Distribute SRv6 Locator by IPv6 Stateless Address Autoconfiguration
draft-cheng-spring-stateless-nd-srv6-locator-00
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Weiqiang Cheng , Ruibo Han , Changwang Lin , Yuanxiang Qiu | ||
| Last updated | 2024-11-06 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-cheng-spring-stateless-nd-srv6-locator-00
SPRING W. Cheng
Internet Draft R. Han
Intended status: Standards Track China Mobile
Expires: May 10, 2025 C. Lin
Y. Qiu
New H3C Technologies
November 6, 2024
Distribute SRv6 Locator by IPv6 Stateless Address Autoconfiguration
draft-cheng-spring-stateless-nd-srv6-locator-00
Abstract
In an SRv6 network, each SRv6 Segment Endpoint Node must be assigned
an SRv6 locator, and segment IDs are generated within the address
space of this SRv6 locator. This document describes a method for
assigning SRv6 locators to SRv6 Segment Endpoint Nodes through IPv6
stateless address autoconfiguration.
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), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on May 10, 2025.
Cheng, et al. Expire May, 2025 [Page 1]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
Copyright Notice
Copyright (c) 2024 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
(http://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 to this document. Code Components extracted from this
document must 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.
Cheng, et al. Expires May, 2025 [Page 2]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
Table of Contents
1. Introduction...................................................4
1.1. Requirements Language.....................................5
2. Terminology....................................................5
3. Scenario for SRv6 Locator......................................5
4. Extension of IPv6 Neighbor Discovery Options...................7
5. Process of Advertising SRv6 Locator by Router Advertisement....8
5.1. Router Behavior...........................................9
5.2. Host Behavior............................................10
6. IANA Considerations...........................................10
7. Security Considerations.......................................11
8. Acknowledgements..............................................11
9. References....................................................11
9.1. Normative References.....................................11
9.2. Informative References...................................11
Authors' Addresses...............................................12
Cheng, et al. Expires May, 2025 [Page 3]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
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. The SRv6 Segment Endpoint Node then
allocates SIDs with various behaviors based on its 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. In such
scenarios, SIDs can only be configured manually on CPEs, and SRv6
Locator routes can only be statically distributed.
To address this issue, this document proposes a method of
dynamically advertising SRv6 locators to SRv6 Segment Endpoint Nodes
through IPv6 stateless address configuration method. It follows the
existing process of IPv6 stateless address configuration,
simplifying the allocation of SRv6 locators and route distribution.
Cheng, et al. Expires May, 2025 [Page 4]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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. Scenario for SRv6 Locator
The application scenario for obtaining SRv6 Locator through IPv6
stateless address autoconfiguration is similar to that of [I-D.ietf-
spring-dhc-distribute-srv6-locator-dhcp].
In the IP backbone network, Telecom providers can use its IP Metro
and Backbone networks to establish connectivity between access users
who are located in different regions.
As shown in Figure 1, access network devices (CPE) are deployed for
access users in different regions. This deployment assumes that all
of the relevant components in Figure 1 are part of a single trusted
SR domain. The CPE must be operator-managed and is only applicable
when different arms of the same company operate their portions of
the network separately, but must trust each other.
Cheng, et al. Expires May, 2025 [Page 5]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
Metropolitan area network
+---------------------------+
| |
+------+ +------+ | +-----+ +------+ |
|Host1 +-----+ CPE1 +----+--+BRAS1+--------+ CR1 | |
+------+ +------+ | +-----+ +---+--+ |
| | |
+---------------------+-----+
|
+--------+-------------+
| |
| Backbone Network |
| |
+--------+-------------+
|
+---------------------+-----+
| | |
+------+ +------+ | +-----+ +--+---+ |
|Host2 +-----+ CPE2 +----+--+BRAS2+---------+ CR2 | |
+------+ +------+ | +-----+ +------+ |
+---------------------------+
Figure 1: Telecom IPv6 Network
CPEs for access users are connected to the local metropolitan area
network (MAN) in various ways. CPEs are responsible for assigning
addresses to access users, so CPEs usually apply for IPv6 subnet
prefix through DHCPv6 or stateless address autoconfiguration from
BRAS.
