GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc7394

Internet Engineering Task Force (IETF) S. Boutros Request for Comments: 7394 S. Sivabalan Category: Standards Track G. Swallow ISSN: 2070-1721 S. Saxena

                                                         Cisco Systems
                                                             V. Manral
                                                        Ionos Networks
                                                             S. Aldrin
                                             Huawei Technologies, Inc.
                                                         November 2014
       Definition of Time to Live TLV for LSP-Ping Mechanisms

Abstract

 LSP-Ping is a widely deployed Operation, Administration, and
 Maintenance (OAM) mechanism in MPLS networks.  However, in the
 present form, this mechanism is inadequate to verify connectivity of
 a segment of a Multi-Segment Pseudowire (MS-PW) and/or bidirectional
 co-routed Label Switched Path (LSP) from any node on the path of the
 MS-PW and/or bidirectional co-routed LSP.  This document defines a
 TLV to address this shortcoming.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7394.

Boutros, et al. Standards Track [Page 1] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

Copyright Notice

 Copyright (c) 2014 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
 (http://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 ....................................................2
 2. Terminology .....................................................3
 3. Time To Live TLV ................................................4
    3.1. TTL TLV Format .............................................4
    3.2. Usage ......................................................4
 4. Operation .......................................................5
    4.1. Traceroute Mode ............................................6
    4.2. Error Scenario .............................................6
 5. Security Considerations .........................................6
 6. IANA Considerations .............................................7
 7. References ......................................................7
    7.1. Normative References .......................................7
 Acknowledgements ...................................................7
 Contributors .......................................................7
 Authors' Addresses .................................................8

1. Introduction

 An MS-PW may span across multiple service provider networks.  In
 order to allow Service Providers (SPs) to verify segments of such
 MS-PWs from any node on the path of the MS-PW, any node along the
 path of the MS-PW, should be able to originate an MPLS Echo Request
 packet to any other node along the path of the MS-PW and receive the
 corresponding MPLS Echo Reply.  If the originator of the MPLS Echo
 Request is at the end of a MS-PW, the receiver of the request can
 send the reply back to the sender without knowing the hop-count
 distance of the originator.  The reply will be intercepted by the
 originator regardless of the TTL value on the reply packet.  But, if
 the originator is not at the end of the MS-PW, the receiver of the
 MPLS Echo Request may need to know how many hops away the originator

Boutros, et al. Standards Track [Page 2] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

 of the MPLS Echo Request is so that it can set the TTL value on the
 MPLS header for the MPLS Echo Reply to be intercepted at the
 originator node.
 In MPLS networks, for bidirectional co-routed LSPs, if it is desired
 to verify connectivity from any intermediate node Label Switching
 Router (LSR) on the LSP to the any other LSR on the LSP the receiver
 may need to know the TTL to send the MPLS Echo Reply with, so as the
 packet is intercepted by the originator node.
 A new optional TTL TLV is defined in this document.  This TLV will be
 added by the originator of the MPLS Echo Request to inform the
 receiver how many hops away the originator is on the path of the
 MS-PW or bidirectional LSP.
 This mechanism only works if the MPLS Echo Reply is sent down the
 co-routed LSP; hence, the scope of this TTL TLV is currently limited
 to MS-PW or bidirectional co-routed MPLS LSPs.  The presence of the
 TLV implies the use of the return path of the co-routed LSP, if the
 return path is any other mechanism, then the TLV in the MPLS Echo
 Request MUST be ignored.

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].
 LSR: Label Switching Router
 MPLS-TP: MPLS Transport Profile
 MS-PW: Multi-Segment Pseudowire
 PW: Pseudowire
 TLV: Type Length Value
 TTL: Time To Live

Boutros, et al. Standards Track [Page 3] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

3. Time To Live TLV

3.1. TTL TLV Format

 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Type = 32769                 |   Length = 8                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Value       |   Reserved    |   Flags                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 1: Time To Live TLV Format
 The TTL TLV has the format shown in Figure 1.
 Value
    The value of the TTL as specified by this TLV
 Flags
    The Flags field is a bit vector with the following format:
     0                   1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             MBZ             |R|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    One flag is defined for now, the R flag.  The rest of the
    flags are Reserved - MUST be zero (MBZ) when sending and
    ignored on receipt.
    The R flag (Reply TTL) is set signify that the value is
    meant to be used as the TTL for the reply packet.  Other bits
    may be defined later to enhance the scope of this TLV.

3.2. Usage

 The TTL TLV MAY be included in the MPLS Echo Request by the
 originator of the request.
 If the TTL TLV is present and the receiver does not understand TTL
 TLVs, it will simply ignore the TLV, as is the case for all optional
 TLVs.  If the TTL TLV is not present or is not processed by the
 receiver, any determination of the TTL value used in the MPLS label
 on the LSP-Ping echo reply is beyond the scope of this document.

Boutros, et al. Standards Track [Page 4] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

 If the TTL TLV is present and the receiver understands TTL TLVs, one
 of the following two conditions apply:
 o  If the TTL TLV value field is zero, the LSP-Ping echo request
    packet SHOULD be dropped.
 o  Otherwise, the receiver MUST use the TTL value specified in the
    TTL TLV when it creates the MPLS header of the MPLS Echo Reply.
    The TTL value in the TTL TLV takes precedence over any TTL value
    determined by other means, such as from the Switching Point TLV in
    the MS-PW.  This precedence will aid the originator of the LSP-
    Ping echo request in analyzing the return path.

