Internet Engineering Task Force (IETF) P. Jain

Internet Engineering Task Force (IETF) P. Jain
Request for Comments: 9489 A. Sajassi
Category: Standards Track S. Salam
ISSN: 2070-1721 Cisco
S. Boutros
Ciena
G. Mirsky
Ericsson
November 2023

Label Switched Path (LSP) Ping Mechanisms for EVPN and Provider Backbone
Bridging EVPN (PBB-EVPN)

Abstract

Label Switched Path (LSP) Ping is a widely deployed Operations,
Administration, and Maintenance (OAM) mechanism in MPLS networks.
This document describes mechanisms for detecting data plane failures
using LSP Ping in MPLS-based Ethernet VPN (EVPN) and Provider
Backbone Bridging EVPN (PBB-EVPN) networks.

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/rfc9489.

Copyright Notice

Copyright (c) 2023 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
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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
2. Specification of Requirements
3. Terminology
4. Target FEC Stack Sub-TLVs
4.1. EVPN MAC/IP Sub-TLV
4.2. EVPN Inclusive Multicast Sub-TLV
4.3. EVPN Ethernet Auto-Discovery (A-D) Sub-TLV
4.3.1. Ethernet Tag Value
4.3.2. Per-ES EVPN Auto-Discovery Route with Different RDs
4.3.3. EVPN VPWS
4.4. EVPN IP Prefix Sub-TLV
5. Encapsulation of OAM Ping Packets
6. Operations
6.1. Unicast Data Plane Connectivity Checks
6.2. Inclusive Multicast Data Plane Connectivity Checks
6.2.1. Ingress Replication
6.2.2. Using P2MP P-Tree
6.2.3. Controlling Echo Responses When Using P2MP P-Tree
6.3. EVPN Aliasing Data Plane Connectivity Check
6.4. EVPN IP Prefix (RT-5) Data Plane Connectivity Check
7. Security Considerations
8. IANA Considerations
8.1. Sub-TLV Type
8.2. New Return Codes
9. Normative References
Acknowledgments
Authors' Addresses

1. Introduction

[RFC7432] describes MPLS-based EVPN technology. An EVPN comprises
one or more Customer Edge devices (CEs) connected to one or more
Provider Edge devices (PEs). The PEs provide Layer 2 (L2) EVPN among
the CE(s) over the MPLS core infrastructure. In EVPN networks, the
PEs advertise the Media Access Control (MAC) addresses learned from
the locally connected CE(s), along with the MPLS label, to remote
PE(s) in the control plane using multiprotocol BGP [RFC4760]. EVPN
enables multihoming of CE(s) connected to multiple PEs and load
balancing of traffic to and from multihomed CE(s).

[RFC7623] describes the use of Provider Backbone Bridging EVPN. PBB-
EVPN maintains the Customer MAC (C-MAC) learning in the data plane
and only advertises Backbone MAC (B-MAC) addresses in a control plane
using BGP.

Procedures for simple and efficient mechanisms to detect data plane
failures using LSP Ping in MPLS networks are well defined in
[RFC8029] and [RFC6425]. The basic idea for the LSP Ping mechanism
is to send an MPLS Echo Request packet along the same data path as
data packets belonging to the same Forwarding Equivalent Class (FEC).
The Echo Request packet carries the FEC being verified in the Target
FEC Stack TLV [RFC8029]. Once the Echo Request packet reaches the
end of the MPLS path, it is sent to the control plane of the egress
PE. The Echo Request packet contains sufficient information to
verify the correctness of data plane operations and validate the data
plane against the control plane. The egress PE sends the results of
the validation in an Echo Reply packet to the originating PE of the
Echo Request packet.

This document defines procedures to detect data plane failures using
LSP Ping in MPLS networks deploying EVPN and PBB-EVPN. This document
defines four new sub-TLVs for the Target FEC Stack TLV with the
purpose of identifying the FEC on the egress PE.

2. Specification of Requirements

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.

