RFC 10038
Distributing the Segment Routing over IPv6 (SRv6) Locator Using DHCPv6
ABSTRACT
In an SRv6 network, each SRv6 Segment Endpoint Node must be assigned an SRv6 Locator, and segment identifiers (SIDs) 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 the Dynamic Host Configuration Protocol for IPv6 (DHCPv6).
StatusPROPOSED STANDARD
StreamIETF
Date2026-08
AuthorsW. Cheng, R. Han, C. Lin, D. Voyer, G. Zhang
Pages17
Erratarfc-editor.org ↗
CONTENTS
Internet Engineering Task Force (IETF) W. Cheng, Ed.
Request for Comments: 10038 R. Han
Category: Standards Track China Mobile
ISSN: 2070-1721 C. Lin, Ed.
New H3C Technologies
D. Voyer
Cisco Systems
G. Zhang
China Mobile
August 2026
Distributing the Segment Routing over IPv6 (SRv6) Locator Using DHCPv6
Abstract
In an SRv6 network, each SRv6 Segment Endpoint Node must be assigned
an SRv6 Locator, and segment identifiers (SIDs) 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 the Dynamic Host Configuration Protocol for IPv6 (DHCPv6).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc10038.
Copyright Notice
Copyright (c) 2026 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 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
1.1. Requirements Language
2. Terminology
3. Motivation
4. DHCPv6 Extensions
4.1. Identity Association for SRv6 Locator Option
4.2. IA Locator Option
5. Process of Assigning the SRv6 Locator
5.1. Procedure of the SRv6 Locator
5.2. DHCPv6 Client Behavior
5.3. DHCPv6 Server Behavior
5.4. DHCPv6 Relay Agent Behavior
5.5. Advertisement of the SRv6 Locator Route
6. Operational Considerations
7. IANA Considerations
8. Security Considerations
9. References
9.1. Normative References
9.2. Informative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
The Segment Routing (SR) architecture [RFC8402] specifies how a node
can steer a packet using an ordered list of instructions called
"segments". These segments are identified using segment identifiers
(SIDs).
SR can be instantiated on the IPv6 data plane using either the
Segment Routing Header (SRH) defined in [RFC8754] or compressed
segment lists defined in [RFC9800]. SR instantiation on the IPv6
data plane is referred to as SRv6.
[RFC8986] introduces the SRv6 Network Programming concept and
specifies the base set of SRv6 behaviors.
In an SRv6 network, each SRv6 Segment Endpoint Node must be assigned
an SRv6 Locator, and SIDs 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 the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6).
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 [RFC9915] and [RFC8986].
The reader is assumed to be familiar with this terminology.
3. Motivation
As shown in Figure 1, in the IP backbone network, access network
devices 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 Customer Premises
Equipment (CPE) must be managed by the operator providing services or
by a trusted partner. If the CPE is located within the customer
premises, it must ensure that the device itself and its ports are
under the same operator's administrative domain; otherwise, security
risks may arise.
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 by requesting DHCPv6 Prefix Delegation (PD)
from a DHCPv6 server, as specified in Section 6.3 of [RFC9915].
[RFC7084] and [RFC7368] describe such use in detail. The DHCPv6
server is usually enabled on or relayed by the Broadband Remote
Access Server (BRAS).
After the DHCPv6 server allocates any delegated prefix, the BRAS will
add a network route corresponding to the delegated prefix to a local
routing table and distribute the network route to the upstream
routers.
Metropolitan Area Network
+---------------------------+
| |
+------+ +------+ | +-----+ +-------+ |
|Host1 +-----+ CPE1 +----+--+BRAS1+--------+Router1| |
+------+ +------+ | +-----+ +---+---+ |
| | |
+---------------------+-----+
|
+--------+-------------+
| |
| Backbone Network |
| |
+--------+-------------+
|
+---------------------+-----+
| | |
+------+ +------+ | +-----+ +--+----+|
|Host2 +-----+ CPE2 +----+--+BRAS2+---------+Router2||
+------+ +------+ | +-----+ +-------+|
+---------------------------+
Figure 1: Telecom IPv6 Network
In this network, operators hope to achieve interconnection between
access users through CPE-to-CPE 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 the CPEs. Other devices within the operator's network
learn the SRv6 Locator routes of the CPEs.
