draft-ietf-mpls-ldp-ipv6-17.txt   rfc7552.txt 
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 Internet Engineering Task Force (IETF) R. Asati
Huawei Request for Comments: 7552 C. Pignataro
Updates: 5036, 6720 K. Raza
February 26, 2015 Category: Standards Track Cisco
ISSN: 2070-1721 V. Manral
Ionos Networks
R. Papneja
Huawei
June 2015
Updates to LDP for IPv6 Updates to LDP for IPv6
draft-ietf-mpls-ldp-ipv6-17
Abstract Abstract
The Label Distribution Protocol (LDP) specification defines The Label Distribution Protocol (LDP) specification defines
procedures to exchange label bindings over either IPv4, or IPv6 or procedures to exchange label bindings over either IPv4 or IPv6
both networks. This document corrects and clarifies the LDP behavior networks, or both. This document corrects and clarifies the LDP
when IPv6 network is used (with or without IPv4). This document behavior when an IPv6 network is used (with or without IPv4). This
updates RFC 5036 and RFC 6720. document updates RFCs 5036 and 6720.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
months and may be updated, replaced, or obsoleted by other documents (IETF). It represents the consensus of the IETF community. It has
at any time. It is inappropriate to use Internet-Drafts as received public review and has been approved for publication by the
reference material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on August 26, 2015. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7552.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction ....................................................4
1.1. Topology Scenarios for Dual-stack Environment.............4 1.1. Topology Scenarios for Dual-Stack Environment ..............5
1.2. Single-hop vs. Multi-hop LDP Peering......................5 1.2. Single-Hop vs. Multi-Hop LDP Peering .......................6
2. Specification Language.........................................6 2. Specification Language ..........................................6
3. LSP Mapping....................................................7 3. LSP Mapping .....................................................7
4. LDP Identifiers................................................7 4. LDP Identifiers .................................................8
5. Neighbor Discovery.............................................8 5. Neighbor Discovery ..............................................8
5.1. Basic Discovery Mechanism.................................8 5.1. Basic Discovery Mechanism ..................................8
5.1.1. Maintaining Hello Adjacencies........................9 5.1.1. Maintaining Hello Adjacencies .......................9
5.2. Extended Discovery Mechanism..............................9 5.2. Extended Discovery Mechanism ..............................10
6. LDP Session Establishment and Maintenance......................9 6. LDP Session Establishment and Maintenance ......................10
6.1. Transport connection establishment.......................10 6.1. Transport Connection Establishment ........................10
6.1.1. Determining Transport connection Roles..............11 6.1.1. Dual-Stack: Transport Connection Preference
6.2. LDP Sessions Maintenance.................................14 and Role of an LSR .................................12
7. Binding Distribution..........................................15 6.2. LDP Session Maintenance ...................................14
7.1. Address Distribution.....................................15 7. Binding Distribution ...........................................15
7.2. Label Distribution.......................................16 7.1. Address Distribution ......................................15
7.2. Label Distribution ........................................16
8. LDP Identifiers and Duplicate Next Hop Addresses..............17 8. LDP Identifiers and Duplicate Next-Hop Addresses ...............17
9. LDP TTL Security..............................................18 9. LDP TTL Security ...............................................18
10. IANA Considerations..........................................18 10. IANA Considerations ...........................................18
11. Security Considerations......................................18 11. Security Considerations .......................................19
12. Acknowledgments..............................................19 12. References ....................................................19
13. Additional Contributors......................................19 12.1. Normative References .....................................19
14. References...................................................21 12.2. Informative References ...................................20
14.1. Normative References....................................21 Appendix A. Additional Considerations .............................21
14.2. Informative References..................................21 A.1. LDPv6 and LDPv4 Interoperability Safety Net ................21
Appendix A.......................................................23 A.2. Accommodating Implementations Not Compliant with RFC 5036 ..21
A.1. LDPv6 and LDPv4 Interoperability Safety Net..............23 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP? ............22
A.2. Accommodating Non-RFC5036-compliant implementations......23 A.4. Why a 32-bit value even for the IPv6 LDP Router Id? ........22
A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........24 Acknowledgments ...................................................23
A.4. Why 32-bit value even for IPv6 LDP Router ID.............24 Contributors ......................................................23
Author's Addresses...............................................25 Authors' Addresses.................................................24
1. Introduction 1. Introduction
The LDP [RFC5036] specification defines procedures and messages for The LDP specification [RFC5036] defines procedures and messages for
exchanging FEC-label bindings over either IPv4 or IPv6 or both (e.g. exchanging FEC-label bindings over either IPv4 or IPv6 networks, or
Dual-stack) networks. both (i.e., Dual-stack networks).
However, RFC5036 specification has the following deficiency (or However, RFC 5036 has the following deficiencies (i.e., lacks
lacks details) in regards to IPv6 usage (with or without IPv4): details) in regard to IPv6 usage (with or without IPv4):
1) LSP Mapping: No rule for mapping a particular packet to a 1. Label Switched Path (LSP) Mapping: No rule for mapping a
particular LSP that has an Address Prefix FEC element containing particular packet to a particular LSP that has an Address Prefix
IPv6 address of the egress router Forwarding Equivalence Class (FEC) element containing the IPv6
address of the egress router
2) LDP Identifier: No details specific to IPv6 usage 2. LDP Identifier: No details specific to IPv6 usage
3) LDP Discovery: No details for using a particular IPv6 destination 3. LDP Discovery: No details for using a particular IPv6 destination
(multicast) address or the source address (multicast) address or the source address
4) LDP Session establishment: No rule for handling both IPv4 and 4. LDP Session Establishment: No rule for handling both IPv4 and IPv6
IPv6 transport address optional objects in a Hello message, and Transport Address optional objects in a Hello message, and
subsequently two IPv4 and IPv6 transport connections subsequently two IPv4 and IPv6 transport connections
5) LDP Address Distribution: No rule for advertising IPv4 or/and 5. LDP Address Distribution: No rule for advertising IPv4 and/or IPv6
IPv6 Address bindings over an LDP session address bindings over an LDP session
6) LDP Label Distribution: No rule for advertising IPv4 or/and IPv6 6. LDP Label Distribution: No rule for advertising IPv4 and/or IPv6
FEC-label bindings over an LDP session, and for handling the co- FEC-label bindings over an LDP session, or for handling the
existence of IPv4 and IPv6 FEC Elements in the same FEC TLV coexistence of IPv4 and IPv6 FEC Elements in the same FEC TLV
7) Next Hop Address Resolution: No rule for accommodating the usage 7. Next-Hop Address Resolution: No rule for accommodating the usage
of duplicate link-local IPv6 addresses of duplicate link-local IPv6 addresses
8) LDP TTL Security: No rule for built-in Generalized TTL Security 8. LDP Time to Live (TTL) Security: No rule for a built-in
Mechanism (GTSM) in LDP with IPv6 (this is a deficiency in Generalized TTL Security Mechanism (GTSM) in LDP with IPv6 (this
RFC6720) is a deficiency in [RFC6720])
This document addresses the above deficiencies by specifying the This document addresses the above deficiencies by specifying the
desired behavior/rules/details for using LDP in IPv6 enabled desired behavior/rules/details for using LDP in IPv6-enabled networks
networks (IPv6-only or Dual-stack networks). This document closes (IPv6-only or Dual-stack networks). This document closes the IPv6
the IPv6 MPLS gap discussed in Sections 3.2.1, 3.2.2, and 3.3.1.1 of MPLS gap discussed in Sections 3.2.1, 3.2.2, and 3.3.1.1 of
[RFC7439]. [RFC7439].
