Bit Index Explicit Replication (BIER) Ping and Trace
draft-ietf-bier-ping-18
| Document | Type | Active Internet-Draft (bier WG) | |
|---|---|---|---|
| Authors | Nagendra Kumar Nainar , Carlos Pignataro , Mach Chen , Greg Mirsky | ||
| Last updated | 2026-03-15 (Latest revision 2026-01-07) | ||
| Replaces | draft-kumarzheng-bier-ping | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews |
INTDIR Telechat review
(of
-16)
by Brian Haberman
Ready w/nits
TSVART IETF Last Call review
(of
-16)
by Marcus Ihlar
Ready w/issues
INTDIR Early review
(of
-08)
by Brian Haberman
Almost ready
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Mankamana Prasad Mishra | ||
| Shepherd write-up | Show Last changed 2023-11-27 | ||
| IESG | IESG state | IESG Evaluation::Revised I-D Needed | |
| Action Holders | |||
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Has 2 DISCUSSes. Has enough positions to pass once DISCUSS positions are resolved. |
||
| Responsible AD | Gunter Van de Velde | ||
| Send notices to | mankamana mishra <mankamis@cisco.com> | ||
| IANA | IANA review state | IANA OK - Actions Needed | |
| IANA expert review state | Expert Reviews OK | ||
| IANA expert review comments | Approval from AD: Short version: once all the remaining blocking DISCUSS ballots are cleared, this IETF Review draft will move forward with the requested port assignment. A bit of context may help. OAM is a very different kind of application compared to most of the more traditional cases the port expert usually reviews. An OAM network service comes with quite different operational and security expectations. Early on, there was some confusion around this being a request for a port to carry multicast traffic. As the port expert rightly pointed out, different rules apply there, and using a dedicated multicast address is preferred over assigning a port number. That misunderstanding was discussed in detail and ultimately resolved by tightening up the text and being more explicit in the draft. Where we landed is that the actual request is for a port used by unicast packets, operating in a closed and well-controlled environment. The protocol does not cause payload amplification in its responses, and payload confidentiality (authentication and/or encryption) is not only unnecessary but would actually be counter-productive for this specific OAM use case. The draft (draft-ietf-bier-ping) has also gone through the Security Directorate review twice and was reviewed during IESG evaluation by two Security ADs, with no security concerns identified. Taking all of that together, once the remaining blocking DISCUSS items are resolved, I’m comfortable proceeding with the port assignment as requested by the document. |
draft-ietf-bier-ping-18
Network Work group N. Kumar
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track C. Pignataro
Expires: 11 July 2026 North Carolina State University
M. Chen
Huawei Technologies
G. Mirsky
Ericsson
7 January 2026
Bit Index Explicit Replication (BIER) Ping and Trace
draft-ietf-bier-ping-18
Abstract
Bit Index Explicit Replication (BIER) is a multicast forwarding
architecture designed to simplify and optimize multicast delivery.
This document describes the mechanism and basic BIER OAM packet
format that can be used to perform failure detection and isolation on
the BIER data plane without any dependency on other layers, like the
IP layer.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 11 July 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology and Acronyms . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. BIER OAM . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. BIER OAM Message Format . . . . . . . . . . . . . . . . . 5
3.2. BIER Echo Request/Reply Message Format . . . . . . . . . 6
3.3. Return Code . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. BIER OAM TLVs . . . . . . . . . . . . . . . . . . . . . . 9
3.4.1. Original SI-BitString TLV . . . . . . . . . . . . . . 10
3.4.2. Target SI-BitString TLV . . . . . . . . . . . . . . . 11
3.4.3. Incoming SI-BitString TLV . . . . . . . . . . . . . . 12
3.4.4. Downstream Mapping TLV . . . . . . . . . . . . . . . 13
3.4.5. Responder BFER TLV . . . . . . . . . . . . . . . . . 16
3.4.6. Responder BFR TLV . . . . . . . . . . . . . . . . . . 17
3.4.7. Ingress Interface TLV . . . . . . . . . . . . . . . . 17
3.4.8. Erroneous Echo Request TLV . . . . . . . . . . . . . 18
4. BIER Ping and Traceroute Operations . . . . . . . . . . . . . 19
4.1. BIER OAM Processing . . . . . . . . . . . . . . . . . . . 19
4.2. Per BFER ECMP Discovery . . . . . . . . . . . . . . . . . 19
4.3. Sending BIER Echo Request . . . . . . . . . . . . . . . . 20
4.4. Receiving BIER Echo Request . . . . . . . . . . . . . . . 21
4.5. Sending Echo Reply . . . . . . . . . . . . . . . . . . . 23
4.6. Receiving Echo Reply . . . . . . . . . . . . . . . . . . 24
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
5.1. UDP Port Number . . . . . . . . . . . . . . . . . . . . . 25
5.2. BIER OAM Registry Group . . . . . . . . . . . . . . . . . 25
5.3. BIER OAM Message Type . . . . . . . . . . . . . . . . . . 25
5.4. BIER Echo Request/Echo Reply Registries . . . . . . . . . 26
5.4.1. BIER Echo Request/Echo Reply Message Types . . . . . 26
5.4.2. BIER Echo Reply Modes . . . . . . . . . . . . . . . . 27
5.4.3. BIER Echo Return Codes . . . . . . . . . . . . . . . 28
5.5. Common Registration Procedures for TLVs and Sub-TLVs . . 29
5.5.1. TLVs . . . . . . . . . . . . . . . . . . . . . . . . 30
5.5.2. Sub-TLVs for TLV Type 4 . . . . . . . . . . . . . . . 31
6. Security Considerations . . . . . . . . . . . . . . . . . . . 32
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 32
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8. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.1. Normative References . . . . . . . . . . . . . . . . . . 33
8.2. Informative References . . . . . . . . . . . . . . . . . 34
Contributors' Addresses . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
[RFC8279] introduces and explains BIER architecture that provides
optimal multicast forwarding through a "BIER domain" without
requiring intermediate routers to maintain any multicast-related per-
flow state. BIER also does not require any explicit tree-building
protocol for its operation. A multicast data packet enters a BIER
domain at a "Bit-Forwarding Ingress Router" (BFIR), and leaves the
BIER domain at one or more "Bit-Forwarding Egress Routers" (BFERs).