At the same time, SRv6 policies need 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 (via command-line interface (CLI), the Network
Configuration Protocol (NETCONF), YANG, APIs, etc.).
This document proposes a method for allocating SRv6 Locators to CPE
via DHCPv6 and distributing SRv6 Locator routes using the DHCPv6
workflow. This approach simplifies network operation and maintains
consistency with existing IPv6 address allocation mechanisms already
deployed in such networks.
4. DHCPv6 Extensions
4.1. Identity Association for SRv6 Locator Option
The Identity Association for SRv6 Locator (IA_SRV6_LOCATOR) option is
used to carry an IA_SRV6_LOCATOR, the parameters associated with the
IA_SRV6_LOCATOR, and the SRv6 Locator associated with the
IA_SRV6_LOCATOR.
The IA_SRV6_LOCATOR option can be carried in DHCPv6 Solicit,
Advertise, Request, Reply, Renew, Release, and Rebind messages.
The format of the IA_SRV6_LOCATOR option is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IA_SRV6_LOCATOR | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IA_SRV6_LOCATOR-Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Identity Association for SRv6 Locator Option Format
Where:
Option-Code: OPTION_IA_SRV6_LOCATOR (149), the option code for the
Identity Association for SRv6 Locator option.
Option-Len: 12 + the length of the IA_SRV6_LOCATOR-Options field in
octets.
IAID: The unique identifier for this IA_SRV6_LOCATOR. The IAID MUST
be unique among the identifiers for all of this client's
IA_SRV6_LOCATORs. The number space for IA_SRV6_LOCATOR IAIDs is
separate from the number space for other IA option types. A
4-octet field containing an unsigned integer.
T1: The time interval after which the client should contact the
server from which the SRv6 Locators in the IA_SRV6_LOCATOR were
obtained to extend the lifetimes of the SRv6 Locators to the
IA_SRV6_LOCATOR. T1 is a time duration relative to the message
reception time expressed in units of seconds. A 4-octet field
containing an unsigned integer.
T2: The time interval after which the client should contact any
available server to extend the lifetimes of the SRv6 Locators
assigned to the IA_SRV6_LOCATOR. T2 is a time duration relative
to the message reception time expressed in units of seconds. A
4-octet field containing an unsigned integer.
IA_SRV6_LOCATOR-Options: Options associated with this
IA_SRV6_LOCATOR. A variable-length field (12 octets less than the
value in the Option-Len field).
The IA_SRV6_LOCATOR-Options field encapsulates those options that are
specific to this IA_SRV6_LOCATOR. For example, all of the IA Locator
options (see Section 4.2) carrying the SRv6 Locators associated with
this IA_SRV6_LOCATOR are in the IA_SRV6_LOCATOR-Options field.
An IA_SRV6_LOCATOR option may only appear in the options area of a
DHCP message. A DHCP message may contain multiple IA_SRV6_LOCATOR
options (though each must have a unique IAID).
The status of any operations involving this IA_SRV6_LOCATOR is
indicated in a Status Code option (see Section 21.13 of [RFC9915]) in
the IA_SRV6_LOCATOR-Options field.
Note that an IA_SRV6_LOCATOR has no explicit "lifetime" or "lease
length" of its own. When the valid lifetimes of all of the SRv6
Locators in an IA_SRV6_LOCATOR have expired, the IA_SRV6_LOCATOR can
be considered as having expired. The T1 and T2 fields are included
to give the server explicit control over when a client should contact
the server about a specific IA_SRV6_LOCATOR.
