Definition of Time-to-Live TLV for LSP-Ping Mechanisms
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 7394.
|Authors||Sami Boutros , Siva Sivabalan , George Swallow , Shaleen Saxena , Vishwas Manral , Sam Aldrin|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
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Network Working Group Sami Boutros INTERNET-DRAFT Siva Sivabalan Intended Status: Standards Track George Swallow Shaleen Saxena Cisco Systems Vishwas Manral Hewlett Packard Co. Sam Aldrin Huawei Technologies, Inc. Expires: April 23, 2013 October 20, 2012 Definition of Time-to-Live TLV for LSP-Ping Mechanisms draft-ietf-mpls-lsp-ping-ttl-tlv-04.txt 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) from any node on the path of the MS-PW. This document defines a TLV to address this shortcoming. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Boutros Expires April 23, 2013 [Page 1] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 Copyright and License Notice Copyright (c) 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Error scenario . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1 Normative References . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Boutros Expires April 23, 2013 [Page 2] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 1. Introduction A MS-PW can span across multiple service provider networks. In order to allow Service Providers (SP) to verify segments of such MS-PW 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 LSP-Ping echo request packet to any another node along the path of the MS-PW and receive the corresponding echo reply. If the originator of the 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. For example, 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 echo request MAY need to know how many hops away the originator of the echo request is so that it can set the TTL value on the MPLS header for the 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 (LSR) on the LSP to the any other LSR on the LSP the receiver may need to know the TTL to send the Echo reply with, so as the packet is intercepted by the originator node. A new optional TTL TLV is being proposed in this document this TLV will be added by the originator of the echo request to inform the receiver how many hops away the originator is on the path of the MS- PW or Bidirectional LSP. The scope of this TTL TLV is currently limited to MS-PW or Bidirectional co-routed MPLS LSPs. 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-OAM: MPLS Operations, Administration and Maintenance MPLS-TP: MPLS Transport Profile MS-PW: Multi-Segment PseudoWire PW: PseudoWire TLV: Type Length Value Boutros Expires April 23, 2013 [Page 3] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 TTL: Time To Live 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 = TBD | 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 bit; the rest MUST be set to zero 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 This TLV shall be included in the echo request by the originator of request. The use of this TLV is optional. If a receiver does not understand the TTL TLV, it will simply ignore the TLV (Type value of TLV is assumed to be in the range of optional TLV's which SHOULD be ignored if an implementation does not support or understand them). In the absence of TTL TLV or if TTL TLV is ignored by a receiver, the Boutros Expires April 23, 2013 [Page 4] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 determination of the TTL value used in the MPLS label on the echo reply is beyond the scope of this document. If a receiver understands the TTL TLV, and the TTL TLV is present in the echo request, and if the value field is zero, the LSP Ping Echo request packet SHOULD be dropped. If a receiver understands the TTL TLV, and the TTL TLV is present in the echo request, the receiver MUST use the TTL value specified in TLV in the MPLS header of the echo reply. In other words, if the value of the TTL provided by this TLV does not match the TTL determined by other means, such as Switching Point TLV in MS-PW, then TTL TLV must be used. This will aid the originator of the 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 ------Echo Request-----> <-----Echo Reply-------- Figure 2: Use-case with MS-PWs Let us assume a 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 LSP-Ping request with the TTL TLV is originated from B and sent towards D. The 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 echo request is intercepted at D because of TTL expiry. D detects the TTL TLV in the request, and use the TTL value (i.e., 2) specified in the TLV on the MPLS label of the echo reply. The echo reply will be intercepted by B because of TTL expiry. The same operation will apply in the case a co-routed bidirectional LSP and we want to check connectivity from an intermediate LSR B to another LSR D, from B. 4.1. Traceroute mode In the traceroute mode TTL value in the TLV is successively set to 1, Boutros Expires April 23, 2013 [Page 5] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 2, 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 echo request packet was punted before the intended destination. This could be due 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 issue, the TTL value used must be modified by deducting the incoming label TTL. If the echo request packet is punted before the incoming TTL is deducted, then another 1 must be deducted. In other words: Return TTL Value = (TTL TLV Value)-(Incoming Label TTL) + 1 5. Security Considerations This draft allows the setting of the TTL value in the MPLS Label of an 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 which 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. 6. IANA Considerations IANA is requested to assign TLV type value to the following TLV from the "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub- registry. Time To Live TLV (See Section 3). The Suggested value is 32769 as suggested by RFC 4379 Section 3. 7. Acknowledgements The authors would like to thank Greg Mirsky for his comments. Boutros Expires April 23, 2013 [Page 6] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 8. References 8.1 Normative References  K. Kompella, G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.  T. Nadeau, et. al, "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires ", RFC 5085, December 2007.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Authors' Addresses Siva Sivabalan Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario, K2K 3E8 Canada Email: email@example.com Sami Boutros Cisco Systems, Inc. 3750 Cisco Way San Jose, California 95134 USA Email: firstname.lastname@example.org George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxborough , MASSACHUSETTS 01719 United States Email: email@example.com Shaleen Saxena Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough , MASSACHUSETTS 01719 United States Email: firstname.lastname@example.org Boutros Expires April 23, 2013 [Page 7] INTERNET DRAFT Lsp-ping-ttl-tlv October 20, 2012 Vishwas Manral Hewlett Packard Co. 19111 Pruneridge Ave, Cupertino, CA 95014 USA United States EMail: email@example.com Michael Wildt Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough , MASSACHUSETTS 01719 United States Email: firstname.lastname@example.org Sam Aldrin Huawei Technologies, Inc. 1188 Central Express Way, Santa Clara, CA 95051 United States Email: email@example.com Boutros Expires April 23, 2013 [Page 8]