forked from roll-wg/useofrplinfo
-
Notifications
You must be signed in to change notification settings - Fork 0
/
draft-ietf-roll-useofrplinfo-34.txt
3080 lines (2053 loc) · 126 KB
/
draft-ietf-roll-useofrplinfo-34.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
ROLL Working Group M. Robles
Internet-Draft Aalto/UTN-FRM
Updates: 6553, 6550, 8138 (if approved) M. Richardson
Intended status: Standards Track SSW
Expires: July 23, 2020 P. Thubert
Cisco
January 20, 2019
Using RPI Option Type, Routing Header for Source Routes and IPv6-in-IPv6
encapsulation in the RPL Data Plane
draft-ietf-roll-useofrplinfo-34
Abstract
This document looks at different data flows through LLN (Low-Power
and Lossy Networks) where RPL (IPv6 Routing Protocol for Low-Power
and Lossy Networks) is used to establish routing. The document
enumerates the cases where RFC6553 (RPI Option Type), RFC6554
(Routing Header for Source Routes) and IPv6-in-IPv6 encapsulation is
required in data plane. This analysis provides the basis on which to
design efficient compression of these headers. This document updates
RFC6553 adding a change to the RPI Option Type. Additionally, this
document updates RFC6550 defining a flag in the DIO Configuration
Option to indicate about this change and updates RFC8138 as well to
consider the new Option Type when the RPL Option is decompressed.
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 July 23, 2020.
Robles, et al. Expires July 23, 2020 [Page 1]
Internet-Draft RPL-data-plane January 2019
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 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Requirements Language . . . . . . . . . . . . 5
3. RPL Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Updates to RFC6553, RFC6550 and RFC8138 . . . . . . . . . . . 7
4.1. Updates to RFC6550: Advertising External Routes with Non-
Storing Mode Signaling. . . . . . . . . . . . . . . . . . 7
4.2. Updates to RFC6553: Indicating the new RPI Option Type. . 8
4.3. Updates to RFC6550: Indicating the new RPI in the
DODAG Configuration Option Flag. . . . . . . . . . . . . 11
4.4. Updates to RFC8138: Indicating the way to decompress with
the new RPI Option Type. . . . . . . . . . . . . . . . . 13
5. Sample/reference topology . . . . . . . . . . . . . . . . . . 14
6. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Storing mode . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Storing Mode: Interaction between Leaf and Root . . . . . 20
7.1.1. SM: Example of Flow from RAL to root . . . . . . . . 20
7.1.2. SM: Example of Flow from root to RAL . . . . . . . . 21
7.1.3. SM: Example of Flow from root to RUL . . . . . . . . 22
7.1.4. SM: Example of Flow from RUL to root . . . . . . . . 22
7.2. SM: Interaction between Leaf and Internet. . . . . . . . 23
7.2.1. SM: Example of Flow from RAL to Internet . . . . . . 23
7.2.2. SM: Example of Flow from Internet to RAL . . . . . . 24
7.2.3. SM: Example of Flow from RUL to Internet . . . . . . 25
7.2.4. SM: Example of Flow from Internet to RUL. . . . . . . 26
7.3. SM: Interaction between Leaf and Leaf . . . . . . . . . . 27
7.3.1. SM: Example of Flow from RAL to RAL . . . . . . . . . 27
7.3.2. SM: Example of Flow from RAL to RUL . . . . . . . . . 28
7.3.3. SM: Example of Flow from RUL to RAL . . . . . . . . . 29
7.3.4. SM: Example of Flow from RUL to RUL . . . . . . . . . 30
8. Non Storing mode . . . . . . . . . . . . . . . . . . . . . . 31
Robles, et al. Expires July 23, 2020 [Page 2]
Internet-Draft RPL-data-plane January 2019
8.1. Non-Storing Mode: Interaction between Leaf and Root . . . 32
8.1.1. Non-SM: Example of Flow from RAL to root . . . . . . 33
8.1.2. Non-SM: Example of Flow from root to RAL . . . . . . 33
8.1.3. Non-SM: Example of Flow from root to RUL . . . . . . 34
8.1.4. Non-SM: Example of Flow from RUL to root . . . . . . 35
8.2. Non-Storing Mode: Interaction between Leaf and Internet . 36
8.2.1. Non-SM: Example of Flow from RAL to Internet . . . . 36
8.2.2. Non-SM: Example of Flow from Internet to RAL . . . . 37
8.2.3. Non-SM: Example of Flow from RUL to Internet . . . . 38
8.2.4. Non-SM: Example of Flow from Internet to RUL . . . . 39
8.3. Non-SM: Interaction between Leafs . . . . . . . . . . . . 40
8.3.1. Non-SM: Example of Flow from RAL to RAL . . . . . . . 40
