rfc9819v1.txt   rfc9819.txt 
Internet Engineering Task Force (IETF) K. Talaulikar Internet Engineering Task Force (IETF) K. Talaulikar
Request for Comments: 9819 K. Raza Request for Comments: 9819 K. Raza
Updates: 9252 Cisco Systems Updates: 9252 Cisco Systems
Category: Standards Track J. Rabadan Category: Standards Track J. Rabadan
ISSN: 2070-1721 Nokia ISSN: 2070-1721 Nokia
W. Lin W. Lin
Juniper Networks Juniper Networks
July 2025 July 2025
Segment Routing over IPv6 Argument Signaling for BGP Services Argument Signaling for BGP Services in Segment Routing over IPv6 (SRv6)
Abstract Abstract
RFC 9252 defines procedures and messages for BGP Overlay Services for RFC 9252 defines procedures and messages for BGP overlay services for
Segment Routing over IPv6 (SRv6), including Layer 3 Virtual Private Segment Routing over IPv6 (SRv6), including Layer 3 Virtual Private
Network (L3VPN), Ethernet VPN (EVPN), and global Internet routing. Network (L3VPN), Ethernet VPN (EVPN), and global Internet routing.
This document updates RFC 9252 and provides more detailed This document updates RFC 9252 and provides more detailed
specifications for the signaling and processing of SRv6 Segment specifications for the signaling and processing of SRv6 Segment
Identifier advertisements for BGP Overlay Service routes associated Identifier advertisements for BGP overlay service routes associated
with SRv6 Endpoint Behaviors that support arguments. with SRv6 Endpoint Behaviors that support arguments.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on Internet Engineering Steering Group (IESG). Further information on
skipping to change at line 79 skipping to change at line 79
1. Introduction 1. Introduction
SRv6 refers to Segment Routing instantiated over the IPv6 data plane SRv6 refers to Segment Routing instantiated over the IPv6 data plane
[RFC8402]. An SRv6 Segment Identifier (SID) [RFC8402] can be [RFC8402]. An SRv6 Segment Identifier (SID) [RFC8402] can be
associated with one of the service-specific SRv6 Endpoint Behaviors associated with one of the service-specific SRv6 Endpoint Behaviors
on the advertising Provider Edge (PE) router for Layer 3 Virtual on the advertising Provider Edge (PE) router for Layer 3 Virtual
Private Network (L3VPN), global Internet routing, and Ethernet VPN Private Network (L3VPN), global Internet routing, and Ethernet VPN
(EVPN) services as defined in [RFC8986]. Such SRv6 SIDs are referred (EVPN) services as defined in [RFC8986]. Such SRv6 SIDs are referred
to as SRv6 Service SIDs. [RFC9252] defines the procedures and to as SRv6 Service SIDs. [RFC9252] defines the procedures and
messages for the signaling of BGP Overlay Services including L3VPN, messages for the signaling of BGP overlay services including L3VPN,
EVPN, and Internet services using SRv6. EVPN, and Internet services using SRv6.
For certain EVPN services, Section 4.12 of [RFC8986] introduced the For certain EVPN services, Section 4.12 of [RFC8986] introduced the
End.DT2M SRv6 Endpoint Behavior, which utilizes arguments (i.e., End.DT2M SRv6 Endpoint Behavior, which utilizes arguments (i.e.,
Arg.FE2). [RFC9252] subsequently specified the encoding and Arg.FE2). [RFC9252] subsequently specified the encoding and
signaling procedures for the SRv6 SID and its associated argument via signaling procedures for the SRv6 SID and its associated argument via
EVPN Route Type 3 and EVPN Route Type 1, respectively. However, the Inclusive Multicast Ethernet Tag route (EVPN Route Type 3) and
during implementation and interoperability testing, it was observed the Ethernet A-D (Auto-Discovery) per ES route (EVPN Route Type 1),
that the specifications outlined in [RFC9252] lack sufficient detail, respectively. However, during implementation and interoperability
leading to ambiguities in interpretation and implementation. testing, it was observed that the specifications outlined in
[RFC9252] lack sufficient detail, leading to ambiguities in
interpretation and implementation.
This document updates [RFC9252] by providing additional details and This document updates [RFC9252] by providing additional details and
clarifications regarding the signaling of SRv6 Service SIDs clarifications regarding the signaling of SRv6 Service SIDs
associated with SRv6 Endpoint Behaviors that utilize arguments. associated with SRv6 Endpoint Behaviors that utilize arguments.
