Advertise SRv6 Locator Information by IPv6 Neighbor Discovery
draft-gong-spring-nd-advertise-srv6-locator-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Liyan Gong , Changwang Lin | ||
| Last updated | 2024-11-08 | ||
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draft-gong-spring-nd-advertise-srv6-locator-00
SPRING L. Gong
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: May 10, 2025 New H3C Technologies
November 9, 2024
Advertise SRv6 Locator Information by IPv6 Neighbor Discovery
draft-gong-spring-nd-advertise-srv6-locator-00
Abstract
In an SRv6 network, each SRv6 segment endpoint has at least one SRv6
locator. Through the SRv6 locator routes, other SRv6 segment nodes
can steer traffic to that node. This document describes a method of
advertising SRv6 locator to neighboring SRv6 Segment Endpoint nodes
through IPv6 Neighbor Discovery protocol.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 10, 2025.
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Copyright Notice
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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...................................................4
1.1. Requirements Language.....................................5
2. Terminology....................................................6
3. Process of Advertising SRv6 Locator by IPv6 ND.................6
4. Extension of IPv6 Neighbor Discovery Options...................8
4.1. Source SRv6 Locator Information Option....................8
4.2. Source SRv6 Capability Option.............................9
5. IANA Considerations...........................................10
6. Security Considerations.......................................11
7. Acknowledgements..............................................11
8. References....................................................11
8.1. Normative References.....................................11
8.2. Informative References...................................11
Authors' Addresses...............................................12
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1. Introduction
Segment Routing (SR) [RFC8402] allows a node to steer a packet flow
along any path. The headend is a node where the instructions for
source routing (i.e., segments) are written into the packet. It
hence becomes the starting node for a specific segment routing path.
Intermediate per-path states are eliminated thanks to source
routing. A Segment Routing Policy (SR Policy) [RFC8402] is an
ordered list of segments (i.e., instructions) that represent a
source-routed policy. The headend node is said to steer a flow into
an SR Policy. The packets steered into an SR Policy have an ordered
list of segments associated with that SR Policy written into them.
[RFC8402] defines an SRv6 Segment Identifier (SID) as an IPv6
address explicitly associated with the segment. When an SRv6 SID is
in the Destination Address field of an IPv6 header of a packet, it
is routed through transit nodes in an IPv6 network as an IPv6
address.
An SRv6 SID [RFC8986] is as consisting 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). L, the locator length, is flexible, and an operator is free
to use the locator length of their choice. F and A may be any value
as long as L+F+A <= 128. 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 parent node instantiating
the SID. When the LOC part of the SRv6 SIDs is routable, it leads to
the node, which instantiates the SID.
The SRv6 locator can be distributed to other IPv6 nodes within the
SRv6 domain through IGP advertisement. This allows other nodes to
learn the locator's route.
However, in the following two scenarios, the SRv6 endpoint can't
advertise its SRv6 Locator information to other SRv6 nodes,
resulting in other nodes being unable to dynamically generate routes
to this node.
* Scenario 1: Deploying SRv6 on hosts.
As shown in Figure 1, the SRv6 network comprises Host, Access, Spin,
and Core segments. Information is exchanged between Access and Spin
through IGP, and between Spin and Core using BGP.
The SRv6 Locator information is transmitted between Access and Spin
using the IGP protocol, and between Spin and Core using the BGP
protocol. However, since Hosts generally do not support complex
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routing protocols, they cannot automatically transmit their SRv6
Locator information to the devices. This limitation complicates the
deployment of SRv6 networks.
+----+ +------+ IGP +------+BGP +------+
|Host+-----+Access+-----+ Spin +----+ Core +
+----+ +------+ +------+ +------+
Figure 1
* Scenario 2: Static manual configuration of SRv6 Locator.
In IP network customer provider edge (CPE) devices often do not
support an IGP protocol, which makes it impossible to advertise SRv6
locator routes for SRv6 Segment Endpoint Nodes through IGP. As shown
in Figure 2, SIDs can only be configured manually on CPEs, and SRv6
Locator routes can only be statically distributed.
Metropolitan area network
+---------------------------+
| |
+------+ +------+ | +-----+ +------+ |
|Host1 +-----+ CPE1 +----+--+BRAS1+--------+ CR1 | |
+------+ +------+ | +-----+ +---+--+ |
| | |
+---------------------+-----+
|
+--------+-------------+
| |
| Backbone Network |
| |
+--------+-------------+
|
+---------------------+-----+
| | |
+------+ +------+ | +-----+ +--+---+ |
|Host2 +-----+ CPE2 +----+--+BRAS2+---------+ CR2 | |
+------+ +------+ | +-----+ +------+ |
+---------------------------+
Figure 2
To address these issues, this document proposes a method of
advertising SRv6 locators to neighboring SRv6 Segment Endpoint Nodes
through IPv6 Neighbor Discovery packets.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology
This document leverages the terms defined in [RFC4861] and
[RFC8986]. The reader is assumed to be familiar with this
terminology.
3. Process of Advertising SRv6 Locator by IPv6 ND
By extending the Neighbor Solicit (NS) and Neighbor Advertisement
(NA) packets of the IPv6 Neighbor Discovery protocol to carry SRv6
locator information, SRv6 segment endpoint nodes can advertise their
own SRv6 locator information to neighboring SRv6 nodes, and can also
obtain the SRv6 locator information of neighboring SRv6 nodes,
thereby achieving the exchange of SRv6 locator information and
facilitating the deployment of SRv6.
Taking the scenario of deploying SRv6 on a host in Section 1 as an
example, illustrate the process flow of exchanging SRv6 Locator
information through IPv6 ND.
