RBS(Recursive BitString Structure) for Multicast Source Routing over IPv6
draft-xu-msr6-rbs-00
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| Last updated | 2022-03-07 | ||
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draft-xu-msr6-rbs-00
Network Working Group B. Xu
Internet-Draft X. Geng
Intended status: Standards Track Huawei
Expires: 8 September 2022 7 March 2022
RBS(Recursive BitString Structure) for Multicast Source Routing over
IPv6
draft-xu-msr6-rbs-00
Abstract
This document defines a new type of segment: End.RBS, and the
corresponding packet processing procedures over the IPv6 data plane
for the MSR6(Multicast Source Routing over IPv6) TE solutions.
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].
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
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Drafts is at https://datatracker.ietf.org/drafts/current/.
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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 8 September 2022.
Copyright Notice
Copyright (c) 2022 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
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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Explicit Multicast Path with RBS . . . . . . . . . . . . . . 3
3.1. RBS Architecture . . . . . . . . . . . . . . . . . . . . 3
3.2. Recursive encoding in packet . . . . . . . . . . . . . . 4
3.3. RBS BIFT . . . . . . . . . . . . . . . . . . . . . . . . 5
4. End.RBS Segment Definition . . . . . . . . . . . . . . . . . 5
5. RBS Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
MSR6(Multicast Source Routing over IPv6) is an IPv6 based multicast
source routing (MSR6) solution, defined in
[I-D.cheng-spring-ipv6-msr-design-consideration], which leverages the
benefits of source routing over IPv6 data plane to provide simplified
multicast TE and BE service in an IPv6 network without unnecessary
multicast tree status and complex control plane protocols. MSR6
needs to reuse the advantages of SRv6 and BIER to implement source
routing.
MSR6 has two basic modes of forwarding: one is based on Shortest Path
First(SPF), which is called MSR6 BE mode; the other is based on
traffic engineered, which is called MSR6 TE mode.
[I-D.geng-msr6-traffic-engineering], [I-D.chen-pim-srv6-p2mp-path]
and [I-D.geng-msr6-rlb-segment] have introduced structured segment
list by defining arguments in each segment.
This document defines IPv6 based RBS [I-D.eckert-bier-cgm2-rbs] which
provides an optional solution for MSR6 TE. A new type of segment
End.RBS and the corresponding RBS type sub-TLV in MRH defined in
[I-D.geng-msr6-traffic-engineering], which could indicate multicast
tree in the a recuisive bitstring and save the header overhead.
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2. Terminologies
MSR6: Multicast Source Routing over IPv6, defined in .
MRH: Multicast Routing Header, a new type of Routing Header which is
used for MSR6 [I-D.cheng-spring-ipv6-msr-design-consideration].
Replication Endpoint: the intermediate node of a multicast tree,
which replicates packet and forwards the packet to the downstream
nodes. For MSR6, the Replication Node is called Replication Endpoint
which can be indicated by the MSR6 Segment and replicate packets
according to the multicast source routing information encapsulation
in the MSR6 header of the packet.
BFR: Bit-Forwarding Router, a router support RBS.
BIFT: Bit Index Forwarding Table, locally to BFR.
RU: RecursiveUnit, a Bit String is to be parsed by BFR along the
multicast tree of the packet, defined in [I-D.eckert-bier-cgm2-rbs]
3. Explicit Multicast Path with RBS
This section describes the encoding of explictit multicast path with
RecursiveUnit BitString Structure (RBS) .
3.1. RBS Architecture
An explicit muliticast path is encapsulated with RBS as shown in
Figure 1.
+----------+---------------------+---------+
| TotalLen | RecursiveUnit | Padding |
+----------+---------------------+---------+
. .
...... TotalLen .......
Figure 1: Architecture of RBS Address
For the reference encoding, TotalLen is an 16-bit field that counts
the size of the RecursiveUnit in bits, permitting for up to 65535 Bit
long RBS addresses.