Note that this document updates RFC5036 and RFC6720. Note that this document updates [RFC5036] and [RFC6720].
1.1. Topology Scenarios for Dual-stack Environment 1.1. Topology Scenarios for Dual-Stack Environment
Two LSRs may involve basic and/or extended LDP discovery in IPv6 Two Label Switching Routers (LSRs) may involve Basic and/or Extended
and/or IPv4 address-families in various topology scenarios. LDP Discovery in IPv6 and/or IPv4 address families in various
topology scenarios.
This document addresses the following 3 topology scenarios in which This document addresses the following three topology scenarios in
the LSRs may be connected via one or more Dual-stack LDP enabled which the LSRs may be connected via one or more Dual-stack
interfaces (figure 1), or one or more Single-stack LDP enabled LDP-enabled interfaces (Figure 1), or one or more Single-stack
interfaces (figure 2 and figure 3): LDP-enabled interfaces (Figures 2 and 3):
R1------------------R2 R1------------------R2
IPv4+IPv6 IPv4+IPv6
Figure 1 LSRs connected via a Dual-stack Interface Figure 1: LSRs Connected via a Dual-Stack Interface
IPv4 IPv4
R1=================R2 R1=================R2
IPv6 IPv6
Figure 2 LSRs connected via two Single-stack Interfaces Figure 2: LSRs Connected via Two Single-Stack Interfaces
R1------------------R2---------------R3
IPv4 IPv6
Figure 3 LSRs connected via a Single-stack Interface R1------------------R2---------------R3
IPv4 IPv6
Note that the topology scenario illustrated in figure 1 also covers Figure 3: LSRs Connected via a Single-Stack Interface
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 Note that the topology scenario illustrated in Figure 1 also covers
the case of two routers getting connected via an additional Single- the case of a Single-stack LDP-enabled interface (say, IPv4) being
stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though converted to a Dual-stack LDP-enabled interface (by enabling IPv6
the LDPoIPv4 session may already be established between the LSRs routing as well as IPv6 LDP), even though the LDP-over-IPv4
over the existing interface(s). (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 This document also addresses the scenario in which the LSRs do the
extended discovery in IPv6 and/or IPv4 address-families: Extended Discovery in IPv6 and/or IPv4 address families:
IPv4 IPv4
R1-------------------R2 R1-------------------R2
IPv6 IPv6
Figure 4 LSRs involving IPv4 and IPv6 address-families Figure 4: LSRs Involving IPv4 and IPv6 Address Families
1.2. Single-hop vs. Multi-hop LDP Peering 1.2. Single-Hop vs. Multi-Hop LDP Peering
LDP TTL Security mechanism specified by this document applies only The LDP TTL Security mechanism specified by this document applies
to single-hop LDP peering sessions, but not to multi-hop LDP peering only to single-hop LDP peering sessions, not to multi-hop LDP peering
sessions, in line with Section 5.5 of [RFC5082] that describes sessions, in line with Section 5.5 of [RFC5082]. [RFC5082] describes
Generalized TTL Security Mechanism (GTSM). the Generalized TTL Security Mechanism (GTSM).
As a consequence, any LDP feature that relies on multi-hop LDP As a consequence, any LDP feature that relies on a multi-hop LDP
peering session would not work with GTSM and will warrant peering session would not work with GTSM and will warrant (statically
(statically or dynamically) disabling GTSM. Please see section 10. or dynamically) disabling GTSM. Please see Section 9.
2. Specification Language 2. Specification Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
Abbreviations: Abbreviations:
LDP - Label Distribution Protocol LDP Label Distribution Protocol
LDPoIPv4 - LDP over IPv4 transport connection
LDPoIPv6 - LDP over IPv6 transport connection LDPoIPv4 LDP-over-IPv4 transport connection
FEC - Forwarding Equivalence Class LDPoIPv6 LDP-over-IPv6 transport connection
TLV - Type Length Value FEC Forwarding Equivalence Class
LSR - Label Switching Router TLV Type Length Value
LSP - Label Switched Path LSR Label Switching Router
LSPv4 - IPv4-signaled Label Switched Path [RFC4798] LSP Label Switched Path
LSPv6 - IPv6-signaled Label Switched Path [RFC4798] LSPv4 IPv4-signaled Label Switched Path
AFI - Address Family Identifier LSPv6 IPv6-signaled Label Switched Path
LDP Id - LDP Identifier AFI Address Family Identifier
LDP Id LDP Identifier
Single-stack LDP - LDP supporting just one address family (for Single-stack LDP LDP supporting just one address family
discovery, session setup, address/label binding (for discovery, session setup, address/label
exchange etc.) binding exchange, etc.)
Dual-stack LDP - LDP supporting two address families (for Dual-stack LDP LDP supporting two address families
discovery, session setup, address/label binding (for discovery, session setup, address/label
exchange etc.) binding exchange, etc.)
Dual-stack LSR - LSR supporting Dual-stack LDP for a peer Dual-stack LSR LSR supporting Dual-stack LDP for a peer
Single-stack LSR - LSR supporting Single-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 Note that an LSR can be a Dual-stack and Single-stack LSR at the same
same time for different peers. This document loosely uses the term time for different peers. This document loosely uses the term
address family to mean IP address family. "address family" to mean "IP address family".
3. LSP Mapping 3. LSP Mapping
Section 2.1 of [RFC5036] specifies the procedure for mapping a Section 2.1 of [RFC5036] specifies the procedure for mapping a
particular packet to a particular LSP using three rules. Quoting the particular packet to a particular LSP using three rules. Quoting the
3rd rule from RFC5036: third rule from [RFC5036]:
"If it is known that a packet must traverse a particular egress 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 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 is a /32 address of that router, then the packet is mapped to
that LSP." that LSP.
This rule is correct for IPv4, but not for IPv6, since an IPv6 This rule is correct for IPv4 (to set up LSPv4), but not for IPv6
router may even have a /64 or /96 or /128 (or whatever prefix (to set up LSPv6), since an IPv6 router may even have a /64 or /96
length) address. Hence, that rule is updated to use IPv4 or IPv6 or /128 (or whatever prefix length) address. Hence, that rule is
address instead of /32 or /128 addresses as shown below: updated here to use IPv4 or IPv6 addresses instead of /32 or /128
addresses, as shown below:
"If it is known that a packet must traverse a particular egress 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 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 that is an IPv4 or IPv6 address of that router, then the packet is
mapped to that LSP." mapped to that LSP.
4. LDP Identifiers 4. LDP Identifiers
In line with section 2.2.2 of [RFC5036], this document specifies the 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 usage of a 32-bit (unsigned non-zero integer) LSR Id on an
enabled LSR (with or without Dual-stacking). IPv6-enabled LSR (with or without Dual-stacking).
This document also qualifies the first sentence of last paragraph of This document also qualifies the first sentence of the last paragraph
Section 2.5.2 of [RFC5036] to be per address family and therefore of Section 2.5.2 of [RFC5036] to be per address family.
updates that sentence to the following:
"For a given address family, an LSR MUST advertise the same From Section 2.5.2 of [RFC5036]:
transport address in all Hellos that advertise the same label
space." An LSR MUST advertise the same transport address in all Hellos
that advertise the same label space.
Updated by this document, as follows:
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 This rightly enables the per-platform label space to be shared
between IPv4 and IPv6. between IPv4 and IPv6.
In summary, this document mandates the usage of a common LDP 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 Identifier (the same LSR Id and label space id) for both IPv4 and
space id) for both IPv4 and IPv6 address families. IPv6 address families.