In a message sent by a client to a server, the T1 and T2 fields
SHOULD be set to 0. The server MUST ignore any values in these
fields in messages received from a client.
In a message sent by a server to a client, the client MUST use the
values in the T1 and T2 fields for the T1 and T2 timers, unless
values in those fields are 0. The values in the T1 and T2 fields are
the number of seconds until T1 and T2.
The server selects the T1 and T2 times to allow the client to extend
the lifetimes of any SRv6 Locators in the IA_SRV6_LOCATOR before the
lifetimes expire, even if the server is unavailable for some short
period of time. Recommended values for T1 and T2 are 0.5 and 0.8
times the shortest preferred lifetime of the SRv6 Locators in the
IA_SRV6_LOCATOR that the server is willing to extend, respectively.
If the time at which the SRv6 Locators in an IA_SRV6_LOCATOR are to
be renewed is to be left to the discretion of the client, the server
sets T1 and T2 to 0. The client MUST follow the rules defined in
Section 14.2 of [RFC9915].
If a client receives an IA_SRV6_LOCATOR with T1 greater than T2 and
both T1 and T2 are greater than 0, the client discards the
IA_SRV6_LOCATOR option and processes the remainder of the message as
though the server had not included the IA_SRV6_LOCATOR option.
4.2. IA Locator Option
The IA Locator option is used to specify an SRv6 Locator associated
with an IA_SRV6_LOCATOR. The IA Locator option MUST be encapsulated
in the IA_SRV6_LOCATOR-Options field of an IA_SRV6_LOCATOR option
(see Section 4.1). 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IALOCATOR | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| LB-Len | LN-Len | Fun-Len | Arg-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
. SRv6-Locator .
. (up to 16 octets) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IALocator-Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IA Locator Option Format
Where:
Option-Code: OPTION_IALOCATOR (150), the option code for the IA
Locator option.
Option-Len: 16 + the length of SRv6-Locator + the length of the
IALocator-Options field in octets.
Preferred-lifetime: The preferred lifetime for the SRv6 Locator in
the option, expressed in units of seconds. A value of 0xffffffff
represents "infinity" (see Section 7.7 of [RFC9915]). A 4-octet
field containing an unsigned integer.
Valid-lifetime: The valid lifetime for the SRv6 Locator in the
option, expressed in units of seconds. A value of 0xffffffff
represents "infinity". A 4-octet field containing an unsigned
integer.
Algorithm: A 1-octet unsigned integer. The algorithm associated
with the SRv6 Locator from which the SID is allocated. Algorithm
values are defined in the "IGP Algorithm Types" registry
[RFC8665]. See also [RFC9350].
Reserved: A 3-octet unsigned integer. MUST be set to zero and
ignored when received.
LB-Len: SRv6 SID Locator Block (LB) length in bits. A 1-octet
unsigned integer.
LN-Len: SRv6 SID Locator Node (LN) length in bits. A 1-octet
unsigned integer.
Fun-Len: SRv6 SID function (FUNCT) length in bits. A 1-octet
unsigned integer.
Arg-Len: SRv6 SID arguments (ARG) length in bits. A 1-octet
unsigned integer.
SRv6-Locator: 0-16 octets. This field encodes the SRv6 Locator.
The SRv6 Locator is encoded in the minimal number of octets for
the SRv6 SID Locator length that is LB-Len plus LN-Len. Trailing
bits MUST be set to zero and ignored when received.
IALocator-Options: Options associated with this SRv6 Locator. A
variable-length field (determined by subtracting the length of
SRv6-Locator from Option-Len minus 12). The status code
NoSRv6LocatorAvail indicates the server has no locators available
to assign to the IA_SRV6_LOCATOR(s).
The SRv6 SID Locator length (LOC-Len) is LB-Len plus LN-Len.
