BIER Working Group W. Wang
Internet-Draft A. Wang
Intended status: Standards Track China Telecom
Expires: April 28, 2022 October 25, 2021
Routing Header Based BIER Information Encapsulation
draft-wang-bier-rh-bier-02
Abstract
This draft proposes one new encapsulation schema of Bit Index
Explicit Replication (BIER) information to transfer the multicast
packets within the IPv6 network. By using a new IPv6 Routing Header
type to forward the packet, the original source address and
destination address of the multicast packet is kept unchanged along
the forwarding path. Such encapsulation schema can make full use of
the existing IPv6 quality assurance solutions to provide high-quality
multicast service.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 28, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. BIER Routing Header . . . . . . . . . . . . . . . . . . . . . 3
4. Multicast Packet Forwarding Procedures . . . . . . . . . . . 5
4.1. All devices in BIER domain support BIER Routing Header . 5
4.2. Some devices in BIER domain do not support BIER Routing
Header . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Bit Index Explicit Replication (BIER) is a new multicast technology
based on IPv6 defined in [RFC8279]. In BIER domain, the set of
destination nodes of multicast message is mapped into a BitString and
encapsulated into the BIER header. The position of each bit in the
BitString represents an BFER. Compared with the traditional
multicast technology, the nodes in BIER domain do not need to
maintain a multicast tree and keep the multicast flow state for each
multicast flow.
Currently, there are two methods for encapsulating BIER information
based on IPv6 in IETF: BIERn6([I-D.ietf-bier-bierin6]) and
BIERv6([I-D.xie-bier-ipv6-encapsulation]).
BIERin6 carries BIER information by defining a new IPv6 next header
type. During the forwarding process, the source address and
destination address in the header will be changed.
BIERv6 carries bier related information by defining an new option
type of destination options header (i.e. bier option). The source
address in the header remains unchanged but the destination address
will be changed along the forwarding path.
The differences between the above two BIER encapsulation and
forwarding schemes are unfavorable for the development of BIER and
its derivatives. In addition, when there is error in the forward
process of the multicast packet, the change of source address and
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destination address during transmission will increase the difficulty
of fault location and traceability.
This draft proposes a BIER information transmission scheme without
changing the multicast source and destination addresses. The
relevant BIER information is encapsulated within the newly defined
IPv6 Routing Header type, each intermediate BIER router will route
the multicast packet based on the BitString information and its
associated BIFT. The multicast source and destination address are
not changed along the forwarding path.
The characteristics of such schema are helpful to the rapid fault
location and traceability, and can make full use of the existing IPv6
quality assurance technologies to provide high-quality multicast
service.
2. Conventions used in this document
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] .
3. BIER Routing Header
One new type of IPv6 Routing Header is defined according to
[RFC8200]. The message format is shown in Figure 1.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segment Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BIFT-id | Ver | TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSL | Entropy | DSCP |OAM|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFIR-id |Rsv| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. BitString .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The format of BIER Routing Header
Where:
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o Next Header(8 bits): indicating the message header type
immediately after the routing header.
o HDR Ext Len(8 bits): indicating the length of the routing header.
o Routing Type(8 bits): TBD. Identifying the newly defined Routing
Header to encode BIER information.
o Segments Left(8 bits): indicating the number of explicitly listed
intermediate nodes to be accessed before reaching the final
destination. It is not used here for the time being, and all are
set to 0.
o BIFT-id(20 bits): each < SD, Si, BSL > is assigned a BIFT-id.
o Ver(4 bits): identifying the version of the BIER header. When an
unsupported BIER header version is received, the BFR needs to
discard the packet and record the error.
o TTL(8 bits): indicating the lifetime of the message. It is used
to prevent ring. The processing process is the same as that in
non MPLS networks.
o BSL(4 bits): indicating the length of BitString.
o Entropy(20 bits): this field specifies an "entropy" for ECMP.
o DSCP(6 bits): this field is used to support different service
codes.
o OAM(2 bits): by default, this value will be set to 0 by BFIR, and
other BFRs will not be modified. Whether to use this field is
optional.
o BFIR-id(16 bits): indicating BFR ID of BFIR.
o Rsv(2 bits): unused, set to 0.
o Reserved (14 bits): reserved field, set to 0.
o BitString(variable): the length must be reflected in the BSL
field. The string saved in this field is used to identify the
destination BFER of the packet.
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4. Multicast Packet Forwarding Procedures
Based on the newly defined BIER Routing Header, the devices support
BIER Routing Header will perform the following steps to forward the
multicast packets:
1) When BFIR receives the IPv6 multicast packets from the mulicast
source, it will add BIER Routing Header to indicate the BFERs that
want to receives such multicast packet. The encapsulated multicast
packet will be forwarded according to the BIFT that identified by the
BIFT-id.
2) Each BFR (includes BFIR) will check whether the direct-connected
device support BIER Routing Header. If yes, proceed to step 3);
otherwise, proceed to step 2.1).
2.1) Calculating the IPv6 address of next hop that support BIER
Routing Header.
2.2) Encapsulating an outer IPv6 Header to the multicast packet. The
calculated IPv6 address is used as the destination address of the
outer IPv6 Header, and its own IPv6 address is used as the source
address of the outer IPv6 Header. BitString will not be changed.
2.3) Sending the encapsulated packet to the direct-connected device,
the device will perform normal IPv6 forwarding according to the outer
IPv6 Header.
3) On the router that supports the BIER Routing Header, perform the
normal BIER forwarding process as described in [RFC8279].
The detail procedures for forwarding the multicast packets based on
the newly defined Routing Header are described in the following
sections.