5. Neighbor Discovery 5. Neighbor Discovery
If Dual-stack LDP is enabled (e.g. LDP enabled in both IPv6 and IPv4 If Dual-stack LDP is enabled (i.e., LDP enabled in both IPv6 and IPv4
address families) on an interface or for a targeted neighbor, then address families) on an interface or for a targeted neighbor, then
the LSR MUST transmit both IPv6 and IPv4 LDP (Link or targeted) the LSR MUST transmit both IPv6 and IPv4 LDP (Link or targeted)
Hellos and include the same LDP Identifier (assuming per-platform Hellos and include the same LDP Identifier (assuming per-platform
label space usage) in them. label space usage) in them.
If Single-stack LDP is enabled (e.g. LDP enabled in either IPv6 or If Single-stack LDP is enabled (i.e., LDP enabled in either an IPv6
IPv4 address family), then the LSR MUST transmit either IPv6 or IPv4 or IPv4 address family), then the LSR MUST transmit either IPv6 or
LDP (Link or targeted) Hellos respectively. IPv4 LDP (Link or targeted) Hellos, respectively.
5.1. Basic Discovery Mechanism 5.1. Basic Discovery Mechanism
Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for
directly connected LSRs. Following this mechanism, LSRs periodically directly connected LSRs. Following this mechanism, LSRs periodically
send LDP Link Hellos destined to "all routers on this subnet" group send LDP Link Hellos destined to the "all routers on this subnet"
multicast IP address. group multicast IP address.
Interesting enough, per the IPv6 addressing architecture [RFC4291], Interestingly enough, per the IPv6 addressing architecture [RFC4291],
IPv6 has three "all routers on this subnet" multicast addresses: IPv6 has three "all routers on this subnet" multicast addresses:
FF01:0:0:0:0:0:0:2 = Interface-local scope ff01:0:0:0:0:0:0:2 = Interface-local scope
FF02:0:0:0:0:0:0:2 = Link-local scope ff02:0:0:0:0:0:0:2 = Link-local scope
FF05:0:0:0:0:0:0:2 = Site-local scope ff05:0:0:0:0:0:0:2 = Site-local scope
[RFC5036] does not specify which particular IPv6 'all routers on [RFC5036] does not specify which particular IPv6 "all routers on this
this subnet' group multicast IP address should be used by LDP Link subnet" group multicast IP address should be used by LDP Link Hellos.
Hellos.
This document specifies the usage of link-local scope e.g. This document specifies the usage of link-local scope (i.e.,
FF02:0:0:0:0:0:0:2 as the destination multicast IP address in IPv6 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 LDP Link Hellos. An LDP Link Hello packet received on any of the
other destination addresses MUST be dropped. Additionally, the link- other destination addresses MUST be dropped. Additionally, the
local IPv6 address MUST be used as the source IP address in IPv6 LDP link-local IPv6 address MUST be used as the source IP address in IPv6
Link Hellos. LDP Link Hellos.
Also, the LDP Link Hello packets MUST have their IPv6 Hop Limit set 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 to 255, be checked for the same upon receipt (before any LDP-specific
specific processing) and be handled as specified in Generalized TTL processing), and be handled as specified in Section 3 of [RFC5082].
Security Mechanism (GTSM) section 3 of [RFC5082]. The built-in The built-in inclusion of GTSM automatically protects IPv6 LDP from
inclusion of GTSM automatically protects IPv6 LDP from off-link off-link attacks.
attacks.
More importantly, if an interface is a Dual-stack LDP interface More importantly, if an interface is a Dual-stack LDP interface
(e.g. LDP enabled in both IPv6 and IPv4 address families), then the (i.e., LDP enabled in both IPv6 and IPv4 address families), then the
LSR MUST periodically transmit both IPv6 and IPv4 LDP Link Hellos LSR MUST periodically transmit both IPv6 and IPv4 LDP Link Hellos
(using the same LDP Identifier per section 4) on that interface and (using the same LDP Identifier per Section 4) on that interface and
be able to receive them. This facilitates discovery of IPv6-only, be able to receive them. This facilitates discovery of IPv6-only,
IPv4-only and Dual-stack peers on the interface's subnet and ensures IPv4-only, and Dual-stack peers on the interface's subnet and ensures
successful subsequent peering using the appropriate (address family) successful subsequent peering using the appropriate (address family)
transport on a multi-access or broadcast interface. transport on a multi-access or broadcast interface.
5.1.1. Maintaining Hello Adjacencies 5.1.1. Maintaining Hello Adjacencies
In case of Dual-stack LDP enabled interface, the LSR SHOULD maintain In the case of a Dual-stack LDP-enabled interface, the LSR SHOULD
link Hello adjacencies for both IPv4 and IPv6 address families. This maintain Link Hello adjacencies for both IPv4 and IPv6 address
document, however, allows an LSR to maintain Rx-side Link Hello families. This document, however, allows an LSR to maintain
adjacency only for the address family that has been used for the Receive-side Link Hello adjacencies only for the address family that
establishment of the LDP session (whether LDPoIPv4 or LDPoIPv6 has been used for the establishment of the LDP session (whether an
session). LDPoIPv4 or LDPoIPv6 session).
5.2. Extended Discovery Mechanism 5.2. Extended Discovery Mechanism
The extended discovery mechanism (defined in section 2.4.2 of The Extended Discovery mechanism (defined in Section 2.4.2 of
[RFC5036]), in which the targeted LDP Hellos are sent to a unicast [RFC5036]), in which the targeted LDP Hellos are sent to a unicast
IPv6 address destination, requires only one IPv6 specific IPv6 address destination, requires only one IPv6-specific
consideration: the link-local IPv6 addresses MUST NOT be used as the consideration: the link-local IPv6 addresses MUST NOT be used as the
targeted LDP hello packet's source or destination addresses. targeted LDP Hello packet's source or destination addresses.
6. LDP Session Establishment and Maintenance 6. LDP Session Establishment and Maintenance
Section 2.5.1 of [RFC5036] defines a two-step process for LDP Section 2.5.1 of [RFC5036] defines a two-step process for LDP session
session establishment, once the neighbor discovery has completed establishment, once the neighbor discovery has completed (i.e., LDP
(i.e. LDP Hellos have been exchanged): Hellos have been exchanged):
1. Transport connection establishment 1. Transport connection establishment
2. Session initialization
The forthcoming sub-section 6.1 discusses the LDP consideration for 2. Session initialization
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.
6.1. Transport connection establishment Section 6.1 discusses the LDP considerations for IPv6 and/or
Dual-stacking in the context of session establishment, whereas
Section 6.2 discusses the LDP considerations for IPv6 and/or
Dual-stacking in the context of session maintenance.
Section 2.5.2 of [RFC5036] specifies the use of an optional 6.1. Transport Connection Establishment
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: Section 2.5.2 of [RFC5036] specifies the use of a Transport Address
optional object (TLV) in LDP Hello messages to convey the transport
(IP) address; however, it does not specify the behavior of LDP if
both IPv4 and IPv6 Transport Address objects (TLVs) 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 session establishment.
1. An LSR MUST NOT send a Hello message containing both IPv4 and This document specifies the following:
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 1. An LSR MUST NOT send a Hello message containing both IPv4 and IPv6
and IPv6 transport address optional objects, but MUST use only Transport Address optional objects. In other words, there MUST be
the transport address whose address family is the same as that at most one Transport Address optional object in a Hello message.
of the IP packet carrying the Hello message. An LSR SHOULD An LSR MUST include only the transport address whose address
accept only the first transport object for a given address family is the same as that of the IP packet carrying the Hello
family in the received Hello message, and ignore the rest, if message.
the LSR receives more than one transport object for a given
address family.
