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1	Network Working Group                                     George Swallow
2	Internet Draft                                       Cisco Systems, Inc.
3	Category: Standards Track
4	Expiration Date: January 2006
5	                                                        Kireeti Kompella
6	                                                  Juniper Networks, Inc.

8	                                                              Dan Tappan
9	                                                     Cisco Systems, Inc.

11	                                                               July 2005

13	                    Label Switching Router Self-Test

15	                  draft-ietf-mpls-lsr-self-test-05.txt

17	Status of this Memo

19	   By submitting this Internet-Draft, each author represents that any
20	   applicable patent or other IPR claims of which he or she is aware
21	   have been or will be disclosed, and any of which he or she becomes
22	   aware will be disclosed, in accordance with Section 6 of BCP 79.

24	   This document is an Internet-Draft and is in full conformance with
25	   all provisions of Section 5 of RFC3667.  Internet-Drafts are working
26	   documents of the Internet Engineering Task Force (IETF), its areas,
27	   and its working groups.  Note that other groups may also distribute
28	   working documents as Internet-Drafts.

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

35	   The list of current Internet-Drafts can be accessed at
36	   http://www.ietf.org/1id-abstracts.html

38	   The list of Internet-Draft Shadow Directories can be accessed at
39	   http://www.ietf.org/shadow.html

41	   Abstract

43	      This document defines a means for a Label-Switching Router (LSR)
44	      to verify that its dataplane is functioning for certain key Multi-
45	      Protocol Label Switching (MPLS) applications, including unicast
46	      forwarding based on LDP [LDP] and traffic engineering tunnels
47	      based on [RSVP-TE].  A new Loopback FEC type is defined to allow
48	      an upstream neighbor to assist in the testing at very low cost.
49	      MPLS Echo Request and MPLS Echo Reply messages [LSP-Ping] are
50	      extended to do the actual probing.

52	Contents

54	 1      Introduction  ..............................................   3
55	 1.1    Conventions  ...............................................   3
56	 2      Loopback FEC  ..............................................   4
57	 2.1    IPv4 Loopback FEC Element  .................................   4
58	 2.2    LDP Procedures  ............................................   5
59	 3      Data Plane Self Test  ......................................   6
60	 3.1    Data Plane Verification Request / Reply Messages  ..........   7
61	 3.2    UDP Port  ..................................................   8
62	 3.3    Reply-To Object  ...........................................   8
63	 3.3.1  IPv4 Reply-To Object  ......................................   9
64	 3.3.2  IPv6 Reply-To Object  ......................................   9
65	 3.4    Sending procedures  ........................................  10
66	 3.5    Receiving procedures  ......................................  11
67	 3.6    Upstream Neighbor Verification  ............................  11
68	 4      Security Considerations  ...................................  12
69	 5      IANA Considerations  .......................................  12
70	 6      Acknowledgments  ...........................................  13
71	 7      References  ................................................  13
72	 7.1    Normative References  ......................................  13
73	 7.2    Informative References  ....................................  13
74	 8      Authors' Addresses  ........................................  14

76	1. Introduction

78	   This document defines a means for a Label-Switching Router (LSR) to
79	   verify that its dataplane is functioning for certain key Multi-Proto-
80	   col Label Switching (MPLS) applications, including unicast forwarding
81	   based on LDP [LDP] and traffic engineering tunnels based on [RSVP-
82	   TE].  MPLS Echo Request and MPLS Echo Reply messages [LSP-Ping] mes-
83	   sages are extended to do the actual probing.  The pings are sent to
84	   an upstream neighbor, looped back through the LSR under test and
85	   intercepted, by means of TTL expiration by a downstream neighbor.
86	   Extensions to LSP-Ping [LSP-Ping] are defined to allow the down
87	   stream neighbor to report the test results.

89	   In order to minimize the load on upstream LSRs a new loopback FEC is
90	   defined. Receipt of a packet labeled with a loopback label will cause
91	   the advertising LSR to pop the label off the label stack and send the
92	   packet out the advertised interface.

94	   Note that use of a loopback allows an LSR to test label entries for
95	   which the LSR is not currently some neighbor's next hop.  In this way
96	   label entries can be verified prior to the occurrence of a routing
97	   change.