3. Terminology

A-D: Auto-Discovery

B-MAC: Backbone MAC

BUM: Broadcast, Unknown Unicast, and Multicast

CE: Customer Edge device

C-MAC: Customer MAC

DF: Designated Forwarder

ES: Ethernet Segment

ESI: Ethernet Segment Identifier

EVI: EVPN Instance Identifier that globally identifies the EVPN
Instance

EVPN: Ethernet Virtual Private Network

FEC: Forwarding Equivalent Class

G-ACh: Generic Associated Channel

GAL: G-ACh Label

MAC-VRF: A Virtual Routing and Forwarding table for MAC addresses on
a PE

ND: Neighbor Discovery

OAM: Operations, Administration, and Maintenance

P2MP: Point-to-Multipoint

PBB-EVPN: Provider Backbone Bridging EVPN

PE: Provider Edge device

VPWS: Virtual Private Wire Service

4. Target FEC Stack Sub-TLVs

This document introduces four new Target FEC Stack sub-TLVs that are
included in the MPLS Echo Request packet. The Echo Request packets
are used for connectivity checks in the data plane in EVPN and PBB-
EVPN networks. The Target FEC Stack sub-TLVs MAY be used to validate
that an identifier for a given EVPN is programmed at the target node.

4.1. EVPN MAC/IP Sub-TLV

The EVPN MAC/IP sub-TLV identifies the target MAC, MAC/IP binding for
ARP/ND, or IP address for an EVI under test at an egress PE. This
sub-TLV is included in the Echo Request sent by an EVPN/PBB-EVPN PE
to a peer PE.

The fields of the EVPN MAC/IP sub-TLV are derived from the MAC/IP
Advertisement route defined in Section 7.2 of [RFC7432] and have the
format shown in Figure 1. The fields of the EVPN MAC/IP sub-TLV
should be set according to the following, which is consistent with
[RFC7432] and [RFC7623]:

* The Ethernet Tag ID field can be 0 or a valid VLAN ID for EVPN
VLAN-aware bundle service [RFC7432]. For PBB-EVPN, the value of
this field is always 0 as per Section 5.2 of [RFC7623].

* The Ethernet Segment Identifier field is a 10-octet field. For
EVPN, it is set to 0 for a single-homed ES or to a valid ESI ID
for a multihomed ES. For PBB-EVPN, the Ethernet Segment
Identifier field must be set to either 0 (for single-homed
segments or multihomed segments with per-I-SID load balancing) or
to MAX-ESI (for multihomed segments with per-flow load balancing)
as described in Section 5.2 of [RFC7623].

* The MAC Addr Len field specifies the MAC length in bits. Only
48-bit MAC addresses are supported as this document follows the
MAC address length supported by [RFC7432].

* The MAC Address field is set to the 6-octet MAC address.

* The IP Address field is optional. When the IP Address field is
not present, the IP Addr Len field is set to 0. When the IP
Address field is present, the IP Addr Len field is in bits and is
set to either 32 for IPv4 addresses or 128 for IPv6 addresses.

* The Must Be Zero fields are set to 0. The receiving PE should
ignore the Must Be Zero fields.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Tag ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Segment Identifier |
| (10 octets) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Must Be Zero | MAC Addr Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+ (6 octets) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Must Be Zero | IP Addr Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (0, 4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: EVPN MAC/IP Sub-TLV Format

The MPLS Echo Request is sent by the ingress PE using the EVPN MPLS
label(s) associated with the MAC/IP Advertisement route announced by
the egress PE and the MPLS transport label(s) to reach the egress PE.

In EVPN, the MAC/IP Advertisement route has multiple uses and is used
for the following cases:

* This route with only a MAC address and MPLS Label1 is used for
populating MAC-VRF and performing MAC forwarding.

* This route with MAC and IP addresses and only MPLS Label1 is used
for populating both MAC-VRF and ARP/ND tables (for ARP
suppression) as well as for performing MAC forwarding.

* This route with MAC and IP addresses and both MPLS Label1 and
Label2 is used for populating MAC-VRF and IP-VRF tables as well as
for both MAC and IP forwarding in the case of symmetric Integrated
Routing and Bridging (IRB).

When an MPLS Echo Request is sent by an ingress PE, the contents of
the Echo Request and the egress PE mode of operation (i.e., IRB mode
or L2 mode) along with EVPN MPLS label of the packet determine which
of the three cases above this Echo Request is for. When the egress
PE receives the EVPN MAC/IP sub-TLV containing only the MAC address,
the egress PE validates the MAC state and forwarding. When the
egress PE receives the EVPN MAC/IP sub-TLV containing both MAC and IP
addresses and if the EVPN label points to a MAC-VRF, then the egress
PE validates the MAC state and forwarding. If the egress PE is not
configured in symmetric IRB mode, it also validates ARP/ND state.
However, if the EVPN label points to an IP-VRF, then the egress PE
validates IP state and forwarding. Any other combinations (e.g., the
egress PE receiving the EVPN MAC/IP sub-TLV containing only the MAC
address but with the EVPN label pointing to an IP-VRF) should be
considered invalid, and the egress PE should send an Echo Reply with
the appropriate Return Code to the ingress PE.