3. An LSR MUST send separate Hello messages (each containing 2. An LSR SHOULD accept the Hello message that contains both IPv4 and
either IPv4 or IPv6 transport address optional object) for each IPv6 Transport Address optional objects but MUST use only the
IP address family, if Dual-stack LDP is enabled (for an transport address whose address family is the same as that of the
interface or neighbor). IP packet carrying the Hello message. An LSR SHOULD accept only
the first Transport Address optional object for a given address
family in the received Hello message and ignore the rest if the
LSR receives more than one Transport Address optional object for a
given address family.
4. An LSR MUST use a global unicast IPv6 address in IPv6 transport 3. An LSR MUST send separate Hello messages (each containing either
address optional object of outgoing targeted Hellos, and check an IPv4 or IPv6 Transport Address optional object) for each IP
for the same in incoming targeted hellos (i.e. MUST discard the address family if Dual-stack LDP is enabled (for an interface or
targeted hello, if it failed the check). neighbor).
5. An LSR MUST prefer using a global unicast IPv6 address in IPv6 4. An LSR MUST use a global unicast IPv6 address in an IPv6 Transport
transport address optional object of outgoing Link Hellos, if Address optional object of outgoing targeted Hellos and check for
it had to choose between global unicast IPv6 address and the same in incoming targeted Hellos (i.e., MUST discard the
unique-local or link-local IPv6 address. targeted Hello if it failed the check).
6. A Single-stack LSR MUST establish either LDPoIPv4 or LDPoIPv6 5. An LSR MUST prefer using a global unicast IPv6 address in an
session with a remote LSR as per the enabled address-family. IPv6 Transport Address optional object of outgoing Link Hellos if
it had to choose between a global unicast IPv6 address and a
unique-local or link-local IPv6 address.
7. A Dual-stack LSR MUST NOT initiate (or accept the request for) 6. A Single-stack LSR MUST establish either an LDPoIPv4 or LDPoIPv6
a TCP connection for a new LDP session with a remote LSR, if session with a remote LSR as per the enabled address family.
they already have an LDPoIPv4 or LDPoIPv6 session (for the same
LDP Identifier) established.
This means that only one transport connection is established 7. A Dual-stack LSR MUST NOT initiate or accept the request for a TCP
regardless of IPv6 or/and IPv4 Hello adjacencies presence connection for a new LDP session with a remote LSR if it already
between two LSRs. has an LDPoIPv4 or LDPoIPv6 session for the same LDP Identifier
established with that remote LSR.
8. A Dual-stack LSR SHOULD prefer establishing an LDPoIPv6 session This means that only one transport connection is established,
(instead of LDPoIPv4 session) with a remote Dual-stack LSR by regardless of IPv6 and/or IPv4 Hello adjacencies present between
following the 'transport connection role' determination logic two LSRs.
in section 6.1.1.
Additionally, to ensure the above preference in case of Dual- 8. A Dual-stack LSR SHOULD prefer establishing an LDPoIPv6 session
stack LDP being enabled on an interface, it would be desirable (instead of an LDPoIPv4 session) with a remote Dual-stack LSR by
that IPv6 LDP Link Hellos are transmitted before IPv4 LDP Link following the 'transport connection role' determination logic in
Hellos, particularly when an interface is coming into service Section 6.1.1.
or being reconfigured.
6.1.1. Determining Transport connection Roles Additionally, to ensure the above preference in the case where
Dual-stack LDP is 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. Dual-Stack: Transport Connection Preference and Role of an LSR
Section 2.5.2 of [RFC5036] specifies the rules for determining Section 2.5.2 of [RFC5036] specifies the rules for determining
active/passive roles in setting up TCP connection. These rules are active/passive roles in setting up a TCP connection. These rules are
clear for a Single-stack LDP, but not for a Dual-stack LDP, in which clear for Single-stack LDP but not for Dual-stack LDP, in which an
an LSR may assume different roles for different address families, LSR may assume different roles for different address families,
causing LDP session to not get established. causing the LDP session to not get established.
To ensure deterministic transport connection (active/passive) role To ensure a deterministic transport connection (active/passive) role
in case of Dual-stack LDP, this document specifies that the Dual- in the case of Dual-stack LDP, this document specifies that the
stack LSR conveys its transport connection preference in every LDP Dual-stack LSR conveys its transport connection preference in every
Hello message. This preference is encoded in a new TLV, named Dual- LDP Hello message. This preference is encoded in a new TLV, named
stack capability TLV, as defined below: the "Dual-Stack capability" TLV, as defined below:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| Dual-stack capability | Length | |1|0| Dual-Stack capability | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TR | Reserved | MBZ | |TR | Reserved | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 Dual-stack capability TLV Figure 5: Dual-Stack Capability TLV
Where: Where:
U and F bits: 1 and 0 (as specified by RFC5036) U and F bits: 1 and 0 (as specified by [RFC5036])
Dual-stack capability: TLV code point (to be assigned by IANA). Dual-Stack capability: TLV code point (Ox0701)
TR, Transport Connection Preference. TR: Transport Connection Preference
This document defines the following 2 values: This document defines the following two values:
0100: LDPoIPv4 connection 0100: LDPoIPv4 connection
0110: LDPoIPv6 connection (default) 0110: LDPoIPv6 connection (default)
Reserved Reserved
This field is reserved. It MUST be set to zero on This field is reserved. It MUST be set to zero on
transmission and ignored on receipt. transmission and ignored on receipt.
A Dual-stack LSR (i.e. LSR supporting Dual-stack LDP for a peer) A Dual-stack LSR (i.e., an LSR supporting Dual-stack LDP for a peer)
MUST include "Dual-stack capability" TLV in all of its LDP Hellos, MUST include the Dual-Stack capability TLV in all of its LDP Hellos
and MUST set the "TR" field to announce its preference for either and MUST set the "TR" field to announce its preference for either an
LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default
preference is LDPoIPv6. preference is LDPoIPv6.
A Dual-stack LSR MUST always check for the presence of "Dual-stack A Dual-stack LSR MUST always check for the presence of the Dual-Stack
capability" TLV in the received hello messages, and take appropriate capability TLV in the received Hello messages and take appropriate
actions as follows: action, as follows:
1. If "Dual-stack capability" TLV is present and remote preference 1. If the Dual-Stack capability TLV is present and the remote
does not match with the local preference (or does not get preference does not match the local preference (or does not get
recognized), then the LSR MUST discard the hello message and recognized), then the LSR MUST discard the Hello message and log
log an error. an error.
If LDP session was already in place, then LSR MUST send a fatal If an LDP session was already in place, then the LSR MUST send a
Notification message with status code [Transport Connection fatal Notification message with status code of 'Transport
mismatch, IANA allocation TBD] and reset the session. Connection Mismatch' (0x00000032) and reset the session.
2. If "Dual-stack capability" TLV is present, and remote 2. If the Dual-Stack capability TLV is present and the remote
preference matches with the local preference, then: preference matches the local preference, then:
a) If TR=0100 (LDPoIPv4), then determine the active/passive a) If TR=0100 (LDPoIPv4), then determine the active/passive roles
roles for TCP connection using IPv4 transport address as for the TCP connection using an IPv4 transport address as
defined in section 2.5.2 of RFC 5036. defined in Section 2.5.2 of RFC 5036.
b) If TR=0110 (LDPoIPv6), then determine the active/passive b) If TR=0110 (LDPoIPv6), then determine the active/passive roles
roles for TCP connection by using IPv6 transport address for the TCP connection by using an IPv6 transport address as
as defined in section 2.5.2 of RFC 5036. defined in Section 2.5.2 of RFC 5036.
