Network Working Group M. Chen Internet-Draft W. Cao Intended status: Standards Track Huawei Technologies Co., Ltd Expires: May 3, 2012 S. Ning Verizon Inc. F. Jounay France Telecom S. Delord Alcatel-Lucent October 31, 2011 Return Path Specified LSP Ping draft-ietf-mpls-return-path-specified-lsp-ping-04.txt Abstract This document defines extensions to the failure-detection protocol for Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) known as "LSP Ping" that allow selection of the LSP to use for the echo reply return path. Enforcing a specific return path can be used to verify bidirectional connectivity and also increase LSP ping robustness. It may also be used by Bidirectional Forwarding Detection (BFD) for MPLS bootstrap signaling thereby making BFD for MPLS more robust. Requirements Language 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]. 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 http://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 May 3, 2012. Chen, et al. Expires May 3, 2012 [Page 1] Internet-Draft Return Path Specified LSP Ping October 2011 Copyright Notice Copyright (c) 2011 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. Problem Statements and Solution Overview . . . . . . . . . . . 3 2.1. Limitations of Existing Mechanisms for Bidirectional LSPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Limitations of Existing Mechanisms for Handling Unreliable Return Paths . . . . . . . . . . . . . . . . . 4 3. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Reply Via Specified Path mode . . . . . . . . . . . . . . 5 3.2. Reply Path (RP) TLV . . . . . . . . . . . . . . . . . . . 6 3.3. RP TLV sub-TLVs . . . . . . . . . . . . . . . . . . . . . 8 3.3.1. IPv4 RSVP Tunnel sub-TLV . . . . . . . . . . . . . . . 8 3.3.2. IPv6 RSVP Tunnel sub-TLV . . . . . . . . . . . . . . . 9 3.3.3. RP TC sub-TLV . . . . . . . . . . . . . . . . . . . . 10 4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 11 4.1. Sending an Echo Request . . . . . . . . . . . . . . . . . 12 4.2. Receiving an Echo Request . . . . . . . . . . . . . . . . 12 4.3. Sending an Echo Reply . . . . . . . . . . . . . . . . . . 13 4.4. Receiving an Echo Reply . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6.1. New TLV . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2. Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2.1. New Sub-TLVs . . . . . . . . . . . . . . . . . . . . . 15 6.2.2. New Reply Mode . . . . . . . . . . . . . . . . . . . . 15 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Chen, et al. Expires May 3, 2012 [Page 2] Internet-Draft Return Path Specified LSP Ping October 2011 1. Introduction This document defines extensions to the failure-detection protocol for Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) known as "LSP Ping" [RFC4379] that can be used to specify the return paths for the echo reply message, increasing the robustness of LSP Ping, reducing the opportunity for error, and improving the reliability of the echo reply message. A new reply mode, which is referred to as "Reply via specified path", is added and a new Type- Length-Value (TLV), which is referred to as Reply Path (RP) TLV, is defined in this memo. With the extensions described in this document, a bidirectional LSP and a pair of unidirectional LSPs (one for each direction) could both be tested with a single operational action, hence providing better control plane scalability. The defined extensions can also be utilized for creating a single Bidirectional Forwarding Detection (BFD)[RFC5880], [RFC5884]session for a bidirectional LSP or for a pair of unidirectional LSPs (one for each direction). In this document, term bidirectional LSP includes the co-routed bidirectional LSP defined in [RFC3945] and the associated bidirectional LSP that is constructed from a pair of unidirectional LSPs (one for each direction), and which are associated with one another at the LSP's ingress/egress points [RFC5654]. 