ROLL                                                     P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Updates: 6550 (if approved)                                   D. Barthel
Intended status: Standards Track                             Orange Labs
Expires: 19 April 2020                                       R.A. Jadhav
                                                             Huawei Tech
                                                         17 October 2019


                  Eliding and Querying RPL Information
             draft-thubert-roll-eliding-dio-information-01

Abstract

   This document presents a method to safely elide a group of global RPL
   options by synchonizing the state associated with each of these
   options between parent and child using a new sequence counter in DIO
   messages.  A child that missed a DIO message with an update of any of
   those protected options detects it by the change of sequence counter
   and queries the update with a DIS Message.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 19 April 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components



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   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  BCP 14  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  References  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Message Formats . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Updated DIO Base Object . . . . . . . . . . . . . . . . .   5
     4.2.  Updated DIS Base Object . . . . . . . . . . . . . . . . .   6
     4.3.  New Abbreviated Option Option . . . . . . . . . . . . . .   7
   5.  RCSS Operation  . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Updating the RCSS . . . . . . . . . . . . . . . . . . . .   8
     5.2.  RCSS Freshness and Parent selection . . . . . . . . . . .   9
     5.3.  RCSS of an Option . . . . . . . . . . . . . . . . . . . .  10
   6.  Synchronizing Options . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  New DODAG Information Object Flags  . . . . . . . . . . .  11
     8.2.  New RPL Control Message Option  . . . . . . . . . . . . .  12
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   11. Informative References  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Classical Link State protocol synchronize their Link State Database
   (LSDB) by sequencing every change.  Each interested node maintains
   the last sequence of the LSDB it is synchronizing with.  If the last
   known sequence number is older than the current, the node needs to
   learn one by one all the state changes between the last known and the
   current state.

   [RPL] does not operate that way.  With RPL, the routing information
   is repeated over and over in DODAG Information Object (DIO) and
   Destination Advertisement Object (DAO) messages.  There is no concept
   of synchronization.  The most recent information overrides a previous
   one and a stale state eventually times out.

   The RPL way was designed to enable routing from most nodes to most
   nodes most of the time in a Low-Power Lossy Network (LLN) where the




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   quality of the links and the cost of communications does not permit
   to maintain a permanent synchronization.

   This principle was applied to both the routing and non-routing
   information such as configuration settings, prefix information, and
   node capabilities.

   This non-routing state is carried in RPL Messages as options.  Some
   of the DIO options may be needed to decide whether a node can join a
   network as a leaf or as a router, and may affect the parent selection
   or the address selection.  It is thus critical that each node
   maintains its state to the freshest and selects parents that are also
   synchronized to the freshest.

   [RPL] allows a parent to elide options in the DIO messages that it
   sends repeatedly, to conserve battery and save bandwidth.  When it
   does so, a newcomer child that missed DIOs that contained the
   configuration option may operate on default or partial information.
   If it is pessimistic, it may query all possible the information even
   when it is not needed.  Conversely, a node that slept may have missed
   a DIO with a change in some critical information and may not be even
   aware of it, so it may fail to query for the update and operate on
   deprecated parameters.

   This document uses a new sequence counter called RCSS to synchronize
   the state in a child node with that of its parent, and recursively
   with that of the whole network, to the latest setting from the Root.

   The protected options are:

   1.  The Route Information Option (RIO) defined in section 6.7.5 of
       [RPL]

   2.  The DODAG Configuration Option (DCO) defined in section 6.7.6 of
       [RPL]

   3.  The Prefix Information Option (PIO) defined in section 6.7.10 of
       [RPL]

   4.  The Extended MOP Option (MOPex) defined in [MOPEX-CAP]

   5.  The Global Capabilities Option (GCO) defined in [MOPEX-CAP]

   Any change in those options causes an increment of the RCSS and
   enables a network-wide synchronization to the new state.  If the
   change impacts the routing substantially, the Root should decide to
   increment the Version Number at the same time to fully rebuild the
   DODAG with the new settings of the options.  It must be noted that



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   the operation of the Version Number in itself provides no guarantee
   that the non-routing state is fully resynchronized everywhere unless
   all the options are present in all the DIO messages.

2.  Terminology

2.1.  BCP 14

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  References

   The Terminology used in this document is consistent with and
   incorporates that described in Terms Used in Routing for Low-Power
   and Lossy Networks [RFC7102].

   Other terms in use in LLNs are found in Terminology for
   Constrained-Node Networks [RFC7228].

   A glossary of classical RPL acronyms is given in Section 2.3.