4.2. EVPN Inclusive Multicast Sub-TLV

The fields of the EVPN Inclusive Multicast sub-TLV are based on the
EVPN Inclusive Multicast Tag route defined in Section 7.3 of
[RFC7432]. This TLV is included in the Echo Request sent to the EVPN
peer PE by the originator of the request to verify the multicast
connectivity state on the peer PE(s) in EVPN and PBB-EVPN networks.

The EVPN Inclusive Multicast sub-TLV has the format shown in
Figure 2. The fields of this sub-TLV should be set according to the
following, which is consistent with [RFC7432] and [RFC7623]:

* The Route Distinguisher (RD) field is a 10-octet field and is set
to the RD of the MAC-VRF on the peer PE.

* For EVPN, the Ethernet Tag ID field can be set to 0 or a valid
VLAN ID for EVPN VLAN-aware bundle service [RFC7432]. For PBB-
EVPN, the value of this field is set to the Service Instance
Identifier (I-SID) value as per Section 5.3 of [RFC7623].

* The IP Addr Len field specifies the length of the Originating
Router's IP Addr field in bits and is set to either 32 for IPv4
addresses or 128 for IPv6 addresses.

* The Originating Router's IP Addr field is set to the IPv4 or IPv6
address of the peer PE.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Tag ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Addr Len | |
+-+-+-+-+-+-+-+ |
~ Originating Router's IP Addr ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: EVPN Inclusive Multicast Sub-TLV Format

BUM traffic can be sent using ingress replication or P2MP P-tree in
EVPN and PBB-EVPN networks. When using ingress replication, the Echo
Request is sent using a label stack of [Transport label, Inclusive
Multicast label] to each egress PE participating in EVPN or PBB-EVPN.
The Inclusive Multicast label is the downstream-assigned label
announced by the egress PE to which the Echo Request is being sent.
The Inclusive Multicast label is the inner label in the MPLS label
stack.

When using P2MP P-tree in EVPN or PBB-EVPN, the Echo Request is sent
using a P2MP P-tree transport label for the Inclusive P-tree
arrangement or using a label stack of [P2MP P-tree Transport label,
upstream-assigned EVPN Inclusive Multicast label] for the Aggregate
Inclusive P2MP P-tree arrangement as described in Section 6.

In an EVPN network, to emulate traffic coming from a multihomed site,
an additional EVPN Ethernet A-D sub-TLV in the Target FEC Stack TLV
and an ESI Split Horizon Group MPLS label as the bottom label are
also included in the Echo Request packet. When using P2MP P-tree,
the ESI Split Horizon Group MPLS label is upstream assigned. Please
see Section 6.2.2 for operations using P2MP P-trees.

4.3. EVPN Ethernet Auto-Discovery (A-D) Sub-TLV

The fields in the EVPN Ethernet A-D sub-TLV are based on the EVPN
Ethernet A-D route advertisement defined in Section 7.1 of [RFC7432].
The EVPN Ethernet A-D sub-TLV only applies to EVPN.

The EVPN Ethernet A-D sub-TLV has the format shown in Figure 3. The
fields of this sub-TLV should be set according to the following,
which is consistent with [RFC7432]:

* The Route Distinguisher (RD) field is a 10-octet field and is set
to the RD of the MAC-VRF on the peer PE. Please see Section 4.3.2
for the case when a per-ES A-D route is announced with different
RDs.

* The Ethernet Tag ID field can be 0, MAX-ET, or a valid VLAN ID as
described in Section 4.3.1.

* The Ethernet Segment Identifier field is a 10-octet field and is
set to 0 for a single-homed ES or to a valid ESI ID for a
multihomed ES.

