Network Working Group M. McBride
Internet-Draft Futurewei
Intended status: Standards Track J. Xie
Expires: January 11, 2021 S. Dhanaraj
Huawei
R. Asati
Cisco
Y. Zhu
China Telecom
G. Mishra
Verizon Inc.
July 10, 2020
BIER IPv6 Requirements
draft-ietf-bier-ipv6-requirements-05
Abstract
The BIER WG charter includes work on developing "a mechanism to use
BIER natively in IPv6". There have been several proposed solutions
in this area. But there hasn't been a document which describes the
problem and lists the requirements. The goal of this document is to
describe the BIER IPv6 requirements, summarize the encapsulation
modes of the proposed solutions, guide the working group in
understanding the benefits and drawbacks of the various solutions,
and help in the development of acceptable solutions.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 11, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Conceptual Models For BIER IPv6 Encapsulation and Forwarding 4
3.1. Transport-Independent Model . . . . . . . . . . . . . . . 5
3.2. Native IPv6 Model . . . . . . . . . . . . . . . . . . . . 6
3.3. Encapsulation Approaches Considered . . . . . . . . . . . 7
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Mandatory Requirements . . . . . . . . . . . . . . . . . 8
4.1.1. L2 Agnostic . . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Support BIER architecture . . . . . . . . . . . . . . 8
4.1.3. Conform to existing IPv6 Spec . . . . . . . . . . . . 8
4.1.4. Support deployment with Non-BFR routers . . . . . . . 8
4.1.5. Support inter-AS multicast deployment . . . . . . . . 8
4.1.6. Support Simple Encapsulation . . . . . . . . . . . . 9
4.1.7. Support Deployment Security . . . . . . . . . . . . . 9
4.2. Optional Requirements . . . . . . . . . . . . . . . . . . 9
4.2.1. Support MVPN . . . . . . . . . . . . . . . . . . . . 9
4.2.2. Support OAM . . . . . . . . . . . . . . . . . . . . . 9
4.2.3. Support IPSEC . . . . . . . . . . . . . . . . . . . . 9
4.2.4. Support Fragmentation . . . . . . . . . . . . . . . . 9
4.2.5. Support hardware fast path . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Solutions Evaluation . . . . . . . . . . . . . . . . 12
A.1. BIER-ETH encapsulation in IPv6 networks . . . . . . . . . 12
A.2. Encode Bitstring in IPv6 destination address . . . . . . 13
A.3. Add BIER header into IPv6 Extension Header . . . . . . . 13
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A.4. Transport BIER as IPv6 payload . . . . . . . . . . . . . 14
A.5. Tunnelling BIER in a IPv6 tunnel . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
that provides optimal multicast forwarding, without requiring
intermediate routers to maintain per-flow state, through the use of a
multicast-specific BIER header. [RFC8296] defines two types of BIER
encapsulation to run on physical links: one is BIER MPLS
encapsulation to run on various physical links that support MPLS, the
other is non-MPLS BIER Ethernet encapsulation to run on ethernet
links, with an ethertype 0xAB37. This document describes using BIER
in non-MPLS IPv6 environments. We explain the requirements of
transporting IPv4/IPv6 multicast payloads through an IPv6 network
using "BIER natively in IPv6". As clarified in the working-group,
"BIER natively in IPv6" means BIER not encapsulated in MPLS or
Ethernet. This may include native IPv6 encapsulation and generic
IPv6 tunnelling. The goal of this document is to help the BIER WG
evaluate the BIER v6 requirements and solutions in order to begin
adopting solution drafts.
1.1. Requirements 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 RFC 2119 [RFC2119].
1.2. Terminology
o BIER: Bit Index Explicit Replication. Provides optimal multicast
forwarding through adding a BIER header and removing state in
intermediate routers.
o BUM: Broadcast, Unknown Unicast, Multicast. Term used to describe
the three types of Ethernet modes that will be forwarded to
multiple destinations
2. Problem Statement
The problem is the ability of the network to transport BUM packets,
with BIER headers, in an IPv6 environment. In many IPv6 network
deployments, non-MPLS encapsulation is used for unicast as the data-
plane and it is likewise expected to have BIER IPv6 deployments which
depend on these same unicast technologies.
