Internet DRAFT - draft-xl-bess-source-segment
draft-xl-bess-source-segment
Network Working Group J. Xie
Internet-Draft X. Geng
Intended status: Standards Track Huawei Technologies
Expires: 8 September 2023 Y. Liu
China Mobile
M. Chen
New H3C Technologies
7 March 2023
Source Segment for SRv6 based Multicast VPN
draft-xl-bess-source-segment-00
Abstract
This document defines the general concept of source segment which is
used as the IPv6 source address in an IPv6 packet. Source segment
for multicast VPN service is introduced in this document.
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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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 8 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Source Segment Definition . . . . . . . . . . . . . . . . . . 3
4. SID Format . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Source Segment for MVPN . . . . . . . . . . . . . . . . . . . 4
5.1. Behaviors . . . . . . . . . . . . . . . . . . . . . . . . 4
5.2. SRC.DT4 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.3. SRC.DT6 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.4. SRC.DT46 . . . . . . . . . . . . . . . . . . . . . . . . 6
5.5. Src.DT2 . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Exception Handling . . . . . . . . . . . . . . . . . . . . . 6
7. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segment Routing ([RFC8402]) leverages the mechanism of source
routing. An ingress node steers a packet through an ordered list of
instructions, called "segments". Each one of these instructions
represents a function to be implemented at a specific location in the
network. A function is locally defined on the node where it is
executed. Network Programming combines Segment Routing functions to
achieve a networking objective that goes beyond mere packet routing.
[RFC8986] defines the SRv6 Network Programming concept and specifies
the main Segment Routing behaviors and network programming functions.
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Previous segments defined in SRv6 can be used as the destination
address of an IPv6 packet. This document introduces the new
segments, source segments, which can be used as the IPv6 source
address of an IPv6 packet. This document defines the general concept
of source segment and the source segment used for multicast VPN
service. Protocol extensions on the control plane are not in the
scope of this document.
This document defines the general concept of source segment and the
source segment used for multicast service. Protocol extensions on
the control plane are not in the scope of this document.
2. Terminologies
The following new terms are used throughout this document:
SRv6: Source Routing over IPv6;
MVPN: Multicast VPN;
3. Source Segment Definition
Source segment is different from the existing SID defined in RFC8402
from the following aspects:
* Source segment is unchanged along the SRv6 multicast path.
* Source segment is distributed by the ingress node but indicates
functions in other nodes along the path, e.g., egress node.
Forwarding table should be maintained in the nodes where the
instruction takes place.
* When the source segment is encapsulated in an SRv6 packet, it is
activated by other instructions in the data plane because source
address is not parsed in existing forwarding process of a unicast
packet
Using source segment for SRv6 Network Programming have several
benefits including:
* Enhance network programming capability for more SRv6 functions and
extend the programming space in IPv6 header;
* Provide sematic for source address with similar IPv6 address
allocation and management method as SRv6;
* Facilitates security management inside the limited domain;
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Source segment should be avoided to process hop by hop. Per-hop
process of source segment which will degrade forwarding performance
and bring compatibility issues.
4. SID Format
Source segment leverages the format of SID defined in SRv6 network
programming.
Source segment consists of LOC:FUNCT:ARG, where a locator (LOC) is
encoded in the L most significant bits of the SID, followed by F bits
of function (FUNCT) and A bits of arguments (ARG).
A locator may be represented as B:N where B is the SRv6 SID block
(IPv6 prefix allocated for SRv6 SIDs by the operator) and N is the
identifier of the ingress node .
The FUNCT is an opaque identification of the behavior bound to the
SID. The behavior could be executed in other nodes except ingress
node.
The behavior indicated by FUNCT may require additional information
for its processing. This information may be encoded in the ARG bits
of the SID.
5. Source Segment for MVPN
In the multicast VPN (MVPN) service, packet is replicated along a
point-to-multipoint path (multicast path) towards a set of leaf
nodes. MVPN routing and the corresponding information could be
encapsulated in the source segment carried in the IPv6 source
address. Source Segment for MVPN is distributed by the multicast
source node and the function is executed by the multicast leaf
nodes.As described in section 3, Source Segment for MVPN is not
changed when the packet is replicated and forwarded along the P2MP
path.
This section defines the source segment for MVPN.
5.1. Behaviors
The following is a set of behaviors that can be associated with a
source segment for MVPN.
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+------------+------------------------------------------------------+
| Src.DT4 |Source address for decapsulation and IPv4 table lookup|
|------------|------------------------------------------------------+
| Src.DT6 |Source address for decapsulation and IPv6 table lookup|
|------------|------------------------------------------------------+
| Src.DT46 |Source address for decapsulation and IP table lookup |
|------------|------------------------------------------------------+
| Src.DT2 |Source address for decapsulation and L2 table lookup |
|------------|------------------------------------------------------+
5.2. SRC.DT4
The "Source address for decapsulation and IPv4 table lookup" behavior
("Src.DT4" for short) is used in MVPNv4 use case where an MFIB lookup
in a specific VRF table T at the egress node is required. The
Src.DT4 SID is an SID associated with an IPv4 MFIB table T on the
egress PE, either through a control-plane message advertised by the
ingress PE, or through a local configuration on the egress PE. When
an IPv6 encapsulated packet with IPv6 source address being S is
received on an egress PE, and S is associated with an Src.DT4 SID on
the egress PE, the egress PE does the following behavior:
S01. If (Upper-Layer header type == 4(IPv4) ) {
S02. Remove the outer IPv6 header with all its extension headers
S03. Set the packet's associated MFIB table to T
S04. Submit the packet to the egress IPv4 MFIB lookup for
transmission to the new multicast downstreams
S05. } Else {
S06. Drop the packet;
S07. }
5.3. SRC.DT6
SRC.DT6 behavior could be used in MVPNv6 use case where a MFIB lookup
in a specific VRF table at the egress node is required.