* The Must Be Zero field is set to 0. The receiving PE should
ignore the Must Be Zero field.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Tag ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Segment Identifier |
| (10 octets) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: EVPN Ethernet A-D Sub-TLV Format

4.3.1. Ethernet Tag Value

The EVPN Ethernet A-D sub-TLV can be sent in the context of per-ES or
per-EVI. When an operator performs a connectivity check for the BUM
L2 service, an Echo Request packet is sent and MAY contain the EVPN
Ethernet A-D sub-TLV to emulate traffic coming from a multihomed
site. In this case, the EVPN Ethernet A-D sub-TLV is added in the
per-ES context. When an Echo Request packet is sent for the
connectivity check for EVPN Aliasing state, the context for the EVPN
Ethernet A-D sub-TLV is per-EVI.

The Ethernet Tag field value in the EVPN Ethernet A-D sub-TLV MUST be
set according to the context:

* For the per-ES context, the Ethernet Tag field in the sub-TLV MUST
be set to the reserved MAX-ET value [RFC7432].

* For the per-EVI context, the Ethernet Tag field in the sub-TLV
MUST be set to the non-reserved value.

4.3.2. Per-ES EVPN Auto-Discovery Route with Different RDs

Section 8.2 of [RFC7432] specifies that a per-ES EVPN A-D route for a
given multihomed ES may be advertised more than once with different
RD values because many EVIs may be associated with the same ES and
Route Targets for all these EVIs may not fit in a single BGP Update
message. In this case, the RD value used in the EVPN Ethernet A-D
sub-TLV MUST be the RD value received for the EVI in the per-ES EVPN
A-D route.

4.3.3. EVPN VPWS

LSP Ping can also be used to detect data plane failures for the EVPN
VPWS described in [RFC8214]. The Echo Request packet carries the
EVPN Ethernet A-D sub-TLV with fields populated from the EVPN
Ethernet A-D per-EVI route announced by the egress PE for the EVPN
VPWS under test. The Echo Request is sent by the ingress PE using
the EVPN MPLS label associated with the EVPN Ethernet A-D route
announced by the egress PE and the MPLS transport label(s) to reach
the egress PE.

The egress PE processes the Echo Request packet and performs checks
for the EVPN Ethernet A-D sub-TLV present in the Target FEC Stack TLV
as described in Section 4.4 of [RFC8029] and responds according to
processing rules in [RFC8029]. The egress PE can identify that the
Echo Request is for the EVPN VPWS instance as EVI (identified by the
RD) for EVPN VPWS is different from EVI assigned for EVPN. The
egress PE will use the information from the EVPN Ethernet A-D sub-TLV
in the Target FEC Stack TLV and validate the VLAN state for the EVPN
VPWS under test. For the success case, the egress PE will reply with
Return Code 3 ("Replying router is an egress for the FEC at stack-
depth <RSC>").

4.4. EVPN IP Prefix Sub-TLV

The EVPN IP Prefix sub-TLV identifies the IP prefix for an EVI under
test at a peer PE.

The EVPN IP Prefix sub-TLV fields are derived from the IP Prefix
route (RT-5) advertisement defined in [RFC9136]. This sub-TLV only
applies to EVPN.

The EVPN IP Prefix sub-TLV has the format shown in Figure 4. The
total length (not shown) of this sub-TLV MUST be either 32 bytes (if
IPv4 addresses are carried) or 56 bytes (if IPv6 addresses are
carried). The IP prefix and gateway IP address MUST be from the same
IP address family, as described in Section 3.1 of [RFC9136].

The fields of the EVPN IP Prefix sub-TLV should be set according to
the following, which is consistent with [RFC9136]:

* The Route Distinguisher (RD) field is a 10-octet field and is set
to the RD of the IP-VRF on the peer PE.

* The Ethernet Tag ID field can be 0 or a valid VLAN ID for EVPN
VLAN-aware bundle service [RFC7432].

* The Ethernet Segment Identifier field is a 10-octet field and is
set to a valid ESI ID if the ESI is used as an Overlay Index as
per Section 3.1 of [RFC9136]. Otherwise, the Ethernet Segment
Identifier field is set to 0.

* The IP Prefix Len field specifies the number of bits in the IP
Prefix field. It is set to a value between 0 and 32 for IPv4 or
between 0 to 128 for IPv6.

* The IP Prefix field is set to a 4-octet IPv4 address (with
trailing 0 bits to make 32 bits in all) or a 16-octet IPv6 address
(with trailing 0 bits to make 128 bits in all). The address
family of this field is inferred from the sub-TLV length field, as
discussed above.