The sum of LB-Len, LN-Len, Fun-Len, and Arg-Len MUST NOT exceed 128
bits. The sum of LB-Len and LN-Len MUST NOT be zero. If either of
these conditions are violated, the IA_SRV6_LOCATOR option MUST be
marked as invalid, and the remainder of the message SHOULD be
processed as if the packet did not include this option.
The values in the Preferred-lifetime and Valid-lifetime fields are
the number of seconds remaining in each lifetime. The value of
0xffffffff for the preferred lifetime or the valid lifetime is taken
to mean "infinity" and should be used carefully. The details about
the use of lifetime values for assigned SRv6 Locators are the same as
the ones specified for PD in Section 18.2.10.1 of [RFC9915].
An IA Locator option may appear only in an IA_SRV6_LOCATOR option.
More than one IA Locator option can appear in a single
IA_SRV6_LOCATOR option.
The status of any operations involving this IA_SRV6_LOCATOR option is
indicated in a Status Code option (see Section 21.13 of [RFC9915]) in
the IALocator-Options field.
5. Process of Assigning the SRv6 Locator
5.1. Procedure of the SRv6 Locator
Consistent with the PD mechanism [RFC9915], the DHCPv6 client obtains
an SRv6 Locator via DHCPv6. The key message exchanges involved are
Solicit, Request, Advertise, and Reply. Once the DHCPv6 server
assigns an SRv6 Locator to the DHCPv6 client, it automatically adds
the associated SRv6 Locator routes.
Figure 4 illustrates the process of SRv6 Locator allocation through
DHCPv6.
DHCPv6 Client DHCPv6 Server
v v
| |
| |
____________ |\ |
____________ | +-----------+ |
| Solicit \|
| EmptyIALocator|
| |
| /|
| +----------+ |
| / Advertise |
|/ IALocator |
| |
|\ |
| +-----------+ |
| Request \|
| IALocator |
| /|
| +----------+ |
| / Reply |
|/ IALocator |
End of | |
4-message | |
exchange | | Issue Locator route locally
Use Locator to | | Distribute Locator route
alloc SRv6 SID | |
Figure 4: SRv6 Locator Exchange
As specified in Section 18.2.1 of [RFC9915], the DHCPv6 client sends
a Solicit message containing an IA_SRV6_LOCATOR option to request a
locator. The client may include its preferred locator value within
the IA_SRV6_LOCATOR option.
The DHCPv6 server processes the Solicit message, assigns a locator to
the client, and returns the allocated locator in an Advertise message
with the IA_SRV6_LOCATOR option.
As specified in Section 18.2.2 of [RFC9915], upon receiving the
Advertise message, the client accepts the assigned locator and sends
a Request message with the IA_SRV6_LOCATOR option to confirm the
requested locator.
The server processes the Request message, confirms the locator
assignment, and responds with a Reply message containing the
IA_SRV6_LOCATOR option with the allocated locator.
As described in Section 18.2.4 of [RFC9915], the client periodically
sends a Renew message with the IA_SRV6_LOCATOR option to refresh the
lease. The server processes the Renew message, updates the lease,
and replies with a Reply message containing the IA_SRV6_LOCATOR
option.
As described in Section 18.2.5 of [RFC9915], if the client does not
receive a Reply message before the T2 timer expires, it sends a
Rebind message with the IA_SRV6_LOCATOR option to attempt lease
renewal.
If the server responds with a Reply message, the client retains its
allocated locator.
If no response is received, the client considers the lease expired
and restarts the process by sending a new Solicit message.
As described in Section 18.2.7 of [RFC9915], if the client is about
to go offline, it sends a Release message with the IA_SRV6_LOCATOR
option to relinquish the locator.
Upon receiving a valid Release message, and when the SRv6 Locator in
the message is valid, the server MUST remove the lease and free the
locator, making it available for allocation to other clients. For
detailed processing procedures, refer to Section 18.3.7 of [RFC9915].