While the focus is primarily on the signaling of the End.DT2M SRv6 While the focus is primarily on the signaling of the End.DT2M SRv6
Endpoint Behavior via EVPN Route Types 1 and 3, the procedures Endpoint Behavior via the Ethernet A-D per ES route and Inclusive
described herein are also applicable to other similar endpoint Multicast Ethernet Tag route, the procedures described herein are
behaviors with arguments that may be signaled using BGP. also applicable to other similar SRv6 Endpoint Behaviors with
arguments that may be signaled using BGP.
Section 6.3 of [RFC9252] specifies that the SRv6 Service SID used in Section 6.3 of [RFC9252] specifies that the SRv6 Service SID used in
the data plane is derived by applying a bitwise logical-OR operation the data plane is derived by applying a bitwise logical-OR operation
between the SID with an argument signaled via Route Type 1 and the between the SID with an argument signaled via the Ethernet A-D per ES
SID with the 'Locator + Function' components signaled via Route Type route and the SID with the 'Locator + Function' components signaled
3. However, this approach assumes a uniform SID structure across all via the Inclusive Multicast Ethernet Tag route. However, this
SIDs advertised via EVPN Route Types 1 and 3. This assumption is not approach assumes a uniform SID structure across all SIDs advertised
universally valid, and the procedures in this document remove this via the Ethernet A-D per ES route and Inclusive Multicast Ethernet
restriction, ensuring greater flexibility in SRv6 SID signaling. Tag route. This assumption is not universally valid, and the
procedures in this document remove this restriction, ensuring greater
flexibility in SRv6 SID signaling.
The descriptions and examples presented in this document do not The descriptions and examples presented in this document do not
utilize the Transposition Scheme (see Section 4 of [RFC9252]). utilize the Transposition Scheme (see Section 4 of [RFC9252]).
Consequently, the Transposition Offset (TPOS-O) and Transposition Consequently, the Transposition Offset (TPOS-O) and Transposition
Length (TPOS-L) are set to zero, and references to MPLS label fields Length (TPOS-L) are set to zero, and references to MPLS label fields
where the function or argument portions may be transposed are where the function or argument portions may be transposed are
omitted. However, the same examples could be applied with the omitted. However, the same examples could be applied with the
Transposition Scheme. This document does not introduce any Transposition Scheme. This document does not introduce any
modifications to the use of the Transposition Scheme in the signaling modifications to the use of the Transposition Scheme in the signaling
of EVPN routes. Implementations are expected to adhere to the of EVPN routes. Implementations are expected to adhere to the
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Section 3.1 of [RFC8986] defines the format of an SRv6 SID as Section 3.1 of [RFC8986] defines the format of an SRv6 SID as
consisting of three components: Locator (LOC), Function (FUNC), and consisting of three components: Locator (LOC), Function (FUNC), and
Argument (ARG). For SRv6 SIDs associated with SRv6 Endpoint Argument (ARG). For SRv6 SIDs associated with SRv6 Endpoint
Behaviors that do not support arguments, the ARG component is not Behaviors that do not support arguments, the ARG component is not
present. Consequently, all bits following the FUNC portion MUST be present. Consequently, all bits following the FUNC portion MUST be
set to zero, and the Argument Length (AL) MUST be zero. set to zero, and the Argument Length (AL) MUST be zero.
Certain SRv6 Endpoint Behaviors (e.g., End.DT2M) support arguments. Certain SRv6 Endpoint Behaviors (e.g., End.DT2M) support arguments.
As specified in Section 3.2.1 of [RFC9252], the SRv6 SID Structure As specified in Section 3.2.1 of [RFC9252], the SRv6 SID Structure
Sub-Sub-TLV MUST be included when signaling an SRv6 SID corresponding Sub-Sub-TLV MUST be included when signaling an SRv6 SID corresponding
to an endpoint behavior that supports argument. This ensures that to an SRv6 Endpoint Behavior that supports argument. This ensures
the receiving router can perform consistency verification of the that the receiving router can perform consistency verification of the
argument and correctly encode the ARG value within the SRv6 SID. argument and correctly encode the ARG value within the SRv6 SID.
In certain use cases, the SRv6 SID can be signaled as a complete In certain use cases, the SRv6 SID can be signaled as a complete
structure, with the LOC:FUNC:ARG components fully encoded within the structure, with the LOC:FUNC:ARG components fully encoded within the
SID. However, there are scenarios where the SRv6 SID, consisting SID. However, there are scenarios where the SRv6 SID, consisting
only of the LOC:FUNC portion, is signaled in one advertisement, while only of the LOC:FUNC portion, is signaled in one advertisement, while
the ARG value is either signaled through a separate advertisement or the ARG value is either signaled through a separate advertisement or
learned via an alternative mechanism. It is the responsibility of learned via an alternative mechanism. It is the responsibility of
the SRv6 source node to append the ARG component to the LOC:FUNC the SRv6 source node to append the ARG component to the LOC:FUNC
portion, thereby constructing the complete SRv6 SID (LOC:FUNC:ARG). portion, thereby constructing the complete SRv6 SID (LOC:FUNC:ARG).