2. Problem Statements and Solution Overview MPLS LSP Ping is defined in [RFC4379]. It can be used to detect data path failures in all MPLS LSPs, and was originally designed for unidirectional LSPs. LSP are increasingly being deployed to provide bidirectional services. The co-routed bidirectional LSP is defined in [RFC3471] and [RFC3473], and the associated bidirectional LSP is defined in [RFC5654]. With the deployment of such services, operators have a desire to test both directions of a bidirectional LSP in a single operation. Additionally, when testing a single direction of an LSP (either a unidirectional LSP, or a single direction of a bidirectional LSP) using LSP Ping, the validity of the result may be affected by the success of delivering the echo reply message. Failure to exchange these messages between the egress Label Switching Router (LSR) and the ingress LSR can lead to false negatives where the LSP under test is reported as "down" even though it is functioning correctly. Chen, et al. Expires May 3, 2012 [Page 3] Internet-Draft Return Path Specified LSP Ping October 2011 2.1. Limitations of Existing Mechanisms for Bidirectional LSPs With the existing LSP Ping mechanisms as defined in [RFC4379], operators have to enable LSP detection on each of the two ends of a bidirectional LSP independently. This not only doubles the workload for the operators, but may also bring additional difficulties when checking the backward direction of the LSP under the following conditions: 1. The LSR that the operator logged on to perform the checking operations might not have out-of-band connectivity to the LSR at the far end of the LSP. That can mean it is not possible to check the return direction of a bidirectional LSP in a single operation - the operator must log on to the LSR at the other end of the LSP to test the return direction. 2. The LSP being tested might be an inter-domain/inter-AS LSP where the operator of one domain/AS may have no right to log on to the LSR at the other end of the LSP since this LSR resides in another domain/AS. That can make it completely impossible for the operator to check the return direction of a bidirectional LSP. Associated bidirectional LSPs have the same issues as those listed for co-routed bidirectional LSPs. This document defines a mechanism to allow the operator to request that both directions of a bidirectional LSP be tested by a single LSP Ping message exchange. 2.2. Limitations of Existing Mechanisms for Handling Unreliable Return Paths [RFC4379] defines 4 reply modes: 1. Do not reply 2. Reply via an IPv4/IPv6 UDP packet 3. Reply via an IPv4/IPv6 UDP packet with Router Alert 4. Reply via application level control channel. Obviously, the issue of the reliability of the return path for an echo reply message does not apply in the first of these cases. [RFC4379] states that the third mode may be used when the IP return path is deemed unreliable. This mode of operation requires that all intermediate nodes must support the Router Alert option and must understand and know how to forward MPLS echo replies. Chen, et al. Expires May 3, 2012 [Page 4] Internet-Draft Return Path Specified LSP Ping October 2011 This is a rigorous requirement in deployed IP/MPLS networks especially since the return path may be through legacy IP-only routers. Furthermore, for inter-domain LSPs, the use of the Router Alert option may encounter significant issues at domain boundaries where the option is usually stripped from all packets. Thus, the use of this mode may itself introduce issues that lead to the echo reply messages not being delivered. And in any case, the use modes 2 or 3 cannot guarantee the delivery of echo responses through an IP network that is fundamentally unreliable. The failure to deliver echo response messages can lead to false negatives making it appear that the LSP has failed. Allowing the ingress LSR to control the path used for echo reply messages, and in particular forcing those messages to use an LSP rather than being sent through the IP network, enables an operator to apply an extra level of deterministic process to the LSP Ping test. This document defines extensions to LSP Ping that can be used to specify the return paths of the echo reply message in an LSP echo request message. 3. Extensions LSP Ping defined in [RFC4379] is carried out by sending an echo request message. It carries the Forwarding Equivalence Class (FEC) information of the tested LSP which indicates which MPLS path is being verified, along the same data path as other normal data packets belonging to the FEC. LSP Ping [RFC4379] defines four reply modes that are used to direct the egress LSR in how to send back an echo reply. This document defines a new reply mode, the Reply Via Specified Path mode. This new mode is used to direct the egress LSR of the tested LSP to send the echo reply message back along the path specified in the echo request message. In addition, a new TLV, the Reply Path (RP) TLV, is defined in this document. The RP TLV consists of one or more sub-TLVs that can be used to carry the specified return path information to be used by the echo reply message. 