Internet DRAFT - draft-xie-6man-bier-encapsulation
draft-xie-6man-bier-encapsulation
Network Working Group J. Xie
Internet-Draft Huawei Technologies
Intended status: Standards Track L. Geng
Expires: March 10, 2019 L. Wang
China Mobile
G. Yan
M. McBride
Y. Xia
Huawei
September 6, 2018
Encapsulation for BIER in Non-MPLS IPv6 Networks
draft-xie-6man-bier-encapsulation-02
Abstract
Bit Index Explicit Replication (BIER) introduces a new multicast-
specific BIER Header. Currently BIER has two types of encapsulation
formats: one is MPLS encapsulation, the other is Ethernet
encapsulation. This document proposes a BIER IPv6 encapsulation for
Non-MPLS IPv6 Networks using an IPv6 Destination Option extension
header.
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 [RFC2119].
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 March 10, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement and Requirements . . . . . . . . . . . . . 3
3.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 3
3.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 3
4. IPv6 BIER Encapsulation . . . . . . . . . . . . . . . . . . . 4
4.1. Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.2. IPv6 BIER Destination Option . . . . . . . . . . . . . . 4
4.3. The whole IPv6 header for BIER packets . . . . . . . . . 5
5. IPv6 BIER Forwarding . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. Appendix A - BIER over IPv6 SRH Tunnel . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
that provides optimal multicast forwarding without requiring
intermediate routers to maintain any per-flow state by using 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 BIER Ethernet encapsulation to run on ethernet links, with
an ethertype 0xAB37. This document proposes a BIER IPv6
encapsulation for Non-MPLS IPv6 Networks using an IPv6 Destination
Option extension header.
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2. Terminology
Readers of this document are assumed to be familiar with the
terminology and concepts of the documents listed as Normative
References.
3. Problem Statement and Requirements
3.1. Problem Statement
MPLS is a very popular and successful encapsulation. With MPLS
encapsulation, packets forwarding can not only run on various
physical links hop-by-hop, but also leverage the MPLS bypass tunnel
to gain the "fast reroute" capability.
This same label benefit is also available for BIER by using an MPLS
encapsulation. For example, an MPLS-encapsulated BIER packet can be
forwarding on various physical links hop-by-hop, as well as on any
MPLS bypass tunnels to support "fast reroute".
With a BIER Ethernet encapsulation, however, a packet can not be
forwarded on any other type of links except for ethernet links in
hop-by-hop case. It can not run on an MPLS bypass tunnel to support
"fast reroute" either.
In an IPv6 network, there are considerations of using a non-MPLS
encapsulation for unicast as the data-plane, such as SRH defined in
[I-D.ietf-6man-segment-routing-header], where the function of a
bypass tunnel uses an SRH header, with one or many Segments (or
SIDs), instead of MPLS Labels. In such case, it is expected to have
a BIER IPv6 encapsulation, which can run on IPv6 to be compliant with
various kind of physical link in hop-by-hop case, as well as on SRH
tunnel to have the significant benefit of "fast reroute" and so on.
3.2. Requirements
This chapter lists the BIER IPv6 encapsulation requirements needed to
make the deployment of BIER on IPv6 network with SRH data-plane the
same as on IPv4/IPv6 network with MPLS data-plane. These BIER IPv6
encapsulation requirements should provide similar benefits to MPLS
encapsulation such as "fast reroute" or "run on any link or
interface".
1. The listed requirements MUST be supported with any L1/L2 over
which BIER layer can be realized.
2. It SHOULD support a hop-by-hop replication to multiple
destinations in a BIER Domain.
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3. It SHOULD support BIER on an "SRH tunnel".
4. It SHOULD align with the recommendations of the 6MAN working
group.
4. IPv6 BIER Encapsulation
4.1. Considerations
BIER is generally a hop-by-hop and one-to-many architecture, and thus
the IPv6 Destination Address (DA) being a Multicast Address is a
proper approach for both the two diagrams in BIER IPv6 encapsulation.
It is also 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.
According to [RFC8200], [RFC6564], and [RFC7045], a new defined IPv6
extention header is not recommended, and an IPv6 Destination Option
extension header is suitable and recommended for such a well-known
BIER header as its Option.
4.2. IPv6 BIER Destination Option
The 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.
The IPv6 BIER Destination Option is encoded in type-length-value
(TLV) format as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Non-MPLS BIER Header (defined in RFC8296) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPv6 BIER Destination Option
Next Header 8-bit selector. Identifies the type of header
immediately following the Destination Options header.
