BIER Working Group IJ. Wijnands
Internet-Draft Cisco Systems
Intended status: Informational X. Xu
Expires: February 16, 2018 Huawei
H. Bidgoli
Nokia
August 15, 2017
An Optional Encoding of the BIFT-id Field in the non-MPLS BIER
Encapsulation
draft-wijnandsxu-bier-non-mpls-bift-encoding-00.txt
Abstract
Bit Index Explicit Replication (BIER) is an architecture that
provides optimal multicast forwarding through a "multicast domain",
without requiring intermediate routers to maintain any per-flow state
or to engage in an explicit tree-building protocol. The Multicast
packet is encapsulated using a BIER Header and transported through an
MPLS or non-MPLS network. When MPLS is used as the transport, the
Bit Indexed Forwarding Table (BIFT) is identified by a MPLS Label.
When non-MPLS transport is used, the BIFT is identified by a 20bit
value. This document describes one way of encoding the 20bit value.
Status of This Memo
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This Internet-Draft will expire on February 16, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Internet-Draft Non-MPLS BIER BIFT-id Encapsulation August 2017
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 3
3. Specification of Requirements . . . . . . . . . . . . . . . . 3
4. The Bit Index Forwarding Table . . . . . . . . . . . . . . . 3
5. The Non-MPLS Static BIFT Encoding . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Bit Index Explicit Replication (BIER) [I-D.ietf-bier-architecture] is
an architecture that provides optimal multicast forwarding through a
"multicast domain", without requiring intermediate routers to
maintain any per-flow state or to engage in an explicit tree-building
protocol. The Multicast packet is encapsulated
[I-D.ietf-bier-mpls-encapsulation] using a BIER Header and
transported through an MPLS or non-MPLS network. When MPLS is used
as the transport, the Bit Indexed Forwarding Table (BIFT) is
identified by a MPLS Label. When non-MPLS transport is used, the
BIFT is identified by a 20bit value. This document describes one way
of encoding the 20bit value, based on the Sub-Domain (SD), Set
Identifier (SI) and BitStringLength (BSL) values.
The BIER architecture requires that a BFR has a BIFT for every
combination of <SD, SI, BSL> that is being used. When processing a
BIER packet, the correct BIFT is inferred from the BIFT-id field of
the encapsulation. When the non-MPLS encapsulation is used in a
given BIER domain, it may be desirable for the a BIFT-id to be unique
in that domain. This document describes an OPTIONAL method that can
be used to form domain-wide unique BIFT-ids based on the <SD, SI,
BSL> triples. If in the future the BIER architecture is extented
with an additonal BIFT argument, this encoding does not generate
domain-wide unique idenifiers anymore.
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This encoding, if used, is only for the convenience of the network
adminstrators. When forwarding a BIER packet, the BIFT-id is used as
an opaque 20-bit value that identifies a BIFT; the forwarding
procedures do not parse the 20-bit value, they just use it as a
lookup key.
2. Terminology and Definitions
Readers of this document are assumed to be familiar with the
terminology and concepts of the documents listed as Normative
References. For convenience, some of the more frequently used terms
appear below.
BIER:
Bit Indexed Explicit Replication.
BIFT-id:
Bit Indexed Forwarding Table Identifier.
3. Specification of Requirements
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].
4. The Bit Index Forwarding Table
In MPLS networks a BIER label is allocated for each Bit Index
Forwarding Table (BIFT) from the platform specific, downstream label
database ([I-D.ietf-bier-mpls-encapsulation]). This label is
associated with a particular combination of BIER Sub-Domain (SD), Set
Identifier (SI) and BitStringLength (BSL). In order for the network
to know which MPLS label represents a particular combination of <SD,
SI, BS>, this mapping has to be advertised through the network. This
is currently done through an IGP or BGP. In MPLS networks this is
not a drawback as the MPLS label has to be advertised anyway.
When the non-MPLS encoding is chosen, there is no need to advertise
the BIFT-id to <SD, SI, BSL> mapping if the BIFT-id is domain-wide
unique. For this reason we're defining an encoding that MAY be used
by operators to compute the domain-wide unique BIFT-id values from
the SD, SI and BSL. Although the BIFT-id is not expected to change,
it may change when the BSL mismatch procedures
[I-D.ietf-bier-architecture] section 6.10.2 are applied.
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5. The Non-MPLS Static BIFT Encoding
Find below the first 32 bits of the BIER header, encoding the SD, SI
and BSL into the 20 bit BIFT-id field.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSL | SD | SI | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|-------- 20 bit BIFT-id Field ---------|
Figure 1
BSL: This 4-bit field encodes the length in bits of the BitString.
These are the same values as documented in
[I-D.ietf-bier-mpls-encapsulation].
SD: This is a 8-bit field that encodes the Sub-Domain as described
in [I-D.ietf-bier-architecture].
SI: This is a 8-bit field that encodes the Set-ID as described in
[I-D.ietf-bier-architecture].
TC: This is a 3-bit field set to 000 (following
[I-D.ietf-bier-mpls-encapsulation]).
S: This is a 1-bit field set to 1 (following
[I-D.ietf-bier-mpls-encapsulation]).
TTL: See [I-D.ietf-bier-mpls-encapsulation].
6. Security Considerations
This document does not introduce any new security considerations
other than already discussed in [I-D.ietf-bier-architecture].
7. IANA Considerations
There is no IANA consideration.
8. Acknowledgments
The authors like to thank the following people for their comments and
contributions to this document; Eric Rosen, Neale Ranns, Jeffrey
Zhang.
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9. Normative 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-07 (work in
progress), June 2017.
[I-D.ietf-bier-mpls-encapsulation]
Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J.,
Aldrin, S., and I. Meilik, "Encapsulation for Bit Index
Explicit Replication in MPLS and non-MPLS Networks",
draft-ietf-bier-mpls-encapsulation-07 (work in progress),
June 2017.
[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>.
Authors' Addresses
IJsbrand Wijnands
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Hooman Bidgoli
Nokia
600 March Rd.
Ottawa, Ontario K2K 2E6
Canada
Email: hooman.bidgoli@nokia.com
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