8.3.2. Non-SM: Example of Flow from RAL to RUL . . . . . . . 42
8.3.3. Non-SM: Example of Flow from RUL to RAL . . . . . . . 43
8.3.4. Non-SM: Example of Flow from RUL to RUL . . . . . . . 44
9. Operational Considerations of supporting
RUL-leaves . . . . . . . . . . . . . . . . . . . . . . . . . 45
10. Operational considerations of introducing 0x23 . . . . . . . 46
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
12. Security Considerations . . . . . . . . . . . . . . . . . . . 47
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 51
14.1. Normative References . . . . . . . . . . . . . . . . . . 51
14.2. Informative References . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
1. Introduction
RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
[RFC6550] is a routing protocol for constrained networks. [RFC6553]
defines the RPL Option carried within the IPv6 Hop-by-Hop Header to
carry the RPLInstanceID and quickly identify inconsistencies (loops)
in the routing topology. The RPL Option is commonly referred to as
the RPL Packet Information (RPI) though the RPI is really the
abstract information that is defined in [RFC6550] and transported in
the RPL Option. RFC6554 [RFC6554] defines the "RPL Source Route
Header" (RH3), an IPv6 Extension Header to deliver datagrams within a
RPL routing domain, particularly in non-storing mode.
These various items are referred to as RPL artifacts, and they are
seen on all of the data-plane traffic that occurs in RPL routed
networks; they do not in general appear on the RPL control plane
traffic at all which is mostly hop-by-hop traffic (one exception
being DAO messages in non-storing mode).
It has become clear from attempts to do multi-vendor
interoperability, and from a desire to compress as many of the above
Robles, et al. Expires July 23, 2020 [Page 3]
Internet-Draft RPL-data-plane January 2019
artifacts as possible that not all implementers agree when artifacts
are necessary, or when they can be safely omitted, or removed.
The ROLL WG analysized how [RFC2460] rules apply to storing and non-
storing use of RPL. The result was 24 data plane use cases. They
are exhaustively outlined here in order to be completely unambiguous.
During the processing of this document, new rules were published as
[RFC8200], and this document was updated to reflect the normative
changes in that document.
This document updates RFC6553, changing the value of the Option Type
of the RPL Option to make RFC8200 routers ignore this option when not
recognized.
A Routing Header Dispatch for 6LoWPAN (6LoRH)([RFC8138]) defines a
mechanism for compressing RPL Option information and Routing Header
type 3 (RH3) [RFC6554], as well as an efficient IPv6-in-IPv6
technique.
Since some of the uses cases here described, use IPv6-in-IPv6
encapsulation. It MUST take in consideration, when encapsulation is
applied, the RFC6040 [RFC6040], which defines how the explicit
congestion notification (ECN) field of the IP header should be
constructed on entry to and exit from any IPV6-in-IPV6 tunnel.
Additionally, it is recommended the reading of
[I-D.ietf-intarea-tunnels] that explains the relationship of IP
tunnels to existing protocol layers and the challenges in supporting
IP tunneling.
Non-constrained uses of RPL are not in scope of this document, and
applicability statements for those uses may provide different advice,
E.g. [I-D.ietf-anima-autonomic-control-plane].
1.1. Overview
The rest of the document is organized as follows: Section 2 describes
the used terminology. Section 3 provides a RPL Overview. Section 4
describes the updates to RFC6553, RFC6550 and RFC 8138. Section 5
provides the reference topology used for the uses cases. Section 6
describes the uses cases included. Section 7 describes the storing
mode cases and section 8 the non-storing mode cases. Section 9
describes the operational considerations of supporting RPL-unaware-
leaves. Section 10 depicts operational considerations for the
proposed change on RPI Option Type, section 11 the IANA
considerations and then section 12 describes the security aspects.
Robles, et al. Expires July 23, 2020 [Page 4]
Internet-Draft RPL-data-plane January 2019
2. Terminology and Requirements Language
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.