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Hdr Ext Len 8-bit unsigned integer. Length of the Destination
Options header in 8-octet units, not including the first 8 octets.
Option Type TBD. Need to be allocated by IANA.
Option Length 8-bit unsigned integer. Length of the option, in
octets, excluding the Option Type and Option Length fields.
Non-MPLS BIER Header The Non-MPLS BIER Header defined in RFC8296,
including the BIFT-id. The function of TTL field is replaced by
the Hop Limit field in IPv6 header and MUST be set to a non-zero
value. The function of Entropy field is replaced by the Flow
Label field in IPv6 header and MUST be set to zero value.
4.3. The whole IPv6 header for BIER packets
[RFC8200] specifies that the Destination Option Header can be located
either before the Routing Header or after the Routing Header.
However, this document requires that the Destination Option Header
with a BIER Destination Option TLV is always located after the
Routing Header if the Routing Header is present.
This is because the BIER header is always handled after the tunnels
(or bypass tunnels) have been handled. BIER MPLS encapsulation has
the same behavior. To quote [RFC8296]:
o It is crucial to understand that in an MPLS network the first four
octets of the BIER encapsulation header are also the last four
octets of the MPLS header. Therefore, any prior MPLS label stack
entries MUST have the S bit (see [RFC3032]) clear (i.e., the S bit
must be 0).
Other IPv6 extension headers are not commonly used in the current
Internet. For Example, [RFC6744] says that "IPv6 Destination Options
headers, and the options carried by such headers, are extremely
uncommon in the deployed Internet". [RFC6564] says that "Extension
headers, with the exception of the Hop-by-Hop Options header, are not
usually processed on intermediate nodes", and that "Reports from the
field indicate that some IP routers deployed within the global
Internet are configured either to ignore the presence of headers with
hop-by-hop behavior or to drop packets containing headers with hop-
by-hop behavior."
Such IPv6 extension headers will even be more uncommon when a BIER
encapsulation is used in data-plane forwarding. The entire IPv6
header, with BIER encapsulation and Routing Header, is expected to
look like this:
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IPv6 header [Multicast Address in DA]
Hop-by-Hop Options header [No use]
Destination Options header [No use]
Routing header [SRH Header may be used, Appendix A]
Fragment header [No use ]
Authentication header [No use]
Encapsulating Security Payload header [No use]
Destination Options header [BIER header in BIER Option TLV]
Upper-layer header [BIER payload]
In a hop-by-hop BIER IPv6 replication scenario, there is only an IPv6
header with DA being a "BIER specific" Multicast address, and an IPv6
Destination Option header with a BIER destination option TLV.
BIER header has a 'proto' field to identify the type of BIER packet
payload, and the IANA has created a registry called "BIER Next
Protocol Identifiers" to assign the value. That means the 'Upper-
layer header' of a BIER packet have already been identified by the
'proto' field of the BIER header in the Destination Option Header.
Thus the 'Next Header' in the Destination Option Header is not need
to identify the 'Upper-layer header' any more, and is recommended to
be set to 'No Next Header (value 59)'.
Procedures for encapsulating a BIER IPv6 packet in SRH tunnel are
outside the scope of this document.
Procedures for encapsulating a BIER IPv6 packet in other types of
tunnels are outside the scope of this document.
5. IPv6 BIER Forwarding
In an IPv6 BIER domain, the Multicast Address of the IPv6 DA in an
incoming BIER IPv6 packet indicates the BIER information of this
'host', and the packet will be forwarded according to the BIER Header
in the BIER Destination Option TLV in the IPv6 Destination Option
extension header. A router is required to ignore the IPv6 BIER
Destination Option if the IPv6 Destination Address of a packet is not
a multicast address, or is a multicast adddress without indicating
the BIER information of this 'host'.
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Below is the procedure that a BFR uses for forwarding a BIER IPv6
encapsulated packet.
1. Read the IPv6 header, get the the IPv6 DA, and get the indication
of the multicast address if the IPv6 DA is a multicast address.
The case when IPv6 DA not being a multicast address is outside
the scope of this document.
2. If the multicast address is interested by this router, and the
'Next Header' of the IPv6 header indicates a IPv6 Destination
Option Header, then read the IPv6 Destination Option Header, and
get the BIER Option (BIER Header). The case when the multicast
address not being interested by this router is outside the scope
of this document.