The BFIR router adds a BIER header to the packet. The BIER header
contains a bit-string in which each bit represents exactly one BFER
to forward the packet to. The set of BFERs to which the multicast
packet needs to be forwarded is specified by setting the bits that
correspond to those routers in the BIER header. Similarly, the
Initiator of the BIER OAM packet controls the set of BFRs to which
the BIER OAM packet is addressed by setting bits in the BitString
field of the BIER header that correspond to the BFR-ID values of
those BFRs.
Operations, Administration, and Maintenance (OAM) mechanisms are
expected to support the detection of network failures. After the
detection, operators localize and characterize the network defect. A
query-based tool, e.g., ICMP [RFC0792] and LSP Ping [RFC8029],
[RFC6425], is broadly used to detect and localize a network defect.
Additionally, this mechanism can be used to check the consistency
between the data and control planes. This document describes the
mechanism and basic BIER OAM packet format that can be used to
perform failure detection and isolation on the BIER data plane
without any dependency on other layers, like the IP layer. The
specification conforms to R-1 through R-3, R-5, and R-11 requirements
listed in [I-D.ietf-bier-oam-requirements]. To conform to R-11, BIER
Echo Request message is encapsulated in the BIER header [RFC8296]
that uses the same values of BIFT-id, BSL, Entropy, and DSCP fields
as in the BIER header of the monitored BIER flow. Note that the BIER
Echo Request/Reply protocol doesn't modify the content of the OAM
field in the BIER header (Section 2 of [RFC8296]).
2. Conventions used in this document
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2.1. Terminology and Acronyms
In this specification, the term "Initiator" is used interchangeably
with the "Sender of a BIER Echo Request".
BFER - Bit-Forwarding Egress Router
BFIR - Bit-Forwarding Ingress Router
BFR - Bit-Forwarding Router
BIER - Bit Index Explicit Replication
DDMAP - Downstream Detailed Mapping TLV
ECMP - Equal Cost Multi-Path
OAM - Operation, Administration, and Maintenance
SI - Set Identifier
QTF - Querier Timestamp Format
RTF - Responder Timestamp Format
NTP - Network Time Protocol
MTU - Maximum Transmission Unit
DA - Downstream Address
DIA - Downstream Interface Address
DoS - Denial-of-Service
PTP - Precision Time Protocol
2.2. 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.
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3. BIER OAM
BIER OAM is defined to stay within the BIER layer by directly
following the BIER header without mandating the need for an IP
header. [RFC8296] defines a 4-bit field as "Proto" to identify the
payload following the BIER header. When the payload is BIER OAM, the
"Proto" field will be set to 5 as defined in [RFC8296]
3.1. BIER OAM Message Format
The BIER OAM packet header format that follows the BIER header is
displayed in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver |MessageType| Proto | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAM Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Message Type Dependent Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BIER OAM Header
Ver - a four-bit field that indicates the version of the BIER OAM
header. The current value is 1. The version number is to be
incremented whenever a change is made that affects the ability of
an implementation to parse or process the BIER OAM header
correctly. For example, if syntactic or semantic changes are made
to any of the fixed fields.
Message Type - a six-bit field that identifies OAM protocol.
Values defined in this document are as follows:
Value Description
-------- ---------------
1 Echo Request
2 Echo Reply
Proto - a six-bit field. This field is used to define whether
there is any data packet immediately following the OAM payload.
For example, the In-situ OAM Direct Export Option header [RFC9326]
can be appended to the BIER OAM message, enabling the collection
of the operational state and performance metrics. This field MUST
be set to 0 if no data packet follows the OAM payload. Otherwise,
the value is one from the IANA registry "BIER Next Protocol
Identifiers" [IANA-Next-Protocol-Identifiers].
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Reserved - a two-octet field. The value MUST be zeroed on
transmission and ignored on receipt.
OAM Message Length - a two-octet field that reflects the length of
the OAM message in octets, including the header and the Messsage
Type Dependent Data.
Message Type Dependant Data - a variable-length field that
includes the OAM message identified by the value of the Message
Type filed.
3.2. BIER Echo Request/Reply Message Format
The Echo Request/Reply header format is displayed in Figure 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Echo Req/Rep | Proto | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Echo Request/Reply Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QTF | RTF | Reply Mode | Return Code | Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp Sent |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp Received |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: BIER Echo Request/Reply Format
Proto field MUST be set to 0 for Echo Request/Reply header.
QTF (Querier Timestamp Format) - a four-bit field. When the field
is set to 2, the Timestamp Sent field is (in seconds and
picoseconds, according to the Initiator's clock) in the 64-bit
long NTP format [RFC5905]. When the value of the QTF field is 3,
the Timestamp Sent's format is the IEEE 1588-2008 (1588v2)
Precision Time Protocol (PTP) [IEEE.1588.2008] format. Any other
value MUST be considered as invalid, the Return Code set to
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Malformed Echo Request received (1). Also, the Erroneous Echo
Request TLV (Section 3.4.8) SHOULD be included in the BIER Echo
Reply.
RTF (Responder Timestamp Format) - a four-bit field. When the
field is set to 2, the Timestamp Received field is (in seconds and
picoseconds, according to the Initiator's clock) in 64-bit long
NTP format [RFC5905]. When filed's value is 3, the format of the
Timestamp Received is as defined in IEEE 1588-2008 (1588v2)
Precision Time Protocol [IEEE.1588.2008]. Any other value MUST be
considered as invalid, the Return Code set to Malformed Echo
Request received (1). Also, the Erroneous Echo Request TLV
(Section 3.4.8) SHOULD be included in the BIER Echo Reply. The
Initiator MUST zero RTF in the Echo Request, and the Responder
MUST ignore the value on receipt.
The sender of the BIER Echo Request might receive the BIER Echo Reply
with RTF different from the Sender's QTF. Thus, to calculate one-way
delay, the Sender MUST be able to interpret both timestamp formats,
i.e., NTP [RFC5905] and PTP [IEEE.1588.2008]. Although the use of
different timestamp formats is permitted, it may cause ambiguity or
even precision loss resulting from format conversion. Thus, the use
of homogeneous formats is RECOMMENDED.
The Reply Mode - a one-octet field. The value MUST be set to one
of the following values:
Value Description
-------- ---------------
1 Do not Reply
2 Reply via IPv4/IPv6 UDP packet
3 Reply via BIER packet
When Reply Mode is set to 1, the receiver will not send any reply.