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node that owns the SRv6 SID and is advertising the LOC:FUNC portion node that owns the SRv6 SID and is advertising the LOC:FUNC portion
of that SID or by another node/mechanism. The advertisement of the of that SID or by another node/mechanism. The advertisement of the
ARG value MUST specify the size of the argument, its value, and the ARG value MUST specify the size of the argument, its value, and the
associated SRv6 Endpoint Behavior of the SID. Additionally, the associated SRv6 Endpoint Behavior of the SID. Additionally, the
specification of the association of the ARG advertisement with the specification of the association of the ARG advertisement with the
corresponding SID(s) for which the argument applies is REQUIRED. corresponding SID(s) for which the argument applies is REQUIRED.
3. End.DT2M Signaling for EVPN ESI Filtering 3. End.DT2M Signaling for EVPN ESI Filtering
As specified in [RFC9252], the LOC:FUNC portion of the SRv6 SID with As specified in [RFC9252], the LOC:FUNC portion of the SRv6 SID with
End.DT2M behavior is signaled via EVPN Route Type 3 (Inclusive End.DT2M behavior is signaled via the Inclusive Multicast Ethernet
Multicast Ethernet Tag route), while the Ethernet Segment Identifier Tag route, while the Ethernet Segment Identifier (ESI) Filtering ARG
(ESI) Filtering ARG (denoted as Arg.FE2 in [RFC8986]) is signaled via (denoted as Arg.FE2 in [RFC8986]) is signaled via the Ethernet A-D
EVPN Route Type 1 (Ethernet Auto-Discovery per Ethernet Segment (A-D per ES route. The following subsections provide a more detailed
per ES) route). The following subsections provide a more detailed
specification of the signaling and processing mechanisms compared to specification of the signaling and processing mechanisms compared to
[RFC9252]. [RFC9252].
ESI Filtering is a split-horizon mechanism used for multihoming ESI Filtering is a split-horizon mechanism used for multihoming
[RFC7432] or Ethernet-Tree (E-Tree) procedures [RFC8317]. ESI [RFC7432] or Ethernet-Tree (E-Tree) procedures [RFC8317]. ESI
Filtering is not applicable in scenarios where: Filtering is not applicable in scenarios where:
* No E-Tree leaf Broadcast, Unknown Unicast, or Multicast (BUM) * No E-Tree leaf Broadcast, Unknown Unicast, or Multicast (BUM)
traffic exists, traffic exists,
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In this document, "ESI Filtering" is used as a general reference to In this document, "ESI Filtering" is used as a general reference to
the procedure performed by the disposition Provider Edge (PE) router the procedure performed by the disposition Provider Edge (PE) router
to prevent forwarding of BUM traffic to local Ethernet Segments or to prevent forwarding of BUM traffic to local Ethernet Segments or
local leaf attachment circuits, based on the presence of the ESI local leaf attachment circuits, based on the presence of the ESI
Filtering ARG. Filtering ARG.
The signaling and processing descriptions outlined in the following The signaling and processing descriptions outlined in the following
sections also apply to End.DT2M behavior flavors designed for SRv6 sections also apply to End.DT2M behavior flavors designed for SRv6
SID list compression [RFC9800]. In deployments where a mix of SID list compression [RFC9800]. In deployments where a mix of
compressed and uncompressed SIDs is present, the behaviors advertised compressed and uncompressed SIDs is present, the behaviors advertised
in the Ethernet Auto-Discovery (A-D) per ES routes (EVPN Route Type in the Ethernet A-D per ES routes and Inclusive Multicast Ethernet
1) and Inclusive Multicast Ethernet Tag routes (EVPN Route Type 3) Tag routes MAY consist of a combination of compressed and
MAY consist of a combination of compressed and uncompressed End.DT2M uncompressed End.DT2M behavior flavors. The procedures in this
behavior flavors. The procedures in this document remain valid for document remain valid for such deployments provided that the AL
such deployments provided that the AL consistency checks between EVPN consistency checks between the Ethernet A-D per ES route and
Route Type 1 and EVPN Route Type 3, as described in the following Inclusive Multicast Ethernet Tag route, as described in the following
subsections, are satisfied. subsections, are satisfied.
3.1. Advertisement of Ethernet A-D per ES Route 3.1. Advertisement of Ethernet A-D per ES Route
Ethernet Auto-Discovery (A-D) per ES routes (EVPN Route Type 1), as Ethernet A-D per ES routes, as defined in [RFC7432], are utilized to
defined in [RFC7432], are utilized to enable split-horizon filtering enable split-horizon filtering and fast convergence in multihoming
and fast convergence in multihoming scenarios. Additionally, A-D per scenarios. Additionally, Ethernet A-D per ES routes facilitate
ES routes facilitate egress filtering of BUM traffic originating from egress filtering of BUM traffic originating from a leaf, as specified
a Leaf, as specified in [RFC8317]. in [RFC8317].