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One such case involves supporting a non-BFR router in a network as
described in section 6.9 of RFC8279. In the context of this
document, an IPv6 based unicast tunnel is needed to support such
deployment where a non-BFR exists. Another case is to support inter-
AS multicast deployment as illustrated in
[I-D.geng-bier-ipv6-inter-domain]. In such deployment, there are
non-BFR routers, or even an entire non-BIER network, that needs the
ability to traverse from one BFR to another.
[I-D.ietf-bier-use-cases] shows it is possible there are other cases
where inter-AS multicast deployment is required.
As with IPv6, another problem of BIER IPv6 technology may be
"Transition Mechanisms and Partial Deployments" which is listed as
the No.1 charter item of BIER WG. Therefore, a basic requirement of
BIER IPv6 is to leverage IPv6 reachability for incremental and inter-
AS BIER deployment.
Below is a simple scenario that needs BIER IPv6 encapsulation and
forwarding:
+--------------------------------------------+
| |
| +------+
| | BFER |
+------+ +-------+ +-----+ +------+
| BFIR | |Non-BFR| | BFR | |
+------+ +-------+ +-----+ +------+
| | BFER |
| IPv6 Network +------+
| (intra-AS or inter-AS) |
+--------------------------------------------+
This scenario depicts the need to replicate bier packets from a BFIR
to BFERs across an IPv6 core. The IPv6 environment may include a
variety of link types, may be entirely IPv6, may be dual stack or any
type of combination which includes IPv6. Regardless of the
environment, there are times when a BIER header, including the BIER
BitString used to determine the set of BIER forwarding egress
routers, will need to traverse a IPv6 domain. The ways in which BIER
will function in an IPv6 environment is the problem that needs to be
solved.
3. Conceptual Models For BIER IPv6 Encapsulation and Forwarding
This analysis introduces two conceptual models for BIER IPv6
encapsulation and forwarding based on the experience and examples
that have been seen in the IETF community.
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3.1. Transport-Independent Model
The first conceptual model is a Transport-Independent Model that
views IP tunnels as links of BIER, and views BIER as an independent
"Layer-2.5".
|<----------(L2.5 BIER(P2MP) Tunnel)-------->|
| |
| +~~~~~~~~~~~~~~~~~~+ +~~~~+ |
| / \ / \ |
+------+ +-------+ +-----+ +------+
| BFIR |-------|Non-BFR|-------| BFR |--------| BFER |
+------+ +-------+ +-----+ +------+
------- physical link
~~~~~~~ IPv6(P2P) tunnel
<-----> BIER(P2MP) tunnel
In this model, an IPv6 tunnel works as a link-layer of BIER, and BIER
works as a transport-independent layer (or layer-2.5) over a virtual-
link (IPv6 tunnel). On each BFR, the IPv6 tunnel of the receiving
packet is decapsulated, and a new IPv6 tunnel is encapsulated before
sending the packet to the next-hop BFR neighbour.
From the view of the IPv6 layer, the BIER header is a kind of Upper-
layer header (Layer-4). From the view of the BIER layer, the IPv6
encapsulation is a tunnel working as a "link" of BIER. With an End-
to-End view, the tunnel from BFIR to BFERs is a Layer-2.5 BIER (P2MP)
tunnel, and the BFIR-id is the BIER packet source-origin identifier,
and is unchanged through the BIER domain from BFIR to BFERs.
This model is similar to the "MPLS over IP" [RFC4023] or "MPLS over
UDP" [RFC7510] approach. A more general output of such approach in
IETF is "MPLS Segment Routing over IP" [RFC8663]. It makes use of
IPv4/IPv6 tunnel, IPv4/IPv6 UDP tunnel and IPv4/IPv6 GRE tunnel to
encapsulate the MPLS-based instructions. In fact, BIER-MPLS could
use this approach directly since BIER-MPLS is based on MPLS.
There may be, however, in certain cases some difficulty with
allocation of an MPLS label and advertisement through the control-
plane. For example, a simple inter-AS BIER deployment may want to
use the auto-configuration of BIFT-id using Non-MPLS BIER
encapsulation [RFC8296] as illustrated in
[I-D.geng-bier-ipv6-inter-domain]. This brings the need of a new
"Next Header" value to indicate the "Non-MPLS" BIER header.