This mode can be used for unidirectional path validation. When
the Reply Mode is set to 2, the Responder Bit-Forwarding Router
(BFR) encapsulates the Echo reply payload with the IP/UDP header.
When the Initiator intends to validate the return BIER path, the
Reply Mode will be set to 3 so that the Responder BFR will
encapsulate the Echo Reply with the BIER header. Also, the Reply
Mode "Reply via BIER packet" can be used if the IP network is
deemed less reliable compared to the BIER layer.
Return Code - a one-octet field. The value MUST be set to zero if
the Type is "BIER Echo Request". The value of the Return Code
filed MUST be set to one of the values defined in Section 3.3, if
the Type is "BIER Echo Reply".
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Reserved2 - a one-octet field. The Reserved field MUST be zeroed
on transmit and MUST be ignored on receipt.
Sender's Handle - a four-octet field. The Sender's Handle is
filled by the Initiator, and returned unchanged by responder BFR.
This value can be used for matching the replies to the request
(see Section 4.3).
Sequence Number - a four-octet field. The value of the field is
assigned by the Initiator and can be used to detect any missed
replies.
Timestamp - each field (Sent and Received) is an eight-octet
field. The Timestamp Sent is the time when the Echo Request is
sent. The Timestamp Received in Echo Reply is the time
(accordingly to responding BFR clock) that the corresponding Echo
Request was received. The format depends on the QTF/RTF value.
The Initiator MUST zero Timestamp Received in the Echo Request,
and the Responder MUST ignore the value on receipt.
TLVs - Carries the TLVs as defined in Section 3.4.
3.3. Return Code
The responder uses the Return Code field to reply with a validity
check or other error message to Initiator. It does not carry any
meaning in Echo Request and MUST be set to zero. The Return Code can
be one of the following:
Value Value Meaning
------ ---------------
0 No return code
1 Malformed Echo Request received
2 One or more of the TLVs is not supported
3 Replying BFR is the only BFER in header BitString
4 Replying BFR is one of the BFERs in header BitString
5 Packet-Forward-Success
6 Invalid Multipath Info Request
8 No matching entry in the forwarding table
9 Set-Identifier Mismatch
10 DDMAP Mismatch
"No return code" will be used by Initiator in the Echo Request. This
value MUST NOT be used in Echo Reply.
"Malformed Echo Request received" will be used by any BFR if the
received Echo Request packet is not properly formatted.
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When a receiver does not support any TLV included in the Echo
Request, the Return code will be set to "One or more of the TLVs is
not supported" carrying the respective TLVs.
When the received header BitString in the Echo Request packet
contains only its BFR-ID, "Replying BFR is the only BFER in header
BitString" is set in the reply. This value implies that the receiver
is BFER, and the packet is not forwarded to any more neighbors.
When the received header BitString in the Echo Request packet
contains its BFR-ID in addition to other BFR-IDs, "Replying BFR is
one of the BFERs in header BitString" is set in the reply. This
value implies that the responder is a BFER and the packet is further
forwarded to one or more neighbors.
Any transit BFR will send the Echo Reply with "Packet-Forward-
Success", if the TLV in the received Echo Request is understood and
the forwarding table has forwarding entries for the BitString. This
behavior is demonstrated by a transit BFR during traceroute mode.
When the Echo Request is received with multipath info
(Section 3.4.4.1) for more than one BFER, the Return Code is set to
"Invalid Multipath Info Request".
If the BitString cannot be matched in the local forwarding table, the
BFR will use "No matching entry in the forwarding table" in the
reply.
If the BIER-MPLS label in the received Echo Request is not the one
assigned for SI in Original SI-BitString TLV, "Set-Identifier
Mismatch" is set in order to report the mismatch.
If the BitString in Header-H does not match the BitString in Egress
BitString Sub-TLV of DDMAP TLV, a responding BFR will use "DDMAP
Mismatch" to report the problem.
3.4. BIER OAM TLVs
This section defines various TLVs that can be used in BIER OAM
packet. The TLVs (Type-Length-Value tuples) have the following
format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Type-Length-Value Format Used in BIER Echo Request/Reply
TLV Types are defined below. A system that receives an Echo Request
with unknown TLV Type with the value in the range 0 - 32767 MUST
transmit an Echo Reply with the Return Code "One or more of the TLVs
is not supported" (2). Also, the Erroneous Echo Request TLV
(Section 3.4.8) SHOULD be included in the BIER Echo Reply. A system
that receives an Echo Request with the value in the range 32768 -
65535 MAY silently drop the packet. Length is the length of the
Value field in octets. The Value field depends on the TLV Type.
3.4.1. Original SI-BitString TLV
The Original SI-BitString TLV carries the set of BFERs and carries
the same BitString that the Initiator includes in the BIER header.
This TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID | Sub-domain ID |BS Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The Format of the Original SI-BitString TLV
Set ID - a one-octet field that is set to the value of the Set
Identifier to which the BitString belongs. This value is derived as
defined in [RFC8279].
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Sub-domain ID - a one-octet field that is set to the Sub-domain value
to which BFER in BitString belongs.
BS Len - a four-bit field that is set based on the length of
BitString as defined in [RFC8296] reflected in four-octet words.
Reserved - a twelve-bit field. Its value MUST be zeroed on
transmission and ignored on receipt.
BitString - a variable length field. The BitString field carries the
set of BFR-IDs that Initiator will include in the BIER header.
Any Initiator MUST include this TLV in the Echo Request packet.
3.4.2. Target SI-BitString TLV
The Target SI-BitString TLV carries the set of BFERs from which the
Initiator expects the reply. This TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID | Sub-domain ID |BS Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The Format of the Target SI-BitString TLV
Set ID field is set to the Set Identifier to which the BitString
belongs.This value is derived as defined in [RFC8279].
Sub-domain ID is set to the Sub-domain value to which BFER in
BitString belongs.
BS Len is set based on the length of BitString as defined in
[RFC8296]
Reserved - the value MUST be zeroed on transmission and ignored on
receipt.
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The BitString field carries the set of BFR-IDs of BFER(s) that
Initiator expects a response. The BitString in this TLV may be
different from the BitString in the BIER header and allows control of
the BFER responding to the Echo Request. This TLV MUST be included
by Initiator in the BIER OAM packet if the Downstream Mapping TLV
(Section 3.4.4) is included.
