MPLS Working Group Rajiv Asati Internet Draft Carlos Pignataro Updates: 5036, 6720 (if approved) Kamran Raza Intended status: Standards Track Cisco Expires: August 2015 Vishwas Manral Hewlett-Packard, Inc Rajiv Papneja Huawei February 26, 2015 Updates to LDP for IPv6 draft-ietf-mpls-ldp-ipv6-17 Abstract The Label Distribution Protocol (LDP) specification defines procedures to exchange label bindings over either IPv4, or IPv6 or both networks. This document corrects and clarifies the LDP behavior when IPv6 network is used (with or without IPv4). This document updates RFC 5036 and RFC 6720. 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 August 26, 2015. Copyright Notice Asati, et. al Expires August 26, 2015 [Page 1] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 Copyright (c) 2015 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction...................................................3 1.1. Topology Scenarios for Dual-stack Environment.............4 1.2. Single-hop vs. Multi-hop LDP Peering......................5 2. Specification Language.........................................6 3. LSP Mapping....................................................7 4. LDP Identifiers................................................7 5. Neighbor Discovery.............................................8 5.1. Basic Discovery Mechanism.................................8 5.1.1. Maintaining Hello Adjacencies........................9 5.2. Extended Discovery Mechanism..............................9 6. LDP Session Establishment and Maintenance......................9 6.1. Transport connection establishment.......................10 6.1.1. Determining Transport connection Roles..............11 6.2. LDP Sessions Maintenance.................................14 7. Binding Distribution..........................................15 7.1. Address Distribution.....................................15 7.2. Label Distribution.......................................16 Asati, et. al Expires August 26, 2015 [Page 2] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 8. LDP Identifiers and Duplicate Next Hop Addresses..............17 9. LDP TTL Security..............................................18 10. IANA Considerations..........................................18 11. Security Considerations......................................18 12. Acknowledgments..............................................19 13. Additional Contributors......................................19 14. References...................................................21 14.1. Normative References....................................21 14.2. Informative References..................................21 Appendix A.......................................................23 A.1. LDPv6 and LDPv4 Interoperability Safety Net..............23 A.2. Accommodating Non-RFC5036-compliant implementations......23 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........24 A.4. Why 32-bit value even for IPv6 LDP Router ID.............24 Author's Addresses...............................................25 1. Introduction The LDP [RFC5036] specification defines procedures and messages for exchanging FEC-label bindings over either IPv4 or IPv6 or both (e.g. Dual-stack) networks. However, RFC5036 specification has the following deficiency (or lacks details) in regards to IPv6 usage (with or without IPv4): 1) LSP Mapping: No rule for mapping a particular packet to a particular LSP that has an Address Prefix FEC element containing IPv6 address of the egress router 2) LDP Identifier: No details specific to IPv6 usage 3) LDP Discovery: No details for using a particular IPv6 destination (multicast) address or the source address 4) LDP Session establishment: No rule for handling both IPv4 and IPv6 transport address optional objects in a Hello message, and subsequently two IPv4 and IPv6 transport connections 5) LDP Address Distribution: No rule for advertising IPv4 or/and IPv6 Address bindings over an LDP session Asati, et. al Expires August 26, 2015 [Page 3] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 6) LDP Label Distribution: No rule for advertising IPv4 or/and IPv6 FEC-label bindings over an LDP session, and for handling the co- existence of IPv4 and IPv6 FEC Elements in the same FEC TLV 7) Next Hop Address Resolution: No rule for accommodating the usage of duplicate link-local IPv6 addresses 8) LDP TTL Security: No rule for built-in Generalized TTL Security Mechanism (GTSM) in LDP with IPv6 (this is a deficiency in RFC6720) This document addresses the above deficiencies by specifying the desired behavior/rules/details for using LDP in IPv6 enabled networks (IPv6-only or Dual-stack networks). This document closes the IPv6 MPLS gap discussed in Sections 3.2.1, 3.2.2, and 3.3.1.1 of [RFC7439]. Note that this document updates RFC5036 and RFC6720. 