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For IPv4/IPv6 GRE, the "Next Header" is the 16-bit "Protocol Type"
field, and has adequate space for such requirement.
For IPv4/IPv6 UDP, the "Next Header" is the 16-bit "Destination Port"
field, and has adequate space for such requirement.
For IPv4/IPv6, the "Next Header" is a 8-bit value and needs to be
allocated from the "Assigned Internet Protocol Numbers" registry.
Reassembly/Re-fragmentation of a packet has to be executed on each
BFR in such case. This may be common and even friendly for a
protocol stack in a BFR software implementation, but it may impose
cost for a BFR hardware implementation.
IPv6 functions that are expected to be executed from BFIR to BFER are
assumed to be broken on the BFRs, for example, IPv6 Fragmentation/
Assembly or IPSEC ESP. This is because the "IPv6 tunnel" and all its
functions is "terminated" on the BFRs. These functions, if desired,
may need to be re-designed in the "Layer-2.5" BIER mode.
For deployment security, it is necessary to ensure the "BIER" packet
is only using the allowed IPv6 tunnel.
3.2. Native IPv6 Model
The second conceptual model is a Native IPv6 Model that integrates
BIER as part of the IPv6 data plane, making it a "Layer-3 BIER"
approach.
|<----------(L3 BIER(P2MP) tunnel)--------->|
| |
+------+ +-------+ +-----+ +------+
| BFIR |-------|Non-BFR|-------| BFR |--------| BFER |
+------+ +-------+ +-----+ +------+
------- physical link
<-----> BIER(P2MP) tunnel
In this model, BIER works as part of the IPv6 data plane. BFIR and
BFERs work as IPv6 (P2MP) tunnel endpoints, and BFRs work as IPv6
segment endpoints. On each BFR, the segment endpoint behaviour of
IPv6 data plane is executed, and there is no decapsulation of
receiving IPv6 tunnel and encapsulation of new IPv6 tunnel for
sending.
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In this mode, BIER is integrated into the IPv6 data plane. The IPv6
source address is the BIER packet source-origin identifier, and is
unchanged through the BIER domain from BFIR to BFERs.
This model is similar to many examples emerging in the IETF community
which soley use the IPv6 data plane. SRv6 introduced in [RFC8754]
and [I-D.ietf-spring-srv6-network-programming] is an example. The
benefits of such approach includes reducing the number of
encapsulation layers, capability of deployment with non-capable
routers in a network, extending the technology in a wider inter-AS
scope using IP reachability, and capability of integrating the
functions of the IPv6 data plane.
This model typically needs an extension to IPv6 data plane, with an
IPv6 extension header or Option introduced.
IPv6 functions that are expected to be executed from BFIR to BFER is
supported if correctly designed, for example, IPv6 Fragmentation/
Assembly or IPSEC ESP.
For deployment security, it is necessary to ensure the "BIER" packet
is in a trusted IPv6-based domain.
3.3. Encapsulation Approaches Considered
A number of approaches to the design of BIER-IPv6 encapsulation were
investigated by the BIER Working Group and were discussed in IETF
meetings and on the BIER list. This section divides these approaches
into the two conceptual models.
Transport-Independent Model approaches include:
Transport-Independent BIER [I-D.xu-bier-encapsulation].
BIERin6 [I-D.zhang-bier-bierin6].
Native IPv6 Model approaches include:
BIER-over-IPv6 [I-D.pfister-bier-over-ipv6].
BIERv6 [I-D.xie-bier-ipv6-encapsulation].
4. Requirements
There have been several suggested requirements, on the BIER email
list and in meetings, which have been used to form BIER IPv6
requirements used to help the wg evaluate against the proposed
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solutions. There is also many further discussions on the list about
BIER IPv6 requirements from different scenarios.
Considering that the importance of requirement for BIER IPv6 solution
is different, in this document, the requirements are divided into two
groups: mandatory and optional. The requirements in the mandatory
group are considered necessary for any BIER IPv6 solution, while the
requirements in the optional group should be considered but are not
mandatory.
4.1. Mandatory Requirements
4.1.1. L2 Agnostic
The solution must be agnostic to the underlying L2 data link type.
The solution needs to support P2P ethernet links as well as shared
media ethernet links without requiring the LAN switch to perform BIER
snooping.