3. If "Dual-stack capability" TLV is NOT present, and 3. If the Dual-Stack capability TLV is NOT present and
a) Only IPv4 hellos are received, then the neighbor is deemed a) only IPv4 Hellos are received, then the neighbor is deemed as a
as a legacy IPv4-only LSR (supporting Single-stack LDP), legacy IPv4-only LSR (supporting Single-stack LDP); hence, an
hence, an LDPoIPv4 session SHOULD be established (similar LDPoIPv4 session SHOULD be established (similar to that of 2a
to that of 2a above). above).
However, if IPv6 hellos are also received at any time However, if IPv6 Hellos are also received at any time during
during the life of session from that neighbor, then the the life of the session from that neighbor, then the neighbor
neighbor is deemed as a non-compliant Dual-stack LSR is deemed as a noncompliant Dual-stack LSR (similar to that of
(similar to that of 3c below), resulting in any 3c below), resulting in any established LDPoIPv4 session being
established LDPoIPv4 session being reset and a fatal reset and a fatal Notification message being sent (with status
Notification message being sent (with status code of code of 'Dual-Stack Noncompliance', 0x00000033).
'Dual-Stack Non-Compliance', IANA allocation TBD).
b) Only IPv6 hellos are received, then the neighbor is deemed b) only IPv6 Hellos are received, then the neighbor is deemed as
as an IPv6-only LSR (supporting Single-stack LDP) and an IPv6-only LSR (supporting Single-stack LDP) and an LDPoIPv6
LDPoIPv6 session SHOULD be established (similar to that of session SHOULD be established (similar to that of 2b above).
2b above).
However, if IPv4 hellos are also received at any time However, if IPv4 Hellos are also received at any time during
during the life of session from that neighbor, then the the life of the session from that neighbor, then the neighbor
neighbor is deemed as a non-compliant Dual-stack LSR is deemed as a noncompliant Dual-stack LSR (similar to that of
(similar to that of 3c below), resulting in any 3c below), resulting in any established LDPoIPv6 session being
established LDPoIPv6 session being reset and a fatal reset and a fatal Notification message being sent (with status
Notification message being sent (with status code of code of 'Dual-Stack Noncompliance', 0x00000033).
'Dual-Stack Non-Compliance', IANA allocation TBD).
c) Both IPv4 and IPv6 hellos are received, then the neighbor c) both IPv4 and IPv6 Hellos are received, then the neighbor is
is deemed as a non-compliant Dual-stack neighbor, and is deemed as a noncompliant Dual-stack neighbor and is not allowed
not allowed to have any LDP session. A Notification to have any LDP session. A Notification message should be sent
message should be sent (with status code of 'Dual-Stack (with status code of 'Dual-Stack Noncompliance', 0x00000033).
Non-Compliance', IANA allocation TBD).
A Dual-stack LSR MUST convey the same transport connection A Dual-stack LSR MUST convey the same transport connection preference
preference ("TR" field value) in all (link and targeted) Hellos that ("TR" field value) in all (link and targeted) Hellos that advertise
advertise the same label space to the same peer and/or on same the same label space to the same peer and/or on the same interface.
interface. This ensures that two LSRs linked by multiple Hello This ensures that two LSRs linked by multiple Hello adjacencies using
adjacencies using the same label spaces play the same connection the same label spaces play the same connection establishment role for
establishment role for each adjacency. each adjacency.
A Dual-stack LSR MUST follow section 2.5.5 of RFC5036 and check for 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 matching Hello messages from the peer (either all Hellos also include
include the Dual-stack capability (with same TR value) or none do). the Dual-Stack capability (with the same TR value) or none do).
A Single-stack LSR do not need to use the Dual-stack capability in A Single-stack LSR does not need to use the Dual-Stack capability in
hello messages and SHOULD ignore this capability, if received. Hello messages and SHOULD ignore this capability if received.
An implementation may provide an option to favor one AFI (IPv4, say) An implementation may provide an option to favor one AFI (say, IPv4)
over another AFI (IPv6, say) for the TCP transport connection, so as over another AFI (say, IPv6) for the TCP transport connection, so as
to use the favored IP version for the LDP session, and force to use the favored IP version for the LDP session and force
deterministic active/passive roles. deterministic active/passive roles.
Note - An alternative to this new Capability TLV could be a new Flag 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 value in an LDP Hello message; however, it would be used even in
Single-stack IPv6 LDP networks and linger on forever, even though Single-stack IPv6 LDP networks and linger on forever, even though
Dual-stack will not. Hence, this alternative is discarded. Dual-stack will not. Hence, the idea of this alternative has been
discarded.
6.2. LDP Sessions Maintenance 6.2. LDP Session Maintenance
This document specifies that two LSRs maintain a single LDP session This document specifies that two LSRs maintain a single LDP session,
regardless of number of Link or Targeted Hello adjacencies between regardless of the number of Link or targeted Hello adjacencies
them, as described in section 6.1. This is independent of whether: 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 - they are connected via a Dual-stack LDP-enabled interface(s) or via
via two (or more) Single-stack LDP enabled interfaces; 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 - a Single-stack LDP-enabled interface is converted to a Dual-stack
(e.g. due to Dual-stack LDP enabled interfaces being converted into LDP-enabled interface (see Figure 1) on either LSR;
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 - an additional Single-stack or Dual-stack LDP-enabled interface is
for the corresponding transport, hello adjacency expiry, preference added or removed between two LSRs (see Figure 2).
mismatch etc.), then the LSRs SHOULD initiate establishing a new LDP
session as per the procedures described in section 6.1 of this
document.
7. Binding Distribution If the last Hello adjacency for a given address family goes down
(e.g., due to Dual-stack LDP-enabled interfaces being converted into
Single-stack LDP-enabled interfaces on one LSR) 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 the establishment of a
new LDP session as per the procedures described in Section 6.1 of
this document.
7. Binding Distribution
LSRs by definition can be enabled for Dual-stack LDP globally and/or 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 per peer so as to exchange the address and label bindings for both
IPv4 and IPv6 address-families, independent of LDPoIPv4 or LDPoIPV6 IPv4 and IPv6 address families, independent of any LDPoIPv4 or
session between them. LDPoIPv6 session between them.
However, there might be some legacy LSRs that are fully RFC 5036 However, there might be some legacy LSRs that are fully compliant
compliant for IPv4, but non-compliant for IPv6 (say, section 3.5.5.1 with RFC 5036 for IPv4 but are noncompliant for IPv6 (for example,
of RFC 5036), causing them to reset the session upon receiving IPv6 see Section 3.5.5.1 of RFC 5036), causing them to reset the session
address bindings or IPv6 FEC (Prefix) label bindings from a peer upon receiving IPv6 address bindings or IPv6 FEC (Prefix) label
compliant with this document. This is somewhat undesirable, as bindings from a peer compliant with this document. This is somewhat
clarified further Appendix A.1 and A.2. undesirable, as clarified further in Appendices A.1 and A.2.