1.1. Topology Scenarios for Dual-stack Environment Two LSRs may involve basic and/or extended LDP discovery in IPv6 and/or IPv4 address-families in various topology scenarios. This document addresses the following 3 topology scenarios in which the LSRs may be connected via one or more Dual-stack LDP enabled interfaces (figure 1), or one or more Single-stack LDP enabled interfaces (figure 2 and figure 3): R1------------------R2 IPv4+IPv6 Figure 1 LSRs connected via a Dual-stack Interface IPv4 R1=================R2 IPv6 Figure 2 LSRs connected via two Single-stack Interfaces Asati, et. al Expires August 26, 2015 [Page 4] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 R1------------------R2---------------R3 IPv4 IPv6 Figure 3 LSRs connected via a Single-stack Interface Note that the topology scenario illustrated in figure 1 also covers the case of a Single-stack LDP enabled interface (IPv4, say) being converted to a Dual-stacked LDP enabled interface (by enabling IPv6 routing as well as IPv6 LDP), even though the LDPoIPv4 session may already be established between the LSRs. Note that the topology scenario illustrated in figure 2 also covers the case of two routers getting connected via an additional Single- stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though the LDPoIPv4 session may already be established between the LSRs over the existing interface(s). This document also addresses the scenario in which the LSRs do the extended discovery in IPv6 and/or IPv4 address-families: IPv4 R1-------------------R2 IPv6 Figure 4 LSRs involving IPv4 and IPv6 address-families 1.2. Single-hop vs. Multi-hop LDP Peering LDP TTL Security mechanism specified by this document applies only to single-hop LDP peering sessions, but not to multi-hop LDP peering sessions, in line with Section 5.5 of [RFC5082] that describes Generalized TTL Security Mechanism (GTSM). As a consequence, any LDP feature that relies on multi-hop LDP peering session would not work with GTSM and will warrant (statically or dynamically) disabling GTSM. Please see section 10. Asati, et. al Expires August 26, 2015 [Page 5] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 2. Specification 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 [RFC2119]. Abbreviations: LDP - Label Distribution Protocol LDPoIPv4 - LDP over IPv4 transport connection LDPoIPv6 - LDP over IPv6 transport connection FEC - Forwarding Equivalence Class TLV - Type Length Value LSR - Label Switching Router LSP - Label Switched Path LSPv4 - IPv4-signaled Label Switched Path [RFC4798] LSPv6 - IPv6-signaled Label Switched Path [RFC4798] AFI - Address Family Identifier LDP Id - LDP Identifier Single-stack LDP - LDP supporting just one address family (for discovery, session setup, address/label binding exchange etc.) Dual-stack LDP - LDP supporting two address families (for discovery, session setup, address/label binding exchange etc.) Dual-stack LSR - LSR supporting Dual-stack LDP for a peer Single-stack LSR - LSR supporting Single-stack LDP for a peer Note that an LSR can be a Dual-stack and Single-stack LSR at the same time for different peers. This document loosely uses the term address family to mean IP address family. Asati, et. al Expires August 26, 2015 [Page 6] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 3. LSP Mapping Section 2.1 of [RFC5036] specifies the procedure for mapping a particular packet to a particular LSP using three rules. Quoting the 3rd rule from RFC5036: "If it is known that a packet must traverse a particular egress router, and there is an LSP that has an Address Prefix FEC element that is a /32 address of that router, then the packet is mapped to that LSP." This rule is correct for IPv4, but not for IPv6, since an IPv6 router may even have a /64 or /96 or /128 (or whatever prefix length) address. Hence, that rule is updated to use IPv4 or IPv6 address instead of /32 or /128 addresses as shown below: "If it is known that a packet must traverse a particular egress router, and there is an LSP that has an Address Prefix FEC element that is an IPv4 or IPv6 address of that router, then the packet is mapped to that LSP." 4. LDP Identifiers In line with section 2.2.2 of [RFC5036], this document specifies the usage of 32-bit (unsigned non-zero integer) LSR Id on an IPv6 enabled LSR (with or without Dual-stacking). This document also qualifies the first sentence of last paragraph of Section 2.5.2 of [RFC5036] to be per address family and therefore updates that sentence to the following: "For a given address family, an LSR MUST advertise the same transport address in all Hellos that advertise the same label space." This rightly enables the per-platform label space to be shared between IPv4 and IPv6. In summary, this document mandates the usage of a common LDP identifier (same LSR Id aka LDP Router Id as well as a common Label space id) for both IPv4 and IPv6 address families. Asati, et. al Expires August 26, 2015 [Page 7] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 5. Neighbor Discovery If Dual-stack LDP is enabled (e.g. LDP enabled in both IPv6 and IPv4 address families) on an interface or for a targeted neighbor, then the LSR MUST transmit both IPv6 and IPv4 LDP (Link or targeted) Hellos and include the same LDP Identifier (assuming per-platform label space usage) in them. If Single-stack LDP is enabled (e.g. LDP enabled in either IPv6 or IPv4 address family), then the LSR MUST transmit either IPv6 or IPv4 LDP (Link or targeted) Hellos respectively. 