3.4.3. Incoming SI-BitString TLV
The Incoming SI-BitString TLV will be included by Responder BFR in
Reply message and copies the BitString from the BIER header of
incoming Echo Request message. This TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID | Sub-domain ID |BS Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: The Format of the Incoming SI-BitString TLV
Set ID field is set to the Set Identifier to which the BitString
belongs. This value is derived as defined in [RFC8279]
Sub-domain ID is set to the Sub-domain value to which BFER in
BitString belongs.
BS Len is set based on the length of BitString as defined in
[RFC8296].
Reserved - the value MUST be zeroed on transmission and ignored on
receipt.
The BitString field copies the BitString from the BIER header of the
incoming Echo Request. A Responder BFR SHOULD include this TLV in
Echo Reply if the Echo Request is received with the I flag set in
Downstream Mapping TLV.
An Initiator MUST NOT include this TLV in Echo Request.
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3.4.4. Downstream Mapping TLV
This TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU | Address Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Interface Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. List of Sub-TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Format of the Downstream Mapping TLV
MTU A two-octet field. The value is the Maximum Transmission Unit
(MTU) value of the egress interface.
Address Type A one-octet field. The Address Type indicates the
address type and length of the IP address for the downstream
interface. The value of the Address Type field is set to one of
the values listed in Figure 8. Any other value MUST be processed
as invalid TLV.
Value Address Type
------- ---------------
1 IPv4 Numbered
2 IPv4 Unnumbered
3 IPv6 Numbered
4 IPv6 Unnumbered
Figure 8: The Address Types
Flags The Flags field has the following format:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |I|
+-+-+-+-+-+-+-+-+
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Figure 9: The Flags Field Format
Reserved - a seven-bit field. Its value MUST be zeroed on
transmission and ignored on receipt.
I - a one-bit field. When I flag is set, the Responding BFR MUST
include the Incoming SI- BitString TLV in Echo Reply message.
Downstream Address and Downstream Interface Address
each field is either four-octet or sixteen-octet, depending on the
value of Address Type field.
Note that values of the Address Type field are mapped to
combinations of lengths of Downstream Address and Donstream
Address Interface fileds as follows:
Value DA Length DIA Length
------- ------------ ------------
1 4 4
2 4 4
3 16 16
4 16 4
where:
DA Length
Downstream Address (DA) field Length
DIA Length
Downstream Interface Address (DIA) field Length
If the Address Type is 1, the Downstream Address MUST be set to
IPv4 BFR-Prefix of downstream BFR and Downstream Interface Address
is set to the downstream interface address.
If the Address Type is 2, the Downstream Address MUST be set to
IPv4 BFR-Prefix of downstream BFR and Downstream Interface Address
is set to the index assigned by the responding BFR to the
interface.
If the Address Type is 3, the Downstream Address MUST be set to
IPv6 BFR-Prefix of downstream BFR and Downstream Interface Address
is set to the downstream interface address.
If the Address Type is 4, the Downstream Address MUST be set to
IPv6 BFR-Prefix of downstream BFR and Downstream Interface Address
is set to the index assigned by the responding BFR to the
interface.
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3.4.4.1. Downstream Detailed Mapping Sub-TLVs
This section defines the optional Sub-TLVs that can be included in
Downstream Mapping TLV.
Sub-TLV Type Value
------------ -------------
1 Multipath Entropy Data
2 Egress BitString
3.4.4.1.1. Multipath Entropy Data
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M| Reserved | Multipath Type| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| (Multipath Information) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: The Format of the Multipath Data Blob
M Flag This flag is set to 0 if all packets will be forwarded out
through the interface defined in the Downstream Mapping TLV. When
set to 1, Multipath Information will be defined by the Bit masked
Entropy data.
Reserved The value MUST be zeroed on transmission and ignored on
receipt.
The interpretaion of the Multipath Type field and Multipath
Entropy Data encoding options are the same defined in
Section 3.4.1.1 of [RFC8029].
3.4.4.1.2. Egress BitString Sub-TLV
Responder BFR MAY include this Sub-TLV with the rewritten BitString
in the outgoing interface as defined in Section 6.1 of [RFC8279].
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID | Sub-domain ID |BS Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: The Egress BitString Sub-TLV Format
Set ID field is set to the Set Identifier to which the BitString
belongs. This value is derived as defined in [RFC8279].
Sub-domain ID is set to the Sub-domain value to which BFER in
BitString belongs.
BS Len is set based on the length of BitString as defined in
[RFC8296].
Reserved - the value MUST be zeroed on transmission and ignored on
receipt.
The BitString field copies the rewritten BitString in the outgoing
interface as defined in Section 6.1 of [RFC8279].
3.4.5. Responder BFER TLV
The BFER replying to the request MAY include the Responder BFER TLV.
This TLV identifies the originator of BIER Echo Reply. This TLV has
the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | BFR-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: The Responder BFER TLV Format
Length A two-octet field. The value MUST be set to four.
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Reserved A two-octet field. The value MUST be zeroed on
transmission and ignored on receipt.
BFR-ID A two-octet field. The BFR-ID field carries the BFR-ID of
the replying BFER. This TLV MAY be included by the Responding
BFER in the BIER Echo Reply packet.
3.4.6. Responder BFR TLV
Any transit BFR replying to the request MAY include the Responder BFR
TLV. This is used to identify the replying BFR without BFR-ID. This
TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type = 6 | Length = 8 or 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Address Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFR-Prefix (4 or 16 bytes) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: The Responder BFR TLV Format
Length The Length field, depending on the Address Type value - 8 or
20.
Reserved A two-octet field. The value MUST be zeroed on
transmission and ignored on receipt.
Address Type A two-octet field. Set to 1 for IPv4 or 2 for IPv6.
BFR-Prefix This field carries the local BFR-Prefix of the replying
BFR. This TLV MAY be included by Responding BFR in BIER Echo
Reply packet.
3.4.7. Ingress Interface TLV
The BFR replying to the request MUST include the Ingress Interface
TLV. This TLV identifies the incoming interface on which the Echo
Request was received. This TLV has the following format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type = 7 | Length = 8 or 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Address Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Ingress Interface Address (4 or 16 bytes) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: The Ingress Interface TLV Format
Length The Length field, depending on the Address Type value - 8 or
20.
Reserved A two-octet field. The value MUST be zeroed on
transmission and ignored on receipt.
Address Type A two-octet field. Set to 1 for IPv4 numbered, 2 for
IPv4 Unnumbered, 3 for IPv6 numbered, or 4 for IPv6 Unnumbered.