To help maintain backward compatibility (i.e. accommodate IPv4-only To help maintain backward compatibility (i.e., accommodate IPv4-only
LDP implementations that may not be compliant with RFC 5036 section LDP implementations that may not be compliant with RFC 5036,
3.5.5.1), this specification requires that an LSR MUST NOT send any Section 3.5.5.1), this specification requires that an LSR MUST NOT
IPv6 bindings to a peer if peer has been determined as a legacy LSR. send any IPv6 bindings to a peer if the peer has been determined to
be a legacy LSR.
The 'Dual-stack capability' TLV, which is defined in section 6.1.1, The Dual-Stack capability TLV, which is defined in Section 6.1.1, is
is also used to determine if a peer is a legacy (IPv4-only Single- also used to determine whether or not a peer is a legacy (IPv4-only
stack) LSR or not. Single-stack) LSR.
7.1. Address Distribution 7.1. Address Distribution
An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6 An LSR MUST NOT advertise (via an Address message) any IPv4-mapped
addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such IPv6 addresses (as defined in Section 2.5.5.2 of [RFC4291]) and MUST
addresses, if ever received. Please see Appendix A.3. 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 If an LSR is enabled with Single-stack LDP for any peer, then it MUST
MUST advertise (via ADDRESS message) its local IP addresses as per advertise (via an Address message) its local IP addresses as per the
the enabled address family to that peer, and process received enabled address family to that peer and process received Address
Address messages containing IP addresses as per the enabled address messages containing IP addresses as per the enabled address family
family from that peer. from that peer.
If an LSR is enabled with Dual-stack LDP for a peer and 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 1. does not find the Dual-Stack capability TLV in the incoming IPv4
incoming IPv4 LDP hello messages from that peer, then the LSR LDP Hello messages from that peer, then the LSR MUST NOT advertise
MUST NOT advertise its local IPv6 Addresses to the peer. its local IPv6 addresses to the peer.
2. Is able to find the Dual-stack capability in the incoming IPv4 2. finds the Dual-Stack capability TLV in the incoming IPv4 (or IPv6)
(or IPv6) LDP Hello messages from that peer, then it MUST LDP Hello messages from that peer, then it MUST advertise (via an
advertise (via ADDRESS message) its local IPv4 and IPv6 Address message) its local IPv4 and IPv6 addresses to that peer.
addresses to that peer.
3. Is NOT able to find the Dual-stack capability in the incoming 3. does not find the Dual-Stack capability TLV in the incoming IPv6
IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS LDP Hello messages, then it MUST advertise (via an Address
message) only its local IPv6 addresses to that peer. message) only its local IPv6 addresses to that peer.
This last point helps to maintain forward compatibility (no This last point helps to maintain forward compatibility (no need
need to require this TLV in case of IPv6 Single-stack LDP). to require this TLV in the case of IPv6 Single-stack LDP).
7.2. Label Distribution 7.2. Label Distribution
An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings An LSR MUST NOT allocate and MUST NOT advertise FEC-label bindings
for link-local or IPv4-mapped IPv6 addresses (defined in section for link-local or IPv4-mapped IPv6 addresses (defined in
2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received. Section 2.5.5.2 of [RFC4291]), and it MUST ignore such bindings if
Please see Appendix A.3. ever received. Please see Appendix A.3.
If an LSR is enabled with Single-stack LDP for any peer, then it If an LSR is enabled with Single-stack LDP for any peer, then it MUST
MUST advertise (via Label Mapping message) FEC-Label bindings for advertise (via a Label Mapping message) FEC-label bindings for the
the enabled address family to that peer, and process received FEC- enabled address family to that peer and process received FEC-label
Label bindings for the enabled address family from that peer. bindings for the enabled address family from that peer.
If an LSR is enabled with Dual-stack LDP for a peer and 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 1. does not find the Dual-Stack capability TLV in the incoming IPv4
incoming IPv4 LDP hello messages from that peer, then the LSR LDP Hello messages from that peer, then the LSR MUST NOT advertise
MUST NOT advertise IPv6 FEC-label bindings to the peer (even if IPv6 FEC-label bindings to the peer (even if IP capability
IP capability negotiation for IPv6 address family was done). negotiation for the IPv6 address family was done).
2. Is able to find the Dual-stack capability in the incoming IPv4 2. finds the Dual-Stack capability TLV in the incoming IPv4 (or IPv6)
(or IPv6) LDP Hello messages from that peer, then it MUST LDP Hello messages from that peer, then it MUST advertise
advertise FEC-Label bindings for both IPv4 and IPv6 address FEC-label bindings for both IPv4 and IPv6 address families to that
families to that peer. peer.
3. Is NOT able to find the Dual-stack capability in the incoming 3. does not find the Dual-Stack capability TLV in the incoming IPv6
IPv6 LDP Hello messages, then it MUST advertise FEC-Label LDP Hello messages, then it MUST advertise FEC-label bindings for
bindings for IPv6 address families to that peer. IPv6 address families to that peer.
This last point helps to maintain forward compatibility (no This last point helps to maintain forward compatibility (no need
need to require this TLV for IPv6 Single-stack LDP). to require this TLV for IPv6 Single-stack LDP).
An LSR MAY further constrain the advertisement of FEC-label bindings An LSR MAY further constrain the advertisement of FEC-label bindings
for a particular address family by negotiating the IP Capability for for a particular address family by negotiating the IP capability for
a given address family, as specified in [IPPWCap] document. This a given address family, as specified in [RFC7473]. This allows an
allows an LSR pair to neither advertise nor receive the undesired LSR pair to neither advertise nor receive the undesired FEC-label
FEC-label bindings on a per address family basis to a peer. bindings on a per-address-family basis to a peer.
If an LSR is configured to change an interface or peer from Single- If an LSR is configured to change an interface or peer from
stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard Single-stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed
FEC procedures [RFC5918] to request the label bindings for the Wildcard FEC procedures [RFC5918] to request the label bindings for
enabled address family. This helps to relearn the label bindings the enabled address family. This helps to relearn the label bindings
that may have been discarded before without resetting the session. that may have been discarded before, without resetting the session.
8. LDP Identifiers and Duplicate Next Hop Addresses 8. LDP Identifiers and Duplicate Next-Hop Addresses
RFC5036 section 2.7 specifies the logic for mapping the IP routing RFC 5036, 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 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 label entry for that FEC. The logic involves using the IP routing
next-hop address as an index into the (peer Address) database (which next-hop address as an index into the (peer address) database (which
is populated by the Address message containing mapping between each is populated by the Address message containing a mapping between each
peer's local addresses and its LDP Identifier) to determine the LDP peer's local addresses and its LDP Identifier) to determine the LDP
peer. peer.
However, this logic is insufficient to deal with duplicate IPv6 However, this logic is insufficient to deal with duplicate IPv6
(link-local) next-hop addresses used by two or more peers. The (link-local) next-hop addresses used by two or more peers. The
reason is that all interior IPv6 routing protocols (can) use link- reason is that all interior IPv6 routing protocols (can) use
local IPv6 addresses as the IP routing next-hops, and 'IPv6 link-local IPv6 addresses as the IP routing next hops, and
Addressing Architecture [RFC4291]' allows a link-local IPv6 address "IP Version 6 Addressing Architecture" [RFC4291] allows a link-local
to be used on more than one links. IPv6 address to be used on more than one link.
Hence, this logic is extended by this specification to use not only 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 the IP routing next-hop address but also the IP routing next-hop
interface to uniquely determine the LDP peer(s). The 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-based LDP peer mapping is to be done through the LDP peer
address database (populated by Address messages received from the address database (populated by Address messages received from the LDP
LDP peers), whereas next-hop interface-based LDP peer mapping is to peers), whereas next-hop interface-based LDP peer mapping is to be
be done through LDP hello adjacency/interface database (populated by done through the LDP Hello adjacency/interface database (populated by
hello messages received from the LDP peers). Hello messages received from the LDP peers).