3. The following steps are the same as step 1 to 9 described in
chapter 6.5 in [RFC8279]. One difference need to point out is
that, the copied packet includes a IPv6 header, a IPv6
Destination Header and its BIER Destination Option Type and
Option Length before the BIER Header. If the copied packet is
forwarded to a BFR-NBR, the 'Hop Limit' field of the IPv6 header
MUST be decremented, whereas the TTL in the BIER header MUST be
unchanged.
Procedures for forwarding a BIER IPv6 packet in SRH tunnel, and hand-
off to a hop-by-hop replication, can refer to Appendix A.
Procedures for forwarding a BIER IPv6 packet in other types of
tunnels, and hand-off to a hop-by-hop replication, are outside the
scope of this document.
6. Security Considerations
An IPv6 BIER Destination Option with Multicast Address Destination
would be used only when an IPv6 BIER state with the specific
Multicast Address Destination has been built by the control-plane.
Otherwise the packet with an IPv6 BIER Destination Option will be
discarded.
7. IANA Considerations
Allocation is expected from IANA for a BIER Destination Option Type
codepoint from the "Destination Options and Hop-by-Hop Options" sub-
registry of the "Internet Protocol Version 6 (IPv6) Parameters"
registry [RFC2780] at <https://www.iana.org/assignments/
ipv6-parameters/>.
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Allocation is expected from IANA for a BIER Multicast Address from
the "Variable Scope Multicast Addresses" sub-registry of the "IPv6
Multicast Address Space Registry" registry at
<https://www.iana.org/assignments/ipv6-multicast-addresses/>.
8. Acknowledgements
TBD.
9. Appendix A - BIER over IPv6 SRH Tunnel
In a Non-MPLS IPv6 Network, BIER may be deployed in a hop-by-hop
manner, or possibly be deployed through an SRH tunnel either for
"bypassing Non-capable BIER routers" or "fast rerouting". Here is an
example where a packet is firstly forwarded through an SRH tunnel and
then through a hop-by-hop BIER domain.
When a router along the Segment Routing path receives an IPv6 BIER
packet with an SRH header, and if the IPv6 destination address is not
one of the router's address, then the packet is forwarded by an IPv6
FIB lookup of the destination address and none of the IPv6 extension
headers will be checked. If the IPv6 Destination Address is one of
the router's address, and also one of the router's Segment (or SID)
of some type, then the router will do a specific function indicated
by the Segment, as defined in
[I-D.filsfils-spring-srv6-network-programming]. If the IPv6
Destination Address is a specific type of Segment, called BIER
Segment or BIER SID, then the according function is called Endpoint
BIER function or 'End.BF' function for short.
When router receives a packet destined to X and X is a local End.BF
SID, the router does:
1. IF SL > 0
2. decrement SL
3. update IPv6 DA with SRH[SL]
4. IF SL = 0 & STATE(SRH[0]) = BIER
5. update IPv6 header NH with SRH NH
6. pop the SRH
7. forward the updated packet
8. ELSE
9. drop the packet
10. ELSE
11. drop the packet
Figure 2: End.BF Function
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The End.BF function is used for the SRH tunnel destination router to
terminate the source-routing SRH forwarding and begin the hop-by-hop
BIER IPv6 forwarding. After the SRH header is popped, the multicast
address in the updated IPv6 Destination Address indicates the BIER
information of this 'host', and the packet will be forwarded
according to the BIER Header in the BIER Destination Option TLV in
the IPv6 Destination Option extension header of this 'host'.
In the following hop-by-hop forwarding procedure, the IPv6
Destination Address in an incoming packet indicates the BIER
information of this 'host', and the packet will be forwarded
according to the BIER Header in the BIER Destination Option TLV in
the IPv6 Destination Option extension header. A router is required
to ignore the IPv6 BIER Destination Option if the IPv6 Destination
Address of a packet is not a multicast address, or is a multicast
adddress without indicating the BIER information of this 'host'.
10. References
10.1. Normative References
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-05 (work in progress), July 2018.
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-14 (work in
progress), June 2018.
[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
RFC 6564, DOI 10.17487/RFC6564, April 2012,
<https://www.rfc-editor.org/info/rfc6564>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
[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>.
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[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>.
10.2. Informative References
[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>.
Authors' Addresses
Jingrong Xie
Huawei Technologies
Email: xiejingrong@huawei.com
Liang Geng
China Mobile
Beijing 10053
Email: gengliang@chinamobile.com
Lei Wang
China Mobile
Beijing 10053
Email: wangleiyjy@chinamobile.com
Gang Yan
Huawei
Email: yangang@huawei.com
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Mike McBride
Huawei
Email: mmcbride7@gmail.com
Yang Xia
Huawei
Email: yolanda.xia@huawei.com
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