5.1. Basic Discovery Mechanism Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for directly connected LSRs. Following this mechanism, LSRs periodically send LDP Link Hellos destined to "all routers on this subnet" group multicast IP address. Interesting enough, per the IPv6 addressing architecture [RFC4291], IPv6 has three "all routers on this subnet" multicast addresses: FF01:0:0:0:0:0:0:2 = Interface-local scope FF02:0:0:0:0:0:0:2 = Link-local scope FF05:0:0:0:0:0:0:2 = Site-local scope [RFC5036] does not specify which particular IPv6 'all routers on this subnet' group multicast IP address should be used by LDP Link Hellos. This document specifies the usage of link-local scope e.g. FF02:0:0:0:0:0:0:2 as the destination multicast IP address in IPv6 LDP Link Hellos. An LDP Link Hello packet received on any of the other destination addresses MUST be dropped. Additionally, the link- local IPv6 address MUST be used as the source IP address in IPv6 LDP Link Hellos. Also, the LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, be checked for the same upon receipt (before any LDP specific processing) and be handled as specified in Generalized TTL Security Mechanism (GTSM) section 3 of [RFC5082]. The built-in inclusion of GTSM automatically protects IPv6 LDP from off-link attacks. Asati, et. al Expires August 26, 2015 [Page 8] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 More importantly, if an interface is a Dual-stack LDP interface (e.g. LDP enabled in both IPv6 and IPv4 address families), then the LSR MUST periodically transmit both IPv6 and IPv4 LDP Link Hellos (using the same LDP Identifier per section 4) on that interface and be able to receive them. This facilitates discovery of IPv6-only, IPv4-only and Dual-stack peers on the interface's subnet and ensures successful subsequent peering using the appropriate (address family) transport on a multi-access or broadcast interface. 5.1.1. Maintaining Hello Adjacencies In case of Dual-stack LDP enabled interface, the LSR SHOULD maintain link Hello adjacencies for both IPv4 and IPv6 address families. This document, however, allows an LSR to maintain Rx-side Link Hello adjacency only for the address family that has been used for the establishment of the LDP session (whether LDPoIPv4 or LDPoIPv6 session). 5.2. Extended Discovery Mechanism The extended discovery mechanism (defined in section 2.4.2 of [RFC5036]), in which the targeted LDP Hellos are sent to a unicast IPv6 address destination, requires only one IPv6 specific consideration: the link-local IPv6 addresses MUST NOT be used as the targeted LDP hello packet's source or destination addresses. 6. LDP Session Establishment and Maintenance Section 2.5.1 of [RFC5036] defines a two-step process for LDP session establishment, once the neighbor discovery has completed (i.e. LDP Hellos have been exchanged): 1. Transport connection establishment 2. Session initialization The forthcoming sub-section 6.1 discusses the LDP consideration for IPv6 and/or Dual-stacking in the context of session establishment, whereas sub-section 6.2 discusses the LDP consideration for IPv6 and/or Dual-stacking in the context of session maintenance. Asati, et. al Expires August 26, 2015 [Page 9] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 6.1. Transport connection establishment Section 2.5.2 of [RFC5036] specifies the use of an optional transport address object (TLV) in LDP Hello message to convey the transport (IP) address, however, it does not specify the behavior of LDP if both IPv4 and IPv6 transport address objects (TLV) are sent in a Hello message or separate Hello messages. More importantly, it does not specify whether both IPv4 and IPv6 transport connections should be allowed, if both IPv4 and IPv6 Hello adjacencies were present prior to the session establishment. This document specifies that: 1. An LSR MUST NOT send a Hello message containing both IPv4 and IPv6 transport address optional objects. In other words, there MUST be at most one optional Transport Address object in a Hello message. An LSR MUST include only the transport address whose address family is the same as that of the IP packet carrying the Hello message. 