* The Gateway (GW) IP Address field is set to a 4-octet IPv4 address
or a 16-octet IPv6 address if it's used as an Overlay Index for
the IP prefixes. If the GW IP Address is not being used, it must
be set to 0 as described in Section 3.1 of [RFC9136]. The address
family of this field is inferred from the sub-TLV length field, as
discussed above.

* The Must Be Zero field is set to 0. The receiving PE should
ignore the Must Be Zero field.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Tag ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Segment Identifier |
| (10 octets) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Must Be Zero | IP Prefix Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ IP Prefix (4 or 16 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ GW IP Address (4 or 16 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: EVPN IP Prefix Sub-TLV Format

The MPLS Echo Request is sent by the ingress PE using the EVPN MPLS
label(s) associated with the IP Prefix route announced by the egress
PE and the MPLS transport label(s) to reach the egress PE.

5. Encapsulation of OAM Ping Packets

The MPLS Echo Request IP/UDP packets MUST be encapsulated with the
Transport and EVPN label(s) followed by the GAL [RFC5586], which is
the bottommost label. The GAL is followed by a G-ACh header carrying
the IPv4(0x0021) or IPv6(0x0057) Channel Type. The code points for
IPv4 and IPv6 channels are defined in the "Generic Associated Channel
(G-ACh) Parameters" IANA registry.

6. Operations

6.1. Unicast Data Plane Connectivity Checks

Figure 5 is an example of a PBB-EVPN network. CE1 is dual-homed to
PE1 and PE2. Assume that PE1 announced a MAC route with RD
192.0.2.1:00 and B-MAC 00-AA-00-BB-00-CC and with MPLS label 16001
for EVI 10. Similarly, PE2 announced a MAC route with RD
203.0.113.2:00 and B-MAC 00-AA-00-BB-00-CC and with MPLS label 16002.

On PE3, when an operator performs a connectivity check for the B-MAC
address 00-AA-00-BB-00-CC on PE1, the operator initiates an LSP Ping
request with the Target FEC Stack TLV containing the EVPN MAC/IP sub-
TLV in the Echo Request packet. The Echo Request packet is sent with
the {Transport label(s) to reach PE1, EVPN label = 16001, GAL} MPLS
label stack and IP ACH Channel header. Once the Echo Request packet
reaches PE1, PE1 will use the GAL and the IP ACH Channel header to
determine if the packet is an IPv4 or IPv6 OAM packet. The PE1 will
process the packet and perform checks for the EVPN MAC/IP sub-TLV
present in the Target FEC Stack TLV as described in Section 4.4 of
[RFC8029] and respond according to the processing rules in [RFC8029].

+-----------------+
| |
| |
+----+ AC1 +-----+ +-----+ +----+
| CE1|------| | | PE3 |-----| CE2|
+----+\ | PE1 | IP/MPLS | | +----+
\ +-----+ Network +-----+
\ | |
AC2\ +-----+ |
\ | | |
\| PE2 | |
+-----+ |
| |
+-----------------+

<-802.1Q-> <------PBB over MPLS------> <-802.1Q->

Figure 5: PBB-EVPN Network

Similarly, on PE3, when an operator performs a connectivity check for
the B-MAC address 00-AA-00-BB-00-CC on PE2, the operator initiates an
LSP Ping request with the Target FEC Stack TLV containing the EVPN
MAC/IP sub-TLV in the Echo Request packet. The Echo Request packet
is sent with the {MPLS Transport label(s) to reach PE2, EVPN label =
16002, GAL} MPLS label stack and IP ACH Channel header.

LSP Ping operations for unicast data plane connectivity checks in
EVPN are similar to those described above for PBB-EVPN, except that
the checks are for C-MAC addresses instead of B-MAC addresses.

In EVPN networks, an operator can also perform a MAC state test using
an aliasing label for the MAC to verify the MAC state on the egress
multihoming PE that did not learn the MAC from the multihomed CE on a
local ESI but has announced Ethernet A-D per-EVI and per-ESI routes
for the ESI. This is due to the fact that MAC state on multihoming
PEs that did not learn the MAC locally get created from EVPN MAC/IP
route advertisement from the multihoming PE that has learned the CE's
MAC address locally.

