Internet DRAFT - draft-pfister-bier-over-ipv6
draft-pfister-bier-over-ipv6
Network Working Group P. Pfister
Internet-Draft IJ. Wijnands
Intended status: Standards Track Cisco Systems
Expires: May 4, 2017 October 31, 2016
An IPv6 based BIER Encapsulation and Encoding
draft-pfister-bier-over-ipv6-01
Abstract
This document specifies the packet format and procedures for
transporting IPv6 payloads to multiple IPv6 destinations using the
Bit Index Explicit Replication (BIER). The BIER BitString is stored
within the low-order bits of the IPv6 destination address while the
high-order bits are used for unicast forwarding before entering the
destination BIER domain, identifying whether a packet is a BIER
packet, the destination Sub-Domain, the Set Identifier and the
BitString length.
Status of This Memo
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This Internet-Draft will expire on May 4, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IPv6 BIER Packet Format . . . . . . . . . . . . . . . . . . . 3
4. Multicast Flow Overlay Operations . . . . . . . . . . . . . . 4
5. Bier Layer Forwarding Operations . . . . . . . . . . . . . . 4
6. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Bit Index Explicit Replication (BIER -
[I-D.ietf-bier-architecture]) forwarding technique enables IP
multicast transport across a BIER domain. Its architecture is based
on three different layers, a multicast flow overlay, a BIER Layer,
and a routing underlay. This document specifies the packet format
and procedures enabling IPv6 payload transport to multiple
destinations, hence defining the transport part of a BIER layer.
BIER BitString is encoded in the low-order bits of the IPv6
destination address of each packet. The high-order bits of the IPv6
destination address are used by intermediate routers for unicast
forwarding, deciding whether a packet is a BIER packet, and if so, to
identify the BIER Sub-Domain, Set Identifier and BitString length.
Transported payloads can be of various types such as IPv6 or IPv4,
unicast or multicast (e.g. using generic packet tunnelling
[RFC2473]), or transported data (e.g. using UDP). Any data that can
be used as payload to an IPv6 packet can be encapsulated, but special
care must be taken when forwarding some types of payloads. For
example, the UDP checksum may become invalid as the BIER BitString is
modified.
This technique is an alternative to the MPLS encapsulation
[I-D.ietf-bier-mpls-encapsulation]. It may be appropriate when
deploying an MPLS network is not an option, e.g., in some data
centers, or in home networks [RFC7368]. It also offers some
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interesting properties with regard to host compatibility (see
Section 6).
2. Terminology
In this document, the key words "MAY", "MUST", "MUST NOT",
"RECOMMENDED", and "SHOULD", are to be interpreted as described in
[RFC2119].
3. IPv6 BIER Packet Format
Payload to be sent to multiple destinations is encapsulated within an
IPv6 packet with no additional extension or encapsulation header.
Information required by BIER to operate is stored in the destination
IP address of the IPv6 header. The BIER BitString is encoded in the
low-order bits of the IPv6 destination address of the packet while
the high-order bits are used by intermediate BIER routers to identify
that the forwarded packet is an IPv6 BIER packet, its BIER sub-
domain, its associated BIER Set Identifier, and the BitString length.
| p bits | 128-p bits |
+---------------------------------------------------------+
| BIER IPv6 Prefix | BitString bits |
+---------------------------------------------------------+
Figure 1: IPv6 BIER destination address format
BIER IPv6 Prefix: This is a prefix used for BIER forwarding within
the domain. BIER routers will consider all packets sent to
this prefix as an IPv6 BIER packets. Each BIER IPv6 Prefix is
associated with a Sub-Domain, a Set Identifier, and a BitString
length.
BitString bits: These bits are used to encode the BIER BitString.
It encodes the set of BFERs the packet should be sent to.
Those bits are modified as the packet is replicated by
intermediate BIER routers.
The mapping between a BIER IPv6 Prefix and the BIER parameters may be
implemented using either algorithmic mapping (e.g., by including the
Sub-Domain and the Set Identifier in the low-order bits of the
prefix), by using a binding table (e.g., by associated each prefix
with configuration parameters), or using a combination of the two.
Although an algorithmic mapping might be advantageous in certain
scenarios, only the binding table model can interoperate with any
other operating mode. Therefore, implementations SHOULD support the
binding table model (in order to interoperate with any other
operating modes), and MAY provide other operating modes too.