Terminology defined in [RFC7102] applies to this document: LLN, RPL,
RPL Domain and ROLL.
RPL Leaf: An IPv6 host that is attached to a RPL router and obtains
connectivity through a RPL Destination Oriented Directed Acyclic
Graph (DODAG). As an IPv6 node, a RPL Leaf is expected to ignore a
consumed Routing Header and as an IPv6 host, it is expected to ignore
a Hop-by-Hop header. It results that a RPL Leaf can correctly
receive a packet with RPL artifacts. On the other hand, a RPL Leaf
is not expected to generate RPL artifacts or to support IP-in-IP
encapsulation. For simplification, this document uses the standalone
term leaf to mean a RPL leaf.
RPL Packet Information (RPI): The abstract information that [RFC6550]
places in IP packets. The term is commonly used, including in this
document, to refer to the RPL Option [RFC6553] that transports that
abstract information in an IPv6 Hob-by-Hop Header.
RPL-aware-node (RAN): A device which implements RPL. Please note
that the device can be found inside the LLN or outside LLN.
RPL-Aware-Leaf(RAL): A RPL-aware-node that is also a RPL Leaf.
RPL-unaware-node: A device which does not implement RPL, thus the
device is not-RPL-aware. Please note that the device can be found
inside the LLN.
RPL-Unaware-Leaf(RUL): A RPL-unaware-node that is also a RPL Leaf.
6LoWPAN Node (6LN): [RFC6775] defines it as: "A 6LoWPAN node is any
host or router participating in a LoWPAN. This term is used when
referring to situations in which either a host or router can play the
role described.". In this document, a 6LN acts as a leaf.
6LoWPAN Router (6LR): [RFC6775] defines it as:" An intermediate
router in the LoWPAN that is able to send and receive Router
Advertisements (RAs) and Router Solicitations (RSs) as well as
forward and route IPv6 packets. 6LoWPAN routers are present only in
route-over topologies."
Robles, et al. Expires July 23, 2020 [Page 5]
Internet-Draft RPL-data-plane January 2019
6LoWPAN Border Router (6LBR): [RFC6775] defines it as:"A border
router located at the junction of separate 6LoWPAN networks or
between a 6LoWPAN network and another IP network. There may be one
or more 6LBRs at the 6LoWPAN network boundary. A 6LBR is the
responsible authority for IPv6 prefix propagation for the 6LoWPAN
network it is serving. An isolated LoWPAN also contains a 6LBR in
the network, which provides the prefix(es) for the isolated network."
Flag Day: A transition that involves having a network with different
values of RPI Option Type. Thus the network does not work correctly
(Lack of interoperation).
Hop-by-hop re-encapsulation: The term "hop-by-hop re-encapsulation"
header refers to adding a header that originates from a node to an
adjacent node, using the addresses (usually the GUA or ULA, but could
use the link-local addresses) of each node. If the packet must
traverse multiple hops, then it must be decapsulated at each hop, and
then re-encapsulated again in a similar fashion.
Non-Storing Mode (Non-SM): RPL mode of operation in which the RPL-
aware-nodes send information to the root about its parents. Thus,
the root know the topology, then the intermediate 6LRs do not
maintain routing state so that source routing is needed.
Storing Mode (SM): RPL mode of operation in which RPL-aware-nodes
(6LRs) maintain routing state (of the children) so that source
routing is not needed.
Note: Due to lack of space in some figures (tables) we refers IPv6-
in-IPv6 as IP6-IP6.
3. RPL Overview
RPL defines the RPL Control messages (control plane), a new ICMPv6
[RFC4443] message with Type 155. DIS (DODAG Information
Solicitation), DIO (DODAG Information Object) and DAO (Destination
Advertisement Object) messages are all RPL Control messages but with
different Code values. A RPL Stack is shown in Figure 1.
Robles, et al. Expires July 23, 2020 [Page 6]
Internet-Draft RPL-data-plane January 2019
+--------------+
| Upper Layers |
| |
+--------------+
| RPL |
| |
+--------------+
| ICMPv6 |
| |
+--------------+
| IPv6 |
| |
+--------------+
| 6LoWPAN |
| |
+--------------+
| PHY-MAC |
| |
+--------------+
Figure 1: RPL Stack.