2. An LSR SHOULD accept the Hello message that contains both IPv4 and IPv6 transport address optional objects, but MUST use only the transport address whose address family is the same as that of the IP packet carrying the Hello message. An LSR SHOULD accept only the first transport object for a given address family in the received Hello message, and ignore the rest, if the LSR receives more than one transport object for a given address family. 3. An LSR MUST send separate Hello messages (each containing either IPv4 or IPv6 transport address optional object) for each IP address family, if Dual-stack LDP is enabled (for an interface or neighbor). 4. An LSR MUST use a global unicast IPv6 address in IPv6 transport address optional object of outgoing targeted Hellos, and check for the same in incoming targeted hellos (i.e. MUST discard the targeted hello, if it failed the check). 5. An LSR MUST prefer using a global unicast IPv6 address in IPv6 transport address optional object of outgoing Link Hellos, if it had to choose between global unicast IPv6 address and unique-local or link-local IPv6 address. 6. A Single-stack LSR MUST establish either LDPoIPv4 or LDPoIPv6 session with a remote LSR as per the enabled address-family. Asati, et. al Expires August 26, 2015 [Page 10] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 7. A Dual-stack LSR MUST NOT initiate (or accept the request for) a TCP connection for a new LDP session with a remote LSR, if they already have an LDPoIPv4 or LDPoIPv6 session (for the same LDP Identifier) established. This means that only one transport connection is established regardless of IPv6 or/and IPv4 Hello adjacencies presence between two LSRs. 8. A Dual-stack LSR SHOULD prefer establishing an LDPoIPv6 session (instead of LDPoIPv4 session) with a remote Dual-stack LSR by following the 'transport connection role' determination logic in section 6.1.1. Additionally, to ensure the above preference in case of Dual- stack LDP being enabled on an interface, it would be desirable that IPv6 LDP Link Hellos are transmitted before IPv4 LDP Link Hellos, particularly when an interface is coming into service or being reconfigured. 6.1.1. Determining Transport connection Roles Section 2.5.2 of [RFC5036] specifies the rules for determining active/passive roles in setting up TCP connection. These rules are clear for a Single-stack LDP, but not for a Dual-stack LDP, in which an LSR may assume different roles for different address families, causing LDP session to not get established. To ensure deterministic transport connection (active/passive) role in case of Dual-stack LDP, this document specifies that the Dual- stack LSR conveys its transport connection preference in every LDP Hello message. This preference is encoded in a new TLV, named Dual- stack capability TLV, as defined below: 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 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| Dual-stack capability | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |TR | Reserved | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5 Dual-stack capability TLV Asati, et. al Expires August 26, 2015 [Page 11] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 Where: U and F bits: 1 and 0 (as specified by RFC5036) Dual-stack capability: TLV code point (to be assigned by IANA). TR, Transport Connection Preference. This document defines the following 2 values: 0100: LDPoIPv4 connection 0110: LDPoIPv6 connection (default) Reserved This field is reserved. It MUST be set to zero on transmission and ignored on receipt. A Dual-stack LSR (i.e. LSR supporting Dual-stack LDP for a peer) MUST include "Dual-stack capability" TLV in all of its LDP Hellos, and MUST set the "TR" field to announce its preference for either LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default preference is LDPoIPv6. A Dual-stack LSR MUST always check for the presence of "Dual-stack capability" TLV in the received hello messages, and take appropriate actions as follows: 1. If "Dual-stack capability" TLV is present and remote preference does not match with the local preference (or does not get recognized), then the LSR MUST discard the hello message and log an error. If LDP session was already in place, then LSR MUST send a fatal Notification message with status code [Transport Connection mismatch, IANA allocation TBD] and reset the session. 2. If "Dual-stack capability" TLV is present, and remote preference matches with the local preference, then: a) If TR=0100 (LDPoIPv4), then determine the active/passive roles for TCP connection using IPv4 transport address as defined in section 2.5.2 of RFC 5036. Asati, et. al Expires August 26, 2015 [Page 12] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 b) If TR=0110 (LDPoIPv6), then determine the active/passive roles for TCP connection by using IPv6 transport address as defined in section 2.5.2 of RFC 5036. 