S01. If (Upper-Layer header type == 41(IPv6) ) {
S02. Remove the outer IPv6 header with all its extension headers
S03. Set the packet's associated IPv6 MFIB table to T
S04. Submit the packet to the egress IPv6 MFIB lookup for
transmission to the new multicast downstreams
S05. } Else {
S06. Drop the packet;
S07. }
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5.4. SRC.DT46
SRC.DT46 behavior could be used in MVPN use case where a MFIB lookup
in a specific VRF table at the egress node is required.
S01. If (Upper-Layer header type == 4(IPv4) ) {
S02. Remove the outer IPv6 header with all its extension headers
S03. Set the packet's associated MFIB table to T
S04. Submit the packet to the egress IPv4 MFIB lookup for
transmission to the new destination
S05. } Else if (Upper-Layer header type == 41(IPv6) ) {
S06. Remove the outer IPv6 header with all its extension headers
S07. Set the packet's associated MFIB table to T
S08. Submit the packet to the egress IPv6 MFIB lookup for
transmission to the new destination
S09. } Else {
S10. Drop the packet;
S11. }
5.5. Src.DT2
SRC.DT2 behavior could be used in MVPN use case where a L2 table
lookup in a specific Layer-2 Multicast forwarding table at the egress
node is required.
S01. If (Upper-Layer header type == 143(Ethernet) ) {
S02. Remove the outer IPv6 header with all its extension headers
S03. Set the packet's associated Layer-2 Multicast forwarding table to T
S04. Submit the packet to the egress Layer-2 Multicast forwarding table
lookup for transmission to the new multicast downstreams
S05. } Else {
S06. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet
S07. }
6. Exception Handling
Once a source segment is used in an SRv6 encapsulated multicast data
packet as source address, it is expected to receive an ICMPv6 error
message with the source segment being the Destination address, and
such a packet is expected to be processed by Ingress PE.
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Additionally, there are cases where a source segment may appear as
destination address of an packet that is not an ICMPv6 message. This
could be a packet without SRH, or a packet with SRH and the active
segment is the source segment. Such a packet is expected to be
dropped.
The following pseudo-code describes how a packet with a source
segment as destination address is handled:
1. IF Upper Layer Protocol = ICMPv6 ;;Ref1: ICMPv6 packet
2. Send to CPU in limited rate.
3. ELSE
4. Drop the packet.
7. Use Case
The source segment could be applied in SRv6-based Multicast cases.
1. MSR6: MSR6 [I-D.lx-msr6-rgb-segment] is considered to be one of
the SRv6-based Multicast solutions, and MVPN is one of the
typical services intended to be running over MSR6. The source
segment defined in this document can be used in this solution as
source address for identifying a VRF.
2. Tree SID over SRv6: MVPN service can use Tree SID over SRv6
[I-D.ietf-bess-mvpn-evpn-sr-p2mp] for point-to-multipoint
transport of a packet. When a Tree SID over SRv6 P-tunnel is
shared across different MVPNs, an IPv6 address in IPv6 source
address for identifying a VRF is possible.
3. MVPN service can use Ingress Replication(IR) [RFC6513] to
simulate a point-to-multipoint P-tunnel. In an IPv6 environment,
Ingress Replication can use IPv6 encapsulation for each branch.
When the egress PE of an Ingress Replication P-tunnel branch
receives a packet, it gets to know the VRF of the packet through
the Destination address in the IPv6 header. This means that,
every egress PE of the IR P-tunnel branch need to allocate an
IPv6 address to identify a VRF. If the source segment is used
for the IPv6 source address, only one IPv6 address of the Ingress
PE is needed for identifying a VRF, and thus save the IPv6
addresses and their operation costs.
8. IANA Considerations
TBD
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9. Security Considerations
TBD
10. References
10.1. Normative References
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
10.2. Informative References
[I-D.ietf-bess-mvpn-evpn-sr-p2mp]
Parekh, R., Filsfils, C., Venkateswaran, A., Bidgoli, H.,
Voyer, D., and Z. J. Zhang, "Multicast and Ethernet VPN
with Segment Routing P2MP and Ingress Replication", Work
in Progress, Internet-Draft, draft-ietf-bess-mvpn-evpn-sr-
p2mp-06, 2 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-evpn-sr-p2mp-06>.
[I-D.lx-msr6-rgb-segment]
Liu, Y., Xie, J., Geng, X., and M. Chen, "RGB (Replication
through Global Bitstring) Segment for Multicast Source
Routing over IPv6", Work in Progress, Internet-Draft,
draft-lx-msr6-rgb-segment-03, 10 July 2022,
<https://datatracker.ietf.org/doc/html/draft-lx-msr6-rgb-
segment-03>.
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[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses
Jingrong Xie
Huawei Technologies
Email: xiejingrong@huawei.com
Xuesong Geng
Huawei Technologies
Email: gengxuesong@huawei.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Mengxiao Chen
New H3C Technologies
Email: chen.mengxiao@h3c.com
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