99	   Some routing protocls, most notably OSPF have no means of exchanging
100	   the "Link Local Identifiers" used to identify unnumbered links and
101	   components of bundled links.  These test procedures can be used to
102	   associate the neighbor's interfaces with the probing LSRs interfaces.
103	   This is achieved by simply having the TTL of the MPLS Ping expire one
104	   hop sooner, i.e. at the testing LSR itself.

106	1.1. Conventions

108	   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
109	   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
110	   document are to be interpreted as described in RFC 2119 [KEYWORDS].

112	2. Loopback FEC

114	   The Loopback FEC type is defined to enable an upstream neighbor to
115	   assist in LSR self-testing at very low cost.  This FEC causes the
116	   loopback to occur in the dataplane without control plane involvement
117	   beyond the initial LDP exchange and dataplane setup.  The FEC also
118	   carries information to indicate the desired encapsulation should it
119	   be the only label in a received label stack.  Values are defined for
120	   IPv4 and IPv6.

122	   An LSR uses a Loopback FEC to selectively advertise loopback labels
123	   to its neighbor LSRs.  Each loopback label is bound to a particular
124	   interface.  For multi-access links, a unique label for each neighbor
125	   is required, since the link-level address is derived from the label
126	   lookup.  When an MPLS packet with its top label set to a loopback
127	   label is received from an interface over which that label was adver-
128	   tised, the loopback label is popped and the packet is sent on the
129	   interface to which the loopback label was bound.  If the label-stack
130	   only contains the one loopback label, the encapsulation of the packet
131	   is determined by the FEC Type.

133	   TTL treatment for loopback labels follows the Uniform model.  I.e.
134	   the TTL carried in the loopback label is decremented and copied to
135	   the exposed label or IP header as the case may be.

137	2.1. IPv4 Loopback FEC Element

139	   FEC element type 130 is used.   The FEC element is encoded as fol-
140	   lows: (note: 130 is provisionally assigned, the actual value will be
141	   assigned by IANA.)

143	       0                   1                   2                   3
144	       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
145	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
146	      |     130       |      Res      | If & Prot Type|   Id Length   |
147	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
148	      |                     Interface Identifier                      |
149	      |                              "                                |
150	      |                              "                                |
151	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
152	      Reserved (Res)

154	         Must be set to zero on transmission and ignored on receipt.

156	      Interface & Protocol Type

158	               #     Type                 Interface Identifier
159	              ---    ----                 --------------------
160	               1     IPv4 Numbered        IPv4 Address
161	               2     IPv4 Unnumbered      A 32 bit Link Identifier as
162	                                             defined in [RFC3477]
163	               3     IPv6 Numbered        IPv6 Address
164	               4     IPv6 Unnumbered      A 32 bit Link Identifier as
165	                                             defined in [RFC3477]

167	       .in 9
168	      Note that this type alos indicates the encapsulation type for payloads
169	      that have a label stack contain the one loopback label.

171	      Identifier Length

173	         Length of the interface identifier in octets.  The length is 4
174	         bytes for the unnumbered types and IPv4, 16 bytes for IPv6.

176	      Address

178	         An identifier encoded according to the Identifier Type field.

180	2.2. LDP Procedures

182	   It is RECOMMENDED that loopback labels only be distributed in
183	   response to a Label Request message, irrespective of the label adver-
184	   tisement mode of the LDP session.  However it is recognized that in
185	   certain cases such as OSPF with unnumbered links, the upstream LSR
186	   may not have sufficiently detailed information of the neighbor's link
187	   identifier to form the request.  In these cases, the downstream LSR
188	   will need to be configured to make unsolicited advertisements.

190	3. Data Plane Self Test

192	   A self test operation involves three LSRs, the LSR doing the test, an
193	   upstream neighbor and a downstream neighbor.  We refer to these as
194	   LSRs T, U, and D respectively.  In order to minimize the processing
195	   load on LSR-D, two new LSP Ping messages are defined, called the MPLS
196	   Data Plane Verification Request and the MPLS Data Plane Verification
197	   Reply.  These messages are used to allow LSR-T to obtain the label
198	   stack, address and interface information of LSR-D.

200	   If FEC verification is required, the MPLS Echo Request and Reply mes-
201	   sages are used.

203	   The packet flow is shown below. Although the figure shows LSR-D adja-
204	   cent to LSR-T it may in some cases be an arbitrary number of hops
205	   away.