Ingress Interface Address
As defined in Section 3.4.4
3.4.8. Erroneous Echo Request TLV
The BFER replying to the request MAY include the Erroneous Echo
Request TLV. This TLV provides information about the type and
location of the problem in the BIER Echo Request. This TLV has the
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 8 | Length = variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking BIER Echo Request |
~ as possible without exceeding path MTU ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: The Erroneous Echo Request TLV Format
Pointer A four-octet field that identifies the octet offset within
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the received BIER Echo Request message where the error was
detected. The Pointer will point beyond the end of the BIER Echo
Reply message if the field in error is beyond what can fit in the
resulting packet.
4. BIER Ping and Traceroute Operations
This section describes aspects of BIER ping and traceroute
operations.
4.1. BIER OAM Processing
A BIER OAM packet MUST be punted to the BIER control plane for OAM
processing if one of the following conditions is true:
* The receiving BFR is a BFER.
* TTL of BIER-MPLS Label (Section 2.1.1.1 of [RFC8296]) expired.
* Hop Limit in the IPv6 header (Section 2 of
[I-D.ietf-bier-bierin6]) expired.
The use of the Router Alert label to be deprecated as proposed in
[RFC9570].
Processing of the received BIER OAM packet with unknown value of the
Message Type field (Figure 1) is stopped and the event SHOULD be
logged although through the rate-controlling system.
A transit BFR, i.e., one that does not punt the BIER OAM packet to
the BIER control plane, forwards the BIER OAM packet according to the
rules specified in Section 6.5 of [RFC8279].
4.2. Per BFER ECMP Discovery
As defined in [RFC8279], BIER follows the unicast forwarding path and
allows load balancing over ECMP paths between BFIR and BFER. BIER
OAM is expected to support ECMP path discovery between a BFIR and a
given BFER and MUST support path validation and failure detection of
any particular ECMP path between BFIR and BFER.
[RFC8296] proposes the BIER header with the Entropy field that can be
leveraged to exercise all ECMP paths. The Initiator/BFIR will use a
traceroute message to query each hop about the Entropy information
for each of the downstream paths. To avoid complexity, it is
suggested that the ECMP query is performed per BFER by carrying the
required information in the BIER OAM message.
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When an operator performs per BFER ECMP discovery, the Initiator MUST
include Multipath Entropy Data Sub-TLV in Downstream Mapping TLV. It
MUST also include the BFER in the BitString TLV to which the
Multipath query is performed.
Any transit BFR will transmit the BIER Echo Reply to the Initiator
with Bit-masked Entropy for each downstream path as defined in
[RFC8029].
4.3. Sending BIER Echo Request
The Initiator MUST set the Message Type as 1 and Return Code as 0.
The Proto field in the OAM packet MUST be set to 0. The choice of
the Sender's Handle and Sequence Number is a local matter to the
Initiator and SHOULD increment the Sequence Number by 1 for every
subsequent Echo Request. The QTF field is set to Initiator's local
timestamp format, and the TimeStamp Sent field is set to the time
that the Echo Request is sent.
The Initiator MUST include Original SI-BitString TLV. The Initiator
MUST NOT include more than one Original SI-BitString TLV. The
Initiator infers the Set Identifier value and Sub-domain ID value
from the respective BitString that will be included in the BIER
header of the packet and includes the values in "SI" and Sub-Domain
ID fields, respectively.
In Ping mode, the Initiator MAY include Target SI-BitString TLV to
control the responding BFER(s) by listing all the BFERs from which
the Initiator expects a response. In the traceroute mode, the
Initiator MAY include Target SI-BitString TLV to control the path
trace towards any specific BFER or set of BFERs. The Initiator on
receiving a reply with the Return code "Replying BFR is the only BFER
in the header BitString" or "Replying router is one of the BFERs in
header BitString" SHOULD unset the respective BFR-ID from Target SI-
BitString for any subsequent Echo Request.
The Initiator MAY include Downstream Mapping TLV (Section 3.4.4) in
the Echo Request to query additional information from transit BFRs
and BFERs. In case of ECMP discovery, the Initiator MUST include the
Multipath Entropy Data Sub-TLV and SHOULD set the Target SI-BitString
TLV carrying a specific BFER ID.
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The Initiator MUST encapsulate the OAM packet with the BIER header
and MUST set the Proto as 5 and further encapsulates with BIER-MPLS
label. In ping mode, the BIER-MPLS Label TTL MUST be set to 255. In
traceroute mode, the BIER-MPLS Label TTL is set successively,
starting from 1 and MUST stop sending the Echo Request if it receives
a reply with Return code as "Replying router is the only BFER in BIER
header BitString" from all BFER listed in Target SI-BitString TLV.
4.4. Receiving BIER Echo Request
Sending a BIER OAM Echo Request to control plane for payload
processing is triggered as mentioned in Section 4.1.
Any BFR on receiving an Echo Request MUST perform the basic sanity
check, including, but not limited to, checking values of the fields
with a priori known values, e.g., Ver, Reply Mode, or Type and Length
if any TLV is present. If, at any stage of processing the received
BIER Echo Request, the BFR encounters an error, it MUST stop
processing and transmit BIER Echo Reply with the Return Code set
accordingly. If the BFR cannot parse the OAM packet completely
because the value in the OAM Message Length field is incorrect, BFR
MUST send Echo Reply with Return Code set to "Malformed Echo Request
received" if the OAM Message Length is incorrect. The Erroneous Echo
Request TLV (Section 3.4.8) SHOULD be included in the BIER Echo
Reply. If the packet sanity check is fine, it SHOULD initiate the
below set of variables:
Reply-Flag
This flag is initially set to 1.
Interface-I
The incoming interface on which the Echo Request was received.
This MAY be used to validate the Downstream Detailed Mapping TLV
(DDMAP) info and populate the Ingress Interface TLV.
BIER-Label-L
The BIER-MPLS Label received as the top label of the received Echo
Request. This MAY be used to validate if the packet is traversing
the desired Set Identifier and sub-domain path.
Header-H
The BIER header of the received Echo Request. It can be used to
validate the DDMAP info and to populate the Incoming SI-BitString
TLV. Also, it can be used to perform entropy calculation
considering a different field in the header and replying with
Multipath Entropy Data Sub-TLV.
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Best-return-code
contains the Return Code for the echo reply packet as currently
best known. As the algorithm progresses, this code may change
depending on the results of further checks that it performs.