3. If "Dual-stack capability" TLV is NOT present, and a) Only IPv4 hellos are received, then the neighbor is deemed as a legacy IPv4-only LSR (supporting Single-stack LDP), hence, an LDPoIPv4 session SHOULD be established (similar to that of 2a above). However, if IPv6 hellos are also received at any time during the life of session from that neighbor, then the neighbor is deemed as a non-compliant Dual-stack LSR (similar to that of 3c below), resulting in any established LDPoIPv4 session being reset and a fatal Notification message being sent (with status code of 'Dual-Stack Non-Compliance', IANA allocation TBD). b) Only IPv6 hellos are received, then the neighbor is deemed as an IPv6-only LSR (supporting Single-stack LDP) and LDPoIPv6 session SHOULD be established (similar to that of 2b above). However, if IPv4 hellos are also received at any time during the life of session from that neighbor, then the neighbor is deemed as a non-compliant Dual-stack LSR (similar to that of 3c below), resulting in any established LDPoIPv6 session being reset and a fatal Notification message being sent (with status code of 'Dual-Stack Non-Compliance', IANA allocation TBD). c) Both IPv4 and IPv6 hellos are received, then the neighbor is deemed as a non-compliant Dual-stack neighbor, and is not allowed to have any LDP session. A Notification message should be sent (with status code of 'Dual-Stack Non-Compliance', IANA allocation TBD). A Dual-stack LSR MUST convey the same transport connection preference ("TR" field value) in all (link and targeted) Hellos that advertise the same label space to the same peer and/or on same interface. This ensures that two LSRs linked by multiple Hello adjacencies using the same label spaces play the same connection establishment role for each adjacency. Asati, et. al Expires August 26, 2015 [Page 13] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 A Dual-stack LSR MUST follow section 2.5.5 of RFC5036 and check for matching Hello messages from the peer (either all Hellos also include the Dual-stack capability (with same TR value) or none do). A Single-stack LSR do not need to use the Dual-stack capability in hello messages and SHOULD ignore this capability, if received. An implementation may provide an option to favor one AFI (IPv4, say) over another AFI (IPv6, say) for the TCP transport connection, so as to use the favored IP version for the LDP session, and force deterministic active/passive roles. Note - An alternative to this new Capability TLV could be a new Flag value in LDP Hello message, however, it will get used even in a Single-stack IPv6 LDP networks and linger on forever, even though Dual-stack will not. Hence, this alternative is discarded. 6.2. LDP Sessions Maintenance This document specifies that two LSRs maintain a single LDP session regardless of number of Link or Targeted Hello adjacencies between them, as described in section 6.1. This is independent of whether: - they are connected via a Dual-stack LDP enabled interface(s) or via two (or more) Single-stack LDP enabled interfaces; - a Single-stack LDP enabled interface is converted to a Dual-stack LDP enabled interface (e.g. figure 1) on either LSR; - an additional Single-stack or Dual-stack LDP enabled interface is added or removed between two LSRs (e.g. figure 2). If the last hello adjacency for a given address family goes down (e.g. due to Dual-stack LDP enabled interfaces being converted into a Single-stack LDP enabled interfaces on one LSR etc.), and that address family is the same as the one used in the transport connection, then the transport connection (LDP session) MUST be reset. Otherwise, the LDP session MUST stay intact. If the LDP session is torn down for whatever reason (LDP disabled for the corresponding transport, hello adjacency expiry, preference mismatch etc.), then the LSRs SHOULD initiate establishing a new LDP session as per the procedures described in section 6.1 of this document. Asati, et. al Expires August 26, 2015 [Page 14] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 7. Binding Distribution LSRs by definition can be enabled for Dual-stack LDP globally and/or per peer so as to exchange the address and label bindings for both IPv4 and IPv6 address-families, independent of LDPoIPv4 or LDPoIPV6 session between them. However, there might be some legacy LSRs that are fully RFC 5036 compliant for IPv4, but non-compliant for IPv6 (say, section 3.5.5.1 of RFC 5036), causing them to reset the session upon receiving IPv6 address bindings or IPv6 FEC (Prefix) label bindings from a peer compliant with this document. This is somewhat undesirable, as clarified further Appendix A.1 and A.2. To