   The term "byte" is used in its now customary sense as a synonym for
   "octet".

   "RPL", "RPL Packet Information" (RPI) and "RPL Instance", DIO, DAO
   and DIS messages are defined in the "RPL: IPv6 Routing Protocol for
   Low-Power and Lossy Networks" [RPL] specification.

   This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware
   Leaf (RAL) consistently with [USE_OF_RPL_INFO].

   The term RPL-Unaware Leaf (RUL) is used to refer to a node that uses
   a RPL router (without necessarily knowing it) as 6LR and depends on
   that router to obtain reachability for its addresses inside the RPL
   domain.  On the contrary, the term RPL-Aware Node (RAN) is used to
   refer to a RAL or a RPL router that participates to RPL and
   advertises its addresses of prefixes by itself.

2.3.  Glossary

   This document often uses the following acronyms:

   DODAG  Destination-Oriented Directed Acyclic Graph




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   LLN  Low-Power and Lossy Network

   RPI  RPL Packet Information (an Option in the Hop-By_Hop Header)

   RAL  RPL-Aware Leaf

   RAN  RPL-Aware Node, a RPL router or a RPL-Aware Leaf

   RS  Router Solicitation

   RCSS  RPL Configuration State Sequence

   RPL  IPv6 Routing Protocol for LLNs (pronounced ripple)

   RUL  RPL-Unaware Leaf

3.  Updating RFC 6550

   This document adds a new field called RCSS to the DIO message.  The
   RCSS is a sequence counter set by the Root and operated as specified
   in Section 7 of [RPL], more in Section 5.

   This document also introduces a new RPL Control Message Option called
   the Abbreviated Option Option (AOO).  The AOO is the compressed
   replacement of a protected option that indicates the RCSS of the last
   change of that option, but elides its content, more in Section 4.3.

   This document modifies the DIS Base Objectto enable the individual
   query of the protected options by a node that missed a change, more
   in Section 4.2.

4.  Message Formats

4.1.  Updated DIO Base Object

   The format of the DIO Base Object is defined in section 6.3.1 of
   [RPL].  This specification uses a 8th octet that was reserved in
   [RPL] to transport the RCSS.













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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | RPLInstanceID |Version Number |             Rank              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |G|0| MOP | Prf |     DTSN      |     Flags     |      RCSS     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                            DODAGID                            +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Option(s)...
     +-+-+-+-+-+-+-+-+

                     Figure 1: Updated DIO Base Object

   Updated fields:

   RCSS
      One Byte, the RPL Configuration State Sequence

4.2.  Updated DIS Base Object

   The DIS Base Object is use by a child to query from a parent the most
   recent changes in protected options.  This specification adds flags
   to indicate which options are requested and the freshest RCSS to
   which the querying node was synchronized.

              0                   1                   2
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |R|D|P[M|O| Flg | LastSync RCSS |   Option(s)...
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 2: Updated DIS Base Object

   Updated fields:

   R
      One Bit, indicates that the RIO is requested

   D
      One Bit, indicates that the DCO is requested




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   P
      One Bit, indicates that the PIO(s) is(are) requested

   M
      One Bit, indicates that the MOPex is requested

   O
      One Bit, indicates that the GCO is requested

   Last Synchronized RCSS
      One Byte, indicates the freshest RCSS to which the querier was
      synchronized

4.3.  New Abbreviated Option Option

   When a protected option is unchanged from the previous DIOs, the Root
   MAY replace it with its abbreviated version.  The abbreviated version
   of an option is transported in a 4-bytes long Abbreviated Option
   Option (AOO).  The AOO indicates the RCSS at which the protected
   option was last changed.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Option Type  | Option Length | Abbrev. opt.  | Last Mod RCSS |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: Abbreviated Option Option Format

   Option fields:

   Option Type
      One byte indicating "Abbreviated Option", see Table 2 in
      Section 8.2

   Option Length
      MUST be set to 2 indicating Option data of 2 bytes

   Abbreviated Option
      The Option Type of the option being abbreviated

   Last Modification RCSS
      The RCSS at which the option was last modified








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5.  RCSS Operation

   Settings and updates to network-wide parameters are initiated by the
   Root and propagated down the DODAG in RPL Control Message Options in
   DIO messages.  The DIO messages arrive asynchronously via different
   parents and may confuse a child.  The RCSS allows the child to keep
   synchronized to the latest settings network-wide parameters that are
   propagated in protected options.