5.2. DHCPv6 Client Behavior
A client uses the Solicit message to discover DHCPv6 servers
configured to assign leases or return other configuration parameters
on the link to which the client is attached.
A client uses Request, Renew, Rebind, Release, and Decline messages
during the normal lifecycle of SRv6 Locator assignment.
In a message sent by a client to a server, the Preferred-lifetime and
Valid-lifetime fields SHOULD be set to 0. The server MUST ignore any
received values in these lifetime fields.
The client MUST NOT send an IA_SRV6_LOCATOR option with 0 in the LB-
Len or LN-Len fields. The client MAY send non-zero values in the LB-
Len and LN-Len fields and the unspecified value (::) in the
SRv6-Locator field to indicate a preference for the size of the SRv6
Locator to be assigned. The LOC-Len (LB-Len + LN-Len) hint provided
by a client is similar to the prefix-length hint in an IA_PD.
Clients and servers are expected to follow the guidance provided in
[RFC8168].
The client MUST discard any SRv6 Locators for which the preferred
lifetime is greater than the valid lifetime.
The process of requesting an SRv6 Locator is the same as that of
requesting prefixes. When requesting an SRv6 Locator, the DHCPv6
client sends a Request message carrying the IA_SRV6_LOCATOR option to
the DHCPv6 server.
Upon the receipt of a valid Reply message with the IA_SRV6_LOCATOR
option in response to a Solicit with a Rapid Commit option, Request,
Renew, or Rebind message, the client MUST process the Reply message
according to the requirements of Section 18.2.10 of [RFC9915] and
configure the assigned SRv6 Locator in the client device
automatically.
DHCP allows a client to obtain multiple addresses as specified in
Section 6.5 of [RFC9915]. The same principle applies to SRv6 Locator
assignment. In scenarios requiring multiple allocations (e.g., when
multiple SRv6 Locators are needed for distinct services, such as
best-effort and low-latency traffic, each with a different
algorithm), the allocation policy between the DHCPv6 client and
DHCPv6 server MUST remain consistent. After obtaining the SRv6
Locator assigned by the DHCPv6 server, how to assign local SRv6 SIDs
based on this SRv6 Locator, how to use multiple assigned SRv6
Locators, and how to advertise these SRv6 SIDs to the rest of the
network are not within the scope of this document. However, and
consistent with the guidance in Section 16 of [RFC7227], the client
MUST NOT make any assumption about the ordering of locators or infer
any service logic from these locators.
The client uses the SRv6 Locators and associated information from any
IAs that do not contain a Status Code option with the
NoSRv6LocatorAvail status code. The client MAY include the IAs for
which it received the NoSRv6LocatorAvail status code, with no SRv6
Locators, in subsequent Renew and Rebind messages sent to the server,
to retry obtaining the SRv6 Locators for these IAs.
To extend the preferred and valid lifetimes for the assigned SRv6
Locators or obtain new assigned SRv6 Locators, the client sends a
Renew/Rebind message to the server with the IA_SRV6_LOCATOR option as
specified in Sections 18.2.4 and 18.2.5 of [RFC9915].
If the client no longer uses the SRv6 Locator, the client can
actively send a Release message to notify the server to reclaim the
SRv6 Locator and delete the corresponding SRv6 Locator. The client
MUST include options containing the IAs for the SRv6 Locators it is
releasing in the IA_SRV6_LOCATOR-Options field of the IA_SRV6_LOCATOR
option.
A client can explicitly request multiple SRv6 Locator prefixes by
sending multiple IA_SRV6_LOCATOR options. A client can send multiple
IA_SRV6_LOCATOR options in its initial transmissions. Alternatively,
it can send an extra Request message with additional new
IA_SRV6_LOCATOR options (or include them in a Renew message).