207	                 +-------+       +-------+       +-------+
208	                 |     ,-|-------|<DPVRq |       |       |
209	                 |     `-|-------|-------|-------|->     |
210	                 |       |       |       |       |       |
211	                 |       |       |     <-|-------|<DPVRp |
212	                 +-------+       +-------+       +-------+
213	                   LSR-U           LSR-T           LSR-D

215	               DPVRq: MPLS Data Plane Verification Request
216	               DPVRp: MPLS Data Plane Verification Reply

218	                    Figure 1: Self Test Message Flow

220	   In order to perform a test on an incoming label stack, LSR-T forms an
221	   MPLS Data Plane Verification Request.  LSR-T prepends the packet with
222	   the incoming label stack being tested and the loopback label received
223	   from LSR-U.  The TTL values are set such that they will expire at
224	   LSR-D.  LSR-T then forwards the packet to LSR-U.

226	   LSR-U receives the packet and performs normal MPLS forwarding.  That
227	   is, the loopback label is popped, the TTL is decremented and propa-
228	   gated (in this case) to the exposed label.

230	   LSR-T receives the packet and performs normal MPLS forwarding.  If
231	   everything is functioning as expected this will cause the packet to
232	   arrive at LSR-D with a TTL of 1.

234	   In this example, we assume that all is working properly.  The TTL
235	   expires at LSR-D causing it to receive the packet.   LSR-D notes the
236	   the interface and the label stack on which the packet was received
237	   and records these in an Interface and Label Stack TLV.  This Object
238	   is sent to LSR-T in an MPLS Data Plane Verification Reply message.

240	3.1. Data Plane Verification Request / Reply Messages

242	   Two new LSP Ping messages are defined for LSR self test.  The purpose
243	   of the new messages is three fold.  First the timestamps are removed
244	   to minimize processing.  Second the message type allows simple recog-
245	   nition that minimal processing is necessary to service this request.
246	   Third, the Verification Request message itself conveys the the
247	   request, thus a Verification Request message with no Objects is both
248	   legal and normal.

250	   The definitions of all fields in the messages are identical to those
251	   found in [LSP-PING].

253	   The new message types are: (Provisionally; to be assigned)

255	      Type     Message
256	      ----     -------
257	        3      MPLS Data Plane Verification Request
258	        4      MPLS Data Plane Verification Reply

260	   The messages have the following format:

262	    0                   1                   2                   3
263	    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
264	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
265	   |         Version Number        |         Must Be Zero          |
266	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
267	   |  Message Type |   Reply mode  |  Return Code  | Return Subcode|
268	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
269	   |                        Sender's Handle                        |
270	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
271	   |                        Sequence Number                        |
272	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
273	   |                            TLVs ...                           |
274	   .                                                               .
275	   .                                                               .
276	   .                                                               .
277	   |                                                               |
278	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
279	   The MPLS Data Plane Verification Request message MAY contain the fol-
280	   lowing objects:

282	          Type #               Object
283	          ------               -----------
284	            3                  Pad
285	            5                  Vendor Enterprise Code
286	           11 (provisional)    IPv4 Reply-to Object
287	           12 (provisional)    IPv6 Reply-to Object

289	   The MPLS Data Plane Verification Reply message MAY contain the fol-
290	   lowing objects:

292	          Type #            Object
293	          ------            -----------
294	            3               Pad
295	            4               Error Code
296	            5               Vendor Enterprise Code
297	            7               IPv4 Interface and Label Stack Object
298	            8               IPv6 Interface and Label Stack Object

300	3.2. UDP Port

302	   MPLS Data Plane Verification Request messages MAY be sent to port
303	   3503 as is used for [LSP-PING].  However to aid implementations that
304	   wish to handle these messages at a lower level than MPLS Echo Request
305	   messages another UDP port, tbd, is provided.  Port tbd SHOULD be used
306	   by default.  The source UDP port, as in [LSP-PING] is chosen by the
307	   sender.

309	3.3. Reply-To Object

311	   In order to perform detailed diagnostics of a particular failing flow
312	   in the face of ECMP, it is useful to be able to use the exact source
313	   and destination addresses of that flow.  The Reply-To Object is an
314	   optional TLV in a MPLS Data Plane Verification Request message.  The
315	   Object has two formats, type 11 for IPv4 and type 12 for IPv6 (to be
316	   assigned by IANA).