In this network, operators hope to achieve interconnection between
access users through End-to-End SRv6 tunnels. Taking the service
traffic from Host1 to Host2 as an example, CPE1 is the SRv6 ingress
node and CPE2 is the SRv6 egress node. The SRv6 locator should be
configured on CPE. Other devices in the network learn the SRv6
locator route of the CPE.
At the same time, SRv6 policies needs to be configured on CPEs to
steer the service traffic between CPEs to the specified SRv6
forwarding path. The SRv6 policy can be manually configured
statically or issued through the controller, and its specific
configuration method is out of the scope of this document.
However, in Metro network, the number of CPEs is very large and
widely distributed geographically. Moreover, the mobility
requirements of CPE are relatively high, and the access location of
the same CPE often changes, so its IPv6 address cannot be fixed.
Cheng, et al. Expires May, 2025 [Page 6]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
At present, an SRv6 locator can only be configured on each CPE
through a controller or the Command Line Interface (CLI), which
increases the configuration complexity.
To solve the difficulties this document proposes a method to
allocate SRv6 locators to CPE through IPv6 stateless address
autoconfiguration.
4. Extension of IPv6 Neighbor Discovery Options
The SRv6 Locator option is used to specify the SRv6 locators that
are used for stateless address autoconfiguration.
The terms Locator Block and Locator Node correspond to the B and N
parts, respectively, of the SRv6 Locator that is defined in Section
3.1 of [RFC8986].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LB-Len | LN-Len | Fun-Len | Arg-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
. SRv6-Locator .
. ( Up to 16 octets ) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
* Type: 8-bit 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.
* Reserved: 16-bit unused field. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
* Valid Lifetime: 32-bit unsigned integer. The valid lifetime for
the SRv6 locator in the option, expressed in units of seconds
Cheng, et al. Expires May, 2025 [Page 7]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
(relative to the time the packet is sent). A value of all one
bits (0xffffffff) represents infinity.
* Preferred Lifetime: 32-bit unsigned integer. The preferred
lifetime for the SRv6 locator in the option, expressed in units of
seconds (relative to the time the packet is sent). A value of all
one bits (0xffffffff) represents infinity. Note that the value of
this field MUST NOT exceed the Valid Lifetime field to avoid SRv6
locator that are no longer valid.
* LB-Len: 8-bit unsigned integer. SRv6 SID Locator Block (LB) length
in bits.
* LN-Len: 8-bit unsigned integer. SRv6 SID locator Node (LN) length
in bits.
* Fun-Len: 8-bit unsigned integer. SRv6 SID function (FUNCT) length
in bits.
* Arg-Len: 8-bit unsigned integer. SRv6 SID arguments (ARG) length
in bits.
* SRv6-Locator: 1-16 octets. This field encodes the SRv6 Locator.
The SRv6 Locator is encoded in the minimal number of octets for
the given number of bits. Trailing bits MUST be set to zero and
ignored when received.
The option only may appear in the Router Advertisement message.
Router Advertisement messages can include zero or more SRv6 Locator
options. If multiple SRv6 Locators need to be advertised to the same
device, multiple SRv6 Locator options MUST be encapsulated in the
same Router Advertisement message. The SRv6 Locator 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. Process of Advertising SRv6 Locator by Router Advertisement
This section describes router and host behavior of adverting SRv6
locator related to the Router Discovery portion of Neighbor
Discovery. Router Discovery is used to locate neighboring routers as
well as learn prefixes and configuration parameters related to
stateless address autoconfiguration.
Cheng, et al. Expires May, 2025 [Page 8]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
The IPv6 stateless autoconfiguration mechanism requires no manual
configuration of hosts, minimal (if any) configuration of routers,
and no additional servers. The stateless mechanism allows a host to
generate its own addresses using a combination of locally available
information and information advertised by routers. Routers advertise
prefixes that identify the subnet(s) associated with a link, while
hosts generate an "interface identifier" that uniquely identifies an
interface on a subnet. An address is formed by combining the two. In
the absence of routers, a host can only generate link-local
addresses. However, link-local addresses are sufficient for allowing
communication among nodes attached to the same link.