DHCP allows a client to request new SRv6 Locators to be assigned by
sending additional new IA_SRV6_LOCATOR options. However, a typical
operator usually prefers to assign a single, larger prefix. In most
deployments, it is RECOMMENDED that the client request a larger SRv6
Locator in its initial transmissions rather than request additional
SRv6 Locators later on.
5.3. DHCPv6 Server Behavior
When the server receives a valid Request message or a valid Solicit
message with a Rapid Commit option, the server creates the bindings
for that client according to the server's policy and configuration
information and records the IAs and other information requested by
the client.
The DHCPv6 server treats the SRv6 Locator as the prefix of the prefix
pool. Upon the receipt of the IA_SRV6_LOCATOR option, the server
searches the SRv6 Locator prefix pool and allocates appropriate SRv6
Locators for the client.
If there is an assignable SRv6 Locator, the server creates the SRv6
Locator binding entry for that client according to the server's
policy and configuration information and constructs a Reply message
that includes an IA_SRV6_LOCATOR option with the SRv6 Locator
information (including LB-Len, LN-Len, Fun-Len, and Arg-Len) assigned
to the client.
The IA_SRV6_LOCATOR option is filled with the SRv6 Locator
information assigned to the client. The IA_SRV6_LOCATOR option
populates the LB-Len, LN-Len, Fun-Len, and Arg-Len fields.
Upon receiving a Release message from the client or when the SRv6
Locator lease expires, the server reclaims the SRv6 Locator prefix
resource and deletes the corresponding binding entry.
For any IA_SRV6_LOCATOR option in the Request message to which the
server cannot assign any SRv6 Locators, the server MUST return the
IA_SRV6_LOCATOR option in the Reply message with no SRv6 Locator
prefixes in the IA_SRV6_LOCATOR and with a Status Code option
containing status code NoSRv6LocatorAvail in the IA_SRV6_LOCATOR.
After receiving a DHCP message with multiple IA_SRV6_LOCATOR options
at the same time, whether the server can assign multiple SRv6
Locators to the client depends on the server policy, which is out of
scope for this document. Note that the configuration behavior of the
server and client SHOULD be consistent (e.g., "clients and servers
assign a single locator unless explicitly configured").
5.4. DHCPv6 Relay Agent Behavior
The allocation of SRv6 Locators to clients that reside on a different
link from the server requires a DHCPv6 relay agent. A DHCPv6 relay
agent forwards messages containing IA_SRV6_LOCATOR options in the
same way as it would relay addresses (i.e., per Sections 19.1.1 and
19.1.2 of [RFC9915]).
+-------------+ +------------+ +-------------+
+DHCPv6 Client+-------+DHCPv6 Relay+-------+DHCPv6 Server|
+-------------+ +------+-----+ +-------------+
|
|
+------+-----+
| Backbone |
| Network |
+------------+
Figure 5: SRv6 Locator Exchange Through DHCPv6 Relay
5.5. Advertisement of the SRv6 Locator Route
This section describes the processing of SRv6 Locator routes.
As shown in Figure 5, when a DHCPv6 Relay or DHCPv6 server receives
an SRv6 Locator allocation request from a client, it MAY assign an
SRv6 Locator to the client and install a corresponding SRv6 Locator
route locally. The next hop of this route SHOULD point to the
requesting client. Through this route, the DHCPv6 Relay or DHCPv6
server can access the Host under the DHCPv6 client, while the DHCPv6
Relay or DHCPv6 server MAY then advertise this route via traditional
routing protocols (e.g., an IGP) to allow other routers to learn it.
SRv6 Locators with an Algorithm value of zero can be advertised as
normal IP prefix reachability information. Conversely, SRv6 Locators
with a non-zero Algorithm value MUST be advertised using the Locators
TLV as defined in [RFC9352] and [RFC9513].
Upon receiving an SRv6 Locator release request from the client, the
DHCPv6 Relay or DHCPv6 server MUST release the allocated SRv6
Locator, remove the local SRv6 Locator route, and withdraw the
previously advertised SRv6 Locator route via traditional routing
protocols.