6.2. Inclusive Multicast Data Plane Connectivity Checks

6.2.1. Ingress Replication

Assume PE1 announced an Inclusive Multicast route for EVI 10, with RD
192.0.2.1:00, Ethernet Tag (ISID 10), PMSI tunnel attribute Tunnel
type set to ingress replication, and downstream-assigned Inclusive
Multicast MPLS label 17001. Similarly, PE2 announced an Inclusive
Multicast route for EVI 10, with RD 203.0.113.2:00, Ethernet Tag
(ISID 10), PMSI tunnel attribute Tunnel type set to ingress
replication, and downstream-assigned Inclusive Multicast MPLS label
17002.

Given CE1 is dual-homed to PE1 and PE2, assume that PE1 is the DF for
ISID 10 for the port corresponding to the ESI 11aa.22bb.33cc.
44dd.5500.

When an operator at PE3 initiates a connectivity check for the
Inclusive Multicast on PE1, the operator initiates an LSP Ping
request with the Target FEC Stack TLV containing the EVPN Inclusive
Multicast sub-TLV in the Echo Request packet. The Echo Request
packet is sent with the {Transport label(s) to reach PE1, EVPN
Inclusive Multicast label = 17001, GAL} MPLS label stack and IP ACH
Channel header. Once the Echo Request packet reaches PE1, PE1 will
use the GAL and the IP ACH Channel header to determine if the packet
is an IPv4 or IPv6 OAM packet. The packet will have the EVPN
Inclusive Multicast label. PE1 will process the packet and perform
checks for the EVPN Inclusive Multicast sub-TLV present in the Target
FEC Stack TLV as described in Section 4.4 of [RFC8029] and respond
according to the processing rules in [RFC8029]. For the success
case, PE1 will reply with Return Code 3 ("Replying router is an
egress for the FEC at stack-depth <RSC>").

Similarly, an operator at PE3 may initiate an LSP Ping to PE2 with
the Target FEC Stack TLV containing the EVPN Inclusive Multicast sub-
TLV in the Echo Request packet. The Echo Request packet is sent with
the {Transport label(s) to reach PE2, EVPN Inclusive Multicast label
= 17002, GAL} MPLS label stack and IP ACH Channel header. Once the
Echo Request packet reaches PE2, PE2 will use the GAL and the IP ACH
Channel header to determine if the packet is an IPv4 or IPv6 OAM
packet. The processing on PE2 will be similar to that on PE1 as
described above. For the success case, PE2 will reply with Return
Code 3 ("Replying router is an egress for the FEC at stack-depth
<RSC>") as per [RFC8029].

In an Echo Request packet for EVPN, a combination of an EVPN Ethernet
A-D sub-TLV and the associated MPLS Split Horizon label, immediately
preceding the GAL in the MPLS label stack, may be used to emulate
traffic coming from a multihomed site. The Split Horizon label is
used by leaf PE(s) attached to the same multihomed site to prevent
forwarding of packets back to the multihomed site. If the behavior
on a leaf PE is to not forward the packet to the multihomed site on
the ESI identified by the EVPN Ethernet A-D sub-TLV because of Split
Horizon filtering, the PE will reply with Return Code 37 (see
Section 8) and drop the BUM packets on the ES corresponding to the
ESI received in the EVPN Ethernet A-D sub-TLV because of the Split
Horizon Group filtering.

6.2.2. Using P2MP P-Tree

Both Inclusive P-tree and Aggregate Inclusive P-tree can be used in
EVPN or PBB-EVPN networks.

When using an Inclusive P-tree arrangement, the P2MP P-tree transport
label itself is used to identify the L2 service associated with the
Inclusive Multicast route. This L2 service could be a Customer
Bridge or a Provider Backbone Bridge.

For an Inclusive P-tree arrangement, when an operator performs a
connectivity check for the multicast L2 service, the operator
initiates an LSP Ping request with the Target FEC Stack TLV
containing the EVPN Inclusive Multicast sub-TLV in the Echo Request
packet. The Echo Request packet is sent over P2MP LSP with the {P2MP
P-tree Transport label, GAL} MPLS label stack and IP ACH Channel
header.

When using an Aggregate Inclusive P-tree arrangement, a PE announces
an upstream-assigned MPLS label along with the P-tree ID, so both the
P2MP P-tree MPLS transport label and the upstream MPLS label can be
used to identify the L2 service.

For an Aggregate Inclusive P-tree arrangement, when an operator
performs a connectivity check for the multicast L2 service, the
operator initiates an LSP Ping request with the Target FEC Stack TLV
containing the EVPN Inclusive Multicast sub-TLV in the Echo Request
packet. The Echo Request packet is sent over P2MP LSP using the IP-
ACH Control channel with the {P2MP P-tree Transport label, EVPN
upstream-assigned Multicast label, GAL} MPLS label stack and IP ACH
Channel header.