318	3.3.1. IPv4 Reply-To Object

320	   The length of an IPv4 Reply-To Object is 4 octets; the value field
321	   has the following format:

323	       0                   1                   2                   3
324	       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
325	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
326	      |                     Reply-to IPv4 Address                     |
327	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

329	      Reply-to IPv4 Address

331	         The address to which the MPLS Data Plane Verification Reply
332	         message is to be sent.

334	3.3.2. IPv6 Reply-To Object

336	   The length of an IPv6 Reply-To Object is 16 octets; the value field
337	   has the following format:

339	       0                   1                   2                   3
340	       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
341	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
342	      |                     Reply-to IPv6 Address                     |
343	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
344	      |                 Reply-to IPv6 Address (Cont.)                 |
345	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
346	      |                 Reply-to IPv6 Address (Cont.)                 |
347	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
348	      |                 Reply-to IPv6 Address (Cont.)                 |
349	      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

351	      Reply-to IPv6 Address

353	         The address to which the MPLS Data Plane Verification Reply
354	         message is to be sent.

356	3.4. Sending procedures

358	   In order to perform a test on an incoming labeled or unlabeled
359	   packet, an LSR first determines the expected outgoing label stack,
360	   next hop router and next hop interface.

362	   The LSR creates an MPLS Data Plane Verification Request message and
363	   includes a Data Plane Verification Object.  Optionally a FEC Stack
364	   TLV may be included.  In this case an MPLS Echo Request Message MUST
365	   be used.

367	   In normal use, the source address is set to an address belonging to
368	   the LSR and the destination set to an address in the range of 127/8.
369	   The incoming label stack (if any) is prepended to the packet.  The
370	   TTL of these labels and the packet header SHOULD be set to appropri-
371	   ate values - 2 for those labels and/or header which will be processed
372	   by this node when the packet is looped back; 1 for those labels
373	   and/or header which will be carried through.  Finally the loopback
374	   label bound to the incoming interface is prepended to the packet.  In
375	   the case of an otherwise unlabeled packet the label's FEC MUST indi-
376	   cate the appropriate IP version.  The TTL is set such that it will
377	   have the value of 3 on the wire.

379	   The packet is sent to the upstream neighbor on an interface for which
380	   the loopback label is valid.

382	   In diagnostic situations, the source and destination addresses MAY be
383	   set to any value.  In this case, a Reply-to IPv4 or IPv6 Object MUST
384	   be included.  The IP TTL MUST be set to 1.  The TTL of labels other
385	   than the loopback label MUST be set to appropriate values - 2 for
386	   those labels which will be process by this LSR when the packet is
387	   looped back; 1 for those labels which will be carried through.

389	   In some MPLS deployments TTL hiding is used to make a providers net-
390	   work appear as a single hop.  That is the TTL in the imposed label
391	   does not refect the TTL of the received packet.  It is RECOMMENDED
392	   that testing of label imposition SHOULD NOT be performed in such cir-
393	   cumstances as the Echo Request will in most case travel multiple
394	   hops.

396	3.5. Receiving procedures

398	   An LSR X that receives an MPLS Verification Request message formats a
399	   MPLS Verification Reply message.  The Sender's Handle and Sequence
400	   Number are copied from the Request message.

402	   X then parses the packet to ensure that it is a well-formed packet,
403	   and that the TLVs that are not marked "Ignore" are understood.  If
404	   not, X SHOULD send an MPLS echo reply with the Return Code set to
405	   "Malformed echo request received" or "TLV not understood" (as appro-
406	   priate), and the Subcode set to zero.  In the latter case, the misun-
407	   derstood TLVs (only) are included in the reply.

409	   If the echo request is good, X notes the interface I over which the
410	   echo was received, and the label stack with which it came. If the
411	   MPLS echo request contained a Downstream Verification object, then X
412	   must format this information as a Downstream Verification object and
413	   include it in its MPLS echo reply message.

415	   The source address of the Reply message MUST be an address of the
416	   replying LSR.  If the request included a Reply-to IPv4 or IPv6
417	   Object, the MPLS Data Plane Verification Reply message MUST be sent
418	   to that address.  Otherwise the Reply message is sent to the source
419	   address of the Verification Request message.

