Definition of Time to Live TLV for LSP-Ping Mechanisms
The information below is for an old version of the document that is already published as an RFC.
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|
|Last updated||2020-01-21 (Latest revision 2014-08-19)|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||Submitted to IESG for Publication|
|Document shepherd||Loa Andersson|
|Shepherd write-up||Show Last changed 2013-10-24|
|IESG||IESG state||RFC 7394 (Proposed Standard)|
|Responsible AD||Adrian Farrel|
|Send notices to||(None)|
|IANA||IANA review state||Version Changed - Review Needed|
|IANA action state||RFC-Ed-Ack|
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: February 20, 2015 August 19, 2014 Definition of Time-to-Live TLV for LSP-Ping Mechanisms draft-ietf-mpls-lsp-ping-ttl-tlv-10.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) and/or bidirectional co-routed 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 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 Boutros Expires February 20, 2015 [Page 1] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 http://www.ietf.org/shadow.html Copyright and License 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 . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Error scenario . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1 Normative References . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Boutros Expires February 20, 2015 [Page 2] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 1. Introduction A MS-PW may 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 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 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 (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 Boutros Expires February 20, 2015 [Page 3] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 PW: Pseudowire TLV: Type Length Value 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 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 Boutros Expires February 20, 2015 [Page 4] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 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. 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 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 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 use 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 Boutros Expires February 20, 2015 [Page 5] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 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". 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 reason other than label TTL expiry. 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, 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 draft 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 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. The recommendation in [RFC4379] security section 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 Boutros Expires February 20, 2015 [Page 6] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 the MPLS Echo Reply. An LSP trace may help identify the faulty transit node. 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 value MUST be assigned from the range (32768-49161) of optional TLVs. IANA is requested to allocate the value 32769. 7. Acknowledgements The authors would like to thank Greg Mirsky for his comments. 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 Sami Boutros Cisco Systems, Inc. 3750 Cisco Way San Jose, California 95134 USA Email: firstname.lastname@example.org Boutros Expires February 20, 2015 [Page 7] INTERNET DRAFT Lsp-ping-ttl-tlv August 19, 2014 Siva Sivabalan Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario, K2K 3E8 Canada Email: email@example.com George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxborough , MASSACHUSETTS 01719 United States Email: firstname.lastname@example.org Shaleen Saxena Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough , MASSACHUSETTS 01719 United States Email: email@example.com Vishwas Manral Hewlett Packard Co. 19111 Pruneridge Ave, Cupertino, CA 95014 USA United States EMail: firstname.lastname@example.org Michael Wildt Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough , MASSACHUSETTS 01719 United States Email: email@example.com Sam Aldrin Huawei Technologies, Inc. 1188 Central Express Way, Santa Clara, CA 95051 United States Email: firstname.lastname@example.org Boutros Expires February 20, 2015 [Page 8]