3.1. Reply Via Specified Path mode A new reply mode is defined to be carried in the Reply Mode field of the LSP Ping echo request message. Chen, et al. Expires May 3, 2012 [Page 5] Internet-Draft Return Path Specified LSP Ping October 2011 The recommended value of the Reply Via Specified Path mode is 5 (This is to be confirmed by the IANA). Value Meaning ----- ------- 5 Reply via specified path The Reply Via Specified Path mode is used to notify the remote LSR receiving the LSP Ping echo request message to send back the echo reply message along the specified paths carried in the Reply Path TLV. 3.2. Reply Path (RP) TLV The Reply Path (RP) TLV is optionally included in an echo request message. It carries the specified return paths that the echo reply message is required to follow. The format of RP TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RP (reply path) TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RP return code | Flag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reply Paths | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure3 IPv6 PSN Tunnel sub-TLV format RP TLV Type field is 2 octets in length, and the type value is TBD by IANA. The Length field is 2 octets in length. It defines the length in octets of the RP return code, Flag and Reply Paths fields. RP return code is 2 octets in length. It is defined for the egress LSR of the forward LSP to report the results of RP TLV processing and return path selection. When sending echo request, these codes MUST be set to zero. RP return code only used when sending echo reply, and it MUST be ignored when processing echo request message. This document defines the following RP return codes: Chen, et al. Expires May 3, 2012 [Page 6] Internet-Draft Return Path Specified LSP Ping October 2011 Value Meaning ----- ---------------------- 0 No return code 1 Malformed RP TLV was received 2 One or more of the sub-TLVs in RP TLV was not understood 3 The echo reply was sent successfully using the specified RP 4 The specified RP was not found, the echo reply was sent via other LSP 5 The specified RP was not found, the echo reply was sent via IP path 6 The Reply mode in echo request was not set to 5(replay via specified path) although RP TLV exists 7 RP TLV was missing in echo request Flag field is also 2 octets in length, it is used to notify the egress how to process the Reply Paths field when performing return path selection. The Flag field is a bit vector and has following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MUST be zero |A|B|E| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A (Alternative path): the egress LSR MUST select a non-default path as the return path. This is very useful when reverse default path problems are suspected which can be confirmed when the echo reply is forced to follow a non-default return path. If A bit is set, there is no need to carry any specific reply path sub-TLVs. B (Bidirectional): the return path is required to follow the reverse direction of the tested bidirectional LSP. E (Exclude): the return path is required to exclude the paths that are identified by the reply path sub-TLVs carried in the Reply Paths field. This is very useful when one or more previous LSP Ping attempts failed. By setting this E bit and carrying the previous failed reply path sub-TLVs, a new LSP Ping echo request could be used to help the egress LSR to select another candidate path when sending echo reply message. A bit MUST NOT be set when any one of other two bits (B bit and E bit) set. The Reply Paths field is variable in length. It has several nested sub-TLVs that describe the specified paths the echo reply message is required to follow. When the Reply Mode field is set to "Reply via specified path" in an LSP echo request message, the RP TLV MUST be present. Chen, et al. Expires May 3, 2012 [Page 7] Internet-Draft Return Path Specified LSP Ping October 2011 3.3. RP TLV sub-TLVs Each of the FEC sub-TLVs for the Target FEC Stack TLV[RFC4379] is applicable to be a sub-TLV for inclusion in the RP TLV for expressing a specific return path. In addition, three more new sub-TLVs are defined: IPv4 RSVP Tunnel sub-TLV, IPv6 RSVP Tunnel sub-TLV, and RP TC (Traffic Class) sub-TLV. Detailed definition is in the following sections. With the Return Path TLV flags and the sub-TLVs defined for the Target FEC Stack TLV and in this document, it could provide following options for return paths specifying: 1. Specify a particular LSP as return path - use those sub-TLVs defined for the Target FEC Stack TLV 2. Specify a more generic tunnel FEC as return path - use the IPv4/IPv6 RSVP Tunnel sub-TLVs defined in Section 3.3.1 and Section 3.3.2 of this document 3. Specify the reverse path of the bidirectional LSP as return path - use B bit defined in Section 3.2 of this document. 