When ESI Filtering is not in use, no ESI Filtering ARG is required to When ESI Filtering is not in use, no ESI Filtering ARG is required to
be conveyed. However, for backward compatibility and consistency be conveyed. However, for backward compatibility and consistency
with [RFC9252], the advertisement of this route SHOULD include the with [RFC9252], the advertisement of this route SHOULD include the
BGP Prefix-SID Attribute with an SRv6 L2 Service TLV carrying an SRv6 BGP Prefix-SID attribute with an SRv6 L2 Service TLV carrying an SRv6
Service SID set to ::0 in the SRv6 SID Information Sub-TLV, with the Service SID set to ::0 in the SRv6 SID Information Sub-TLV, with the
SRv6 Endpoint Behavior set to End.DT2M. Since the End.DT2M behavior SRv6 Endpoint Behavior set to End.DT2M. Since the End.DT2M behavior
supports the use of an ARG, an SRv6 SID Structure Sub-Sub-TLV MUST be supports the use of an ARG, an SRv6 SID Structure Sub-Sub-TLV MUST be
included. As no ARG value is required to be signaled in this case, included. As no ARG value is required to be signaled in this case,
the AL MUST be set to 0. the AL MUST be set to 0.
The following is an example representation of the BGP Prefix-SID The following is an example representation of the BGP Prefix-SID
Attribute encoding in this case: attribute encoding in this case:
BGP Prefix SID Attr: BGP Prefix-SID attribute:
SRv6 L2 Service TLV: SRv6 L2 Service TLV:
SRv6 SID Information Sub-TLV: SRv6 SID Information Sub-TLV:
SID: :: SID: ::
Behavior: End.DT2M Behavior: End.DT2M
SRv6 SID Structure Sub-Sub-TLV: SRv6 SID Structure Sub-Sub-TLV:
LBL: 32, LNL: 16, FL: 16, AL: 0, TPOS-L: 0, TPOS-O: 0 LBL: 32, LNL: 16, FL: 16, AL: 0, TPOS-L: 0, TPOS-O: 0
Figure 1: EVPN Route Type 1 Without ARG for ESI Filtering Figure 1: Ethernet A-D per ES Route Without ARG for ESI Filtering
When ESI Filtering is in use, the advertisement of this route MUST When ESI Filtering is in use, the advertisement of this route MUST
include the BGP Prefix-SID Attribute with an SRv6 L2 Service TLV include the BGP Prefix-SID attribute with an SRv6 L2 Service TLV
carrying the SRv6 Service SID that contains the ESI Filtering ARG carrying the SRv6 Service SID that contains the ESI Filtering ARG
value within the SRv6 SID Information Sub-TLV (when not using the value within the SRv6 SID Information Sub-TLV (when not using the
Transposition Scheme), with the SRv6 Endpoint Behavior set to Transposition Scheme), with the SRv6 Endpoint Behavior set to
End.DT2M. Since the End.DT2M behavior supports the use of an ARG, an End.DT2M. Since the End.DT2M behavior supports the use of an ARG, an
SRv6 SID Structure Sub-Sub-TLV MUST be included. Additionally, as a SRv6 SID Structure Sub-Sub-TLV MUST be included. Additionally, as a
non-zero ARG value is being signaled, the AL MUST be set to the size non-zero ARG value is being signaled, the AL MUST be set to the size
of the ARG, and the size SHOULD be a multiple of 8 to ensure of the ARG, and the size SHOULD be a multiple of 8 to ensure
consistency across implementations for ease of operations. The SRv6 consistency across implementations for ease of operations. The SRv6
SID Structure Sub-Sub-TLV MUST set the LBL, LNL, and FL fields with SID Structure Sub-Sub-TLV MUST set the LBL, LNL, and FL fields with
values that indicate the offset at which the ARG value is encoded values that indicate the offset at which the ARG value is encoded
within the 128-bit SRv6 SID. within the 128-bit SRv6 SID.