help maintain backward compatibility (i.e. accommodate IPv4-only LDP implementations that may not be compliant with RFC 5036 section 3.5.5.1), this specification requires that an LSR MUST NOT send any IPv6 bindings to a peer if peer has been determined as a legacy LSR. The 'Dual-stack capability' TLV, which is defined in section 6.1.1, is also used to determine if a peer is a legacy (IPv4-only Single- stack) LSR or not. 7.1. Address Distribution An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6 addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such addresses, if ever received. Please see Appendix A.3. If an LSR is enabled with Single-stack LDP for any peer, then it MUST advertise (via ADDRESS message) its local IP addresses as per the enabled address family to that peer, and process received Address messages containing IP addresses as per the enabled address family from that peer. If an LSR is enabled with Dual-stack LDP for a peer and 1. Is NOT able to find the Dual-stack capability TLV in the incoming IPv4 LDP hello messages from that peer, then the LSR MUST NOT advertise its local IPv6 Addresses to the peer. 2. Is able to find the Dual-stack capability in the incoming IPv4 (or IPv6) LDP Hello messages from that peer, then it MUST advertise (via ADDRESS message) its local IPv4 and IPv6 addresses to that peer. Asati, et. al Expires August 26, 2015 [Page 15] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 3. Is NOT able to find the Dual-stack capability in the incoming IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS message) only its local IPv6 addresses to that peer. This last point helps to maintain forward compatibility (no need to require this TLV in case of IPv6 Single-stack LDP). 7.2. Label Distribution An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings for link-local or IPv4-mapped IPv6 addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received. Please see Appendix A.3. If an LSR is enabled with Single-stack LDP for any peer, then it MUST advertise (via Label Mapping message) FEC-Label bindings for the enabled address family to that peer, and process received FEC- Label bindings for the enabled address family from that peer. If an LSR is enabled with Dual-stack LDP for a peer and 1. Is NOT able to find the Dual-stack capability TLV in the incoming IPv4 LDP hello messages from that peer, then the LSR MUST NOT advertise IPv6 FEC-label bindings to the peer (even if IP capability negotiation for IPv6 address family was done). 2. Is able to find the Dual-stack capability in the incoming IPv4 (or IPv6) LDP Hello messages from that peer, then it MUST advertise FEC-Label bindings for both IPv4 and IPv6 address families to that peer. 3. Is NOT able to find the Dual-stack capability in the incoming IPv6 LDP Hello messages, then it MUST advertise FEC-Label bindings for IPv6 address families to that peer. This last point helps to maintain forward compatibility (no need to require this TLV for IPv6 Single-stack LDP). An LSR MAY further constrain the advertisement of FEC-label bindings for a particular address family by negotiating the IP Capability for a given address family, as specified in [IPPWCap] document. This allows an LSR pair to neither advertise nor receive the undesired FEC-label bindings on a per address family basis to a peer. Asati, et. al Expires August 26, 2015 [Page 16] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 If an LSR is configured to change an interface or peer from Single- stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard FEC procedures [RFC5918] to request the label bindings for the enabled address family. This helps to relearn the label bindings that may have been discarded before without resetting the session. 8. LDP Identifiers and Duplicate Next Hop Addresses RFC5036 section 2.7 specifies the logic for mapping the IP routing next-hop (of a given FEC) to an LDP peer so as to find the correct label entry for that FEC. The logic involves using the IP routing next-hop address as an index into the (peer Address) database (which is populated by the Address message containing mapping between each peer's local addresses and its LDP Identifier) to determine the LDP peer. However, this logic is insufficient to deal with duplicate IPv6 (link-local) next-hop addresses used by two or more peers. The reason is that all interior IPv6 routing protocols (can) use link- local IPv6 addresses as the IP routing next-hops, and 'IPv6 Addressing Architecture [RFC4291]' allows a link-local IPv6 address to be used on more than one links. Hence, this logic is extended by this specification to use not only the IP routing next-hop address, but also the IP routing next-hop interface to uniquely determine the LDP peer(s). The next-hop address-based LDP peer mapping is to be done through LDP peer