DHCPv6 Client-------(DHCPv6 Relay/DHCPv6 Server)-------------Router
Alloc Locator --> Add SRv6 Locator route
Advertise SRv6 Locator route -->
Release Locator--> Del SRv6 Locator route
Withdraw SRv6 Locator route -->
Figure 6: Advertisement of the SRv6 Locator Route
6. Operational Considerations
This section outlines some operational considerations for assigning
SRv6 Locators through DHCPv6.
The SRv6 Locator can be used to allocate SIDs with SR Endpoint
Behaviors as defined in [RFC8986] and also to allocate SIDs with the
NEXT and REPLACE flavors defined in [RFC9800]. Operators can
allocate corresponding SIDs based on the LB and LN lengths of the
SRv6 Locator, as well as local policies.
When processing the SRv6 Locator defined in this document, if an
error occurs in packet processing, SRv6 Locator allocation fails, or
lease aging is handled, the DHCPv6 client and DHCPv6 server SHOULD
log or record these SRv6 Locators as required by local policy.
Section 4.4 of [RFC8987] provides necessary functional requirements
for operating DHCPv6 relays with PD. These requirements also apply
to the allocation of SRv6 Locators in DHCPv6 Relay scenarios.
Routing Stability is an additional operational consideration.
Network operators may advertise an aggregated route rather than
individual prefixes in certain deployments to optimize Routing
Information Base (RIB) performance. The withdrawal of specific
routes triggered by address releases may lead to a reduction in
advertised routes. An alternative approach is to implement a policy
that governs this behavior. In such cases, delegating routers will
discard packets destined for specific prefixes that are not
"delegated" on the customer-facing interface.
7. IANA Considerations
IANA has assigned the following DHCPv6 option codes in the "Option
Codes" registry at <https://www.iana.org/assignments/
dhcpv6-parameters>:
+=======+========================+========+===========+===========+
| Value | Description | Client | Singleton | Reference |
| | | ORO | Option | |
+=======+========================+========+===========+===========+
| 149 | OPTION_IA_SRV6_LOCATOR | No | No | RFC 10038 |
+-------+------------------------+--------+-----------+-----------+
| 150 | OPTION_IALOCATOR | No | No | RFC 10038 |
+-------+------------------------+--------+-----------+-----------+
Table 1
IANA has also assigned the following DHCPv6 status code in the
"Status Codes" registry at <http://www.iana.org/assignments/
dhcpv6-parameters>:
+======+====================+===========+
| Code | Name | Reference |
+======+====================+===========+
| 23 | NoSRv6LocatorAvail | RFC 10038 |
+------+--------------------+-----------+
Table 2
8. Security Considerations
See Section 22 of [RFC9915] and Section 23 of [RFC7227] for the DHCP
security considerations. See [RFC8200] for the IPv6 security
considerations.
As discussed in Section 22 of [RFC9915], "DHCP lacks end-to-end
encryption between clients and servers; thus, hijacking, tampering,
and eavesdropping attacks are all possible as a result."
In some network environments, it is possible to secure the
communication between clients and servers, as discussed in Section 22
of [RFC9915].
If not all parties use this mechanism to obtain an SRv6 Locator from
the DHCPv6 server, there is the possibility of the same SRv6 Locator
being used by more than one device. Note that this issue could exist
on these networks even if DHCP were not used to obtain the SRv6
Locator. A potential mitigation is to partition the available
address prefixes, ensuring that different allocation mechanisms draw
from non-overlapping pools.
Server implementations SHOULD consider configuration options to limit
the maximum number of SRv6 Locators to allocate (both in a single
request and in total) to a client. However, note that this does not
prevent a bad client actor from pretending to be many different
clients and consuming all available SRv6 Locators.