RPL supports two modes of Downward traffic: in storing mode (SM), it
is fully stateful; in non-storing mode (Non-SM), it is fully source
routed. A RPL Instance is either fully storing or fully non-storing,
i.e. a RPL Instance with a combination of storing and non-storing
nodes is not supported with the current specifications at the time of
writing this document.
4. Updates to RFC6553, RFC6550 and RFC8138
4.1. Updates to RFC6550: Advertising External Routes with Non-Storing
Mode Signaling.
Section 6.7.8. of [RFC6550] introduces the 'E' flag that is set to
indicate that the 6LR that generates the DAO redistributes external
targets into the RPL network. An external Target is a Target that
has been learned through an alternate protocol, for instance a route
to a prefix that is outside the RPL domain but reachable via a 6LR.
Being outside of the RPL domain, a node that is reached via an
external target cannot be guaranteed to ignore the RPL artifacts and
cannot be expected to process the [RFC8138] compression correctly.
This means that the RPL artifacts should be contained in an IP-in-IP
encapsulation that is removed by the 6LR, and that any remaining
compression should be expanded by the 6LR before it forwards a packet
outside the RPL domain.
Robles, et al. Expires July 23, 2020 [Page 7]
Internet-Draft RPL-data-plane January 2019
This specification updates [RFC6550] to RECOMMEND that external
targets are advertised using Non-Storing Mode DAO messaging even in a
Storing-Mode network. This way, external routes are not advertised
within the DODAG and all packets to an external target reach the Root
like normal Non-Storing Mode traffic. The Non-Storing Mode DAO
informs the Root of the address of the 6LR that injects the external
route, and the root uses IP-in-IP encapsulation to that 6LR, which
terminates the IP-in-IP tunnel and forwards the original packet
outside the RPL domain free of RPL artifacts. In the other
direction, for traffic coming from an external target into the LLN,
the parent (6LR) that injects the traffic always encapsulates to the
root. This whole operation is transparent to intermediate routers
that only see traffic between the 6LR and the Root, and only the Root
and the 6LRs that inject external routes in the network need to be
upgraded to add this function to the network.
A RUL is a special case of external target when the target is
actually a host and it is known to support a consumed Routing Header
and to ignore a HbH header as prescribed by [RFC8200]. The target
may have been learned through as a host route or may have been
registered to the 6LR using [RFC8505]. IP-in-IP encapsulation MAY be
avoided for Root to RUL communication if the RUL is known to process
the packets as forwarded by the parent 6LR without decapsulation.
In order to enable IP-in-IP all the way to a 6LN, it is beneficial
that the 6LN supports decapsulating IP-in-IP, but that is not assumed
by [RFC8504]. If the 6LN is a RUL, the Root that encapsulates a
packet SHOULD terminate the tunnel at a parent 6LR unless it is aware
that the RUL supports IP-in-IP decapsulation.
A node that is reachable over an external route is not expected to
support [RFC8138]. Whether a decapsulation took place or not and
even when the 6LR is delivering the packet to a RUL, the 6LR that
injected an external route MUST uncompress the packet before
forwarding over that external route.
4.2. Updates to RFC6553: Indicating the new RPI Option Type.
This modification is required to be able to send, for example, IPv6
packets from a RPL-Aware-Leaf to a RPL-unaware node through Internet
(see Section 7.2.1), without requiring IPv6-in-IPv6 encapsulation.
[RFC6553] (Section 6, Page 7) states as shown in Figure 2, that in
the Option Type field of the RPL Option, the two high order bits must
be set to '01' and the third bit is equal to '1'. The first two bits
indicate that the IPv6 node must discard the packet if it doesn't
recognize the Option Type, and the third bit indicates that the
Robles, et al. Expires July 23, 2020 [Page 8]
Internet-Draft RPL-data-plane January 2019
Option Data may change in route. The remaining bits serve as the
Option Type.
+-------+-------------------+----------------+-----------+
| Hex | Binary Value | Description | Reference |
+ Value +-------------------+ + +
| | act | chg | rest | | |
+-------+-----+-----+-------+----------------+-----------+
| 0x63 | 01 | 1 | 00011 | RPL Option | [RFC6553] |
+-------+-----+-----+-------+----------------+-----------+
Figure 2: Option Type in RPL Option.
This document illustrates that is is not always possible to know for
sure at the source that a packet will only travel within the RPL
domain or may leave it.