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4. Multicast Flow Overlay Operations
When a multicast packet enters the BIER domain, the BFIR first
consults the multicast flow overlay and obtains the Sub-Domain
Identifier and the set of BFERs the packet must be sent to. This set
is used in order to compute the set of bit indexes representing the
set of destination BFERs. All indexes that have the same Set
Identifier are grouped in order to create a set of BitStrings
associated with their respective SI. For each SI, the multicast
packet is encapsulated within an IPv6 BIER packet, as specified in
Section 3.
The same process is used when a given IPv6 payload is sent to a set
of destinations. But instead of encapsulating the packet, the
payload is attached to the BIER IPv6 header and the IPv6 protocol
number is set to the type of the payload.
5. Bier Layer Forwarding Operations
Each BIER IPv6 Prefix is inserted in the IPv6 FIB. When a packet is
received, a longest prefix match is performed on the destination IPv6
address. If the result of the lookup returns a BIER entry, the BIER
Sub-Domain, Set Identifier and BitString length are retrieved. The
packet is then processed according to the BIER forwarding algorithm.
For each replicated packet, the BitString, included in the IPv6
destination address is modified and the packet is sent on the
outgoing interface.
It is worth noting that this algorithm may interact with unicast
forwarding. For example, BIER IPv6 Prefixes corresponding to a sub-
domain in which a BIER router is not included in MAY be implemented
as a unicast forwarding FIB entry.
6. Applicability Statement
The technique described in this document enables transport of IPv6
payloads towards multiple destinations using BIER. The information
required by BIER is stored in the destination IPv6 address. In
particular, the length of the BIER BitString is limited by the prefix
length assigned to BIER forwarding. For example, lengths from 16 to
72 could be used while lengths of 128 or greater are impractical.
Therefore, this proposal does not comply with the current version of
the BIER architecture document [I-D.ietf-bier-architecture] which
mandates fixed, power of 2, values from 64 to 4096, with a minimal
supported value of 256. It appears to the authors that such values
depend on the underlying technology that is used. In particular,
mandated values seem to fit MPLS [I-D.ietf-bier-mpls-encapsulation]
requirements, but may be impractical in other scenarios.
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Past the BitString length limitation, this proposal offers different
advantages:
BIER IPv6 packets are not different from IPv6 unicast packets. If
the BIER IPv6 Prefix is a globally unique IPv6 prefix, reachable
from outside the BIER domain, it is possible to send a packet from
outside the BIER domain to multiple destinations within the BIER
domain.
It may be used for transporting IP multicast packets, but also for
sending IP payloads directly to multiple destinations.
It does not rely on a new IPv6 extension header, which simplifies
deployment and is likely to improve performances.
It is possible to configure a host with an address which
corresponds to a BIER address with a single bit set. From the
host perspective, such address is not different from a unicast
IPv6 address. Which means a BIER-unaware host may receive BIER
packets transparently. As an example, if multicast traffic is
being transported over BIER using standard IP-in-IPv6
encapsulation, an end-host could behave as tunnel end-point for
this traffic without requiring any BIER specific configuration.
Finally, it is worth mentioning that this proposal relies on routers
modifying the IPv6 destination address from IPv6 packets. Just like
other BIER encapsulations, this technique will likely require the
development of specific monitoring tools and techniques.
7. Security Considerations
This technique allows IPv6 BIER packets to be sent across the
internet toward multiple destination located in a given BIER domain.
If this is considered a threat, a firewall at the entrance of the
BIER domain in order to avoid BIER packets from being injected and
replicated within the network.
8. IANA Considerations
This specification does not require any action from IANA.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <http://www.rfc-editor.org/info/rfc2473>.
[RFC7368] Chown, T., Arkko, J., Brandt, A., Troan, O., and J. Weil,
"IPv6 Home Networking Architecture Principles", RFC 7368,
October 2014.
9.2. Informative References
[I-D.ietf-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-ietf-bier-architecture-01 (work in
progress), June 2015.
[I-D.ietf-bier-mpls-encapsulation]
Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J., and
S. Aldrin, "Encapsulation for Bit Index Explicit
Replication in MPLS Networks", draft-ietf-bier-mpls-
encapsulation-02 (work in progress), August 2015.
Appendix A. Acknowledgements
The authors would like to thank the BIER Interim Meeting participants
as well as Eric Rosen, Toerless Eckert and Xiaohu Xu for their
comments on the mailing list.
Authors' Addresses
Pierre Pfister
Cisco Systems
Paris
France
Email: pierre.pfister@darou.fr
IJsbrand Wijnands
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
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