The following is an example representation of the BGP Prefix-SID The following is an example representation of the BGP Prefix-SID
Attribute encoding in this scenario for a 16-bit argument value of attribute encoding in this scenario for a 16-bit argument value of
'aaaa': 'aaaa':
BGP Prefix SID Attr: BGP Prefix-SID attribute:
SRv6 L2 Service TLV: SRv6 L2 Service TLV:
SRv6 SID Information Sub-TLV: SRv6 SID Information Sub-TLV:
SID: ::aaaa:0:0:0 SID: ::aaaa:0:0:0
Behavior: End.DT2M Behavior: End.DT2M
SRv6 SID Structure Sub-Sub-TLV: SRv6 SID Structure Sub-Sub-TLV:
LBL: 32, LNL: 16, FL: 16, AL: 16, TPOS-L: 0, TPOS-O: 0 LBL: 32, LNL: 16, FL: 16, AL: 16, TPOS-L: 0, TPOS-O: 0
Figure 2: EVPN Route Type 1 with ARG for ESI Filtering Figure 2: Ethernet A-D per ES Route with ARG for ESI Filtering
In the examples above, it would have been possible to set the LBL, In the examples above, it would have been possible to set the LBL,
LNL, and FL values to 0 and to encode the SRv6 SID as either ::0 or LNL, and FL values to 0 and to encode the SRv6 SID as either ::0 or
aaaa::. However, such an encoding would not be backward compatible aaaa::. However, such an encoding would not be backward compatible
with [RFC9252], as further detailed in Section 4. with [RFC9252], as further detailed in Section 4.
Therefore, it is REQUIRED that the LBL, LNL, and FL values be set in Therefore, it is REQUIRED that the LBL, LNL, and FL values be set in
accordance with the SID structure for End.DT2M SRv6 Service SIDs, accordance with the SID structure for End.DT2M SRv6 Service SIDs,
ensuring compliance with [RFC9252]. ensuring compliance with [RFC9252].
3.2. Advertisement of Inclusive Multicast Ethernet Tag Route 3.2. Advertisement of Inclusive Multicast Ethernet Tag Route
The Inclusive Multicast Ethernet Tag route (EVPN Route Type 3), as The Inclusive Multicast Ethernet Tag route, as defined in [RFC7432],
defined in [RFC7432], is used to advertise multicast traffic is used to advertise multicast traffic reachability information via
reachability information via Multiprotocol BGP (MP-BGP) to all other Multiprotocol BGP (MP-BGP) to all other PE routers within a given
PE routers within a given EVPN instance. When utilizing SRv6 EVPN instance. When utilizing SRv6 transport, the advertisement of
transport, the advertisement of this route MUST include the BGP this route MUST include the BGP Prefix-SID attribute with an SRv6 L2
Prefix-SID Attribute with an SRv6 L2 Service TLV to indicate the use Service TLV to indicate the use of SRv6.
of SRv6.
Regardless of whether ESI Filtering is in use, the SRv6 Service SID Regardless of whether ESI Filtering is in use, the SRv6 Service SID
MUST include only the LOC:FUNC portion within the SRv6 SID MUST include only the LOC:FUNC portion within the SRv6 SID
Information Sub-TLV (when not utilizing the Transposition Scheme), Information Sub-TLV (when not utilizing the Transposition Scheme),
with the SRv6 Endpoint Behavior set to End.DT2M. Since the End.DT2M with the SRv6 Endpoint Behavior set to End.DT2M. Since the End.DT2M
behavior supports the use of an ARG, an SRv6 SID Structure Sub-Sub- behavior supports the use of an ARG, an SRv6 SID Structure Sub-Sub-
TLV MUST be included. The LBL, LNL, and FL fields MUST be set to TLV MUST be included. The LBL, LNL, and FL fields MUST be set to
indicate the structure of the SRv6 Service SID being advertised. indicate the structure of the SRv6 Service SID being advertised.
When ESI Filtering is not in use, no ARG is expected to be received When ESI Filtering is not in use, no ARG is expected to be received
by the router along with the advertised SRv6 Service SID. Therefore, by the router along with the advertised SRv6 Service SID. Therefore,
the AL MUST be set to 0. the AL MUST be set to 0.