At the time [RFC6553] was published, leaking a Hop-by-Hop header in
the outer IPv6 header chain could potentially impact core routers in
the internet. So at that time, it was decided to encapsulate any
packet with a RPL Option using IPv6-in-IPv6 in all cases where it was
unclear whether the packet would remain within the RPL domain. In
the exception case where a packet would still leak, the Option Type
would ensure that the first router in the Internet that does not
recognize the option would drop the packet and protect the rest of
the network.
Even with [RFC8138] that compresses the IPv6-in-IPv6 header, this
approach yields extra bytes in a packet which means consuming more
energy, more bandwidth, incurring higher chances of loss and possibly
causing a fragmentation at the 6LoWPAN level. This impacts the daily
operation of constrained devices for a case that generally does not
happen and would not heavily impact the core anyway.
While intention was and remains that the Hop-by-Hop header with a RPL
Option should be confined within the RPL domain, this specification
modifies this behavior in order to reduce the dependency on IPv6-in-
IPv6 and protect the constrained devices. Section 4 of [RFC8200]
clarifies the behaviour of routers in the Internet as follows: "it is
now expected that nodes along a packet's delivery path only examine
and process the Hop-by-Hop Options header if explicitly configured to
do so".
When unclear about the travel of a packet, it becomes preferable for
a source not to encapsulate, accepting the fact that the packet may
leave the RPL domain on its way to its destination. In that event,
the packet should reach its destination and should not be discarded
by the first node that does not recognize the RPL Option. But with
Robles, et al. Expires July 23, 2020 [Page 9]
Internet-Draft RPL-data-plane January 2019
the current value of the Option Type, if a node in the Internet is
configured to process the Hop-by-Hop header, and if such node
encounters an option with the first two bits set to 01 and conforms
to [RFC8200], it will drop the packet. Host systems should do the
same, irrespective of the configuration.
Thus, this document updates the Option Type of the RPL Option
[RFC6553], abusively naming it RPI Option Type for simplicity, to
(Figure 3): the two high order bits MUST be set to '00' and the third
bit is equal to '1'. The first two bits indicate that the IPv6 node
MUST skip over this option and continue processing the header
([RFC8200] Section 4.2) if it doesn't recognize the Option Type, and
the third bit continues to be set to indicate that the Option Data
may change en route. The five rightmost bits remain at 0x3. This
ensures that a packet that leaves the RPL domain of an LLN (or that
leaves the LLN entirely) will not be discarded when it contains the
RPL Option.
With the new Option Type, if an IPv6 (intermediate) node (RPL-not-
capable) receives a packet with an RPL Option, it should ignore the
Hop-by-Hop RPL Option (skip over this option and continue processing
the header). This is relevant, as it was mentioned previously, in
the case that there is a flow from RAL to Internet (see
Section 7.2.1).
This is a significant update to [RFC6553].
+-------+-------------------+-------------+------------+
| Hex | Binary Value | Description | Reference |
+ Value +-------------------+ + +
| | act | chg | rest | | |
+-------+-----+-----+-------+-------------+------------+
| 0x23 | 00 | 1 | 00011 | RPL Option |[RFCXXXX](*)|
+-------+-----+-----+-------+-------------+------------+
Figure 3: Revised Option Type in RPL Option. (*)represents this
document
Without the signaling described below, this change would otherwise
create a lack of interoperation (flag day) for existing networks
which are currently using 0x63 as the RPI Option Type value. A move
to 0x23 will not be understood by those networks. It is suggested
that RPL implementations accept both 0x63 and 0x23 when processing
the header.
When forwarding packets, implementations SHOULD use the same value as
it was received. This is required because, RPI Option Type can not
be changed by [RFC8200] - Section 4.2. It allows to the network to
Robles, et al. Expires July 23, 2020 [Page 10]
Internet-Draft RPL-data-plane January 2019
be incrementally upgraded, and for the DODAG root to know which parts
of the network are upgraded.
When originating new packets, implementations SHOULD have an option
to determine which value to originate with, this option is controlled
by the DIO option described below.
