MPLS Working Group Vishwas Manral
Internet Draft IPInfusion Inc.
Intended status: Standards Track
Expires: May 2011 Rajiv Papneja
Isocore
Rajiv Asati
Cisco Systems
November 8, 2010
Updates to LDP for IPv6
draft-ietf-mpls-ldp-ipv6-00
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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.
Table of Contents
1. Introduction...................................................3
2. Specification Language.........................................3
3. LSP Mapping....................................................4
4. LDP Identifiers................................................4
5. Peer Discovery.................................................5
5.1. Basic Discovery Mechanism.................................5
5.2. Extended Discovery Mechanism..............................5
6. LDP Session Establishment......................................6
6.1. Transport connection establishment........................6
6.2. Session initialization....................................7
7. IANA Considerations............................................7
8. Security Considerations........................................7
9. Acknowledgments................................................7
10. References....................................................8
10.1. Normative References.....................................8
10.2. Informative References...................................8
Author's Addresses................................................9
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1. Introduction
The LDP [RFC5036] specification defines procedures and messages for
exchanging label bindings over either IPv4 or IPv6 or both (e.g.
dual-stack) networks.
However, RFC5036 specification has the following deficiencies in
regards to IPv6 usage:
1) LSP mapping: No rule defined 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 multicast
address (with or without IPv4 co-existence)
4) LDP Session establishment: No prescription for handling both IPv4
and IPv6 transport address optional objects in a Hello message,
and subsequently two IPv4 and IPv6 transport connections.
This document addresses the above deficiencies by specifying the
desired behavior.
Note that this document updates RFC5036.
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].
LDP - Label Distribution Protocol
FEC - Forwarding Equivalence Class
TLV - Type Length Value
LSR - Label Switch Router
LSP - Label Switched Path
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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."
Suffice to say, this rule is correct for IPv4, but not for IPv6,
since an IPv6 router may not have any /32 address.
This document proposes to modify this rule by also including a /128
address (for IPv6). In fact, it should be reasonable to just 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
Section 2.2.2 of [RFC5036] specifies formulating at least one LDP
Identifier, however, it doesn't provide any consideration in case of
IPv6 (with or without dual-stacking).
This document preserves the usage of 32-bit LSR Id on an IPv6 only
LSR and allows the usage of a common LDP identifier i.e. same LSR-Id
and same Label space id for IPv4 and IPv6 on a dual-stack LSR. This
rightly enables the per-platform label space to be shared between
IPv4 and IPv6.
Editor's note: The possible conflict with last paragraph of
section 2.5.2 of RFC5036 needs to be addressed or clarified.
Additionally, this document reserves 0.0.0.0 as the LSR-Id, and
prohibits its usage.
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5. Peer Discovery
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
sends LDP Link Hellos destined to "all routers on this subnet" group
multicast IP address.
Interesting enough, per [IANA-IPv6] [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 for IPv6
LDP Link Hellos. An LDP Hello packet received on any of the other
addresses should be dropped. Also, the LDP Link Hello packets must
have their IPv6 Hop Limit set to 1.
More importantly, if an interface is a dual-stack LDP interface
(e.g. enabled with both IPv4 and IPv6 LDP), then the LSR must
periodically send both IPv4 and IPv6 LDP Link Hellos and must
separately maintain the Hello adjacency for IPv4 and IPv6. This
ensures labeled IPv4 and labeled IPv6 traffic forwarding on a dual-
stacked interface, as well as the LDP peerings using the appropriate
transport can be established on a multi-access interface (even if
there are IPv4-only, IPv6-only and dual-stack routers on that multi-
access segment). Needless to say, the IPv4 and IPv6 LDP Link Hellos
must carry the same LDP identifier (assuming per-platform label
space usage).
5.2. Extended Discovery Mechanism
Suffice to say, the extended discovery mechanism (defined in section
2.4.2 of [RFC5036]) doesn't require any additional IPv6 specific
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consideration, since the targeted LDP Hellos are sent to a pre-
configured destination IP address.
6. LDP Session Establishment
Section 2.5.1 of [RFC5036] defines a two-step process for LDP
session establishment:
1. Transport connection establishment
2. Session initialization
Next two sections discuss the LDP consideration for IPv6 and/or
dual-stacking.
6.1. Transport connection establishment
Section 2.5.2 of [RFC5036] specifies the use of an optional
transport address object (TLV) in LDP Link 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. Moreover, it does not specify
whether both IPv4 and IPv6 transport connections should be allowed,
if there were Hello adjacencies for both IPv4 and IPv6.
This document specifies that:
- An LSR should not send a Hello containing both IPv4 and IPv6
transport address optional objects. In other words, there
should be at most one optional Transport Address object in a
Hello message. An LSR should include only the transport address
whose address family is the same as that of the IP packet
carrying Hello.
- An LSR should accept the Hello message that contains both IPv4
and IPv6 transport address optional objects, but use only the
transport address whose address family is the same as that of
the IP packet carrying Hello.
- An LSR should not create (or honor the request for creating) a
TCP connection for a new LDP session with a remote LSR, if they
already have an LDP session (for the same label spaces)
established using whatever IP version. This means that only one
transport connection should be established, even if there are
two Hello adjacencies (one for IPv4 and another for IPv6).
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- An LSR should prefer the TCP connection over IPv6 for a new LDP
session with a remote LSR, if they attempted two TCP
connections using IPv4 and IPv6 transports simultaneously.
6.2. Session initialization
No additional consideration needed.
7. IANA Considerations
None.
8. Security Considerations
The extensions defined in this document only clarify the behavior of
LDP, they do not define any new protocol procedures. All the
security issues relevant for the [RFC5036] are relevant for this
document as well.
Moreover, this document allows the use of IPsec [RFC4301] for IPv6
protection, hence, LDP can benefit from the additional security as
specified in [RFC4835].
9. Acknowledgments
A lot of the text in this document is borrowed from [RFC5036]. The
authors of the document are acknowledged. The authors also
aknowledge the help of Manoj Dutta and Vividh Siddha. Thanks to Bob
Thomas for providing critical feedback to improve this document
early on.
This document was prepared using 2-Word-v2.0.template.dot.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP
Specification", RFC 5036, October 2007.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
10.2. Informative References
[RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet
Protocol", RFC 4301, December 2005.
[RFC4853] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, April 2007.
[IANA-IPv6] http://www.iana.org/assignments/ipv6-address-space.
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Author's Addresses
Vishwas Manral
IP Infusion Inc.,
Bamankhola, Bansgali,
Almora, Uttarakhand 263601
Email: vishwas@ipinfusion.com
Rajiv Papneja
ISOCORE
12359 Sunrise Valley Dr, STE 100
Reston, VA 20190
Email: rpapneja@isocore.com
Rajiv Asati
Cisco Systems,
7025-6 Kit Creek Rd, RTP, NC, 27709-4987
Email: rajiva@cisco.com
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