
>            D
>
>In the above, the label space of each LSR is independent so the interface
>and topLabel from the out-segment table cannot be used to uniquely determine
>the destination LSR.

         I think that you need to look at it from a different perspective.
Let me also redraw your diagram and delete LSR D without loss of generallity:

                               |-----C (1.2.3.4)
          A - [hub] -- Eth1 ---|
                               |-----B (2.3.4.5)

Now, if we have a example TFIB at LSR A that looks like:

         InLabel         OutLabel        OutIfIndex      NextHopIPv4Addr
         15              17              10      (Eth1)  1.2.3.4
         18              17              10      (Eth1)  1.2.3.4
         15              21              10      (Eth1)  1.2.3.4

At LSR A, it might call that interface Eth1 (ifIndex = 10).
If a label swapping of (15, 17, ifIndex=10, NextHop=1.2.3.4) occurs,
then outSegmentIndex might = 1, and outSegmentIfIndex = 10,
outSegmentTopLabel = 17. If another entry is desired which goes to LSR
B, say (18,17, ifIndex=10, NextHop=2.3.4.5), then another outSegmentIndex
might be created say, 2, with outSegmentIfIndex = 10, outSegmentTopLabel = 17.
Both entries are unique, and both indicate that the two different LSPs
can come into A, and go out on the same interface under the same label to 
different
peers. You might also be thinking of the case where (15,21, ifIndex=10, 
1.2.3.4)
too. Again, outSegmentIndex = 122, outSegmentIfIndex = 10, 
outSegmentTopLabel = 21,
NextHopIpV4Addr=1.2.3.4.

>Do we need to add a MAC address object to the mplsOutSegmentTable?

         I don't believe that we need the MAC address. The IPv4/v6NextHopAddr
handles where the next hop is located, and the outSegmentIfIndex handles
which MPLS-enabled interface the labels will leave "this" LSR at.
The thing to keep in mind is that the outSegment Table's index is a plain
integer to allow multiple copies of the same outgoing label to be used,
either on the same outgoing interface, or even different interfaces.

         I hope this answers your question. Let me know if it does not.

         --Tom