The following is an example representation of the BGP Prefix-SID The following is an example representation of the BGP Prefix-SID
Attribute encoding in this case: attribute encoding in this case:
BGP Prefix SID Attr: BGP Prefix-SID attribute:
SRv6 L2 Service TLV: SRv6 L2 Service TLV:
SRv6 SID Information Sub-TLV: SRv6 SID Information Sub-TLV:
SID: 2001:db8:1:fbd1:: SID: 2001:db8:1:fbd1::
Behavior: End.DT2M Behavior: End.DT2M
SRv6 SID Structure Sub-Sub-TLV: SRv6 SID Structure Sub-Sub-TLV:
LBL: 32, LNL: 16, FL: 16, AL: 0, TPOS-L: 0, TPOS-O: 0 LBL: 32, LNL: 16, FL: 16, AL: 0, TPOS-L: 0, TPOS-O: 0
Figure 3: EVPN Route Type 3 Without ESI Filtering Figure 3: Inclusive Multicast Ethernet Tag Route Without ESI
Filtering
When ESI Filtering is in use, the router expects to receive traffic When ESI Filtering is in use, the router expects to receive traffic
in the data path to the SRv6 Service SID that it has signaled along in the data path to the SRv6 Service SID that it has signaled along
with the ARG portion embedded in it. Consequently, the AL MUST be with the ARG portion embedded in it. Consequently, the AL MUST be
set to the size of the ARG supported by the advertising router for set to the size of the ARG supported by the advertising router for
the specific SRv6 Service SID. The AL value is unique per End.DT2M the specific SRv6 Service SID. The AL value is unique per End.DT2M
behavior signaled by the egress PE. Therefore, the egress PE MUST behavior signaled by the egress PE. Therefore, the egress PE MUST
use the same AL for all local Ethernet Segments with attachment use the same AL for all local Ethernet Segments with attachment
circuits within the same broadcast domain. circuits within the same broadcast domain.
The following is an example representation of the BGP Prefix-SID The following is an example representation of the BGP Prefix-SID
Attribute encoding for this scenario with a 16-bit argument: attribute encoding for this scenario with a 16-bit argument:
BGP Prefix SID Attr: BGP Prefix-SID attribute:
SRv6 L2 Service TLV: SRv6 L2 Service TLV:
SRv6 SID Information Sub-TLV: SRv6 SID Information Sub-TLV:
SID: 2001:db8:1:fbd1:: SID: 2001:db8:1:fbd1::
Behavior: End.DT2M Behavior: End.DT2M
SRv6 SID Structure Sub-Sub-TLV: SRv6 SID Structure Sub-Sub-TLV:
LBL: 32, LNL: 16, FL: 16, AL: 16, TPOS-L: 0, TPOS-O: 0 LBL: 32, LNL: 16, FL: 16, AL: 16, TPOS-L: 0, TPOS-O: 0
Figure 4: EVPN Route Type 3 with ESI Filtering Figure 4: Inclusive Multicast Ethernet Tag Route with ESI Filtering
When ESI Filtering is in use, the advertising router MUST ensure that When ESI Filtering is in use, the advertising router MUST ensure that
the AL signaled in the EVPN Route Type 3 is equal to the AL signaled the AL signaled in the Inclusive Multicast Ethernet Tag route is
in the corresponding EVPN Route Type 1. equal to the AL signaled in the corresponding Ethernet A-D per ES
route.
3.3. Processing at Ingress PE 3.3. Processing at Ingress PE
An ingress PE receives the LOC:FUNC portion of the SRv6 Service SID An ingress PE receives the LOC:FUNC portion of the SRv6 Service SID
to be used for BUM traffic through EVPN Route Type 3 advertisements. to be used for BUM traffic through Inclusive Multicast Ethernet Tag
route advertisements.
When ESI Filtering is not in use, the SRv6 Service SID to be used When ESI Filtering is not in use, the SRv6 Service SID to be used
consists solely of the LOC:FUNC portion received via EVPN Route Type consists solely of the LOC:FUNC portion received via the Inclusive
3. Multicast Ethernet Tag route.
When ESI Filtering is in use, the ESI Filtering ARG of the SRv6 When ESI Filtering is in use, the ESI Filtering ARG of the SRv6
Service SID is signaled through EVPN Route Type 1 (Ethernet Auto- Service SID is signaled through the Ethernet A-D per ES route. The
Discovery per Ethernet Segment route). The ARG, in combination with ARG, in combination with the LOC:FUNC portion received via the
the LOC:FUNC portion received via EVPN Route Type 3, forms the SRv6 Inclusive Multicast Ethernet Tag route, forms the SRv6 Service SID to
Service SID to be used. be used.
Since the LOC:FUNC and ARG portions of the SRv6 Service SID are Since the LOC:FUNC and ARG portions of the SRv6 Service SID are
signaled via different route advertisements, there may be cases where signaled via different route advertisements, there may be cases where
the ingress PE receives inconsistent AL values from the two route the ingress PE receives inconsistent AL values from the two route
types. If the ingress PE expects ESI Filtering to be in use (i.e., types. If the ingress PE expects ESI Filtering to be in use (i.e.,
when forwarding BUM traffic to other PEs attached to a shared when forwarding BUM traffic to other PEs attached to a shared
Ethernet Segment) but does not receive a usable ARG value during Ethernet Segment) but does not receive a usable ARG value during
processing, it SHOULD log a message to facilitate troubleshooting. processing, it SHOULD log a message to facilitate troubleshooting.