By extending the IPv6 ND protocol to carry SRv6 Locator information,
Hosts and Access devices can exchange all SRv6 Locator information
within an SRv6 network, facilitating the deployment of SRv6.
The srv6 locator are advertised in IPv6 ND NS and NA packets between
the host and access, and are advertised via IGP within the domain.
This information is collected by the controller using NETCONF or
BGP-LS.
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+----------+ BGP-LS
|Controller|<-----------------+
+----------+ |
^ ^ |
NETCONF | | NETCONF |
| +----------+ |
| | |
FC00:0:11::/48 | | |
+----+ +------+ IGP +------+BGP +------+
|Host+-----+Access+-----+ Spin +----+ Core +
+----+ +------+ +------+ +------+
^ ^
| |
+---- ND ---+
SRv6 Locator
Figure 3
The process is as follows:
1) Manually configure SRv6 Locator statically on the host.
2) The Host advertises the SRv6 locator (For example, FC00:0:11::/48)
and its SRv6 capability through IPv6 NS and NA packets.
3) The Access device learns the SRv6 locator (FC00:0:11::/48) via ND
packets.
4) Using IGP, the Access device re-advertises the SRv6 locator
(FC00:0:11::/48) obtained from ND packets to the Spine device.
5) The Spine device learns the SRv6 locator (FC00:0:11::/48) route
through IGP.
6) A BGP neighbor relationship is established between the Spine and
Core devices, and the learned SRv6 locator (FC00:0:11::/48) is
sent to the Core using BGP-LS routes.
7) The Core device learns the SRv6 locator (FC00:0:11::/48) via BGP-
LS.
8) A BGP neighbor relationship is established between the Core device
and the controller, and the SRv6 locator (FC00:0:11::/48) is sent
to the controller via BGP-LS routes.
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4. Extension of IPv6 Neighbor Discovery Options
4.1. Source SRv6 Locator Information Option
The Source SRv6 Locator Information (SSLI) option is used to
advertise the SRv6 locator information of the sending node to IPv6
neighbor.
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 |R|R|R|R| MTID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LOC Size | Locator (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Type: 8 bits, identifier of the type of option. The value is TBA
by IANA.
* Length: 8 bits, unsigned integer. The length of the option
(including the type and length fields) in units of 8 octets. The
value 0 is invalid. Nodes MUST silently discard an ND packet that
contains an option with length zero.
* R: 4 bits, reserved field. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
* MTID: 12 bits, Multi-Topology Identifier.
* Metric: 32 bits, Cost.
* Flags: 8 bits, Reserved.
* Algorithm: 8 bits Algorithm:
* - 0: Shortest Path First (SPF).
* - 1: Strict Shortest Path First (Strict SPF).
* LOC Size: 8 bits, Locator Length.
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* Locator (variable): Variable length, indicates the advertised SRv6
Locator.
* Sub-TLVs (variable): Variable length, contains Sub-TLVs such as
SRv6 End SID Sub-TLV.
The option only may appear in Neighbor Solicit message and Neighbor
Advertisement message.
Neighbor Solicit message and Neighbor Advertisement message can
include zero or more Source SRv6 Locator Information options. If
multiple SRv6 Locators need to be advertised, multiple Source SRv6
Locator Information options MUST be encapsulated in the same
Neighbor Discovery message. The Source SRv6 Locator Information
Option should be padded when necessary to ensure that it end on its
natural 64-bit boundary.
Receivers MUST silently ignore the option if they can't recognize
and continue processing the message.
4.2. Source SRv6 Capability Option
To support the SRv6 functionality, the source node also needs to
advertise SRv6-related capabilities through IPv6 ND packets. The
Source SRv6 Capability (SSC) option is used to advertise the SRv6
capability information of the sending node to IPv6 neighbor.
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 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 8 bits, identifier of the type of option. The value is TBA
by IANA.
* Length: 8 bit, unsigned integer. The length of the option
(including the type and length fields) in units of 8 octets. The
value 0 is invalid. Nodes MUST silently discard an ND packet that
contains an option with length zero.
* Flags: 8 bits, Reserved.
* Sub-TLVs: Variable length, contains Sub-TLVs such as MSD sub-TLV.
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For optional MSD sub-sub-TLVs, the format is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* sub-Type: 8 bits, The sub-TLV Type value for MSD is TBA.
* Length: 8 bits, variable.
* MSD-Type: 8 bits.
* MSD-Value: 8 bits.
The option only may appear in Neighbor Solicit message and Neighbor
Advertisement message.
Neighbor Solicit message and Neighbor Advertisement message can only
include a maximum of one Source SRv6 Capability option. The Source
SRv6 Capability Option should be padded when necessary to ensure
that it end on its natural 64-bit boundary.
Receivers MUST silently ignore the option if they can't recognize
and continue processing the message.
5. IANA Considerations
IANA is asked to assign a new value for the "IPv6 Neighbor Discovery
Option Formats" registry under the heading "Internet Control Message
Protocol version 6 (ICMPv6) Parameters", as follows:
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+========+========================================+===============+
| Value | Description | Reference |
+--------+----------------------------------------+---------------+
| TBA | Source SRv6 Locator Information Option | This document |
+--------+----------------------------------------+---------------+
| TBA | Source SRv6 Capability Option | This document |
+--------+----------------------------------------+---------------+
Table 1
6. Security Considerations
See Section 11 of [RFC4861] for the Neighbor Discovery security
considerations.
7. Acknowledgements
TBD
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017.
[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>.
8.2. Informative References
TBD
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Authors' Addresses
Liyan Gong
China Mobile
China
Email: gongliyan@chinamobile.com
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
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