This extension solves the problem of two or more peers using the This extension solves the problem of two or more peers using the same
same link-local IPv6 address (in other words, duplicate peer link-local IPv6 address (in other words, duplicate peer addresses) as
addresses) as the IP routing next-hops. the IP routing next hops.
Lastly, for better scale and optimization, an LSR may advertise only Lastly, for better scale and optimization, an LSR may advertise only
the link-local IPv6 addresses in the Address message, assuming that the link-local IPv6 addresses in the Address message, assuming that
the peer uses only the link-local IPv6 addresses as static and/or the peer uses only the link-local IPv6 addresses as static and/or
dynamic IP routing next-hops. dynamic IP routing next hops.
9. LDP TTL Security 9. LDP TTL Security
This document recommends enabling Generalized TTL Security Mechanism This document mandates the use of the Generalized TTL Security
(GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport Mechanism (GTSM) [RFC6720] for LDP Link Hello packets over IPv6 (see
connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended Section 5.1).
to automatically protect IPv6 LDP peering session from off-link
attacks.
[RFC6720] allows for the implementation to statically This document further recommends enabling GTSM for the LDP/TCP
(configuration) and/or dynamically override the default behavior transport connection over IPv6 (i.e., LDPoIPv6). This GTSM inclusion
(enable/disable GTSM) on a per-peer basis. Such a configuration an is intended to automatically protect IPv6 LDP peering sessions from
option could be set on either LSR (since GTSM negotiation would off-link attacks.
ultimately disable GTSM between LSR and its peer(s)).
LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, [RFC6720] allows for the implementation to statically (via
and be checked for the same upon receipt before any further configuration) and/or dynamically override the default behavior
processing, as per section 3 of [RFC5082]. (enable/disable GTSM) on a per-peer basis. Such an option could be
set on either LSR in a peering session (since GTSM negotiation would
ultimately disable GTSM between the LSR and its peer(s)).
10. IANA Considerations 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 This document defines a new optional parameter for the LDP Hello
Message and two new status codes for the LDP Notification Message. message and two new status codes for the LDP Notification message.
The 'Dual-Stack capability' parameter requires a code point from the The "Dual-Stack capability" parameter has been assigned a code point
TLV Type Name Space. IANA is requested to allocated a code point (0x0701) from the "TLV Type Name Space" registry. IANA has allocated
from the IETF Consensus range 0x0700-0x07ff for the 'Dual-Stack this code point from the IETF Consensus range 0x0700-0x07ff for the
capability' TLV. Dual-Stack capability TLV.
The 'Transport Connection Mismatch' status code requires a code The 'Transport Connection Mismatch' status code has been assigned a
point from the Status Code Name Space. IANA is requested to allocate code point (0x00000032) from the "Status Code Name Space" registry.
a code point from the IETF Consensus range and mark the E bit column IANA has allocated this code point from the IETF Consensus range and
with a '1'. marked the E bit column with a '1'.
The 'Dual-Stack Non-Compliance' status code requires a code point The 'Dual-Stack Noncompliance' status code has been assigned a code
from the Status Code Name Space. IANA is requested to allocate a point (0x00000033) from the "Status Code Name Space" registry. IANA
code point from the IETF Consensus range and mark the E bit column has allocated this code point from the IETF Consensus range and
with a '1'. marked the E bit column with a '1'.
11. Security Considerations 11. Security Considerations
The extensions defined in this document only clarify the behavior of The extensions defined in this document only clarify the behavior of
LDP, they do not define any new protocol procedures. Hence, this LDP; they do not define any new protocol procedures. Hence, this
document does not add any new security issues to LDP. document does not add any new security issues to LDP.
While the security issues relevant for the [RFC5036] are relevant While the security issues relevant for [RFC5036] are relevant for
for this document as well, this document reduces the chances of off- this document as well, this document reduces the chances of off-link
link attacks when using IPv6 transport connection by including the attacks when using an IPv6 transport connection by including the use
use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL of GTSM procedures [RFC5082]. Please see Section 9 for LDP TTL
Security details. Security details.
Moreover, this document allows the use of IPsec [RFC4301] for IPv6 Moreover, this document allows the use of IPsec [RFC4301] for IPv6
protection, hence, LDP can benefit from the additional security as protection; hence, LDP can benefit from the additional security as
specified in [RFC7321] as well as [RFC5920]. specified in [RFC7321] as well as [RFC5920].
12. Acknowledgments 12. References
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 12.1. Normative References
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. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
13. Additional Contributors [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291,
February 2006, <http://www.rfc-editor.org/info/rfc4291>.
The following individuals contributed to this document: [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <http://www.rfc-editor.org/info/rfc5036>.
Kamran Raza [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Cisco Systems, Inc. Pignataro, "The Generalized TTL Security Mechanism
2000 Innovation Drive (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
Kanata, ON K2K-3E8, Canada <http://www.rfc-editor.org/info/rfc5082>.
Email: skraza@cisco.com
Nagendra Kumar
Cisco Systems, Inc.
SEZ Unit, Cessna Business Park,
Bangalore, KT, India
Email: naikumar@cisco.com
Andre Pelletier [RFC5918] Asati, R., Minei, I., and B. Thomas, "Label Distribution
Cisco Systems, Inc. Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
2000 Innovation Drive (FEC)", RFC 5918, DOI 10.17487/RFC5918, August 2010,
Kanata, ON K2K-3E8, Canada <http://www.rfc-editor.org/info/rfc5918>.
Email: apelleti@cisco.com
14. References 12.2. Informative References
14.1. Normative References [RFC4038] Shin, M-K., Ed., Hong, Y-G., Hagino, J., Savola, P., and
E. Castro, "Application Aspects of IPv6 Transition",
RFC 4038, DOI 10.17487/RFC4038, March 2005,
<http://www.rfc-editor.org/info/rfc4038>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Requirement Levels", BCP 14, RFC 2119, March 1997. Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
(IPv6) Addressing Architecture", RFC 4291, February 2006. for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>.
[RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Specification", RFC 5036, October 2007. Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
[RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and [RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
Savola, P., "The Generalized TTL Security Mechanism Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
(GTSM)", RFC 5082, October 2007. June 2011, <http://www.rfc-editor.org/info/rfc6286>.
[RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution [RFC6720] Pignataro, C. and R. Asati, "The Generalized TTL Security
Protocol (LDP) 'Typed Wildcard Forward Equivalence Class Mechanism (GTSM) for the Label Distribution Protocol
(FEC)", RFC 5918, October 2010. (LDP)", RFC 6720, DOI 10.17487/RFC6720, August 2012,
<http://www.rfc-editor.org/info/rfc6720>.
14.2. Informative References [RFC7321] McGrew, D. and P. Hoffman, "Cryptographic Algorithm
Implementation Requirements and Usage Guidance for
Encapsulating Security Payload (ESP) and Authentication
Header (AH)", RFC 7321, DOI 10.17487/RFC7321, August 2014,
<http://www.rfc-editor.org/info/rfc7321>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet [RFC7439] George, W., Ed., and C. Pignataro, Ed., "Gap Analysis for
Protocol", RFC 4301, December 2005. Operating IPv6-Only MPLS Networks", RFC 7439,
DOI 10.17487/RFC7439, January 2015,
<http://www.rfc-editor.org/info/rfc7439>.
[RFC7321] Manral, V., "Cryptographic Algorithm Implementation [RFC7473] Raza, K. and S. Boutros, "Controlling State Advertisements
Requirements for Encapsulating Security Payload (ESP) and of Non-negotiated LDP Applications", RFC 7473,
Authentication Header (AH)", RFC 7321, April 2007. DOI 10.17487/RFC7473, March 2015,
<http://www.rfc-editor.org/info/rfc7473>.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Appendix A. Additional Considerations
Networks", RFC 5920, July 2010.
[RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS A.1. LDPv6 and LDPv4 Interoperability Safety Net
Using IPv6 Provider Edge Routers (6PE)", RFC 4798,
February 2007.
[IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp- It is not safe to assume that implementations compliant with RFC 5036
ip-pw-capability, October 2014. have supported the handling of an IPv6 address family (IPv6
FEC-label) in a Label Mapping message all along.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF If a router upgraded per this specification advertised both IPv4 and
for IPv6", RFC 5340, July 2008. 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
FEC-labels), as per Section 3.4.1.1 of [RFC5036].
[RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP This would result in LDPv6 being somewhat undeployable in existing
Identifier for BGP-4", RFC 6286, June 2011. production networks.
[RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security Section 7 of this document provides a good safety net and makes LDPv6
Mechanism (GTSM) for the Label Distribution Protocol incrementally deployable without making any such assumption on the
(LDP)", RFC 6720, August 2012. routers' support for IPv6 FEC processing in current production
networks.
[RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M. A.2. Accommodating Implementations Not Compliant with RFC 5036
Castro, "Application Aspects of IPv6 Transition", RFC
4038, March 2005.
[RFC7439] W. George, and C. Pignataro, "Gap Analysis for Operating It is not safe to assume that implementations have been [RFC5036]
IPv6-Only MPLS Networks", RFC 7439, January 2015. compliant in gracefully handling an IPv6 address family (IPv6 Address
List TLV) in an Address message all along.
Appendix A. If a router upgraded per this specification advertised IPv6 addresses
(with or without IPv4 addresses) in an 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 may tear down the LDP
session.
A.1. LDPv6 and LDPv4 Interoperability Safety Net This would result in LDPv6 being somewhat undeployable in existing
production networks.
It is not safe to assume that RFC5036 compliant implementations have Sections 6 and 7 of this document provide a good safety net and make
supported handling IPv6 address family (IPv6 FEC label) in Label LDPv6 incrementally deployable without making any such assumption on
Mapping message all along. the routers' support for IPv6 FEC processing in current production
networks.
If a router upgraded with this specification advertised both IPv4 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP?
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 Per discussion with the 6MAN and V6OPS working groups, the
production networks. overwhelming consensus was to not promote IPv4-mapped IPv6 addresses
appearing in the routing table, as well as in LDP (address and label)
databases.
The change proposed in section 7 of this document provides a good Also, [RFC4038], Section 4.2 suggests that IPv4-mapped IPv6-addressed
safety net and makes LDPv6 incrementally deployable without making packets should never appear on the wire.
any such assumption on the routers' support for IPv6 FEC processing
in current production networks.
A.2. Accommodating Non-RFC5036-compliant implementations A.4. Why a 32-bit value even for the IPv6 LDP Router Id?
It is not safe to assume that implementations have been RFC5036 The first four octets of the LDP Identifier, the 32-bit LSR Id (i.e.,
compliant in gracefully handling IPv6 address family (IPv6 Address LDP router Id), identify the LSR and provide a globally unique value
List TLV) in Address message all along. within the MPLS network, regardless of the address family used for
the LDP session.
If a router upgraded with this specification advertised IPv6 Please note that the 32-bit LSR Id value would not map to any IPv4
addresses (with or without IPv4 addresses) in Address message, then address in an IPv6-only LSR (i.e., Single-stack), nor would there be
an IPv4-only peer (not knowing how to process such a message) may an expectation of it being IP routable or DNS resolvable. In IPv4
not follow section 3.5.5.1 of RFC5036, and tear down the LDP deployments, the LSR Id is typically derived from an IPv4 address,
session. 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 the BGP Identifier [RFC6286] and the OSPF router Id
[RFC5340].
This would result in LDPv6 to be somewhat undeployable in existing This document reserves 0.0.0.0 as the LSR Id and prohibits its usage
production networks. with IPv6, in line with the OSPF router Id in OSPF version 3
[RFC5340].
The changes proposed in section 6 and 7 of this document provides a Acknowledgments
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.3. Why prohibit IPv4-mapped IPv6 addresses in LDP We acknowledge the authors of [RFC5036], since some text in this
document is borrowed from [RFC5036].
Per discussion with 6MAN and V6OPS working groups, the overwhelming Thanks to Bob Thomas for providing critical feedback to improve this
consensus was to not promote IPv4-mapped IPv6 addresses appear in document early on.
the routing table, as well as in LDP (address and label) databases.
Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane
packets should never appear on the wire. 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 for
providing insightful comments and multiple improvements.
A.4. Why 32-bit value even for IPv6 LDP Router ID Contributors
The first four octets of the LDP identifier, the 32-bit LSR Id (e.g. The following individuals contributed to this document:
(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- Nagendra Kumar
address in an IPv6 only LSR (i.e., single stack), nor would there be Cisco Systems, Inc.
an expectation of it being IP routable, nor DNS-resolvable. In IPv4 7200 Kit Creek Road
deployments, the LSR Id is typically derived from an IPv4 address, Research Triangle Park, NC 27709, United States
generally assigned to a loopback interface. In IPv6 only EMail: naikumar@cisco.com
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 Andre Pelletier
usage with IPv6, in line with OSPF router Id in OSPF version 3 Cisco Systems, Inc.
[RFC5340]. 2000 Innovation Drive
Kanata, ON K2K-3E8, Canada
EMail: apelleti@cisco.com
Author's Addresses Authors' Addresses
Rajiv Asati Rajiv Asati
Cisco Systems, Inc. Cisco Systems, Inc.
7025 Kit Creek Road 7025 Kit Creek Road
Research Triangle Park, NC 27709-4987 Research Triangle Park, NC 27709-4987
Email: rajiva@cisco.com United States
Vishwas Manral EMail: rajiva@cisco.com
Hewlet-Packard, Inc.
19111 Pruneridge Ave., Cupertino, CA, 95014 Carlos Pignataro
Phone: 408-447-1497 Cisco Systems, Inc.
Email: vishwas@ionosnetworks.com 7200 Kit Creek Road
Research Triangle Park, NC 27709-4987
United States
EMail: cpignata@cisco.com
Kamran Raza Kamran Raza
Cisco Systems, Inc., Cisco Systems, Inc.
2000 Innovation Drive, 2000 Innovation Drive
Ottawa, ON K2K-3E8, Canada. Ottawa, ON K2K-3E8
E-mail: skraza@cisco.com Canada
EMail: skraza@cisco.com
Vishwas Manral
Ionos Networks
4100 Moorpark Ave., Ste. #122
San Jose, CA 95117
United States
Phone: +1 408 447 1497
EMail: vishwas@ionosnetworks.com
Rajiv Papneja Rajiv Papneja
Huawei Technologies Huawei Technologies
2330 Central Expressway 2330 Central Expressway
Santa Clara, CA 95050 Santa Clara, CA 95050
United States
Phone: +1 571 926 8593 Phone: +1 571 926 8593
EMail: rajiv.papneja@huawei.com
Carlos Pignataro EMail: rajiv.papneja@huawei.com
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709-4987
Email: cpignata@cisco.com
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