4. Force return path to non-default path - use A bit defined in Section 3.2 of this document. 5. Allow any LSPs except specific or general ones as return path - use E bit (Section 3.2 of this document) and combine with the specific paths identified by the sub-TLVs carried in Reply Path field. 3.3.1. IPv4 RSVP Tunnel sub-TLV The IPv4 RSVP Tunnel sub-TLV is used in the RP TLV to allow the operator to specify a more generic tunnel FEC other than a particular LSP as the return path. The egress LSR chooses any LSP from the LSPs that have the same Tunnel attributes and satisfy the conditions carried in the Flag field. The format of IPv4 RSVP Tunnel sub-TLV is as follows: Chen, et al. Expires May 3, 2012 [Page 8] Internet-Draft Return Path Specified LSP Ping October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 RSVP Tunnel sub-TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 tunnel end point address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flag | Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 tunnel sender address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The IPv4 RSVP Tunnel sub-TLV is derived from the RSVP IPv4 FEC TLV that is defined in Section 3.2.3 [RFC4379]. All fields have the same semantics as defined in [RFC4379] except that the LSP-ID field is omitted and a new Flag field is defined. The IPv4 RSVP Tunnel sub-TLV Type field is 2 octets in length, and the recommended type value is 18 (to be confirmed by IANA). The Flag field is 2 octets in length, it is used to notify the egress LSR how to choose the return path. The Flag field is a bit vector and has following format: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MUST be zero |S|P| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ P (Primary): the return path MUST be chosen from the LSPs that have the same Tunnel attributes and the LSP MUST be the primary LSP. S (Secondary): the return path MUST be chosen from the LSPs that have the same Tunnel attributes and the LSP MUST be the secondary LSP. P bit and S bit MUST NOT both be set. If P bit and S bit are both not set, the return path could be any one of the LSPs that have the same Tunnel attributes. 3.3.2. IPv6 RSVP Tunnel sub-TLV The IPv6 RSVP Tunnel sub-TLV is used in the RP TLV to allow the operator to specify a more generic tunnel FEC other than a particular LSP as the return path. The egress LSR chooses an LSP from the LSPs that have the same Tunnel attributes and satisfy the conditions carried in the Flag field. The format of IPv6 RSVP Tunnel sub-TLV is as follows: Chen, et al. Expires May 3, 2012 [Page 9] Internet-Draft Return Path Specified LSP Ping October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 RSVP Tunnel sub-TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 tunnel end point address | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flag | Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Tunnel ID | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 tunnel sender address | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The IPv6 RSVP Tunnel sub-TLV is derived from RSVP IPv6 FEC TLV that is defined in Section 3.2.4 of [RFC4379].All fields have the same semantics as defined in [RFC4379] except that the LSP-ID field is omitted and a new Flag field is defined. The IPv6 RSVP Tunnel sub-TLV Type field is 2 octets in length, and the recommended type value is 19 (to be confirmed by IANA). The Flag field is 2 octets in length and is identical to that described in Section 3.3. 