   The RCSS is a sequence number that is operated as specified in
   section 7.2 of [RPL].  The scope of an RCSS is one DODAG within one
   RPL Instance.  The RCSS applies to a DIO Message and a same value of
   the RCSS can be used in DIO messages that are sent consecutively with
   no change in the protected options.

   The Root of the DODAG is autoritative to set and update the RCSS and
   the options that it protects.  The RCSS and the protected options are
   propagated together down the DODAG without a change, more in
   Section 5.1.

   The RCSS allows a child node to recognize the fresher DIO Message(s)
   as received from one or more advertising parents and to use only
   parents with a consistent state of network-wide parameters, more in
   Section 5.2.

   By extension, the RCSS is also defined for each protected option.  A
   child associates an option with the values of the RCSS indicated in
   DIO Messages in which the option is advertised and uses it to assess
   the relative freshness of different versions of an option, more in
   Section 5.3.

   Unchanged options may be sent in full, elided, or in the abbreviated
   form specified in Section 4.3.  Eliding an option is NOT RECOMMENDED
   as it may cause multiple children to resynchronize the option even if
   it was not changed.

   If the link MTU does not permit to send a single DIO message with all
   the options packaged then the options may be spread over multiple
   consecutive DIO messages with the same RCSS that are sent in a rapid
   sequence.

5.1.  Updating the RCSS

   The RCSS is incremented by the Root using a lollipop technique as
   specified in section 7.2 of [RPL].  RCSS values are comparable if
   they are within a window of comparison of SEQUENCE_WINDOW increments
   or one indicates a reboot.




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   A reboot of the Root is detected when the RCSS moves from the
   circular to the straight part of the lollipop.  In order to maximize
   the chances of detection, the straight part should be kept very short
   with a RECOMMENDED initialization at 252 or above.

   During the straight part of the lollipop, a second reboot of the Root
   might not be recognized and a same value of the RCSS may reappear
   with different settings in the protected options.  For that reason
   the protected options MUST be provided in full with each increment on
   the RCSS during the straight part of the lollipop.

   When a field is modified in one of the protected options, the Root
   MUST send a DIO with an incremented RCSS and the modified protected
   option(s) in full.  The Root MAY also update the Version Number to
   form a new DODAG altogether.

   The Root SHOULD jump rapidly away from the straight part once the
   network has sufficiently settled by resetting the RCSS to 0, which
   places the RCSS in the circular region of the lollipop, where the
   protected options MAY be elided or abbreviated.

5.2.  RCSS Freshness and Parent selection

   A child node maintains the freshest RCSS received from its parents in
   each of the RPL Instances that it participates to, and uses that RCSS
   for its own DIO messages.

   A child and a candidate parent are out-of-sync when the RCSS values
   that they maintain for a RPL Instance are not comparable.  A child
   MUST NOT use a parent that is out-of-sync unless no other parent is
   available, in which case it MAY align its RCSS and resynchronize to
   that parent.

   When a child receives from a candidate parent a DIO with an RCSS that
   is fresher than the one it is using, the child MUST synchronize the
   state relative to the protected options with that parent.  The child
   node MUST refrain from using that parent and the new state including
   the RCSS, until it has synchronized all of the protected options to
   that RCSS.  When it is fully synchronized, the child may then use
   that parent and the new RCSS.

   Using a back-level parent may cause packets to be dropped,
   misunderstood or misrouted.  The child SHOULD refrain from using a
   parent that exposes an older RCSS if the change causes an
   incompatibility issue.






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5.3.  RCSS of an Option

   By extension, the RCSS of an option is maintained by a child as the
   freshest RCSS indicated by a DIO message from a candidate parent in
   which the option was present in the abbreviated form or in full.  A
   child maintains a state for the freshest RCSS received for each of
   the protected options and synchronizes its state for each option to
   the freshest RCSS of that option.

   When a child receives a DIO from a candidate parent, for each option:

   If the Option is advertised in the abbreviated form  then the RCSS
      that the DIO advertises for the option is the Last Modification
      RCSS of the AOO, else

   If the Option is advertised in full  then the RCSS that the DIO
      advertises for the option is the RCSS of the DIO, else

   If the Option is elided  then the RCSS is unspecified but it is at
      most as fresh as the RCSS of the DIO, and the RCSS of the DIO is
      assumed for the comparison

   This means that if an Option is advertised in both the abbreviated
   form and in full in a same DIO message then the RCSS in the AOO has
   precedence.

   To keep the RCSS comparable for each option, the RCSS of an option
   must lazily progress along with the global RCSS even if there was no
   change in the options.  Each parent including the Root MUST advertise
   a new RCSS for each of the protected options at least once within a
   sliding window of SEQUENCE_WINDOW increments.