4.1.2. Support BIER architecture
The solution must support the BIER architecture.
Multiple sub-domains bound to one or many topologies or algorithms,
multiple sets for more BFERs, multiple Bit String Lengths for
different forwarding capabilities, and multiple BIFTs for ECMP are
considered essential functions of BIER and need to be supported.
4.1.3. Conform to existing IPv6 Spec
The proposed encapsulation must conform to the IPv6 specification and
guidelines as described in RFC8200. If new extensions to existing
IPv6 specification are required, it needs to be discussed and
reviewed by the 6man working-group.
4.1.4. Support deployment with Non-BFR routers
The solution must support deployments with Non-BFR routers. This is
beneficial to the deployment of BIER, especially in early deployments
when some routers do not support BIER forwarding but support IPv6
forwarding. This is also the No.1 charter item, "Transition
Mechanisms and Partial Deployments" of the BIER WG.
4.1.5. Support inter-AS multicast deployment
Inter-AS multicast support is needed for ease of provisioning the
P2MP transport service to enterprises. This could greatly increase
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the scalability of BIER, as it is usually considered to be suitable
only for small intra-AS scenarios.
4.1.6. Support Simple Encapsulation
The solution must avoid requiring different encapsulation types. A
solution needs to do careful trade-off analysis and select one
encapsulation as its proposal for best coverage of various scenarios.
4.1.7. Support Deployment Security
The proposed solution must include careful security considerations,
including all that is already considered in BIER architecture RFC8279
and RFC8296, and other security concerns that may raise due to the
addition of IPv6.
4.2. Optional Requirements
4.2.1. Support MVPN
The solution MAY support MVPN services that is defined in [RFC6513].
When MVPN is supported, it should work in a "tunnel" mode,
encapsulating IP or IPv6 multicast packet in an outer IPv6 header.
When MVPN is supported, it is suggested to think about both intra-AS
and inter-AS deployment.
4.2.2. Support OAM
BIER OAM MAY be supported, either directly using existing method, or
specify some variant method for the same function. It may be
considered essential as part of the BIER architecture in some cases.
4.2.3. Support IPSEC
IPSEC is optional to IPv6 and multicast. It is preferred to support
IPSEC, including AH/ESP. If IPSEC is to be supported, it shouldn't
require hop-by-hop encryption/decryption.
4.2.4. Support Fragmentation
As part of IPv6 specification [RFC8200], BIER IPv6 may support
fragmentation on BFIR and assembly on BFER. Support of Fragmentation
can enhance the capability of BIER leveraging the BIER-MTU as
introduced in section 3 of [RFC8296]. If Fragmentation is to be
supported, it shouldn't require fragmentation and re-assembly at each
hop.
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4.2.5. Support hardware fast path
If a proposed solution is intended for some scenarios like service-
provider networks, it should enable the processing and forwarding of
BIER packets in hardware fast path.
5. IANA Considerations
Some BIERv6 encapsulation proposals do not require any action from
IANA while other proposals require new BIER Destination Option
codepoints from IPv6 sub-registries, new "Next header" values, or
require new IP Protocol codes. This document, however, does not
require anything from IANA.
6. Security Considerations
There are no security issues introduced by this draft.
7. Acknowledgement
Thank you to Eric Rosen for his listed set of requirements on the
bier wg list.
8. Normative References
[I-D.geng-bier-ipv6-inter-domain]
Geng, L., Xie, J., McBride, M., and G. Yan, "Inter-Domain
Multicast Deployment using BIERv6", draft-geng-bier-ipv6-
inter-domain-01 (work in progress), January 2020.
[I-D.ietf-bier-use-cases]
Nainar, N., Asati, R., Chen, M., Xu, X., Dolganow, A.,
Przygienda, T., Gulko, A., Robinson, D., Arya, V., and C.
Bestler, "BIER Use Cases", draft-ietf-bier-use-cases-11
(work in progress), March 2020.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-16 (work in
progress), June 2020.
[I-D.pfister-bier-over-ipv6]
Pfister, P. and I. Wijnands, "An IPv6 based BIER
Encapsulation and Encoding", draft-pfister-bier-over-
ipv6-01 (work in progress), October 2016.