BFR MUST initialize the internal, to the implementation, Best-return-
code variable to the null value.
BFR will populate the Interface-I with the identifier of the
interface over which the Echo Request is received, the top label in
the MPLS stack of the received Echo Request to BIER-Label-L, and the
BIER header to Header-H. If the received Echo Request carries Target
SI-BitString TLV, a BFR SHOULD run the boolean AND operation between
BitString in Header-H and BitString in Target SI-BitString TLV. If
the resulting BitString is all-zero, reset Reply-Flag=0 and go to
Section 4.5. Else:
* If the BIER-Label-L does not correspond to the local label
assigned for {sub-domain, BitStringLen, SI} in Original SI-
BitString TLV, Set the Best-return-code to "Set-Identifier
Mismatch" and Go to Section 4.5.
The step above allows the detection of a synchronization problem in
the upstream BFR between BIER-Label and {sub-domain, BitStringLen,
SI} that might cause an unintended packet leak between sub-domains.
* Set the Best-return-code to "One or more of the TLVs is not
supported" if any of the TLVs in the Echo Request message is not
supported. Go to Section 4.5.
* If the BitString in Header-H does not match the BitString in
Egress BitString Sub-TLV of DDMAP TLV, set the Best-return-code to
"DDMAP Mismatch" and go to Section 4.5. When there are more than
one DDMAP TLV in the received Request packet, the Downstream
Address and Downstream Interface Address should be matched with
Interface-I to identify the right DDMAP TLV and then perform the
BitString match.
The step above allows the detection of a deviation between the BIER
control plane and the BIER forwarding plane in the upstream node that
may result in a forwarding loop or packet duplication.
* Set the Best-return-code to "Invalid Multipath Info Request", when
the DDMAP TLV carries Multipath Entropy Data Sub-TLV, and if the
Target SI-BitString TLV in the received Echo Request carries more
than 1 BFER id. Go to Section 4.5. Else, list the ECMP
downstream neighbors to reach BFR-ID in Target SI-BitString TLV,
calculate the Entropy considering the BitString in Header-H and
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Multipath Entropy Data Sub-TLV from received Echo Request. Store
the Data for each Downstream interface in a temporary variable.
Set the Best-return-code to 5 (Packet-Forward-Success) and goto
Section 4.5
This step instructs the node to calculate the Entropy Data for each
downstream interface to reach the BFER in Target SI-BitString TLV by
considering the incoming BitString and Entropy Data.
* Set the Best-return-code to "Replying router is the only BFER in
BIER header BitString", and go to Section 4.5 if the responder is
BFER and there are no more bits in the BIER header BitString left
for forwarding.
* Set the Best-return-code to "Replying router is one of the BFERs
in BIER header BitString", and include Downstream Mapping TLV if
the responder is BFER and there are more bits in BitString left
for forwarding. Also, include the Multipath information as
defined in Section 4.2 if the received Echo Request carries
Multipath Entropy Data Sub-TLV. Go to Section 4.5.
* Set the Best-return-code to "No matching entry in the forwarding
table", if the forwarding lookup, defined in Section 6.5 of
[RFC8279] does not match any entry for the received BitString in
BIER header.
The step above allows the detection of the missing BFR-ID in the
node's BIER forwarding table. It is difficult to detect the absence
of the BFR-ID if the Request includes more than one BFR-IDs in the
BitString and so may need to include the BFER-id that is not
responding to detect such failure.
* Set the Best-return-code to "Packet-Forward-Success", and include
Downstream Mapping TLV. Go to Section 4.5.
4.5. Sending Echo Reply
If Reply-Flag=0, BFR MUST release the variables and MUST NOT send any
response to the Initiator. If Reply-Flag=1, proceed as below:
The Responder BFR SHOULD include the BitString from Header-H to
Incoming SI-BitString TLV and include the Set ID, Sub-domain ID and
BS Len that corresponds to BIER-Label-L. Responder BFR SHOULD
include the Ingress Interface TLV and populate the address from
Interface-I.
When the Best-return-code is "Replying BFR is one of the BFERs in
header BitString", it MUST include Responder BFER TLV.
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If the received Echo Request had DDMAP with Multipath Entropy Data
Sub-TLV, Responder BFR MUST include DDMAP as defined in
Section 3.4.4 for each outgoing interface over which the packet
will be replicated and include the respective Multipath Entropy
Data Sub-TLV. For each outgoing interface, the respective Egress
BitString MUST be included in DDMAP TLV.
If the received Echo Request had DDMAP without Multipath Entropy
Data Sub-TLV, Responder BFR MUST include DDMAP as defined in
Section 3.4.4 for each outgoing interface over which the packet
will be replicated. For each outgoing interface, respective
Egress BitString MUST be included in DDMAP TLV.
When the Best-return-code is "Replying BFR is the only BFER in header
BitString", it MUST include Responder BFER TLV.
The Responder MUST set the Message Type as 2 and Return Code as Best-
return-code. The Proto field MUST be set to 0.
The Echo Reply can be sent as BIER-encapsulated, or IP/UDP
encapsulated, depending on the Reply Mode in the received Echo
Request. When the Reply Mode in the received Echo Request is set to
3, Responder appends the BIER header listing the BitString with BFIR
ID (from Header-H), sets the Proto to 5, and sets the BFIR as 0.
When the Reply Mode in the received Echo Request is set to 2,
Responder encapsulates with the IP/UDP header. The UDP destination
port MUST be set to TBD1 (Section 5.1), and the source port MAY be
set to TBD1 or other value selected from the Dynamic range of port
numbers. The source IP address is any non-link-local address
associated with the responder, and the destination IP address is
derived from the BFIR-id of the BIER header [RFC8296] in the received
Echo Request.
4.6. Receiving Echo Reply
The Initiator, upon receiving the Echo Reply, will use the Sender's
Handle to match with Echo Request sent. If no match is found, the
Initiator MUST ignore the Echo Reply.
If receiving Echo Reply has Downstream Mapping, the Initiator SHOULD
copy the same to subsequent Echo Request(s).
If one of the Echo Reply is received with Return Code as "Replying
BFR is one of the BFERs in header BitString", it SHOULD reset the
BFR-ID of the responder from Target SI-BisString TLV in subsequent
Echo Request. This step helps avoid any BFR that is both BFER and
transit BFR to respond with Echo Reply continuously.