3.3.3. RP TC sub-TLV Reply TOS Byte TLV [RFC4379] is used by the originator of the echo request to request that an echo reply be sent with the IP header TOS byte set to the value specified in the TLV. Similarly, in this document, a new sub-TLV: RP TC sub-TLV is defined and MAY be used by the originator of the echo request to request that an echo reply be sent with the TC bits of the specified return LSP set to the value specified in this sub-TLV. Since there may be more than one FEC sub- TLVs (return paths) specified in the RP TLV, the relevant RP TC sub- TLV MUST directly follow the FEC sub-TLV that identifies the corresponding specified return LSP. The format of RP TC sub-TLV is as follows: Chen, et al. Expires May 3, 2012 [Page 10] Internet-Draft Return Path Specified LSP Ping October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RP TC sub-TLV type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TC | MUST be zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The RP TC sub-TLV Type field is 2 octets in length, and the recommended type value is 17 (to be confirmed by IANA). The Length field is 2 octets in length, the value of length field is fixed 4. 4. Theory of Operation The procedures defined in this document currently only apply to "ping" mode. The "traceroute" mode is out of scope for this document. In [RFC4379], the echo reply is used to report the LSP checking result to the LSP Ping initiator. This document defines a new reply mode and a new TLV (RP TLV) which enable the LSP ping initiator to specify or constrain the return path of the echo reply. Similarly the behavior of echo reply is extended to detect the requested return path by looking at a specified path FEC TLV. This enables LSP Ping to detect failures in both directions of a path with a single operation, this of course cuts in half the operational steps required to verify the end to end bidirectional connectivity and integrity of an LSP. When the echo reply message is intended to test the return MPLS LSP path(when the A bit and E bit is not set in the previous received echo request message), the destination IP address of the echo reply message MUST never be used in a forwarding decision. To avoid this possibility the destination IP address of the echo reply message that is transmitted along the specified return path MUST be set to numbers from the range 127/8 for IPv4 or 0:0:0:0:0:FFFF:127/104 for IPv6, and the IP TTL MUST be set 1. Of course when the echo reply message is not intended for testing the specified return path (when the A bit or E bit is set in the previous received echo request message) , the procedures defined in [RFC4379] (the destination IP address is copied from the source IP address) apply unchanged. Chen, et al. Expires May 3, 2012 [Page 11] Internet-Draft Return Path Specified LSP Ping October 2011 4.1. Sending an Echo Request When sending an echo request, in addition to the rules and procedures defined in Section 4.3 of [RFC4379], the reply mode of the echo request MUST be set to "Reply via specified path", and a RP TLV MUST be carried in the echo request message correspondingly. The RP TLV includes one or several reply path sub-TLV(s) to identify the return path(s) the egress LSR should use for its reply. For a bidirectional LSP, since the ingress LSR and egress LSR of a bidirectional LSP are aware of the relationship between the forward and backward direction LSPs, only the B bit SHOULD be set in the RP TLV. If the operator wants the echo reply to be sent along a different path other than the reverse direction of the bidirectional LSP, "A" bit SHOULD be set or another FEC sub-TLV SHOULD be carried in the RP TLV instead, and the B bit MUST be clear. In some cases, operators may want to treat two unidirectional LSPs (one for each direction) as a pair. There may not be any binding relationship between the two LSPs. Using the mechanism defined in this document, operators can run LSP Ping one time from one end to complete the failure detection on both unidirectional LSPs. To accomplish this, the echo request message MUST carry (in the RP TLV) a FEC sub-TLV that belongs to the backward LSP. 4.2. Receiving an Echo Request "Ping" mode processing as defined in Section 4.4 of [RFC4379] applies in this document. In addition, when an echo request is received, if the egress LSR does not know the reply mode defined in this document, an echo reply with the return code set to "Malformed echo request" and the Subcode set to zero will be send back to the ingress LSR according to the rules of [RFC4379]. If the egress LSR knows the reply mode, according to the RP TLV, it SHOULD find and select the desired return path. If there is a matched path, an echo reply with RP TLV that identify the return path SHOULD be sent back to the ingress LSR, the RP return code SHOULD be set to "The echo reply was sent successfully using the specified RP". If there is no such path, an echo