Encapsulation for BIER in Non-MPLS IPv6 Networks
draft-xie-bier-6man-encapsulation-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Jingrong Xie , Gang Yan , Mike McBride , Yang Xia | ||
| Last updated | 2018-04-28 | ||
| Replaced by | draft-xie-bier-ipv6-encapsulation | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-xie-bier-6man-encapsulation-00
Network Working Group J. Xie
Internet-Draft G. Yan
Intended status: Standards Track M. McBride
Expires: October 30, 2018 Y. Xia
Huawei Technologies
April 28, 2018
Encapsulation for BIER in Non-MPLS IPv6 Networks
draft-xie-bier-6man-encapsulation-00
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-
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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 October 30, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement and Requirements . . . . . . . . . . . . . 3
3.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 3
3.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 4
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. BIER Forwarding in Non-MPLS IPv6 Networks . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 formats: one is MPLS encapsulation, the other is non-
MPLS encapsulation. The Non-MPLS encapsulation defined in [RFC8296]
is in fact an Ethernet encapsulation with an ethertype 0xAB37, and an
'Ethernet encapsulation' will be used to refer to such an
encapsulation in the following text. 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. One of the
benefits of MPLS is its ability to easily stack a label onto another,
thus forming a label stack. This same label stacking benefit is also
available for BIER by using an MPLS encapsulation. For example, an
MPLS-encapsulated BIER packet can easily run over an MPLS tunnel,
either a legacy RSVP-TE/LDP LSP, or an MPLS Segment Routing tunnel.
Such a mechanism is the key to obtain the capability of "fast
reroute" or "bypass a Non-capable router". To quote [RFC8279]:
o In the event that unicast traffic to the BFR-NBR is being sent via
a "bypass tunnel" of some sort, the BIER-encapsulated multicast
traffic sent to the BFR-NBR SHOULD also be sent via that tunnel.
This allows any existing "fast reroute" schemes to be applied to
multicast traffic as well as to unicast traffic.
o Unicast tunnels are used to bypass non-BFRs.
Some other scenarios also need BIER to run on a tunnel, such as
transferring a BIER packet through a whole Non-BIER network or
domain.
The capability to run BIER on a tunnel, especially the widely
deployed mpls tunnel, can be obtained by using a BIER MPLS
encapsulation, but cannot be obtained by using a BIER Ethernet
encapsulation. It is not possible either, to run BIER on other links
such as POS, by using BIER Ethernet encapsulation.
The capability of running BIER on various kinds of links and tunnels,
by using an MPLS encapsulation, is beneficial to BIER deployments.
In an IPv6 network, however, 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.
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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.
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, while
Segment Routing is a source-routing and one-to-one architecture. One
of the challenges of an BIER IPv6 Encapsulation is how to allow BIER
to run over a Segment Routing tunnel. A suitable method for such a
combination is to use a Multicast Address as the Last Segment (or
SID). After all the source-routing hops have been processed, the
remaining Multicast Address becomes the IPv6 Destination Address. A
hop-by-hop replicating diagram begins by using the Destination
Multicast Address.
We then need to decide where to place the BIER header. According to
[RFC8200], [RFC6564], and [RFC7045], a suitable place for a well-
known BIER header is an IPv6 Destination Option extension header.
Such a Destination Option carrying BIER header is only used for a
hop-by-hop Multicast Address destination, but not for the transit
router along the source-routing path.
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 used in a
packet sent by an IPv6 BFIR router to inform the routers in an IPv6
BIER domain to replicate to destination BFER routers.
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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.
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.
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).
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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:
IPv6 header
Hop-by-Hop Options header [Not Used]
Destination Options header [Not Used]
Routing header [SRH Header with Multicast Address as last SID]
Fragment header [Not Used]
Authentication header [Not Used]
Encapsulating Security Payload header [Not Used]
Destination Options header [BIER header in BIER Option TLV]
Upper-layer header [Data-plane Data]
Once a packet is encapsulated with a BIER Destination Option, it is
basically assumed to be a data-plane multicast packet, so the 'OAM'
or similar functions in the SRH Header Optional TLV Objects field
should not exist.
The last Segment (SID) in the SRH header, or Segment List[0], should
be a Multicast Address to indicate a hop-by-hop behavior. Such a
Multicast Address can be reserved or unreserved as the Destination
Option Header can inform the routers to do the address check. A
reserved multicast address should be indicating a 'BIER specific'
address.
BIER header has a 'proto' field to identify the type of BIER packet
payload, and the IANA has created a registry called "BIER Next
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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)'.
5. BIER Forwarding in Non-MPLS IPv6 Networks
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 first forwarded through an SRH tunnel and
then through a hop-by-hop manner.
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
The End.BF function is used for the SRH tunnel destination router to
terminate the source-routing SRH forwarding while begining the hop-
by-hop BIER IPv6 forwarding. After the SRH header is popped, the
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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.
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'.
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 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/>.
8. Acknowledgements
TBD.
9. References
9.1. Normative References
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Li, Z., Leddy, J., daniel.voyer@bell.ca, d.,
daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R.,
Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,
Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P., and
M. Sharif, "SRv6 Network Programming", draft-filsfils-
spring-srv6-network-programming-04 (work in progress),
March 2018.
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[I-D.ietf-6man-segment-routing-header]
Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-12 (work in
progress), April 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>.
[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>.
9.2. 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
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Gang Yan
Huawei Technologies
Email: yangang@huawei.com
Mike McBride
Huawei Technologies
Email: mmcbride7@gmail.com
Yang Xia
Huawei Technologies
Email: yolanda.xia@huawei.com
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