The change of RPI Option Type from 0x63 to 0x23, makes all [RFC8200]
Section 4.2 compliant nodes tolerant of the RPL artifacts. There is
therefore no longer a necessity to remove the artifacts when sending
traffic to the Internet. This change clarifies when to use an IPv6-
in-IPv6 header, and how to address them: The Hop-by-Hop Options
Header containing the RPI MUST always be added when 6LRs originate
packets (without IPv6-in-IPv6 headers), and IPv6-in-IPv6 headers MUST
always be added when a 6LR find that it needs to insert a Hop-by-Hop
Options Header containing the RPL Option. The IPv6-in-IPv6 header is
to be addressed to the RPL root when on the way up, and to the end-
host when on the way down.
In the non-storing case, dealing with not-RPL aware leaf nodes is
much easier as the 6LBR (DODAG root) has complete knowledge about the
connectivity of all DODAG nodes, and all traffic flows through the
root node.
The 6LBR can recognize not-RPL aware leaf nodes because it will
receive a DAO about that node from the 6LR immediately above that
not-RPL aware node. This means that the non-storing mode case can
avoid ever using hop-by-hop re-encapsulation headers for traffic
originating from the root to the leafs.
The non-storing mode case does not require the type change from 0x63
to 0x23, as the root can always create the right packet. The type
change does not adversely affect the non-storing case.
4.3. Updates to RFC6550: Indicating the new RPI in the DODAG
Configuration Option Flag.
In order to avoid a Flag Day caused by lack of interoperation between
new RPI Option Type (0x23) and old RPI Option Type (0x63) nodes, this
section defines a flag in the DIO Configuration Option, to indicate
when then new RPI Option Type can be safely used. This means, the
flag is going to indicate the value of Option Type that the network
is using for the RPL Option. Thus, when a node join to a network
will know which value to use. With this, RPL-capable nodes know if
it is safe to use 0x23 when creating a new RPL Option. A node that
forwards a packet with an RPI MUST NOT modify the Option Type of the
RPL Option.
Robles, et al. Expires July 23, 2020 [Page 11]
Internet-Draft RPL-data-plane January 2019
This is done using a DODAG Configuration Option flag which will
signal "RPI 0x23 enable" and propagate through the network.
Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP)
in the DIO Base Object. The flag is defined only for MOP value
between 0 to 6. For a MOP value of 7 or above, the flag MAY indicate
something different and MUST NOT be interpreted as "RPI 0x23 enable"
unless the specification of the MOP indicates to do so.
As stated in [RFC6550] the DODAG Configuration option is present in
DIO messages. The DODAG Configuration option distributes
configuration information. It is generally static, and does not
change within the DODAG. This information is configured at the DODAG
root and distributed throughout the DODAG with the DODAG
Configuration option. Nodes other than the DODAG root do not modify
this information when propagating the DODAG Configuration option.
Currently, the DODAG Configuration Option in [RFC6550] states: "the
unused bits MUST be initialize to zero by the sender and MUST be
ignored by the receiver". If the flag is received with a value zero
(which is the default), then new nodes will remain in RFC6553
Compatible Mode; originating traffic with the old-RPI Option Type
(0x63) value. If the flag is received with a value of 1, then the
option value for the RPL Option MUST be set to 0x23.
Bit number three of the flag field in the DODAG Configuration option
is to be used as shown in Figure 4 :
+------------+-----------------+---------------+
| Bit number | Description | Reference |
+------------+-----------------+---------------+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
Figure 4: DODAG Configuration Option Flag to indicate the RPI-flag-
day.
In case of rebooting, the node (6LN or 6LR) does not remember the RPI
Option Type, that is if the flag is set, so DIO messages sent by the
node would be set with the flag unset until a DIO message is received
with the flag set indicating the new RPI Option Type. The node sets
to 0x23 if the node supports this feature.
Robles, et al. Expires July 23, 2020 [Page 12]
Internet-Draft RPL-data-plane January 2019
4.4. Updates to RFC8138: Indicating the way to decompress with the new
RPI Option Type.
This modification is required to be able to decompress the RPL Option
with the new Option Type of 0x23.
RPI-6LoRH header provides a compressed form for the RPL RPI [RFC8138]
in section 6. A node that is decompressing this header MUST
decompress using the RPI Option Type that is currently active: that
is, a choice between 0x23 (new) and 0x63 (old). The node will know
which to use based upon the presence of the flag in the DODAG
Configuration Option defined in Section 4.3. E.g. If the network is
in 0x23 mode (by DIO option), then it should be decompressed to 0x23.
[RFC8138] section 7 documents how to compress the IPv6-in-IPv6
header.