The stateless approach is used when a site is not particularly
concerned with the exact addresses hosts use, so long as they are
unique and properly routable.
Global addresses generated through stateless autoconfiguration
mechanism are formed by appending an interface identifier to a
prefix of appropriate length. Prefixes are obtained from Prefix
Information options contained in Router Advertisements.
Router Advertisements are sent periodically to the all-nodes
multicast address. To obtain an advertisement quickly, a host sends
out Router Solicitations as described in [RFC4861].
When the router sends a Router Advertisement, it carries the SRv6
locator prefix information assigned to the host in the SRv6 Locator
Option. After receiving the Router Advertisement, the host extracts
the SRv6 Locator Option, obtains the SRv6 Locator prefix.
The detailed process of routers and hosts when advertising SRv6
locators during the IPv6 stateless autoconfiguration is as follows.
5.1. Router Behavior
The Router follows the specifications in Section 6.2 of [RFC4861] to
send out Router Advertisement messages periodically, or in response
to Router Solicitations.
When receiving a Router Solicitation from a host, if the router has
already assigned an SRv6 locator to the host, it will include the
SRv6 Locator Option in the Router Advertisement message of the
responding host and advertise the SRv6 locator to the host.
In the scenario where all hosts under the advertising interface
share the SRv6 Locator prefix, the SRv6 Locator option SHOULD be
included in the Router Advertisement message sent periodically.
Cheng, et al. Expires May, 2025 [Page 9]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
5.2. Host Behavior
On receipt of a Router Advertisement, the host follows the
specifications in Section 6.3 of [RFC4861] to verify the packet. For
valid Router Advertisement, continue to extract the SRv6 Locator
option.
For each SRv6 Locator option, a host does the following:
* If the SRv6 locator is not already present in the SRv6 Locator
List, and the SRv6 Locator Option's Valid Lifetime field is non-
zero, create a new entry for the SRv6 locator and initialize its
invalidation timer to the Valid Lifetime value in the SRv6 Locator
option.
* If the SRv6 locator is already present in the host's SRv6 Locator
List as the result of a previously received advertisement, reset
its invalidation timer to the Valid Lifetime value in the SRv6
Locator option. If the new Lifetime value is zero, time-out the
SRv6 locator immediately.
* If the SRv6 Locator option's Valid Lifetime field is zero, and the
SRv6 locator is not present in the host's SRv6 Locator List,
silently ignore the option.
Whenever the invalidation timer expires for a SRv6 Locator entry,
that entry is discarded.
After processing the SRv6 Locator Option, the host records the SRv6
Locator prefix, and generates the corresponding SID based on the
local configuration. The method of generating SID based on SRv6
locator is out of the scope of this document.
6. 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:
+===============+=====================+================+
| Value | Description | Reference |
+---------------+---------------------+----------------+
| TBA | SRv6 Locator Option | This document |
+---------------+---------------------+----------------+
Cheng, et al. Expires May, 2025 [Page 10]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
Table 1
7. Security Considerations
See Section 11 of [RFC4861] for the Neighbor Discovery security
considerations.
8. Acknowledgements
TBD
9. References
9.1. 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>.
[I-D.ietf-spring-dhc-distribute-srv6-locator-dhcp] Cheng, W., Han,
R., Lin, C., Qiu, Y., Zhang, G., "Distribute SRv6 Locator
by DHCP", draft-ietf-spring-dhc-distribute-srv6-locator-
dhcp-03 (work in progress), June 2024.
9.2. Informative References
TBD
Cheng, et al. Expires May, 2025 [Page 11]
Internet-Draft Distribute SRv6 Locator by NDRA November 2024
Authors' Addresses
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
Ruibo Han
China Mobile
Email: hanruibo@chinamobile.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Yuanxiang Qiu
New H3C Technologies
Email: qiuyuanxiang@h3c.com
Cheng, et al. Expires May, 2025 [Page 12]