4. Operation

 In this section, we explain a use case for the TTL TLV with an MPLS
 MS-PW.
          <------------------MS-PW --------------------->
          A          B          C           D           E
          o -------- o -------- o --------- o --------- o
                     ---MPLS Echo Request--->
                     <--MPLS Echo Reply------
          Figure 2: Use-Case with MS-PWs
 Let us assume an MS-PW going through LSRs A, B, C, D, and E.
 Furthermore, assume that an operator wants to perform a connectivity
 check between B and D, from B.  Thus, an MPLS Echo Request with the
 TTL TLV is originated from B and sent towards D.  The MPLS Echo
 Request packet contains the FEC of the PW Segment between C and D.
 The value field of the TTL TLV and the TTL field of the MPLS label
 are set to 2, the choice of the value 2 will be based on the operator
 input requesting the MPLS Echo Request or from the optional LDP
 switching point TLV.  The MPLS Echo Request is intercepted at D
 because of TTL expiry.  D detects the TTL TLV in the request and uses
 the TTL value (i.e., 2) specified in the TLV on the MPLS label of the
 MPLS Echo Reply.  The MPLS Echo Reply will be intercepted by B
 because of TTL expiry.
 The same operation will apply when we have a co-routed bidirectional
 LSP and we want to check connectivity from an intermediate LSR "B" to
 another LSR "D".

Boutros, et al. Standards Track [Page 5] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

4.1. Traceroute Mode

 In traceroute mode, the TTL value in the TLV is set to 1 for the
 first Echo Request, then to 2 for the next, and so on.  This is
 similar to the TTL values used for the label set on the packet.

4.2. Error Scenario

 It is possible that the MPLS Echo Request packet was intercepted
 before the intended destination for reasons other than label TTL
 expiry.  This could be due to network faults, misconfiguration, or
 other reasons.  In such cases, if the return TTL is set to the value
 specified in the TTL TLV, then the echo response packet will continue
 beyond the originating node.  This becomes a security issue.
 To prevent this, the label TTL value used in the MPLS Echo Reply
 packet MUST be modified by deducting the incoming label TTL on the
 received packet from TTL TLV value.  If the MPLS Echo Request packet
 is punted to the CPU before the incoming label TTL is deducted, then
 another 1 MUST be added.  In other words:
 Return TTL Value on the MPLS Echo Reply packet = (TTL TLV Value) -
 (Incoming Label TTL) + 1

5. Security Considerations

 This document allows the setting of the TTL value in the MPLS Label
 of an MPLS Echo Reply, so that it can be intercepted by an
 intermediate device.  This can cause a device to get a lot of LSP-
 Ping packets that get redirected to the CPU.
 However, the same is possible even without the changes mentioned in
 this document.  A device should rate limit the LSP-Ping packets
 redirected to the CPU so that the CPU is not overwhelmed.
 The recommendation in the Security Considerations of [RFC4379]
 applies, to check the source address of the MPLS Echo Request;
 however, the source address can now be any node along the LSP path.
 A faulty transit node changing the TTL TLV value could make the wrong
 node reply to the MPLS Echo Request, and/or the wrong node to receive
 the MPLS Echo Reply.  An LSP trace may help identify the faulty
 transit node.

Boutros, et al. Standards Track [Page 6] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

6. IANA Considerations

 IANA has assigned a TLV type value to the following TLV from the
 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
 Ping Parameters" registry in the "TLVs" subregistry.
    Time To Live TLV (see Section 3).
 IANA has allocated the value 32769.

7. References

7.1 Normative References

 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997,
           <http://www.rfc-editor.org/info/rfc2119>.
 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
           Label Switched (MPLS) Data Plane Failures", RFC 4379,
           February 2006, <http://www.rfc-editor.org/info/rfc4379>.
 [RFC5085] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual
           Circuit Connectivity Verification (VCCV): A Control Channel
           for Pseudowires", RFC 5085, December 2007,
           <http://www.rfc-editor.org/info/rfc5085>.

Acknowledgements

 The authors would like to thank Greg Mirsky for his comments.

Contributors

 Michael Wildt
 Cisco Systems, Inc.
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 United States
 EMail: mwildt@cisco.com

Boutros, et al. Standards Track [Page 7] RFC 7394 TTL TLV for LSP-Ping Mechanisms November 2014

Authors' Addresses

 Sami Boutros
 Cisco Systems, Inc.
 3750 Cisco Way
 San Jose, CA 95134
 United States
 EMail: sboutros@cisco.com
 Siva Sivabalan
 Cisco Systems, Inc.
 2000 Innovation Drive
 Kanata, Ontario, K2K 3E8
 Canada
 EMail: msiva@cisco.com
 George Swallow
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA 01719
 United States
 EMail: swallow@cisco.com
 Shaleen Saxena
 Cisco Systems, Inc.
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 United States
 EMail: ssaxena@cisco.com
 Vishwas Manral
 Ionos Networks
 4100 Moorpark Ave, Suite 122
 San Jose, CA 95117
 United States
 EMail: vishwas@ionosnetworks.com
 Sam Aldrin
 Huawei Technologies, Inc.
 1188 Central Express Way,
 Santa Clara, CA 95051
 United States
 EMail: aldrin.ietf@gmail.com

Boutros, et al. Standards Track [Page 8]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7394.txt · Last modified: 2014/11/14 23:34 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki