wdiff draft-ietf-mpls-ldp-ipv6-13.txt draft-ietf-mpls-ldp-ipv6-14.txt

MPLS Working Group Rajiv Asati
Internet Draft Cisco Carlos Pignataro
Updates: 5036 5036, 6720 (if approved) Kamran Raza
Intended status: Standards Track Vishwas Manral Cisco
Expires: January April 2015
Vishwas Manral
Hewlett-Packard, Inc. Inc

Rajiv Papneja
Huawei

Carlos Pignataro
Cisco

July 3,

October 2, 2014

Updates to LDP for IPv6
draft-ietf-mpls-ldp-ipv6-13
draft-ietf-mpls-ldp-ipv6-14

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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. 5036 and RFC 6720.

Table of Contents

1. Introduction...................................................3
1.1. Topology Scenarios for Dual-Stack Dual-stack Environment.............4
1.2. Single-hop vs. Multi-hop LDP Peering......................5
2. Specification Language.........................................6
3. LSP Mapping....................................................6 Mapping....................................................7
4. LDP Identifiers................................................7
5. Neighbor Discovery.............................................7 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........................9 establishment.......................10
6.1.1. Determining Transport connection Roles..............11
6.2. LDP Sessions Maintenance.................................13 Maintenance.................................14
7. Address Binding Distribution..........................................14
8.
7.1. Address Distribution.....................................15
7.2. Label Distribution............................................14
9. Distribution.......................................15

8. LDP Identifiers and Duplicate Next Hop Addresses..............15
10. Addresses..............16
9. LDP TTL Security.............................................16
11. Security..............................................17
10. IANA Considerations..........................................16
12. Considerations..........................................18
11. Security Considerations......................................16 Considerations......................................18
12. Acknowledgments..............................................19
13. Acknowledgments..............................................17
14. Additional Contributors......................................17
15. References...................................................18
15.1. Contributors......................................19
14. References...................................................20
14.1. Normative References....................................18
15.2. References....................................20
14.2. Informative References..................................18 References..................................20
Appendix A.......................................................20 A.......................................................22
A.1. LDPv6 and LDPv4 Interoperability Safety Net..............20 Net..............22
A.2. Accommodating Non-RFC5036-compliant implementations......22
A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........23
A.4. Why 32-bit value even for IPv6 LDP Router ID.............20
A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........20 ID.............23
Author's Addresses...............................................22 Addresses...............................................24

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)
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 (with or without IPv4
co-existence)

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 FEC-Address Address bindings over an LDP session

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).

Note that this document updates RFC5036 and RFC6720.

1.1. Topology Scenarios for Dual-Stack 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 Dual-stack LDP enabled
interfaces (figure 1), or one or more single-stack 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 Single-stack Interfaces
R1------------------R2---------------R3
IPv4 IPv6

Figure 3 LSRs connected via a single-stack Single-stack Interface

Note that the topology scenario illustrated in figure 1 also covers
the case of a single-stack Single-stack LDP enabled interface (IPv4, say) being
converted to a dual-stacked Dual-stacked LDP enabled interface by (by enabling IPv6
routing as well as IPv6
LDP, LDP), even though the IPv4 LDP 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- Single-
stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though
the IPv4
LDP 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.

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 session connection

LDPoIPv6 - LDP over IPv6 transport session 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.

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, it is reasonable to say IPv4 or IPv6 address
instead of /32 or /128 addresses as shown below in the updated rule:

"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). 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 on a dual-stack
LSR. families.

5. Neighbor Discovery

If an LSR Dual-stack LDP is enabled with dual-stack LDP (e.g. LDP enabled in both IPv6 and IPv4
address families), families) on an interface or for a targeted neighbor, then
the LSR MUST advertise transmit both IPv6 and IPv4 LDP Link (Link or targeted targeted)
Hellos and include the same LDP Identifier (assuming per-platform
label space usage) in them.

If an LSR Single-stack LDP is enabled with single-stack LDP (e.g. LDP enabled in either IPv6 or
IPv4 address family), then the LSR MUST advertise transmit either IPv6 or IPv4
LDP Link (Link or targeted 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 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.

More importantly, if an interface is a dual-stack Dual-stack LDP interface
(e.g. LDP enabled in both IPv6 and IPv4 address families), then the
LSR MUST periodically send 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 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.

An implementation MUST send transmit IPv6 LDP link Hellos before sending IPv4 LDP
Link Hellos on a dual-stack interface. Dual-stack interface, particularly during the
interface coming into service or configuration time.

5.1.1. Maintaining Hello Adjacencies

In case of dual-stack LDP interface (e.g. Dual-stack LDP enabled in both IPv6
and IPv4 address families), 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 (either IPv4 (whether LDPoIPv4 or IPv6). 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 pre-
configured (unicast) destination unicast
IPv6 address, 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 peer neighbor discovery has completed (LDP
(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 Dual-stacking in the context of session establishment,
whereas sub-section 6.2 discusses the LDP consideration for IPv6
and/or dual-stacking Dual-stacking in the context of session maintenance.

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 there were both IPv4 and IPv6 Hello
adjacencies. 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 address
family in the received Hello message, and ignore the rest, if
the LSR receives more than one transport object. 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 was enabled for both IP address
families. enabled.

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. An A Dual-stack LSR SHOULD MUST NOT create initiate (or honor accept the request for creating) for)
a TCP connection for a new LDP session with a remote LSR, if
they already have an LDP LDPoIPv4 or LDPoIPv6 session (for the same
LDP Identifier)
established over whatever IP version transport. established.

This means that only one transport connection is established
regardless of IPv6 or/and IPv4 Hello adjacencies presence
between two LSRs.

7. An A Dual-stack LSR SHOULD MUST prefer the LDP/TCP connection over IPv6 for a new
LDP establishing LDPoIPv6 session with
a remote LSR, if it is able to determine the
IPv6 presence (e.g. IPv6 Hello adjacency), LSR by following the 'transport connection role'
determination logic in section 6.1.1.

8. A Single-stack LSR MUST establish LDPoIPv4 or LDPoIPv6 session
with a remote LSR as per the enabled address-family.

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 (IPv4 or IPv6) Single-stack LDP, but not for a dual-
stack (IPv4 and IPv6) 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
for dual-stack LDP peering,
in case of Dual-stack LDP, this document specifies that the Dual-
stack LSR convey its transport connection preference in every LDP
Hello message. A new optional parameter, This preference is encoded as in a new TLV, named Dual-
stack capability TLV, (section 3.5.2
of RFC5036) is defined as follows (for Hello Message): 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| IPv4orIPv6 Preference Dual-stack capability | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TR | Reserved | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5 IPv4 or IPv6 Transport Preference Dual-stack capability TLV

Where:

U and F bits: 1 and 0 (as specified by RFC5036)

IPv4orIPv6 Preference:

Dual-stack capability: TLV code point for IPv4 or IPv6 Preference (to be assigned by IANA).

TR, Transport Preference

00: IPv4

01: IPv6 (default value) Connection Preference.

This document defines the following 2 values:

0100: LDPoIPv4 connection

0110: LDPoIPv6 connection

Reserved

This field is reserved. It MUST be set to zero on
transmission and ignored on receipt.

A dual-stack LDP enabled Dual-stack LSR (capable of supporting both IPv4 and
IPv6 transports for LDP) MUST include "IPv4orIPv6 Transport
Preference" optional parameter "Dual-stack capability" TLV in all of
its LDP Hellos, and MUST set the "TR" field to announce its
preference for either IPv4 LDPoIPv4 or
IPv6 LDPoIPv6 transport connection. The
default preference is IPv6. LDPoIPv6.

Upon receiving the hello message with this TLV, messages from the neighbor, a dual-stack capable
receiving Dual-stack
LSR MUST do check for the following: presence of "Dual-stack capability" TLV and
take appropriate actions as follows:

1. If it understands the TLV, "Dual-stack capability" TLV is present and if neighbor's remote preference
does not match with the local preference, then it discards the LSR MUST
discard the hello
(and no adjacency is formed) message and logs log an error.

If it understands 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 TLV, session.

2. If "Dual-stack capability" TLV is present, and if neighbor's remote
preference matches with the local preference, then:

a) If TR=0 (IPv4), 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.

b) If TR=1 (IPv6), TR=0110 (LDPoIPv6), then determine the active/passive
roles for TCP connection by comparing 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 Id part (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 from
that neighbor, then the LDP
Identifiers of LSRs.

The LSR with higher neighbor is deemed as a non-
compliant Dual-stack LSR Id MUST assume the active role (similar to that of 3c below),
resulting in any established LDPoIPv4 session being reset
and
other LSR MUST assume the passive role for the a fatal Notification message being sent (with status
code of 'Dual-Stack Non-Compliance', IANA allocation TBD).

b) Only IPv6 TCP
connection.

3. If it does not understand the TLV, hellos are received, then it MUST silently
discard this TLV and process the rest of the Hello message.

If neighbor is deemed
as an IPv6-only LSR receives (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 from
that neighbor, then the hello 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 without the "IPv4orIPv6
Transport Preference" TLV, being sent (with status
code of 'Dual-Stack Non-Compliance', IANA allocation TBD).

c) Both IPv4 and IPv6 hellos are received, then it MUST proceed with session
establishment using single-stack rules, the neighbor
is deemed as per section 2.5.2 of RFC
5036. a non-compliant Dual-stack neighbor, and is
not allowed to have any LDP session.

An LSR MUST convey the same transport connection preference ("TR"
field)
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.

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
Single-stack IPv6 scenarios LDP networks and linger on forever, even though dual-stack
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 Dual-stack LDP enabled interface(s) or
via two (or more) single-stack Single-stack LDP enabled interfaces;
- a single-stack Single-stack LDP enabled interface is converted to a dual-stack Dual-stack
LDP enabled interface (e.g. figure 1) on either LSR;
- an additional single-stack Single-stack or dual-stack Dual-stack LDP enabled interface is
added or removed between two LSRs (e.g. figure 2).

The procedures defined in section 6.1 SHOULD result in preferring
LDPoIPv6 setting up
the LDP session in preferred AFI only after the loss of an existing
LDP session (because of link failure, node failure, reboot etc.).

If the last hello adjacency for a given address family goes down
(e.g. due to dual-stack Dual-stack LDP enabled interfaces being converted into
a single-stack 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) SHOULD MUST be
reset. Otherwise, the LDP session SHOULD MUST stay intact.

If the LDP session is torn down for whatever reason (LDP disabled
for the corresponding transport, hello adjacency expiry 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.

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 compliant
with RFC 5036 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.
This is somewhat undesirable, as clarified further Appendix A.1 and
A.2.

To help maintain backward compatibility (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 dual-stack LDP (i.e. Dual-stack LDP for a peer and

1. Is NOT able to find the Dual-stack capability TLV in both the
incoming IPv4 and LDP hello messages from that peer, then the LSR
MUST NOT advertise its local IPv6 address families) for any (discovered or targeted) 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 by default, independent of peer.

3. Is NOT able to find the transport
connection (address family) used for Dual-stack capability in the incoming
IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS
message) only its local IPv6 addresses to that peering. peer.

The last point helps to maintain forward compatibility (no need
to require this TLV in case of IPv6 Single-stack LDP).

If an LSR, compliant with this specification, LSR is enabled with
single-stack Single-stack LDP (i.e. LDP in either IPv6 or IPv4 address family) for any (discovered or targeted) peer, then it
MUST advertise (via ADDRESS message) its local IP addresses as per
the enabled address
family by default, family, and SHOULD accept a received Address message messages
containing both IPv4 and IPv6 addresses.

8. IP addresses as per the enabled address family.

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.

Additionally, to ensure backward compatibility (and interoperability

If an LSR enabled with IPv4-only Dual-stack LDP implementations) in light of section 3.4.1.1 of
RFC5036, as rationalized for a peer and

1. Is NOT able to find the Dual-stack capability TLV in the Appendix section A.1 later, this
document specifies
incoming IPv4 LDP hello messages from that -

1. An peer, then the LSR
MUST NOT send a label mapping message with a FEC TLV
containing two or more Prefix FEC Elements of different advertise IPv6 FEC-label bindings 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 FEC-Label bindings for both IPv4 and IPv6 address
families. This means
families to that a FEC TLV in peer.

3. Is NOT able to find the label mapping
message must contain all Dual-stack capability in the Prefix FEC Elements belonging to incoming
IPv6 LDP Hello messages, then it MUST advertise FEC-Label
bindings for IPv6 address family or IPv4 address family, but not both. families to that peer.

The last point helps to maintain forward compatibility (no need
to require this TLV for IPv6 Single-stack LDP).

If an LSR is enabled with dual-stack Single-stack LDP (i.e. LDP in both IPv4 and
IPv6 address families) for any peer, then it
MUST advertise the FEC-
Label (via ADDRESS message) FEC-Label bindings for both IPv4 the
enabled address family, and IPv6 accept FEC-Label bindings for the
enabled address families to that peer.
However, an family.

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. basis to a peer.

If an LSR is configured to move change an interface or peer from single- Single-
stack (IPv6 or IPv4 address family) to dual-stack LDP (IPv6 and IPv4
address families), to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard
FEC procedures [RFC5918] to request the FEC-label label bindings for the
enabled address family. This helps to relearn the FEC-label label bindings
that may have been discarded before without resetting the peering.

9. 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.

10.

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. Suffice to say that such
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].

11.

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 type 'Dual-Stack capability' parameter requires a code needs point from the
TLV Type Name Space. [RFC5036] partitions the TLV Type Name Space
into 3 regions: IETF Consensus region, First Come First Served
region, and Private Use region. The authors recommend that a code
point from the IETF Consensus range be assigned to the 'Dual-Stack
capability' TLV.

The 'Transport Connection Mismatch' status code requires a code
point from the Status Code Name Space. [RFC5036] partitions the
Status Code Name Space into 3 regions: IETF Consensus region, First
Come First Served region, and Private Use region. The authors
recommend that a code point from the IETF Consensus range be
assigned by IANA.

12. to the 'Transport Connection Mismatch ' status code.

The 'Dual-Stack Non-Compliance' status code requires a code point
from the Status Code Name Space. [RFC5036] partitions the Status
Code Name Space into 3 regions: IETF Consensus region, First Come
First Served region, and Private Use region. The authors recommend
that a code point from the IETF Consensus range be assigned to the
'Dual-Stack Non-Compliance' status code.

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.

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 [RFC4835] [RFC7321] as well as [RFC5920].

13.

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.

14.

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

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

15.

14. References

15.1.

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.

15.2.

14.2. Informative References

[RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet
Protocol", RFC 4301, December 2005.

[RFC4835]

[RFC7321] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, 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, June 2011.

[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.

[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.

Appendix A.

A.1. LDPv6 and LDPv4 Interoperability Safety Net

It is naive not safe to assume that RFC5036 compliant implementations have
supported handling IPv6 address family (IPv6 FEC processing, in particular) label) in label advertisement Label
Mapping message all along. And if that assumption turned out
to be not true,

If a router upgraded with this specification advertised both IPv4
and IPv6 FECs in the same label mapping message, then section 3.4.1.1 of RFC5036 would cause LSRs 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 8 of this document provides a good
safety net and generate 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
error. 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 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.

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].

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.

Author's Addresses

Vishwas Manral
Hewlet-Packard, Inc.
19111 Pruneridge Ave., Cupertino, CA, 95014
Phone: 408-447-1497
Email: vishwas.manral@hp.com

Rajiv Papneja
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
Phone: +1 571 926 8593
EMail: rajiv.papneja@huawei.com

Rajiv Asati
Cisco Systems, Inc.
7025 Kit Creek Road
Research Triangle Park, NC 27709-4987
Email: rajiva@cisco.com

Carlos Pignataro
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709-4987
Email: cpignata@cisco.com