The ingress PE router MUST follow the processing steps outlined below The ingress PE router MUST follow the processing steps outlined below
when handling SRv6 Service SID advertisements: when handling SRv6 Service SID advertisements:
1. If AL=0 is signaled via EVPN Route Type 3, then the egress PE 1. If AL=0 is signaled via the Inclusive Multicast Ethernet Tag
either does not support ESI Filtering or does not require an ESI route, then the egress PE either does not support ESI Filtering
Filtering ARG for the specific SID. In this case, the SRv6 or does not require an ESI Filtering ARG for the specific SID.
Service SID is formed using only the LOC:FUNC portion, and all In this case, the SRv6 Service SID is formed using only the
bits after LBL + LNL + FL MUST be set to zero for encoding on the LOC:FUNC portion, and all bits after LBL + LNL + FL MUST be set
data path. Additionally, the router MUST ignore the SID value to zero for encoding on the data path. Additionally, the router
and its SID structure advertised in the corresponding EVPN Route MUST ignore the SID value and its SID structure advertised in the
Type 1. corresponding Ethernet A-D per ES route.
2. If a non-zero AL is signaled via EVPN Route Type 3, then the 2. If a non-zero AL is signaled via the Inclusive Multicast Ethernet
matching EVPN Route Type 1 for the Ethernet Segment is located Tag route, then the matching Ethernet A-D per ES route for the
and the presence of an SRv6 SID advertisement with the End.DT2M Ethernet Segment is located and the presence of an SRv6 SID
behavior is verified. advertisement with the End.DT2M behavior is verified.
a. If the presence of such a SRv6 SID is not verified, or if the a. If the presence of such a SRv6 SID is not verified, or if the
AL is zero in the EVPN Route Type 1, then no usable ARG value AL is zero in the Ethernet A-D per ES route, then no usable
is available. The SRv6 Service SID MUST be formed as ARG value is available. The SRv6 Service SID MUST be formed
described in (1) above. as described in (1) above.
b. If the AL values in EVPN Route Type 1 and EVPN Route Type 3 b. If the AL values in the Ethernet A-D per ES route and
are both non-zero but not equal, then no usable ARG value is Inclusive Multicast Ethernet Tag route are both non-zero but
available. This inconsistency in signaling from the egress not equal, then no usable ARG value is available. This
PE indicates a configuration error. To prevent potential inconsistency in signaling from the egress PE indicates a
looping, BUM traffic MUST NOT be forwarded for such routes configuration error. To prevent potential looping, BUM
from the specific Ethernet Segment. Implementations SHOULD traffic MUST NOT be forwarded for such routes from the
log an error message for troubleshooting this condition. specific Ethernet Segment. Implementations SHOULD log an
error message for troubleshooting this condition.
c. If the AL values in EVPN Route Type 1 and EVPN Route Type 3 c. If the AL values in the Ethernet A-D per ES route and
are both non-zero and equal, then the ARG value from EVPN Inclusive Multicast Ethernet Tag route are both non-zero and
Route Type 1 is considered valid. This ARG value MUST be equal, then the ARG value from the Ethernet A-D per ES route
encoded within the SRv6 SID (LOC:FUNC) at the ARG offset as is considered valid. This ARG value MUST be encoded within
specified in the SID structure (i.e., LBL + LNL + FL) in EVPN the SRv6 SID (LOC:FUNC) at the ARG offset as specified in the
Route Type 3. All bits beyond LBL + LNL + FL + AL MUST be SID structure (i.e., LBL + LNL + FL) in the Inclusive
set to zero. Multicast Ethernet Tag route. All bits beyond LBL + LNL + FL
+ AL MUST be set to zero.
Based on the above procedures, the SRv6 Service SID encoding for the Using the procedures above with the examples in Figures 1 and 3, the
data plane without an ESI Filtering ARG, based on the examples in SRv6 Service SID encoding for the data plane without an ESI Filtering
Figures 1 and 3, is as follows: ARG is as follows:
Route Type 3: Inclusive Multicast Ethernet Tag route:
SID: 2001:db8:1:fbd1:: SID: 2001:db8:1:fbd1::
Structure: LBL: 32, LNL: 16, FL: 16, AL: 0 Structure: LBL: 32, LNL: 16, FL: 16, AL: 0
SRv6 Service SID Encoded for Datapath: 2001:db8:1:fbd1:: SRv6 Service SID Encoded for Datapath: 2001:db8:1:fbd1::
Figure 5: SRv6 Service SID Encoding for Data Plane Without ARG Figure 5: SRv6 Service SID Encoding for Data Plane Without ARG
Based on the above procedures, the SRv6 Service SID encoding for the Using the procedures above with the examples in Figures 2 and 4, the
data plane along with an ESI Filtering ARG, based on the examples in SRv6 Service SID encoding for the data plane along with an ESI
2 and 4, is as follows: Filtering ARG is as follows:
Route Type 1: Ethernet A-D per ES route:
SID: ::aaaa:0:0:0 SID: ::aaaa:0:0:0
Structure: LBL: 32, LNL: 16, FL: 16, AL: 16 Structure: LBL: 32, LNL: 16, FL: 16, AL: 16
Route Type 3: Inclusive Multicast Ethernet Tag route:
SID: 2001:db8:1:fbd1:: SID: 2001:db8:1:fbd1::
Structure: LBL: 32, LNL: 16, FL: 16, AL: 16 Structure: LBL: 32, LNL: 16, FL: 16, AL: 16
SRv6 Service SID Encoded for Datapath: 2001:db8:1:fbd1:aaaa:: SRv6 Service SID Encoded for Datapath: 2001:db8:1:fbd1:aaaa::
Figure 6: SRv6 Service SID Encoding for Data Plane with ARG Figure 6: SRv6 Service SID Encoding for Data Plane with ARG
Figure 7 provides another example that illustrates the signaling and Figure 7 provides another example that illustrates the signaling and
processing of multiple bridge domains in a deployment design. processing of multiple bridge domains in a deployment design.