reply with RP TLV SHOULD be sent back to the ingress LSR, the RP return code SHOULD be set to relevant code (defined Section 3.2) for the real situation to reflect the result of RP TLV processing and return path selection. For example, if the specified LSP is not found, the egress then chooses another LSP as the return path to send the echo reply, the RP return code SHOULD be set to "The specified RP was not found, the echo reply was sent via other LSP", and if the egress chooses an IP path to send the echo reply, the RP return code SHOULD be set to "The specified RP was not found, the echo reply was sent via IP path". If there is unknown sub-TLV in the received RP Chen, et al. Expires May 3, 2012 [Page 12] Internet-Draft Return Path Specified LSP Ping October 2011 TLV, the RP return code SHOULD be set to "One or more of the sub-TLVs in RP TLV was not understood". If the A bit of the RP TLV in a received echo request message is set, the egress LSR SHOULD send the echo reply along an non-default return path. IF the B bit of the RP TLV in a received echo request message is set, the egress LSR SHOULD send the echo reply along the reverse direction of the bidirectional LSP. If the E bit of the RP TLV in a received echo request message is set, the egress LSR MUST exclude the paths identified by those FEC sub- TLVs carried in the RP TLV and select other path to send the echo reply. If the A and E bit of the RP TLV in a received echo request message is not set, the echo reply is REQUIRED not only to send along the specified path, but to test the selected return path as well (by carrying the FEC stack information of the return path). In addition, the FEC validate results of the forward path LSP SHOULD NOT affect the egress LSR continue to test return path LSP. 4.3. Sending an Echo Reply As described in [RFC4379], the echo reply message is a UDP packet, and it MUST be sent only in response to an MPLS echo request. The source IP address is a routable IP address of the replier, the source UDP port is the well-know UDP port for LSP ping. When the echo reply is intended to test the return path (both A and E bit are not set in the previous received echo request), the destination IP address of the echo reply message MUST never be used in a forwarding decision. To avoid this problem, the IP destination address of the echo reply message that is transmitted along the specified return path MUST be set to numbers from the range 127/8 for IPv4 or 0:0:0:0:0:FFFF:127/104 for IPv6, and the IP TTL MUST be set to 1. Otherwise, the same as defined in [RFC4379], the destination IP address and UDP port are copied from the source IP address and source UDP port of the echo request. When sending the echo reply, a RP TLV that identifies the return path MUST be carried, the RP return code SHOULD be set to relevant code that reflects results about how the egress processes the RP TLV in a previous received echo request message and return path selection. By carrying the RP TLV in an echo reply, it gives the Ingress LSR enough information about the reverse direction of the tested path to verify Chen, et al. Expires May 3, 2012 [Page 13] Internet-Draft Return Path Specified LSP Ping October 2011 the consistency of the data plane against control plane. Thus a single LSP Ping could achieve both directions of a path test. If the return path is pure IP path, no sub-TLVs are carried in the RP TLV. 4.4. Receiving an Echo Reply The rules and process defined in Section 4.6 of [RFC4379] apply here. When an echo reply is received, if the reply mode is "Reply via specified path" and the RP return code is "The echo reply was sent successfully using the specified RP", and if both the A bit and E bit are not set. The ingress LSR MUST do FEC validation (based on the FEC stack information of the return path carried in the RP TLV) as an egress LSR does when receiving an echo request, the FEC validation process (relevant to "ping" mode) defined in Section 4.4.1 of [RFC4379] applies here. When an echo reply is received with return code set to "Malformed echo request received" and the Subcode set to zero. It is possible that the egress LSR may not know the "Reply via specified path" reply mode, the operator may choose to re-perform another LSP Ping by using one of the four reply modes defined [RFC4379]. On receipt of an echo reply with RP return code in the RP TLV set to "The specified RP was not found, ...", it means that the egress LSR could not find a matched return path as specified. Operators may choose to specify another LSP as the return path or use other methods to detect the path further. When the LSP Ping initiator fails after some time to receive the echo reply message, the operator MAY initiate another LSP Ping by resending a new echo request carrying a RP TLV with E bit set, the sub-TLVs and/or B bit (when the tested LSP is a bidirectional LSP) identify the previous tried reply paths that are used to notify the egress LSR to send echo reply message along any other workable path other than these failed return paths. 