   When an option was not changed for a new RCSS, one parent may
   advertise it in the abbreviated form while another sends the option
   in full only, e.g., in response to a DIS message.  A fresher RCSS
   indicates that the option is either the same or carries a more recent
   update than the one with an older RCSS.

   The RCSS of an option may be obtained from a DIO message that carries
   the option in full even if the RCSS of the DIO is not the freshest
   across parents, as long as the RCSS of the DIO is fresher than the
   current one for that option.

   If current value of the maintained RCSS for an given option is not as
   fresh or fresher than that advertised in a DIO message, then the
   child MUST update its state for that option as specified in
   Section 6.




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6.  Synchronizing Options

   A child can resynchronize any of the protected options to the latest
   RCSS by sending a DIS Message to a candidate parent that advertises
   that RCSS in DIO messages.  The child MUST set the desired
   combination of 'R', 'D', 'P', 'M' and 'O' flags to indicate the
   option(s) that it needs updated.  The child MUST signal in the Last
   Synchronized RCSS field of the DIS the freshest value of RCSS for
   which it was fully synchronized, or a conventional value of OUT-OF-
   SYNC-RCSS of 129 if it was never synchronized or is out-of-sync with
   the parent.

   The DIO message that is sent in response MUST contain in full all the
   options that are requested and that were updated since the Last
   Synchronized RCSS in the DIS Message.  This means all of the
   protected options of the child was never synchronized or is out-of-
   sync with the parent.  The other options MUST be added in the
   abbreviated form.  The options MAY be spread over more than one DIO
   message sent in a quick sequence and the child SHOULD wait a
   reasonable technology-dependent time before it retries the request.

7.  Security Considerations

   TBD

8.  IANA Considerations

8.1.  New DODAG Information Object Flags

   5 new bits are allocated in the Registry for the DODAG Information
   Object (DIO) Flags defined for [RPL].

        +------------+----------------------------+--------------+
        | Bit Number | Capability description     | Defining RFC |
        +============+============================+==============+
        | 0          | 'R' bit "RIO requested"    | THIS RFC     |
        +------------+----------------------------+--------------+
        | 1          | 'D' bit "DCO requested"    | THIS RFC     |
        +------------+----------------------------+--------------+
        | 2          | 'P' bit "PIO(s) requested" | THIS RFC     |
        +------------+----------------------------+--------------+
        | 3          | 'M' bit "MOPex requested"  | THIS RFC     |
        +------------+----------------------------+--------------+
        | 4          | 'O' bit "GCO irequested"   | THIS RFC     |
        +------------+----------------------------+--------------+

                          Table 1: New DIO Flags




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8.2.  New RPL Control Message Option

   A new entry is required for the new option of type "Abbreviated
   Option", from the "RPL Control Message Options" space defined for
   [RPL].

             +----------+--------------------+--------------+
             | Code     | Description        | Defining RFC |
             +==========+====================+==============+
             | TBD IANA | Abbreviated Option | THIS RFC     |
             +----------+--------------------+--------------+

                         Table 2: New Option Type

9.  Acknowledgments


10.  Normative References

   [MOPEX-CAP]
              Jadhav, R. and P. Thubert, "Mode of Operation extension
              and Capabilities", Work in Progress, Internet-Draft,
              draft-ietf-roll-mopex-cap-00, 9 August 2019,
              <https://tools.ietf.org/html/draft-ietf-roll-mopex-cap-
              00>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <https://www.rfc-editor.org/info/rfc7102>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RPL]      Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,



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              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.

   [USE_OF_RPL_INFO]
              Robles, I., Richardson, M., and P. Thubert, "Using RPL
              Option Type, Routing Header for Source Routes and IPv6-in-
              IPv6 encapsulation in the RPL Data Plane", Work in
              Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-31,
              7 August 2019, <https://tools.ietf.org/html/draft-ietf-
              roll-useofrplinfo-31>.

11.  Informative References

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D, 45 Allee des Ormes - BP1200
   06254 Mougins - Sophia Antipolis
   France

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com


   Dominique Barthel
   Orange Labs
   28 chemin du Vieux ChĂȘne
   38243 Meylan
   France

   Email: dominique.barthel@orange.com


   Rahul Arvind Jadhav
   Huawei Tech
   Kundalahalli Village, Whitefield,
   Bangalore 560037
   Karnataka
   India

   Phone: +91-080-49160700
   Email: rahul.ietf@gmail.com








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