The leaf PE(s) of the P2MP P-tree will process the packet and perform
checks for the EVPN Inclusive Multicast sub-TLV present in the Target
FEC Stack TLV as described in Section 4.4 of [RFC8029] and respond
according to the processing rules in [RFC8029]. For the success
case, the leaf PE will reply with Return Code 3 ("Replying router is
an egress for the FEC at stack-depth <RSC>").

In an Echo Request packet for EVPN, a combination of an EVPN Ethernet
A-D sub-TLV and the associated MPLS Split Horizon label, immediately
preceding the GAL in the MPLS label stack, may be used to emulate
traffic coming from a multihomed site. When using P2MP P-tree, the
Split Horizon label is upstream assigned and is received by all the
leaf PEs of the P2MP P-tree. The Split Horizon label is used by leaf
PE(s) attached to the same multihomed site so that packets will not
be forwarded back to the multihomed site. If the behavior on a leaf
PE is to not forward the packet to the multihomed site on the ESI in
the EVPN Ethernet A-D sub-TLV because of Split Horizon filtering, the
PE will reply with Return Code 37 (see Section 8) and drop the BUM
packets on the ES corresponding to the ESI received in the EVPN
Ethernet A-D sub-TLV because of the Split Horizon Group filtering.
If the leaf PE does not have the ESI identified in the EVPN Ethernet
A-D sub-TLV, the PE MAY reply with Return Code 38 (see Section 8),
and the BUM packets are forwarded because there is no ES
corresponding to the ESI received in the EVPN Ethernet A-D sub-TLV.

6.2.3. Controlling Echo Responses When Using P2MP P-Tree

The procedures described in [RFC6425] for preventing congestion of
Echo Responses (Echo Jitter TLV) and limiting the Echo Reply to a
single egress node (P2MP Responder Identifier TLV with either the
IPv4 Node Address P2MP Responder sub-TLV or the IPv6 Node Address
P2MP Responder sub-TLV) can be applied to LSP Ping in EVPN and PBB-
EVPN when using P2MP P-trees for BUM traffic.

6.3. EVPN Aliasing Data Plane Connectivity Check

Assume PE1 announced an Ethernet A-D per-EVI route with the ESI set
to CE1 system ID and MPLS label 19001. Additionally, assume PE2
announced an Ethernet A-D per-EVI route with the ESI set to CE1
system ID and MPLS label 19002.

At PE3, when an operator performs a connectivity check for the
aliasing aspect of the EVPN Ethernet A-D route on PE1, the operator
initiates an LSP Ping request with the Target FEC Stack TLV
containing the EVPN Ethernet A-D sub-TLV in the Echo Request packet.
The Echo Request packet is sent with the {Transport label(s) to reach
PE1, EVPN Ethernet A-D label 19001, GAL} MPLS label stack and IP ACH
Channel header.

When PE1 receives the packet, it will process the packet and perform
checks for the EVPN Ethernet A-D sub-TLV present in the Target FEC
Stack TLV as described in Section 4.4 of [RFC8029] and respond
according to the processing rules in [RFC8029].

6.4. EVPN IP Prefix (RT-5) Data Plane Connectivity Check

Assume PE1 in Figure 5 announced an IP Prefix route (RT-5) with an IP
prefix reachable behind CE1 and MPLS label 20001. When an operator
on PE3 performs a connectivity check for the IP prefix on PE1, the
operator initiates an LSP Ping request with the Target FEC Stack TLV
containing the EVPN IP Prefix sub-TLV in the Echo Request packet.
The Echo Request packet is sent with the {Transport label(s) to reach
PE1, EVPN IP Prefix label 20001 } MPLS label stack.

When PE1 receives the packet, it will process the packet and perform
checks for the EVPN IP Prefix sub-TLV present in the Target FEC Stack
TLV as described in Section 4.4 of [RFC8029] and respond according to
the processing rules in [RFC8029].

7. Security Considerations

This document does not introduce any new security considerations
beyond those that apply in [RFC7432], [RFC7623], and [RFC6425].
Furthermore, the security considerations discussed in [RFC8029] apply
to this document and need to be considered. As described in
[RFC8029], these security considerations are:

* A Denial-of-Service (DoS) attack by sending MPLS Echo Requests/
Replies to Label Switching Routers (LSRs) and thereby increasing
their workload.