5. Security Considerations Security considerations discussed in [RFC4379] apply to this document. In addition to that, in order to prevent using the extension defined in this document for "proxying" any possible attacks, the return path LSP MUST have destination to the same node where the forward path is from. Chen, et al. Expires May 3, 2012 [Page 14] Internet-Draft Return Path Specified LSP Ping October 2011 6. IANA Considerations IANA is requested to assign one new TLV from the "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub- registry; and a set of sub-TLVs under this new TLV; one new Reply Mode from the "Multi- Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Parameters" registry, the "Reply Mode" subregistry. 6.1. New TLV The IANA is requested to as assign a new TLV from the "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub- registry. Value Meaning Reference ----- ------- --------- 21 Reply Path TLV this document (sect 3.2) 6.2. Sub-TLVs Since all existing sub-TLVs and any new sub-TLVs added to the Target FEC Stack TLV apply to the Reply Path TLV, except for the range of 31744-32767 that is left for "Vendor Private Use" in the sub-type space of Target FEC Stack TLV, the sub-TLV space and assignment for Reply Path TLV and Target FEC Stack TLV MUST be kept the same. All new sub-types dedicated added to the Reply Path TLV MUST be assigned from the range of 31744-32767. 6.2.1. New Sub-TLVs IANA is also requested to assign three new sub-TLV types from "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub- registry for the Reply Path TLV (Type 21). Sub-type Value Field Reference ------- ----------- --------- TBD RP TC this document (sect 3.3.3) TBD IPv4 RSVP Tunnel this document (sect 3.3.2) TBD IPv6 RSVP Tunnel this document (sect 3.3.1) 6.2.2. New Reply Mode IANA is requested to assign a new reply mode code point from the from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Parameters" registry, the "Reply Mode" subregistry. Chen, et al. Expires May 3, 2012 [Page 15] Internet-Draft Return Path Specified LSP Ping October 2011 Value Meaning Reference ----- ------- ---------- 5 Reply via specified path this document (sect 3.1) 7. Contributors The following individuals also contributed to this document: Ehud Doron Orckit-Corrigent EMail: ehudd@orckit.com Ronen Solomon Orckit-Corrigent EMail: RonenS@orckit.com Ville Hallivuori Tellabs Sinimaentie 6 C FI-02630 Espoo, Finland EMail: ville.hallivuori@tellabs.com Xinchun Guo EMail: guoxinchun@huawei.com 8. Acknowledgements The authors would like to thank Adrian Farrel and Peter Ashwood-Smith for their review, suggestion and comments to this document. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006. Chen, et al. Expires May 3, 2012 [Page 16] Internet-Draft Return Path Specified LSP Ping October 2011 9.2. Informative References [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport Profile", RFC 5654, September 2009. [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, June 2010. [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884, June 2010. Authors' Addresses Mach(Guoyi) Chen Huawei Technologies Co., Ltd Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District Beijing 100095 China Email: mach@huawei.com Wei Cao Huawei Technologies Co., Ltd Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District Beijing 100095 China Email: wayne.caowei@huawei.com Chen, et al. Expires May 3, 2012 [Page 17] Internet-Draft Return Path Specified LSP Ping October 2011 So Ning Verizon Inc. 2400 N. Glenville Rd., Richardson, TX 75082 USA Email: ning.so@verizonbusiness.com Frederic Jounay France Telecom 2, avenue Pierre-Marzin Lannion Cedex 22307 FRANCE Email: frederic.jounay@orange-ftgroup.com Simon Delord Alcatel-Lucent Building 3, 388 Ningqiao Road, Jinqiao, Pudong Shanghai 201206 China Email: simon.delord@alcatel-lucent.com Chen, et al. Expires May 3, 2012 [Page 18]