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[I-D.xie-bier-ipv6-encapsulation]
Xie, J., Geng, L., McBride, M., Asati, R., Dhanaraj, S.,
Zhu, Y., Qin, Z., Shin, M., and X. Geng, "Encapsulation
for BIER in Non-MPLS IPv6 Networks", draft-xie-bier-
ipv6-encapsulation-07 (work in progress), June 2020.
[I-D.xu-bier-encapsulation]
Xu, X., somasundaram.s@alcatel-lucent.com, s., Jacquenet,
C., Raszuk, R., and Z. Zhang, "A Transport-Independent Bit
Index Explicit Replication (BIER) Encapsulation Header",
draft-xu-bier-encapsulation-06 (work in progress),
September 2016.
[I-D.zhang-bier-bierin6]
Zhang, Z., Przygienda, T., Wijnands, I., Bidgoli, H., and
M. McBride, "BIER in IPv6 (BIERin6)", draft-zhang-bier-
bierin6-04 (work in progress), January 2020.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<https://www.rfc-editor.org/info/rfc4023>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/info/rfc7510>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8663] Xu, X., Bryant, S., Farrel, A., Hassan, S., Henderickx,
W., and Z. Li, "MPLS Segment Routing over IP", RFC 8663,
DOI 10.17487/RFC8663, December 2019,
<https://www.rfc-editor.org/info/rfc8663>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
Appendix A. Solutions Evaluation
The following are solutions that have been proposed to solve BIER in
IPv6 environments. Some solutions propose encoding while others
propose encapsulation. It is recommended for the wg to evaluate
these solutions against the requirements listed previously in order
to make informed decisions on solution readiness.
As illustrated in these examples, the BIER header, or the BitString,
may appear in the IPv6 Header, IPv6 Extension Header, IPv6 Payload,
or IPv6 Tunnel Packet:
A.1. BIER-ETH encapsulation in IPv6 networks
+---------------+-----------------+-------------------
| Ethernet | BIER header | payload
| (ethType = | (BIFT-id, ...) |
| 0xAB37) | |
| | Next Header |
+---------------+-----------------+-------------------
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BIER-ETH encapsulation (BIER header for Non-MPLS networks as defined
in [RFC8296]) can be used to transport the multicast data in the IPv6
network by encapsulating the multicast user data payload within the
BIER-ETH header. However, BIER-ETH in IPv6 networks is not
considered to be a "BIER natively in IPv6" solution which utilizes
the IPv6 header to forward the packet.
Mixed use of BIER-ETH in a native IPv6 solution is up to the solution
and is outside the scope of this document.
A.2. Encode Bitstring in IPv6 destination address
+---------------+-------------------
| IPv6 header | payload
| (BitString in |
| DA lower bits)|
| Next Header |
+---------------+-------------------
As described in [I-D.pfister-bier-over-ipv6], The information
required by BIER is stored in the destination IPv6 address. The 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. No
additional extension or encapsulation header is required. Instead of
encapsulating the packet in IPv6, the payload is attached to the BIER
IPv6 header and the IPv6 protocol number is set to the type of the
payload. If the payload is UDP, the UDP checksum needs to change
when the BitString in the IPv6 destination address changes.
A.3. Add BIER header into IPv6 Extension Header
+---------------+-----------------+-------------------
| IPv6 header | IPv6 Ext header | payload
| | (BIER header in |
| | TLV Type = X) |
| Next Header | Next Header |
+---------------+-----------------+-------------------
According to [RFC8200] In IPv6, optional internet-layer information
is encoded in separate headers that may be placed between the IPv6
header and the upper- layer header in a packet. There is a small
number of such extension headers, each one identified by a distinct
Next Header value. An IPv6 packet may carry zero, one, or more
extension headers, each identified by the Next Header field of the
preceding header. Extension headers (except for the Hop-by-Hop
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Options header) are not processed, inserted, or deleted by any node
along a packet's delivery path, until the packet reaches the node (or
each of the set of nodes, in the case of multicast) identified in the
Destination Address field of the IPv6 header. The Hop-by-Hop Options
header is not inserted or deleted, but may be examined or processed
by any node along a packet's delivery path, until the packet reaches
the node (or each of the set of nodes, in the case of multicast)
identified in the Destination Address field of the IPv6 header. The
Hop-by-Hop Options header, when present, must immediately follow the
IPv6 header. Its presence is indicated by the value zero in the Next
Header field of the IPv6 header.