There are potential significant advantages to having a single code
path that always processes IPv6-in-IPv6 headers with no conditional
branches.
In Storing Mode, for the examples of Flow from RAL to RUL and RUL to
RUL comprise an IPv6-in-IPv6 and RPI compressed headers. The use of
the IPv6-in-IPv6 header is MANDATORY in this case, and it SHOULD be
compressed with [RFC8138] section 7. Figure 5 illustrates the case
in Storing mode where the packet is received from the Internet, then
the root encapsulates the packet to insert the RPI. In that example,
the leaf is not known to support RFC 8138, and the packet is
encapsulated to the 6LR that is the parent and last hop to the final
destination.
+-+ ... -+-+ ... +-+- ... -+-+- +-+-+-+ ... +-+-+ ... -+++ ... +-...
|11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP
|Page 1 |Type1 S=0| 6LoRH |6LoRH |LOWPAN_IPHC| UDP | hdr |Payld
+-+ ... -+-+ ... +-+- ... -+-+-.+-+-+-+-+ ... +-+-+ ... -+ ... +-...
<-4bytes-> <- RFC 6282 ->
No RPL artifact
Figure 5: RPI Inserted by the Root in Storing Mode
In Figure 5, the source of the IPv6-in-IPv6 encapsulation is the
Root, so it is elided in the IP-in-IP 6LoRH. The destination is the
parent 6LR of the destination of the inner packet so it cannot be
elided. It is placed as the single entry in an SRH-6LoRH as the
first 6LoRH. There is a single entry so the SRH-6LoRH Size is 0. In
that example, the type is 1 so the 6LR address is compressed to 2
bytes. It results that the total length of the SRH-6LoRH is 4 bytes.
Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP
Robles, et al. Expires July 23, 2020 [Page 13]
Internet-Draft RPL-data-plane January 2019
6LoRH is removed, all the router headers that precede it are also
removed. The Paging Dispatch [RFC8025] may also be removed if there
was no previous Page change to a Page other than 0 or 1, since the
LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and
in Page 1. The resulting packet to the destination is the inner
packet compressed with [RFC6282].
5. Sample/reference topology
A RPL network in general is composed of a 6LBR, Backbone Router
(6BBR), 6LR and 6LN as leaf logically organized in a DODAG structure.
Figure 6 shows the reference RPL Topology for this document. The
letters above the nodes are there so that they may be referenced in
subsequent sections. In the figure, 6LR represents a full router
node. The 6LN is a RPL aware router, or host (as a leaf).
Additionally, for simplification purposes, it is supposed that the
6LBR has direct access to Internet and is the root of the DODAG, thus
the 6BBR is not present in the figure.
The 6LN leaves (RAL) marked as (F, H and I) are RPL nodes with no
children hosts.
The leafs marked as RUL (G and J) are devices which do not speak RPL
at all (not-RPL-aware), but uses Router-Advertisements, 6LowPAN DAR/
DAC and efficient-ND only to participate in the network [RFC6775].
In the document these leafs (G and J) are also referred to as an IPv6
node.
The 6LBR ("A") in the figure is the root of the Global DODAG.
Robles, et al. Expires July 23, 2020 [Page 14]
Internet-Draft RPL-data-plane January 2019
+------------+
| INTERNET ----------+
| | |
+------------+ |
|
|
|
A |
+-------+
|6LBR |
+-----------|(root) |-------+
| +-------+ |
| |
| |
| |
| |
| B |C
+---|---+ +---|---+
| 6LR | | 6LR |
+---------| |--+ +--- ---+
| +-------+ | | +-------+ |
| | | |
| | | |
| | | |
| | | |
| D | E | |
+-|-----+ +---|---+ | |
| 6LR | | 6LR | | |
| | +------ | | |
+---|---+ | +---|---+ | |
| | | | |
| | +--+ | |
| | | | |
| | | | |
| | | I | J |
F | | G | H | |
+-----+-+ +-|-----+ +---|--+ +---|---+ +---|---+
| RAL | | RUL | | RAL | | RAL | | RUL |
| 6LN | | 6LN | | 6LN | | 6LN | | 6LN |
+-------+ +-------+ +------+ +-------+ +-------+
Figure 6: A reference RPL Topology.
