Internet DRAFT - draft-wang-bier-lite-ospf-extension
draft-wang-bier-lite-ospf-extension
BIER WG C. Wang
Internet-Draft Z. Zhang
Intended status: Standards Track ZTE Corporation
Expires: April 18, 2016 October 16, 2015
OSPF Extension for BIER-Lite
draft-wang-bier-lite-ospf-extension-01
Abstract
Bit Index Explicit Replication (BIER) [I-D.ietf-bier-architecture] is
an architecture that provides optimal multicast forwarding through a
"BIER domain" without requiring intermediate routers to maintain any
multicast related per-flow state. BIER also does not require any
explicit tree-building protocol for its operation. Currently, the
data plane of BIER is apt to use BIER-MPLS encapsulation to transmit
multicast traffic. However, this document tries to propose a
solution name BIER-Lite about how to extend OSPF protocol to support
BIER forwarding in non-MPLS underlay network instead of MPLS underlay
network.
Status of this Memo
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This Internet-Draft will expire on April 18, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Convention and Terminology . . . . . . . . . . . . . . . . . . 5
3. BIER-Lite Sub-TLV in OSPF extension . . . . . . . . . . . . . 6
4. Flooding scope of BIER-Lite Information . . . . . . . . . . . 8
5. Considerations on BIER-Lite . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Bit Index Explicit Replication (BIER) [I-D.ietf-bier-architecture] is
an architecture that provides optimal multicast forwarding through a
"BIER domain" without requiring intermediate routers to maintain any
multicast related per-flow state. BIER also does not require any
explicit tree-building protocol for its operation. A multicast data
packet enters a BIER domain at a "Bit-Forwarding Ingress Router"
(BFIR), and leaves the BIER domain at one or more "Bit-Forwarding
Egress Routers" (BFERs). The BFIR router adds a BIER header to the
packet. The BIER header contains a bit-string in which each bit
represents exactly one BFER to forward the packet to. The set of
BFERs to which the multicast packet needs to be forwarded is
expressed by setting the bits that correspond to those routers in the
BIER header.
Currently, the data plane of BIER is defined in BIER-MPLS
encapsulation [I-D.ietf-bier-mpls-encapsulation] to transmit
multicast traffic in MPLS encapsulation. Admittedly, BIER-MPLS
introduces the advantages of MPLS forwarding. However, this requires
the underlay network is an MPLS network, and along the path, there
need label switching and label lookup. Additionally, every BFR
requires per-label forwarding table to assist BIER forwarding.
What!_s more, prior of that, IGP protocol or BGP protocol requires a
precise mechanism to generate these label information, after that, to
advertise these label information to form the per-label forwarding
table between the label and the bit index forwarding table(BIFT).
Sometimes, how to categorize this label information in differentiated
MPLS Encapsulation sub-sub-TLV is a difficult decision. And some
other times, after the label information advertisement, there may be
some redundant label information as well as some redundant label
forwarding table because each BFR advertises continuous labels for
different Set Identifiers for each combination of Sub-domain and
BitStringLength which may be redundant because traffic to some BFERs
may not transit this advertising node, especially when these BFERs
belonging to the same Set Identifier reside together geographically.
In fact, some multicast scenario may be not in MPLS network, or may
be in a relatively simple network. In other words, if BIER
forwarding uses IP forwarding instead of MPLS forwarding in these
kind of networks, it would be much easier to deploy BIER in current
deployment. Of course, if the BIER forwarding is compatible with
BIER-MPLS encapsulation forwarding, that would be much more
significant.
The following section tries to propose how to extend OSPF protocol to
support BIER forwarding in non-MPLS underlay network instead of MPLS
underlay network.
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And this document names this solution as BIER-Lite.
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2. Convention and Terminology
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].
The terms about BIER are defined in [I-D.ietf-bier-architecture].
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3. BIER-Lite Sub-TLV in OSPF extension
Given that the BIER-Lite-specific information that a BFR needs to
advertise to other BFRs are associated with the BFR-Prefix, the OSPF
Extended Prefix Opaque LSA [I-D.ietf-ospf-prefix-link-attr] is used
to flood BIER-Lite-specific information.
Here, in order to implement the BIER forwarding in non-MPLS network
and simplify the BIER forwarding mentioned in
[I-D.ietf-bier-mpls-encapsulation] , a new BIER-Lite sub-TLV of the
Extended Prefix Opaque LSA is defined to advertise BIER-Lite-specific
information, which is illustrated as follow in Figure 1. Multiple
BIER-Lite Sub-TLVs may be included in the Extended Prefix TLV.