Two of the currently-defined extension headers are the Hop-by-Hop
Options header and the Destination Options header which carry a
variable number of type-length-value (TLV) encoded "options".
In [I-D.xie-bier-ipv6-encapsulation] an IPv6 BIER Destination Option
is carried by the IPv6 Destination Option Header (indicated by a Next
Header value 60). It is initialized in a packet sent by an IPv6 BFIR
router to inform the following BFR routers in an IPv6 BIER domain to
replicate to destination BFER routers hop-by-hop. BIER is generally
a hop-by-hop and one-to-many architecture and it is required for a
BIER IPv6 encapsulation to include the BIER Header ([RFC8296]) as an
IPv6 Extension Header, to pilot the hop-by-hop BIER replication.
Hop by hop Options Headers may be considered. The Hop-by-Hop Options
header is used to carry optional information that may be examined and
processed by every node along a packet's delivery path. The Hop-by-
Hop Options header is identified by a Next Header value of 0 in the
IPv6 header.
Defining New Extension Headers and Options may also be considered, if
the IPv6 Destination Option Header is not good enough and new
extension headers can solve the problem better.
Such proposals may include requests to IANA to allocate a "BIER
Option" code from "Destination Options and Hop-by-Hop Options", and/
or a "BIER Option Header" code from "IPv6 Extension Header Types".
A.4. Transport BIER as IPv6 payload
+---------------+-----------------+-------------------
| IPv6 header | IPv6 Ext header | BIER Hdr + payload
| | (optional) | as IPv6 payload
| | |
| Next Header | Next Header = X |
+---------------+-----------------+-------------------
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There is a proposal for a transport-independent BIER encapsulation
header which is applicable regardless of the underlying transport
technology. As described in [I-D.xu-bier-encapsulation] and
[I-D.zhang-bier-bierin6], the BIER header, and the payload following
it, can be combined as an IPv6 payload, and be indicated by a new
Upper-layer IPv6 Next-Header value. A unicast IPv6 destination
address is used for the replication and changes when replicating a
packet out to a neighbor.
Such proposals may include a request to IANA to allocate an IPv6
Next-Header code from "Assigned Internet Protocol Numbers".
A.5. Tunnelling BIER in a IPv6 tunnel
+---------------+-----------------+------------+----------------
| IPv6 header | IPv6 Ext header | GRE header |
| | (optional) | | BIER Hdr +
| | | | payload as GRE
| Next Header | Next Header | Proto = X | Payload
+---------------+-----------------+------------+----------------
A generic IPv6 Tunnel could be used to encapsulate the bier packet
within an IPv6 domain.
GRE is a mechanism by which any ethernet payload can be carried by an
IP GRE tunnel due to the 16-bits 'Protocol Type' field. Both IPv4
and IPv6 can be used to carry GRE. The Ethernet type codepoint
0xAB37, defined for BIER, can be used in a GRE header to indicate the
subsequent BIER header and payload in an IPv6 network.
+---------------+-----------------+------------+----------------
| IPv6 header | IPv6 Ext header | UDP header |
| | (optional) | | BIER Hdr +
| | | | payload as UDP
| Next Header | Next Header | DPort = X | Payload
+---------------+-----------------+------------+----------------
UDP-based tunnelling is another mechanism which uses a specific UDP
port to indicate a UDP payload format. Both IPv4 and IPv6 can
support UDP. Such UDP-based tunnels can be used for BIER in a IPv6
network by defining a new UDP port to indicate the BIER header and
payload.
Authors' Addresses
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Mike McBride
Futurewei
Email: michael.mcbride@futurewei.com
Jingrong Xie
Huawei
Email: xiejingrong@huawei.com
Senthil Dhanaraj
Huawei
Email: senthil.dhanaraj@huawei.com
Rajiv Asati
Cisco
Email: rajiva@cisco.com
Yongqing Zhu
China Telecom
Email: zhuyq8@chinatelecom.cn
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Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring
,
MD 20904
United States of America
Phone:
301 502-1347
Email:
gyan.s.mishra@verizon.com
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