4.1. All devices in BIER domain support BIER Routing Header
+---+
+-----------+ B +----------+
| +---+ |
| 0:01000000 |
| |
| |
| |
+-+-+ +-+-+ (Packet 2) +---+ (Packet 3)+---+
| A |0:10000000 0:00100000| C +------------+ E +-----------+ F |
+-+-+ +-+-+ +---+ +---+
| | 0:00001000 0:00000100
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| |
| |
| |
| 0:00010000 |
| +---+ |
+-----------+ D +----------+
(Packet 1) +---+
Packet 1
+------------------------------------+
IPv6 | IPv6 Address of Multicast Source |
Header +------------------------------------+
| IPv6 Multicast Destination Address |
BIER +------------------------------------+
Routing| BitString = 00101100 |
Header +------------------------------------+
Packet 2
+------------------------------------+
IPv6 | IPv6 Address of Multicast Source |
Header +------------------------------------+
| IPv6 Multicast Destination Address |
BIER +------------------------------------+
Routing| BitString = 00001100 |
Header +------------------------------------+
Packet 3
+------------------------------------+
IPv6 | IPv6 Address of Multicast Source |
Header +------------------------------------+
| IPv6 Multicast Destination Address |
BIER +------------------------------------+
Routing| BitString = 00000100 |
Header +------------------------------------+
Figure 2: All devices in BIER domain support BIER Routing Header
The topology is shown in Figure 2, device A-F support BIER Routing
Header. The packet need to be transmitted from A to F. The changes
of the Routing Header have been given in Figure 2. Each device will
perform the following steps after receiving the packet:
1). Checking whether there is BIFT corresponding to the BIFT-id
locally. If yes, proceed to step 2); otherwise, discard the packet.
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2). Checking whether the direct-connected device support BIER
Routing Header. If yes, forwarding the packet according to the BIFT
related to the BIFT-id; otherwise, see sectionSection 4.2 for detail
procedures.
During the forwarding procedures, the source address and destination
address of the IPv6 multicast packet are not changed, only the
BitString in BIER Routing Header is updated.
4.2. Some devices in BIER domain do not support BIER Routing Header
+---+
+-----------+ B +-----------+
| +---+ |
| 0:01000000 |
| |
| |
| |
+-+-+ +-+-+ +---+ (Packet 3) +---+
| A |0:10000000 | C +------------+ E +------------+ F |
+-+-+ +-+-+ +---+ +---+
| | 0:00001000 0:00000100
| |
| |
| |
| 0:00010000 |
| +---+ |
+-----------+ D +-----------+
(Packet 1) +---+(Packet 2)
Packet 1
+------------------------------------+
IPv6 | IPv6 Address of Multicast Source |
Header +------------------------------------+
| IPv6 Multicast Destination Address |
BIER +------------------------------------+
Routing| BitString = 00101100 |
Header +------------------------------------+
Packet 2
+------------------------------------+
Outer | Source IP Address = D |
IPv6 +------------------------------------+
Header | Destination IP Address = E |
+------------------------------------+
Inner | IPv6 Address of Multicast Source |
IPv6 +------------------------------------+
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Header | IPv6 Multicast Destination Address |
+------------------------------------+
BIER | BitString = 00001100 |
Routing+------------------------------------+
Header
Packet 3
+-------------------------------------+
IPv6 | IPv6 Address of Multicast Source |
Header +-------------------------------------+
| IPv6 Multicast Destination Address |
BIER +-------------------------------------+
Routing| BitString = 00000100 |
Header +-------------------------------------+
Figure 3: Some devices in BIER domain do not support BIER Routing Header
The topology is shown in Figure 3, all devices expect device C
support BIER Routing Header. The packet need to be transmitted from
A to F. The change of the Header has been given in the Figure 3.
When it is found that device C does not support BIER Routing Header,
device D will perform the following steps after receiving the packet:
1. Calculating the IPv6 address of next hop device(Node E) that
supports BIER Routing Header.
2. Encapsulating an outer IPv6 Header to the packet. The calculated
IPv6 address(E) is used as the destination address of the outer IPv6
Header, and its own IPv6 address(D) is used as the source address of
the outer IPv6 Header. BitString will not be changed.
3. Sending the packet to directed-connected device C.
After receiving the packet, device C will perform IPv6 forwarding
according the information in outer IPv6 Header, and send the packet
to device E. Device E will send it to device F according the
information in BIER Routing Header. In the forwarding process, the
source address and destination address in the Inner IPv6 Header are
not changed.
5. Security Considerations
TBD
6. IANA Considerations
This document defines a new IPv6 Routing Header - BIER Routing
Header. The code point is from the "Internet Protocol Version 6
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(IPv6) Parameters - Routing Types". It is recommended to set the
code point of BIER Routing Header to 7.
7. References
7.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
7.2. Informative References
[I-D.ietf-bier-bierin6]
Zhang, Z., Zhang, Z., Wijnands, I., Mishra, M., Bidgoli,
H., and G. Mishra, "Supporting BIER in IPv6 Networks
(BIERin6)", draft-ietf-bier-bierin6-00 (work in progress),
June 2021.
[I-D.xie-bier-ipv6-encapsulation]
Xie, J., Geng, L., McBride, M., Asati, R., Dhanaraj, S.,
Zhu, Y., Qin, Z., Shin, M., Mishra, G., and X. Geng,
"Encapsulation for BIER in Non-MPLS IPv6 Networks", draft-
xie-bier-ipv6-encapsulation-10 (work in progress),
February 2021.
Authors' Addresses
Wei Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: weiwang94@foxmail.com
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Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj3@chinatelecom.cn
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