421	   An LSR MUST be capable of filtering addresses that are to be replied
422	   to.  If a filter has been invoked (i.e. configured) and an address
423	   does not pass the filter, then a reply MUST NOT be sent, and the
424	   event SHOULD be logged.

426	3.6. Upstream Neighbor Verification

428	   To verify that an upstream neighbor is properly echoing packets an
429	   LSR may send an MPLS Data Plane Verification Request packet with the
430	   TTL set so that the packet will expire upon reaching reaching itself.
431	   This procedure not only tests that the neighbor is correctly process-
432	   ing the loopback label, it also allows the node to verify the neigh-
433	   bor's interface mapping.

435	                      +-------+       +-------+
436	                      |       |       |       |
437	                      |     ,-|-------|<DPVRq |
438	                      |     `-|-------|->     |
439	                      |       |       |       |
440	                      +-------+       +-------+
441	                        LSR-U           LSR-T

443	             DPVRq: MPLS Data Plane Verification Request

445	              Figure 2: Upstream Neighbor Verification

447	   No TLVs need to be included in the MPLS Data Plane Verification
448	   Request.  By noting the Sender's Handle and Sequence Number, as well
449	   as the loopback label, LSR-T is able to detect that a) the packet was
450	   looped, and b) determine (or verify) the interface on which the
451	   packet was received.

453	4. Security Considerations

455	   Were loopback labels widely known, they might be subject to abuse.
456	   It is therefore RECOMMENDED that loopback labels only be shared
457	   between trusted neighbors.  Further, if the loopback labels are drawn
458	   from the Global Label Space, or any other label space shared across
459	   multiple LDP sessions, it is RECOMMENDED that all loopback labels be
460	   filtered from a session except those labels pertaining to interfaces
461	   directly connected to the neighbor participating in that session.

463	5. IANA Considerations

465	   This document makes the following codepoint assigments (pending IANA
466	   action):

468	       Registry             Codepoint    Purpose

470	       UDP Port                tbd       MPLS Verification Request

472	       LSP Ping Message Type    3        MPLS Data Plane Verification
473	                                           Request
474	       LSP Ping Message Type    4        MPLS Data Plane Verification
475	                                           Reply
476	       LSP Ping Object Type    11        IPv4 Reply-to Object
477	       LSP Ping Object Type    12        IPv6 Reply-to Object

479	6. Acknowledgments

481	   The authors would like to thank Vanson Lim, Tom Nadeau, and Bob
482	   Thomas for their comments and suggestions.

484	7. References

486	7.1. Normative References

488	   [RFC3036]  Andersson, L. et al., "LDP Specification", January 2001.

490	   [LSP-Ping] Bonica, R. et al., "Detecting MPLS Data Plane Liveness",
491	              work-in-progress.

493	   [RFC3477]  Kompella, K. & Y. Rekhter, "Signalling Unnumbered Links
494	              in Resource ReSerVation Protocol - Traffic Engineering
495	              (RSVP-TE)", January 2003.

497	   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
498	              Requirement Levels", BCP 14, RFC 2119, March 1997.

500	7.2. Informative References

502	   [RSVP-TE]  Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP
503	              tunnels", RFC 3209, December 2001.

505	8. Authors' Addresses

507	      Kireeti Kompella
508	      Juniper Networks, Inc.
509	      1194 N. Mathilda Ave.
510	      Sunnyvale, CA 94089
511	      Email:  kireeti@juniper.net

513	      George Swallow
514	      Cisco Systems, Inc.
515	      1414 Massachusetts Ave
516	      Boxborough, MA 01719

518	      Email:  swallow@cisco.com

520	      Dan Tappan
521	      Cisco Systems, Inc.
522	      1414 Massachusetts Ave
523	      Boxborough, MA 01719

525	      Email:  tappan@cisco.com

527	Copyright Notice

529	   Copyright (C) The Internet Society (2005).  This document is subject
530	   to the rights, licenses and restrictions contained in BCP 78, and
531	   except as set forth therein, the authors retain all their rights.

533	Expiration Date

535	   January 2006

537	Disclaimer of Validity

539	   This document and the information contained herein are provided on an
540	   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
541	   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
542	   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
543	   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
544	   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
545	   OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.