Robles, et al. Expires July 23, 2020 [Page 15]
Internet-Draft RPL-data-plane January 2019
6. Use cases
In the data plane a combination of RFC6553, RFC6554 and IPv6-in-IPv6
encapsulation are going to be analyzed for a number of representative
traffic flows.
This document assumes that the LLN is using the no-drop RPI Option
Type of 0x23.
The use cases describe the communication in the following cases: -
Between RPL-aware-nodes with the root (6LBR) - Between RPL-aware-
nodes with the Internet - Between RUL nodes within the LLN (e.g. see
Section 7.1.4) - Inside of the LLN when the final destination address
resides outside of the LLN (e.g. see Section 7.2.3).
The uses cases are as follows:
Interaction between Leaf and Root:
RAL to root
root to RAL
RUL to root
root to RUL
Interaction between Leaf and Internet:
RAL to Internet
Internet to RAL
RUL to Internet
Internet to RUL
Interaction between Leafs:
RAL to RAL
RAL to RUL
RUL to RAL
RUL to RUL
Robles, et al. Expires July 23, 2020 [Page 16]
Internet-Draft RPL-data-plane January 2019
This document is consistent with the rule that a Header cannot be
inserted or removed on the fly inside an IPv6 packet that is being
routed. This is a fundamental precept of the IPv6 architecture as
outlined in [RFC8200].
As the rank information in the RPI artifact is changed at each hop,
it will typically be zero when it arrives at the DODAG root. The
DODAG root MUST force it to zero when passing the packet out to the
Internet. The Internet will therefore not see any SenderRank
information.
Despite being legal to leave the RPI artifact in place, an
intermediate router that needs to add an extension header (e.g. RH3
or RPL Option) MUST still encapsulate the packet in an (additional)
outer IP header. The new header is placed after this new outer IP
header.
A corollary is that an RH3 or RPL Option can only be removed by an
intermediate router if it is placed in an encapsulating IPv6 Header,
which is addressed TO the intermediate router. When it does so, the
whole encapsulating header must be removed. (A replacement may be
added). This sometimes can result in outer IP headers being
addressed to the next hop router using link-local address.
Both the RPL Option and the RH3 headers may be modified in very
specific ways by routers on the path of the packet without the need
to add and remove an encapsulating header. Both headers were
designed with this modification in mind, and both the RPL RH3 and the
RPL Option are marked mutable but recoverable: so an IPsec AH
security header can be applied across these headers, but it can not
secure the values which mutate.
The RPI MUST be present in every single RPL data packet.
Prior to [RFC8138], there was significant interest in removing the
RPI for downward flows in non-storing mode. The exception covered a
very small number of cases, and causes significant interoperability
challenges, yet costed significant code and testing complexity. The
ability to compress the RPI down to three bytes or less removes much
of the pressure to optimize this any further
[I-D.ietf-anima-autonomic-control-plane].
The earlier examples are more extensive to make sure that the process
is clear, while later examples are more concise.
The uses cases are delineated based on the following requirements:
The RPIhas to be in every packet that traverses the LLN.
Robles, et al. Expires July 23, 2020 [Page 17]
Internet-Draft RPL-data-plane January 2019
- Because of the previous requirement, packets from the Internet
have to be encapsulated.
- A Header cannot be inserted or removed on the fly inside an IPv6
packet that is being routed.
- Extension headers may not be added or removed except by the
sender or the receiver.
- RPI and RH3 headers may be modified by routers on the path of
the packet without the need to add and remove an encapsulating
header.
- An RH3 or RPL Option can only be removed by an intermediate
router if it is placed in an encapsulating IPv6 Header, which is
addressed to the intermediate router.
- Non-storing mode requires downstream encapsulation by root for
RH3.
The uses cases are delineated based on the following assumptions:
This document assumes that the LLN is using the no-drop RPI Option
Type (0x23).
- Each IPv6 node (including Internet routers) obeys [RFC8200] RFC
8200, so that 0x23 RPI Option type can be safely inserted.
- All 6LRs obey RFC 8200 [RFC8200].
- The RPI is ignored at the IPv6 dst node (RUL).
- In the uses cases, we assume that the RAL supports IP-in-IP
encapsulation.
- In the uses cases, we dont assume that the RUL supports IP-in-IP
encapsulation.
- Non-constrained uses of RPL are not in scope of this document.
- Compression is based on [RFC8138].
- The flow label [RFC6437] is not needed in RPL.