address database (populated by Address messages received from the LDP peers), whereas next-hop interface-based LDP peer mapping is to be done through LDP hello adjacency/interface database (populated by hello messages received from the LDP peers). This extension solves the problem of two or more peers using the same link-local IPv6 address (in other words, duplicate peer addresses) as the IP routing next-hops. Lastly, for better scale and optimization, an LSR may advertise only the link-local IPv6 addresses in the Address message, assuming that the peer uses only the link-local IPv6 addresses as static and/or dynamic IP routing next-hops. Asati, et. al Expires August 26, 2015 [Page 17] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 9. LDP TTL Security This document recommends enabling Generalized TTL Security Mechanism (GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended to automatically protect IPv6 LDP peering session from off-link attacks. [RFC6720] allows for the implementation to statically (configuration) and/or dynamically override the default behavior (enable/disable GTSM) on a per-peer basis. Such a configuration an option could be set on either LSR (since GTSM negotiation would ultimately disable GTSM between LSR and its peer(s)). LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, and be checked for the same upon receipt before any further processing, as per section 3 of [RFC5082]. 10. IANA Considerations This document defines a new optional parameter for the LDP Hello Message and two new status codes for the LDP Notification Message. The 'Dual-Stack capability' parameter requires a code point from the TLV Type Name Space. IANA is requested to allocated a code point from the IETF Consensus range 0x0700-0x07ff for the 'Dual-Stack capability' TLV. The 'Transport Connection Mismatch' status code requires a code point from the Status Code Name Space. IANA is requested to allocate a code point from the IETF Consensus range and mark the E bit column with a '1'. The 'Dual-Stack Non-Compliance' status code requires a code point from the Status Code Name Space. IANA is requested to allocate a code point from the IETF Consensus range and mark the E bit column with a '1'. 11. Security Considerations The extensions defined in this document only clarify the behavior of LDP, they do not define any new protocol procedures. Hence, this document does not add any new security issues to LDP. Asati, et. al Expires August 26, 2015 [Page 18] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 While the security issues relevant for the [RFC5036] are relevant for this document as well, this document reduces the chances of off- link attacks when using IPv6 transport connection by including the use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL Security details. Moreover, this document allows the use of IPsec [RFC4301] for IPv6 protection, hence, LDP can benefit from the additional security as specified in [RFC7321] as well as [RFC5920]. 12. Acknowledgments We acknowledge the authors of [RFC5036], since some text in this document is borrowed from [RFC5036]. Thanks to Bob Thomas for providing critical feedback to improve this document early on. Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane Amante, Pranjal Dutta, Mustapha Aissaoui, Matthew Bocci, Mark Tinka, Tom Petch, Kishore Tiruveedhula, Manoj Dutta, Vividh Siddha, Qin Wu, Simon Perreault, Brian E Carpenter, Santosh Esale, Danial Johari and Loa Andersson for thoroughly reviewing this document, and providing insightful comments and multiple improvements. This document was prepared using 2-Word-v2.0.template.dot. 13. Additional Contributors The following individuals contributed to this document: Kamran Raza Cisco Systems, Inc. 2000 Innovation Drive Kanata, ON K2K-3E8, Canada Email: skraza@cisco.com Asati, et. al Expires August 26, 2015 [Page 19] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 Nagendra Kumar Cisco Systems, Inc. SEZ Unit, Cessna Business Park, Bangalore, KT, India Email: naikumar@cisco.com Andre Pelletier Cisco Systems, Inc. 2000 Innovation Drive Kanata, ON K2K-3E8, Canada Email: apelleti@cisco.com Asati, et. al Expires August 26, 2015 [Page 20] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 4291, February 2006. [RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP Specification", RFC 5036, October 2007. [RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and Savola, P., "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007. [RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution Protocol (LDP) 'Typed Wildcard Forward Equivalence Class (FEC)", RFC 5918, October 2010. 