The Rsv filed,which is defined in [I-D.eckert-bier-cgm2-rbs] , is
omitted in this scenario.
Padding is used to align the RBS address as required by the IPv6
encapsulation.
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3.2. Recursive encoding in packet
This section uses a hierarchical multicast tree as an example to
describe the RecursiveUnit coding format.
+---+
| R |
+-+-+
|
+----------+----+-----+-----------+
| | | |
+-v-+ +-v-+ +-v-+ +-v-+
| A1| | A2| | A3| ... | AM|
+-+-+ +---+ +---+ +---+
|
+----------+----+-----+----------+
| | | |
+-v-+ +-v-+ +-v-+ +-v-+
| B1| | B2| | B3| ... | BN|
+---+ +---+ +---+ +---+
Figure 2: Hierarchical multicast tree
As Shown in Figure 2, the whole explicit multicast path should be
encapsulated (See Section 3.1) in-packet, which will be parsed by
each Router along the delivery tree.
The RecursiveUnit filed is structured as shown in Figure 3. To
abbreviate the size of the figure, we use AF for AddressingFiled, and
RU for RecursiveUnit In the following figures.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TotalLen| BitString | AF 1 | AF 2 | ...| AF M-1 | RU 1 | RU 2 | ...| RU M | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ \
/ \
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+
|BitString|AF 1...N-1|RU 1 ...N|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+
Figure 3: RecursiveUnit Filed Structure
The BitString field guides the first-hop node 'R' to locally
duplicate packets and forwarding. The length of BitString matches
the Maxnumber of adjacencies in node 'R' (See Section 3.3).
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The AddressingField consists M-1 fields. Each filed is an 8-bits
filed and the value of it is the length of relative RecursiveUnit,
and may be the offset in some scenario . The length of last
RecursiveUnit M could be caculated by TotalLen.
And each RecursiveUnit is structured in same mechnism as shown in
Figurse 3.
3.3. RBS BIFT
RBS BIFT as shown in Figure 4 are containing for each BP an
adjacency.
+--+---------+-------------+
|BP|RecuFlag | Adjacency|
+--+---------+-------------+
| 1| 1|adjacenct BFR|
+--+---------+-------------+
| 2| 0| punt/host|
+--+---------+-------------+
| ..... ... |
+--+---------+-------------+
| N| ...| ... |
+--+---------+-------------+
Figure 4: RBS BIFT
The BP of the BIFT are all local to the BFR. When a BFR receives a
packet encapuslated with RBS, it expects that the BitString filed
length must be matched with N, which is configured by BFR.
4. End.RBS Segment Definition
When the packet is received by an Replication Endpoint and the DA of
this packet is a local SID with the function of End.RBS, the packet
will be replicated based on the RBS sub-TLV defined in section 5.
The DA of the replicated packets is replaced by the End.RBS for the
next Replication Endpoinds.
The behavior of End.RBS is defined in section 5 of
[I-D.eckert-bier-cgm2-rbs].
5. RBS Sub-TLV
MRH defined in [I-D.geng-msr6-traffic-engineering] is as follows:
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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 | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MRH Sub-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5.MRH of RBS Type Encapsulation
MRH Sub-type: 8-bit identifier of the sub-type. The sub-type of RBS
is to be assigned by IANA.
Segments Left: MUST be set to 0 when the MRH sub-type is RBS sub-
type.
Type Length Value objects: Must habe RBS sub-TLV when the MRH sub-
type is RBS sub-type.
A "RBS" type sub-TLV is defined for RBS in the feild of Optional Type
Length Value Objects. The format is shown as below
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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| RBS Address(variable) //
| //
| //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6.RBS Sub-TLV
Type: 8-bit identifier of the type of sub-TLV. The type of RBS
option is to be assigned by IANA.
Length: 16-bit unsigned integer indicates the length of the option
Data field of this option, in octets. The value of Opt Data Len of
RBS option depends on the encoding of multicast tree, according to
the mechanism defined in section 3.