skipping to change at line 465 skipping to change at line 473
| +-----+ | | FL:16 FL:32 | | +-----+ | | FL:16 FL:32 |
| +-----+ | RT1 | | +-----+ | RT1 |
| | BD2 | | ESI-1 | | | BD2 | | ESI-1 |
| +-----+ | AL:16 | | +-----+ | AL:16 |
+---------+ | +---------+ |
PE2 | | PE2 | |
| | | |
| | | |
+-------------------------------+ +-------------------------------+
Route Type 1 ESI-1: Ethernet A-D per ES route for ESI-1:
SID: ::aaaa:0:0:0 SID: ::aaaa:0:0:0
Structure: LBL: 32, LNL: 16, FL: 16, AL: 16 Structure: LBL: 32, LNL: 16, FL: 16, AL: 16
Route Type 3 from BD1: Inclusive Multicast Ethernet Tag route from BD1:
SID: 2001:db8:1:fbd1:fbd1: SID: 2001:db8:1:fbd1:fbd1:
Structure: LBL: 32, LNL: 16, FL: 32, AL: 16 Structure: LBL: 32, LNL: 16, FL: 32, AL: 16
Route Type 3 from BD2: Inclusive Multicast Ethernet Tag route from BD2:
SID: 2001:db8:1:fbd2:: SID: 2001:db8:1:fbd2::
Structure: LBL: 32, LNL: 16, FL: 16, AL: 16 Structure: LBL: 32, LNL: 16, FL: 16, AL: 16
SRv6 Service SID for datapath from ingress PE1 to egress PE2 on BD1: SRv6 Service SID for datapath from ingress PE1 to egress PE2 on BD1:
2001:db8:1:fbd1:fbd1:aaaa:: 2001:db8:1:fbd1:fbd1:aaaa::
SRv6 Service SID for datapath from ingress PE1 to egress PE2 on BD2: SRv6 Service SID for datapath from ingress PE1 to egress PE2 on BD2:
2001:db8:1:fbd2:aaaa:: 2001:db8:1:fbd2:aaaa::
Figure 7: Example with Multiple Bridge Domains Figure 7: Example with Multiple Bridge Domains
4. Backward Compatibility 4. Backward Compatibility
Existing implementations that rely on the bitwise logical-OR Existing implementations that rely on the bitwise logical-OR
operation, as specified in Section 6.3 of [RFC9252], function operation, as specified in Section 6.3 of [RFC9252], function
correctly only when the SID structures of the two EVPN route types correctly only when the SID structures of the two EVPN route types
are identical. are identical.
Backward compatibility with implementations performing the bitwise Backward compatibility with implementations performing the bitwise
logical-OR operation is maintained when EVPN Route Type 3 and its logical-OR operation is maintained when the Inclusive Multicast
corresponding EVPN Route Type 1 advertise SIDs with the same SID Ethernet Tag route and its corresponding Ethernet A-D per ES route
structure, as outlined in Sections 3.1 and 3.2. advertise SIDs with the same SID structure, as outlined in Sections
3.1 and 3.2.
However, when the SID structures of the two route types are not However, when the SID structures of the two route types are not
identical, the bitwise logical-OR operation specified in [RFC9252] identical, the bitwise logical-OR operation specified in [RFC9252]
cannot be applied. Instead, the alternative method specified in cannot be applied. Instead, the alternative method specified in
Section 3.3 MUST be used to correctly derive the SRv6 Service SID in Section 3.3 MUST be used to correctly derive the SRv6 Service SID in
such cases. such cases.
5. IANA Considerations 5. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
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