14.2. Informative References [RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet Protocol", RFC 4301, December 2005. [RFC7321] Manral, V., "Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH)", RFC 7321, April 2007. [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010. [RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE)", RFC 4798, February 2007. [IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp- ip-pw-capability, October 2014. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008. Asati, et. al Expires August 26, 2015 [Page 21] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 [RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP Identifier for BGP-4", RFC 6286, June 2011. [RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM) for the Label Distribution Protocol (LDP)", RFC 6720, August 2012. [RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M. Castro, "Application Aspects of IPv6 Transition", RFC 4038, March 2005. [RFC7439] W. George, and C. Pignataro, "Gap Analysis for Operating IPv6-Only MPLS Networks", RFC 7439, January 2015. Asati, et. al Expires August 26, 2015 [Page 22] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 Appendix A. A.1. LDPv6 and LDPv4 Interoperability Safety Net It is not safe to assume that RFC5036 compliant implementations have supported handling IPv6 address family (IPv6 FEC label) in Label Mapping message all along. If a router upgraded with this specification advertised both IPv4 and IPv6 FECs in the same label mapping message, then an IPv4-only peer (not knowing how to process such a message) may abort processing the entire label mapping message (thereby discarding even the IPv4 label FECs), as per the section 3.4.1.1 of RFC5036. This would result in LDPv6 to be somewhat undeployable in existing production networks. The change proposed in section 7 of this document provides a good safety net and makes LDPv6 incrementally deployable without making any such assumption on the routers' support for IPv6 FEC processing in current production networks. A.2. Accommodating Non-RFC5036-compliant implementations It is not safe to assume that implementations have been RFC5036 compliant in gracefully handling IPv6 address family (IPv6 Address List TLV) in Address message all along. If a router upgraded with this specification advertised IPv6 addresses (with or without IPv4 addresses) in Address message, then an IPv4-only peer (not knowing how to process such a message) may not follow section 3.5.5.1 of RFC5036, and tear down the LDP session. This would result in LDPv6 to be somewhat undeployable in existing production networks. The changes proposed in section 6 and 7 of this document provides a good safety net and makes LDPv6 incrementally deployable without making any such assumption on the routers' support for IPv6 FEC processing in current production networks. Asati, et. al Expires August 26, 2015 [Page 23] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP Per discussion with 6MAN and V6OPS working groups, the overwhelming consensus was to not promote IPv4-mapped IPv6 addresses appear in the routing table, as well as in LDP (address and label) databases. Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed packets should never appear on the wire. A.4. Why 32-bit value even for IPv6 LDP Router ID The first four octets of the LDP identifier, the 32-bit LSR Id (e.g. (i.e. LDP Router Id), identify the LSR and is a globally unique value within the MPLS network. This is regardless of the address family used for the LDP session. Please note that 32-bit LSR Id value would not map to any IPv4- address in an IPv6 only LSR (i.e., single stack), nor would there be an expectation of it being IP routable, nor DNS-resolvable. In IPv4 deployments, the LSR Id is typically derived from an IPv4 address, generally assigned to a loopback interface. In IPv6 only deployments, this 32-bit LSR Id must be derived by some other means that guarantees global uniqueness within the MPLS network, similar to that of BGP Identifier [RFC6286] and OSPF router ID [RFC5340]. This document reserves 0.0.0.0 as the LSR Id, and prohibits its usage with IPv6, in line with OSPF router Id in OSPF version 3 [RFC5340]. Asati, et. al Expires August 26, 2015 [Page 24] Internet-Draft draft-ietf-mpls-ldp-ipv6 February 26, 2015 Author's Addresses Rajiv Asati Cisco Systems, Inc. 7025 Kit Creek Road Research Triangle Park, NC 27709-4987 Email: rajiva@cisco.com Vishwas Manral Hewlet-Packard, Inc. 19111 Pruneridge Ave., Cupertino, CA, 95014 Phone: 408-447-1497 Email: vishwas@ionosnetworks.com Kamran Raza Cisco Systems, Inc., 2000 Innovation Drive, Ottawa, ON K2K-3E8, Canada. E-mail: skraza@cisco.com Rajiv Papneja Huawei Technologies 2330 Central Expressway Santa Clara, CA 95050 Phone: +1 571 926 8593 EMail: rajiv.papneja@huawei.com Carlos Pignataro Cisco Systems, Inc. 7200 Kit Creek Road Research Triangle Park, NC 27709-4987 Email: cpignata@cisco.com Asati, et. al Expires August 26, 2015 [Page 25]