RBS Address: defined in [I-D.eckert-bier-cgm2-rbs]. The packet is
forwarded based on the multicast tree indicated by the RBS Address.
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6. Illustration
Figure 7 shows an example for RBS forwarding.
+-+
/-=>-|C|-=> Client2
/ +-+
/
+-+ +-+ +-+ +-+
Client1 =>-|B|-=>-|R|-=>-|S|-=>-|D|-=> Client3
+-+ +-+ +-+ +-+
\
\ +-+
\-=>-|E|-=> Client4
+-+
Figure 7: Example Network Topology
A packet from Client1 connected to BFR B is intended to be replicated
to Client2,3,4.
The encapsulation of RBS at BFR-B is shown in Figure 8.
........................ RecursiveUnit ...................................
. .
+-----------+------------+-----------------------------------------------------------+-------+
|TotalLen:34|BitString:01|RU1:(R:011|AF:00010010|S:011|AF:00000011|C:001|D:0001|E:001)|Padding|
+-----------+------------+-----------------------------------------------------------+-------+
Figure 8: Encapsulation of RBS at BFR-B
Since there is only one RecursiveUnit, the AddressingField is omitted
at BFR-B.
BFR-B rewrites the RBS by replacing the RecursiveUnit with
RecursiveUnit 1 and adjusts the TotalLen and Padding fileds.
And BFR-R receives the packet with RBS, which has been processed by
BFR-B, shown in Figure 9.
.......................... RecursiveUnit ..............................
. .
+-----------+-------------+------------+----------------------------------------------+-------+
|TotalLen:32|BitString:011|AF1:00010010|RU1(S:011|AF1:00000011|C:001|D:0001)RU2(E:001)|Padding|
+-----------+-------------+------------+----------------------------------------------+-------+
Figure 9: Encapsulation of RBS at BFR-R
And BFR-R parse the Bitstring filed using BIFT shown in Figure 10.
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Because there are two recursive BP set in the BitString for R, one
AddressingFiled is required to indicate the length of RecursiveUnit
1.
+--+---------+---------+
|BP|RecuFlag |Adjacency|
+--+---------+---------+
| 1| 1| B |
+--+---------+---------+
| 2| 1| S |
+--+---------+---------+
| 3| 1| E |
+--+---------+---------+
Figure 10: RBS BIFT on BFR-R
BFR-R accordingly creates one copy for BFR-S using RecursiveUnit 1,
and only copy for BFR-E using RecursiveUnit 2, updating Padding
accordingly for each copy.
BFR-S receives from BFR-R the packet as shown in Figure 11.
............. RecursiveUnit ......................
. .
+-----------+-------------+------------+---------------------+-------+
|TotalLen:18|BitString:011|AF1:00000011|RU1(C:001)RU2(D:0001)|Padding|
+-----------+-------------+------------+---------------------+-------+
Figure 11: Encapsulation of RBS at BFR-S
BFR-E receives from BFR-R the packet as shown in Figure 12.
+-----------+-------------+-------+
|TotalLen:32|BitString:001|Padding|
+-----------+-------------+-------+
Figure 12: Encapsulation of RBS at BFR-E
BFR-E would impose or rewrite a unicast encapsulation to make the
packet become a unicast packet directed to Client 4.
The procedures for processing of the packet on BFR-S are very much
the same as on BFR-R.
BFR-C receives from BFR-R the packet as shown in Figure 13. And it
will make the packet become a unicast packet directed to Client 2.
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+-----------+-------------+-------+
|TotalLen:3 |BitString:001|Padding|
+-----------+-------------+-------+
Figure 13: Encapsulation of RBS at BFR-C
BFR-D receives from BFR-R the packet as shown in Figure 14. And it
will make the packet become a unicast packet directed to Client 3.
+-----------+--------------+-------+
|TotalLen:4 |BitString:0001|Padding|
+-----------+--------------+-------+
Figure 14: Encapsulation of RBS at BFR-D
The brief of RBS BitString conversion is shown in Figure 15.