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5. IANA Considerations
The terms used in the IANA Considerations below are intended to be
consistent with [RFC8126].
5.1. UDP Port Number
This document requests a UDP port TBD1 to be allocated by IANA for
BIER Echo.
Service Name bier-echo
Transport Protocol UDP, TCP
Assignee IESG iesg@ietf.org
Contact IETF Chair chair@ietf.org
Description The UDP destination port number for the IP/UDP
encapsulated BIER Echo Reply message.
Reference This document
Port Number TBD1
5.2. BIER OAM Registry Group
IANA is requested to create and maintain the "BIER OAM" registry
group containing the registries listed below.
5.3. BIER OAM Message Type
IANA is requested to create in the BIER OAM Message Type registry in
the BIER OAM registry group as follows:
Registry Name: BIER OAM Message Type.
Assignment Policy:
0-31 - IETF Review
32-58 - RFC Required
59 - 61 - Experimental Use (Reserved, not to be assigned)
62 - 63 - Private Use (Reserved, not to be assigned)
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+=========+===============================+===============+
| Value | Description | Reference |
+=========+===============================+===============+
| 0 | Reserved | This document |
+---------+-------------------------------+---------------+
| 1 | BIER Echo Request/Echo Reply | This document |
+---------+-------------------------------+---------------+
| 2 - 58 | Unassigned | This document |
+---------+-------------------------------+---------------+
| 59 - 61 | Reserved for Experimental Use | This document |
+---------+-------------------------------+---------------+
| 62 - 63 | Reserved for Private Use | This document |
+---------+-------------------------------+---------------+
Table 1: BIER OAM Message Type
5.4. BIER Echo Request/Echo Reply Registries
IANA is requested to create three BIER Echo Request/Echo Reply
registries in the BIER OAM registry group, as described below.
5.4.1. BIER Echo Request/Echo Reply Message Types
IANA is requested to create in the in the BIER OAM registry group the
BIER Echo Request/Echo Reply Message Types registry as follows:
Registry Name: BIER Echo Request/Echo Reply Message Types
Assignment Policy:
0 - 191 - IETF Review
192 - 247 - RFC Required
248 - 251 - Experimental Use (Reserved, not to be assigned)
252 - 255 - Private Use (Reserved, not to be assigned)
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+===========+===============================+===============+
| Value | Description | Reference |
+===========+===============================+===============+
| 0 | Reserved | This document |
+-----------+-------------------------------+---------------+
| 1 | BIER Echo Request | This document |
+-----------+-------------------------------+---------------+
| 2 | BIER Echo Reply | This document |
+-----------+-------------------------------+---------------+
| 3 - 175 | Unassigned | This document |
+-----------+-------------------------------+---------------+
| 176 - 247 | Unassigned | This document |
+-----------+-------------------------------+---------------+
| 248-251 | Reserved for Experimental Use | This document |
+-----------+-------------------------------+---------------+
| 252-255 | Reserved for Private Use | This document |
+-----------+-------------------------------+---------------+
Table 2: BIER Echo Request/Echo Reply Message Types
5.4.2. BIER Echo Reply Modes
IANA is requested to create in the BIER OAM registry group the new
BIER Echo Reply Mode registry as follows:
Registry Name: BIER Echo Reply Mode
Assignment Policy:
0 - 191 - IETF Review
192 - 247 - RFC Required
248 - 251 - Experimental Use (Reserved, not to be assigned)
252 - 255 - Private Use (Reserved, not to be assigned)
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+===========+===================================+===============+
| Value | Description | Reference |
+===========+===================================+===============+
| 0 | Reserved | This document |
+-----------+-----------------------------------+---------------+
| 1 | Do Not Reply | This document |
+-----------+-----------------------------------+---------------+
| 2 | Reply via an IPv4/IPv6 UDP Packet | This document |
+-----------+-----------------------------------+---------------+
| 3 | Reply via BIER packet | This document |
+-----------+-----------------------------------+---------------+
| 4 - 175 | Unassigned | This document |
+-----------+-----------------------------------+---------------+
| 176 - 247 | Unassigned | This document |
+-----------+-----------------------------------+---------------+
| 248-251 | Reserved for Experimental Use | This document |
+-----------+-----------------------------------+---------------+
| 252-255 | Reserved for Private Use | This document |
+-----------+-----------------------------------+---------------+
Table 3: BIER Echo Reply Modes
5.4.3. BIER Echo Return Codes
IANA is requested to create in the BIER OAM registry group the new
BIER Echo Return Codes registry as follows:
Registry Name: BIER Echo Return Codes
Assignment Policy:
0 - 191 - IETF Review
192 - 247 - RFC Required
248 - 251 - Experimental Use (Reserved, not to be assigned)
252 - 255 - Private Use (Reserved, not to be assigned)
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+=========+=================================+===============+
| Value | Description | Reference |
+=========+=================================+===============+
| 0 | No Return Code | This document |
+---------+---------------------------------+---------------+
| 1 | Malformed Echo Request received | This document |
+---------+---------------------------------+---------------+
| 2 | One or more of the TLVs is not | This document |
| | supported | |
+---------+---------------------------------+---------------+
| 3 | Replying BFR is the only BFER | This document |
| | in header BitString | |
+---------+---------------------------------+---------------+
| 4 | Replying BFR is one of the | This document |
| | BFERs in header BitString | |
+---------+---------------------------------+---------------+
| 5 | Packet-Forward-Success | This document |
+---------+---------------------------------+---------------+
| 6 | Invalid Multipath Info Request | This document |
+---------+---------------------------------+---------------+
| 7 | Unassigned | This document |
+---------+---------------------------------+---------------+
| 8 | No matching entry in the | This document |
| | forwarding table | |
+---------+---------------------------------+---------------+
| 9 | Set-Identifier Mismatch | This document |
+---------+---------------------------------+---------------+
| 10 | DDMAP Mismatch | This document |
+---------+---------------------------------+---------------+
| 11 - | Unassigned | This document |
| 247 | | |
+---------+---------------------------------+---------------+
| 248-251 | Reserved for Experimental Use | This document |
+---------+---------------------------------+---------------+
| 252-255 | Reserved for Private Use | This document |
+---------+---------------------------------+---------------+
Table 4: BIER Echo Return Codes
5.5. Common Registration Procedures for TLVs and Sub-TLVs
This section describes registration procedures for Type registries in
BIER Echo Request/Reply TLVs and sub-TLVs.