The SR domain is a trusted domain, as defined in Sections 2 and 8.2
of [RFC8402]. Having such a well-defined trust boundary is necessary
in order to operate SRv6-based services for internal traffic while
preventing any external traffic from accessing or exploiting the
SRv6-based services. Care and rigor in IPv6 address allocation for
use for SRv6 SID allocations and network infrastructure addresses, as
distinct from IPv6 addresses allocated for end users and systems (as
illustrated in Section 5.1 of [RFC8754]), can provide the clear
distinction between internal and external address space that is
required to maintain the integrity and security of the SRv6 domain.
When assigning SRv6 Locators to SRv6 Segment Endpoint Nodes using
DHCPv6 as specified in this document, DHCPv6 clients and DHCPv6
servers MUST operate within a single trusted SR domain. As a border
node device, a DHCPv6 client may reside in customer premises, while
the DHCPv6 server is located within the provider network. Although
they belong to the same trusted SR domain, the DHCPv6 client MUST
implement appropriate traffic filtering capabilities on both its
internal and external interfaces, as required by Section 5.1 of
[RFC8754].
9. References
9.1. 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>.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<https://www.rfc-editor.org/info/rfc7227>.
[RFC8168] Li, T., Liu, C., and Y. Cui, "DHCPv6 Prefix-Length Hint
Issues", RFC 8168, DOI 10.17487/RFC8168, May 2017,
<https://www.rfc-editor.org/info/rfc8168>.
[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>.
[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>.
[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>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[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>.
[RFC8987] Farrer, I., Kottapalli, N., Hunek, M., and R. Patterson,
"DHCPv6 Prefix Delegating Relay Requirements", RFC 8987,
DOI 10.17487/RFC8987, February 2021,
<https://www.rfc-editor.org/info/rfc8987>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
[RFC9513] Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
"OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
RFC 9513, DOI 10.17487/RFC9513, December 2023,
<https://www.rfc-editor.org/info/rfc9513>.
[RFC9800] Cheng, W., Ed., Filsfils, C., Li, Z., Decraene, B., and F.
Clad, Ed., "Compressed SRv6 Segment List Encoding",
RFC 9800, DOI 10.17487/RFC9800, June 2025,
<https://www.rfc-editor.org/info/rfc9800>.
[RFC9915] Mrugalski, T., Volz, B., Richardson, M., Jiang, S., and T.
Winters, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", STD 102, RFC 9915, DOI 10.17487/RFC9915,
January 2026, <https://www.rfc-editor.org/info/rfc9915>.
9.2. Informative References
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
DOI 10.17487/RFC7084, November 2013,
<https://www.rfc-editor.org/info/rfc7084>.
[RFC7368] Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
Weil, "IPv6 Home Networking Architecture Principles",
RFC 7368, DOI 10.17487/RFC7368, October 2014,
<https://www.rfc-editor.org/info/rfc7368>.
Acknowledgements
The authors would like to thank Gunter Van de Velde, Ketan
Talaulikar, Mohamed Boucadair, Chongfeng Xie, Joel Halpern, Robert
Raszuk, Aihua Liu, Cheng Li, Xuewei Wang, Hao Li, Junjie Wang,
Mengxiao Chen, Fang Gao, Aijun Wang, Xinxin Yi, Shenchao Xu, Yisong
Liu, Xueshun Wang, Min Xiao, Liyan Gong, Linda Dunbar, Quan Xiong,
Adrian Farrel, and Bernie Volz for their comments on this document.
Contributors
Yuanxiang Qiu
New H3C Technologies
Email: qiuyuanxiang@h3c.com
Authors' Addresses
Weiqiang Cheng (editor)
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Ruibo Han
China Mobile
Beijing
China
Email: hanruibo@chinamobile.com
Changwang Lin (editor)
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Daniel Voyer
Cisco Systems
Montreal
Canada
Email: davoyer@cisco.com
Geng Zhang
China Mobile
Beijing
China
Email: zhanggeng@chinamobile.com