+------------+
|{S=S , D=C} |
+------------+
|[BitStr=001]|
+============+
| (C-MC Pkt) |
+============+ +-+
/--------=>------|C|----=>---Client2
+------------+ +------------+ /+------------+ +-+ +==========+
|{S=B , D=R} | |{S=R , D=S} | / |{S=S , D=D} | |(C-MC Pkt)|
+------------+ +------------+ / +------------+ +==========+
|[BitStr=011]| |[BitStr=011]| / |[BitStr=0001]|
+==========+ +============+ +=============+ / +============+
|(C-MC Pkt)| | (C-MC Pkt) | | (C-MC Pkt) | / | (C-MC Pkt) |
+==========+ +-+ +============+ +-+ +============+ +-+ +============+ +-+
Client1---=>---|B|-------=>-------|R|-------=>-------|S|---------=>-=--------|D|----=>----Client3
+-+ +-+ +-+ +-+ +==========+
+------------+ \ |(C-MC Pkt)|
|{S=R , D=E}| \ +-+ +==========+
+------------+ \-=>-|E|-----=>------ Client4
|[BitStr=001]| +-+ +==========+
+============+ |(C-MC Pkt)|
| (C-MC Pkt) | +==========+
+============+
Figure 15: Brief of RBS BitString coversion
7. IANA Considerations
This document makes no request of IANA.
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Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
9. Acknowledgements
10. Normative References
[I-D.chen-pim-srv6-p2mp-path]
Chen, H., McBride, M., Fan, Y., Li, Z., Geng, X., Toy, M.,
Mishra, G. S., Wang, A., Liu, L., and X. Liu, "Stateless
SRv6 Point-to-Multipoint Path", Work in Progress,
Internet-Draft, draft-chen-pim-srv6-p2mp-path-05, 11
November 2021, <https://www.ietf.org/archive/id/draft-
chen-pim-srv6-p2mp-path-05.txt>.
[I-D.cheng-spring-ipv6-msr-design-consideration]
Cheng, W., Mishra, G., Li, Z., Wang, A., Qin, Z., and C.
Fan, "Design Consideration of IPv6 Multicast Source
Routing (MSR6)", Work in Progress, Internet-Draft, draft-
cheng-spring-ipv6-msr-design-consideration-01, 25 October
2021, <https://www.ietf.org/archive/id/draft-cheng-spring-
ipv6-msr-design-consideration-01.txt>.
[I-D.eckert-bier-cgm2-rbs]
Eckert, T. and B. (. Xu, "Carrier Grade Minimalist
Multicast (CGM2) using Bit Index Explicit Replication
(BIER) with Recursive BitString Structure (RBS)
Addresses", Work in Progress, Internet-Draft, draft-
eckert-bier-cgm2-rbs-01, 9 February 2022,
<https://www.ietf.org/archive/id/draft-eckert-bier-cgm2-
rbs-01.txt>.
[I-D.geng-msr6-rlb-segment]
Geng, X., Li, Z., and J. Xie, "RLB (Replication through
Local Bitstring) Segment for Multicast Source Routing over
IPv6", Work in Progress, Internet-Draft, draft-geng-msr6-
rlb-segment-00, 10 February 2022,
<https://www.ietf.org/archive/id/draft-geng-msr6-rlb-
segment-00.txt>.
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[I-D.geng-msr6-traffic-engineering]
Geng, X., Li, Z., and J. Xie, "IPv6 Multicast Source
Routing Traffic Engineering", Work in Progress, Internet-
Draft, draft-geng-msr6-traffic-engineering-01, 7 March
2022, <https://www.ietf.org/archive/id/draft-geng-msr6-
traffic-engineering-01.txt>.
[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
Bing Xu
Huawei
Email: bing.xu@huawei.com
Xuesong Geng
Huawei
Email: gengxuesong@huawei.com
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