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 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-domain-ID | MT-ID | BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | Resvered | BSL Identifier|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BIER-Lite Sub-TLV in OSPF extension
Type: indicates BIER-Lite sub-TLV
Length: 8 octet.
Sub-domain-ID: unique value identifying the BIER sub-domain within
the BIER domain, as described in section 1 of
[I-D.ietf-bier-architecture].
MT-ID: Multi-Topology ID (as defined in [RFC4915]) that identifies
the topology that is associated with the BIER sub-domain.
BFR-id: a 2 octet field encoding the BFR-id, as documented in
section 2 [I-D.ietf-bier-architecture]. If the BFR-id is zero, it
means, the advertising router is not advertising any BFR-id.
M: indicating whether is compatible with BIER MPLS Encapsulation
sub-sub-TLV. When M is set to 1, it means if there has BIER MPLS
Encapsulation sub-sub-TLV, validating and using the BSL information
and label information in BIER MPLS Encapsulation sub-sub-TLV. When M
is set to 0, it means validating and using the BSL information in the
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BSL Identifier even if there has BIER MPLS Encapsulation sub-sub-TLV
and ignoring all the information in BIER MPLS Encapsulation sub-sub-
TLV.
BSL Identifier: indicating the BSL the sending BFR supporting.
The sending BFR may support one or several BSLs, as following:
00000001: represents BSL 64 bits;
00000010: represents BSL 128 bits;
00000100: represents BSL 256 bits;
00001000: represents BSL 512 bits;
00010000: represents BSL 1024 bits;
00100000: represents BSL 2048 bits;
01000000: represents BSL 4096 bits;
Each bit represents one BSL. When there are two or more bits set,
that means the sending BFR supports more than one BSL. For example,
if the BSL Identifier is 00010101, it means the sending BFR supports
1024 bits, 256 bits and 64 bits.
Each BFR sub-domain MUST be associated with a single OSPF topology
that is identified by the MT-ID. If the association between BIER
sub-domain and OSPF topology advertised in the BIER-Lite sub-TLV is
different from the association on the receiving router, BIER-Lite
sub-TLV SHOULD be ignored.
On the other hand, the BIER-Lite sub-TLV, which encapsulates the BSL
information together with the BIER Info sub-TLV, may be a
complementation and an extension of BIER Info sub-TLV defined in
[I-D.ietf-bier-ospf-bier-extensions]. Additionally, adding an M
identifier in the BIER Info sub-TLV
[I-D.ietf-bier-ospf-bier-extensions] to be compatible with BIER MPLS
encapsulation sub-sub-TLV. So, BIER-Lite sub-TLV can also multiplex
and extend BIER Info sub-TLV defined in
[I-D.ietf-bier-ospf-bier-extensions] instead of defining a new TLV.
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4. Flooding scope of BIER-Lite Information
Flooding scope of the OSPF Extended Prefix Opaque LSA
[I-D.ietf-ospf-prefix-link-attr] that is used for advertising BIER-
Lite sub-TLV is set to area. To allow BIER deployment in a multi-
area environment, OSPF must propagate BIER-Lite information between
areas.
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5. Considerations on BIER-Lite
TBD.
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6. Security Considerations
It will be considered in a future revision.
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7. IANA Considerations
This document can request a new allocation from OSPF Extended Prefix
sub-TLV registry for BIER-Lite sub-TLV. Or it can multiplex the BIER
Info sub-TLV defined in [I-D.ietf-bier-ospf-bier-extensions] and
extend M information and BSL Identifier information to BIER Info sub-
TLV.
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8. References
8.1. Normative References
[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>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<http://www.rfc-editor.org/info/rfc4915>.
8.2. 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-02 (work in
progress), July 2015.
[I-D.ietf-bier-isis-extensions]
Ginsberg, L., Aldrin, S., Zhang, J., and T. Przygienda,
"BIER support via ISIS",
draft-ietf-bier-isis-extensions-00 (work in progress),
April 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.
[I-D.ietf-bier-ospf-bier-extensions]
Psenak, P., Kumar, N., Wijnands, I., Dolganow, A.,
Przygienda, T., Zhang, J., and S. Aldrin, "OSPF Extensions
For BIER", draft-ietf-bier-ospf-bier-extensions-00 (work
in progress), April 2015.
[I-D.ietf-ospf-prefix-link-attr]
Psenak, P., Gredler, H., rjs@rob.sh, r., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", draft-ietf-ospf-prefix-link-attr-13 (work
in progress), August 2015.
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Authors' Addresses
Cui Wang
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: wang.cui1@zte.com.cn
Zheng Zhang
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: zhang.zheng@zte.com.cn
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