The MPLS WG Archive

["Carlos M. Pignataro" <cpignata@cisco.com>]

Hi,

The current definitions in draft-ietf-mpls-lc-if-mib-01.txt seem not to be accounting for "indirectly" LC-ATM connections via an ATM VP.

As defined in RFC3035, LC-ATM can be "directly" connected (ie. physically connected) or "indirectly" connected (via ATM VP, VP-Tunnel). See RFC3035 sections 7.1 and 7.2.
One difference between the 2 connectivity types is that for "directly" connected the label space is the VPI/VCI while for "indirectly" connected the label space is only the VCI. From RFC3035 regarding indirectly connected: "via an ATM Virtual Path. In this case, the VPI field is not available to MPLS, and the label MUST be encoded entirely within the VCI field."

As defined in RFC3036, the VPI field in the label range must be zero for indirectly connected LC-ATMs: "When peer LSRs are connected indirectly by means of an ATM VP, the sending LSR should set the Minimum and Maximum VPI fields to 0, and the receiving LSR must ignore the Minimum and Maximum VPI fields."

Therefore, the objects defined in MPLS-LSR MIB for MPLS interface [ifType = mpls(166)] would not include the VPI for the indirectly connected LC-ATMs in the mplsInterfaceLabel[Min|Max][In|Out] objects. That's because the VPI is not part of the label space.
However, the mplsLcAtmIfConfTable does not include this information either. So for "indirectly" connected (VP-Tunnel) interfaces, the MIBs do not provide the VPI used for the LC-ATM.

For indirectly connected the VPI is not part of the labels space, it should be zeroed out in the mplsInterfaceLabel[Min|Max][In|Out], and that makes possible having indirectly connected interfaces using different VPIs at both ends of the VP. One interface can have 1 VPI for the LC-VPI range, and can be configured to be directly or indirectly connected. And if 2 adjacent switches differ in the connectivity configuration although using the same VPI, it won't work because they won't negotiate ranges.

It seems like there should be 2 more objects in the MplsLcAtmIfConfEntry, like:
mplsLcAtmDirectlyConnected (TruthValue) and mplsLcAtmVPI (AtmVpIdentifier) such that for example:

mplsLcAtmVcDirectlyConnected OBJECT-TYPE
   SYNTAX      TruthValue
   MAX-ACCESS  read-create
   STATUS      current
   DESCRIPTION
       "This value indicates whether an LC-ATM is 
        directly or indirectly (by means of a VP)
        connected. If set to true(0), indicates 
        that this interface is directly connected
        LC-ATM, otherwise it MUST be set to false(1)."
   DEFVAL     { true }
   ::= { mplsLcAtmIfConfEntry X }

mplsLcAtmLcAtmVPI OBJECT-TYPE
   SYNTAX        AtmVpIdentifier
   MAX-ACCESS    read-create
   STATUS        current
   DESCRIPTION
       "This is the VPI value used for indirectly
        connected LC-ATM interfaces For indirectly
        connected interfaces, the VPI field is not 
        available to MPLS, and the label MUST be 
        encoded entirely within the VCI field.
        (see RFC 3035). If the interface is directly
        connected, this value MUST be set to zero."
   ::= { mplsLcAtmIfConfEntry X }


Thanks,

--Carlos.
=================================================================
                            |  Carlos Pignataro - CCIE 4619
     cisco Systems, Inc.    |  Escalation RTP
                            |  cpignata@cisco.com
       ||         ||        |  +1 919 392 7428 - office
      .||.       .||.       |  +1 919 345 3028 - mobile
     .||||.     .||||.      |  +1 919 392 6470 - fax
  .:||||||||:.:||||||||:.   |  7025 Kit Creek Road, PO Box 14987
      Are you Ready ?       |  Research Triangle Park, NC 27709
=================================================================