* Obfuscating the state of the MPLS data plane liveness by spoofing,
hijacking, replaying, or otherwise tampering with MPLS Echo
Requests and Replies.

* Obtaining information about the network through an unauthorized
source using an LSP Ping.

There are mitigations described in [RFC8029]. The same mitigations
can be applied to the LSP Ping procedures described in this document;
thus, this document doesn't require additional security
considerations beyond the ones described in [RFC8029].

This document does not introduce any new privacy concerns because
these TLVs contain the same information that are present in data
packets and EVPN routes.

8. IANA Considerations

8.1. Sub-TLV Type

This document defines four new sub-TLV types to be included in the
Target FEC Stack TLV (TLV types 1, 16, and 21) [RFC9041] in Echo
Request and Echo Reply messages in EVPN and PBB-EVPN networks.

IANA has assigned the following values from the "Standards Action"
(0-16383) range in the "Sub-TLVs for TLV Types 1, 16, and 21"
subregistry within the "TLVs" registry of the "Multiprotocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" name
space.

+==========+==============================+===========+
| Sub-Type | Sub-TLV Name | Reference |
+==========+==============================+===========+
| 42 | EVPN MAC/IP | RFC 9489 |
+----------+------------------------------+-----------+
| 43 | EVPN Inclusive Multicast | RFC 9489 |
+----------+------------------------------+-----------+
| 44 | EVPN Ethernet Auto-Discovery | RFC 9489 |
+----------+------------------------------+-----------+
| 45 | EVPN IP Prefix | RFC 9489 |
+----------+------------------------------+-----------+

Table 1

8.2. New Return Codes

[RFC8029] defines values for the Return Code field of Echo Reply
messages. This document defines two new Return Codes that SHOULD be
included in the Echo Reply message by a PE in response to an Echo
Request message in EVPN and PBB-EVPN networks.

IANA has assigned the following values in the "Return Codes" registry
of the "Multiprotocol Label Switching (MPLS) Label Switched Paths
(LSPs) Ping Parameters" name space.

+=======+=============================================+===========+
| Value | Meaning | Reference |
+=======+=============================================+===========+
| 37 | Replying router is egress for the FEC at | RFC 9489 |
| | the stack depth. In addition, the BUM | |
| | packets are dropped on the ES corresponding | |
| | to the ESI received in the EVPN Ethernet | |
| | Auto-Discovery sub-TLV because of the Split | |
| | Horizon Group filtering. | |
+-------+---------------------------------------------+-----------+
| 38 | Replying router is egress for the FEC at | RFC 9489 |
| | the stack depth. In addition, the BUM | |
| | packets are forwarded because there is no | |
| | ES corresponding to the ESI received in the | |
| | EVPN Ethernet Auto-Discovery sub-TLV. | |
+-------+---------------------------------------------+-----------+

Table 2

9. 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>.

[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.

[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.

[RFC6425] Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
Failures in Point-to-Multipoint MPLS - Extensions to LSP
Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
<https://www.rfc-editor.org/info/rfc6425>.

[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.

[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <https://www.rfc-editor.org/info/rfc7623>.

[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.

[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>.

[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.

[RFC9041] Andersson, L., Chen, M., Pignataro, C., and T. Saad,
"Updating the MPLS Label Switched Paths (LSPs) Ping
Parameters IANA Registry", RFC 9041, DOI 10.17487/RFC9041,
July 2021, <https://www.rfc-editor.org/info/rfc9041>.

[RFC9136] Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
(EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
<https://www.rfc-editor.org/info/rfc9136>.

Acknowledgments

The authors would like to thank Loa Andersson, Alexander Vainshtein,
Ron Sdayoor, Jim Guichard, Lars Eggert, John Scudder, Éric Vyncke,
Warren Kumari, Patrice Brissette, and Weiguo Hao for their valuable
comments.

Authors' Addresses

Parag Jain
Cisco
Canada
Email: [email protected]

Ali Sajassi
Cisco
United States of America
Email: [email protected]

Samer Salam
Cisco
Canada
Email: [email protected]

Sami Boutros
Ciena
United States of America
Email: [email protected]

Greg Mirsky
Ericsson
United States of America
Email: [email protected]