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+=============+==============+================================+
| Range | Registration | Note |
| | Procedures | |
+=============+==============+================================+
| 0-16383 | Standards | This range is for TLVs and |
| | Action | sub-TLVs that require an error |
| | | message if not recognized. |
+-------------+--------------+--------------------------------+
| 16384-31739 | RFC Required | This range is for TLVs and |
| | | sub-TLVs that require an error |
| | | message if not recognized. |
+-------------+--------------+--------------------------------+
| 31740-31743 | Experimental | Not to be assigned. |
| | Use | |
+-------------+--------------+--------------------------------+
| 31744-32767 | First Come, | This range is for TLVs and |
| | First Served | sub-TLVs that require an error |
| | | message if not recognized. |
+-------------+--------------+--------------------------------+
| 32768-49161 | Standards | his range is for TLVs and sub- |
| | Action | TLVs that can be silently |
| | | dropped if not recognized. |
+-------------+--------------+--------------------------------+
| 49162-64507 | RFC Required | This range is for TLVs and |
| | | sub-TLVs that can be silently |
| | | dropped if not recognized. |
+-------------+--------------+--------------------------------+
| 64508-64511 | Experimental | Not to be assigned. |
| | Use | |
+-------------+--------------+--------------------------------+
| 64512-65535 | First Come, | This range is for TLVs and |
| | First Served | sub-TLVs that can be silently |
| | | dropped if not recognized. |
+-------------+--------------+--------------------------------+
Table 5: TLVs
5.5.1. TLVs
IANA is requested to create in the BIER OAM registry group a registry
for the Type field of top-level TLVs. as well as sub-registries for
the associated sub-TLVs. Note that the meaning of a sub-TLV is
scoped by the TLV. The number of spaces for the sub-TLVs of various
TLVs is independent.
Registry Name: TLVs
Assignment Policy: Section 5.5
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The TLVs requested by this document for the IANA consideration are
listed in Table 6.
+======+==============+===============+=========================+
| Type | TLV Name | Reference | Sub-TLV Registry |
+======+==============+===============+=========================+
| 0 | Reserved | This document | |
+------+--------------+---------------+-------------------------+
| 1 | Original SI- | This document | No Sub-TLVs |
| | BitString | | |
+------+--------------+---------------+-------------------------+
| 2 | Target SI- | This document | No Sub-TLVs |
| | BitString | | |
+------+--------------+---------------+-------------------------+
| 3 | Incoming SI- | This document | No Sub-TLVs |
| | BitString | | |
+------+--------------+---------------+-------------------------+
| 4 | Downstream | This document | Link the Sub-TLVs for |
| | Mapping | | TLV Type 4 sub-registry |
+------+--------------+---------------+-------------------------+
| 5 | Responder | This document | No Sub-TLVs |
| | BFER | | |
+------+--------------+---------------+-------------------------+
| 6 | Responder | This document | No Sub-TLVs |
| | BFR | | |
+------+--------------+---------------+-------------------------+
| 7 | Ingress | This document | No Sub-TLVs |
| | Interface | | |
+------+--------------+---------------+-------------------------+
Table 6: TLVs
5.5.2. Sub-TLVs for TLV Type 4
IANA is requested to create in the registry for the Type 4
(Downstream Mapping) a sub-registry Sub-TLVs for Type 4.
Registry Name: Sub-TLVs for Type 4
Assignment Policy: Section 5.5
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+======+========================+===============+
| Type | Sub-TLV Name | Reference |
+======+========================+===============+
| 0 | Reserved | This document |
+------+------------------------+---------------+
| 1 | Multipath Entropy Data | This document |
+------+------------------------+---------------+
| 2 | Egress BitString | This document |
+------+------------------------+---------------+
Table 7: TLVs
6. Security Considerations
The security considerations of [RFC8296], and through it of
[RFC8279], apply to this specification.
The security consideration for BIER Ping is similar to ICMP [RFC0792]
or LSP Ping [RFC8029], [RFC6425]. As with ICMP or LSP Ping, BFR can
be exposed to Denial-of-Service (DoS) attacks, and it is RECOMMENDED
to regulate the BIER Ping packet flow to the control plane. A rate
limiter SHOULD be applied to avoid any attack. Specifically, a rate
limiter SHOULD be applied to the well-known UDP port defined in
Section 5.1. Although using BIER Echo Request in a DoS amplification
attack is theoretically possible, spoofing BFIR ID in the BIER Header
presents itself as a serious challenge. As a result, this threat is
not a big concern.
As with ICMP or LSP Ping, a traceroute can be used to obtain network
information. It is RECOMMENDED that the implementation checks the
integrity of BFIR of the Echo messages against any locally secured
list before processing the message further.
In some BIER environments, transmitting a single BIER Echo Request
message can result in the sender receiving an overwhelming number of
BIER Echo Reply messages. In that case, an operator MAY choose to
address the BIER Echo Request to a subset of BFERs rather than to all
BFERs in the domain.
7. Acknowledgement
The authors would like to thank Antoni Przygienda, Eric Rosen, Faisal
Iqbal, Jeffrey (Zhaohui) Zhang, and Shell Nakash for their review and
comments.
The authors would like to thank Mankamana Mishra for his thorough
review and comments.
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8. References
8.1. 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>.
[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>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[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>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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[IEEE.1588.2008]
"Standard for a Precision Clock Synchronization Protocol
for Networked Measurement and Control Systems",
IEEE Standard 1588, March 2008.
[IANA-Next-Protocol-Identifiers]
IANA, "IANA BIER Next Protocol Identifiers Registry",
<https://www.iana.org/assignments/bier/bier.xhtml#bier-
next-protocol-identifiers>.
8.2. Informative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
Mizrahi, "In Situ Operations, Administration, and
Maintenance (IOAM) Direct Exporting", RFC 9326,
DOI 10.17487/RFC9326, November 2022,
<https://www.rfc-editor.org/info/rfc9326>.
[RFC9570] Kompella, K., Bonica, R., and G. Mirsky, Ed., "Deprecating
the Use of Router Alert in LSP Ping", RFC 9570,
DOI 10.17487/RFC9570, May 2024,
<https://www.rfc-editor.org/info/rfc9570>.
[I-D.ietf-bier-oam-requirements]
Mirsky, G., Nainar, N. K., Chen, M., and S. Pallagatti,
"Operations, Administration and Maintenance (OAM)
Requirements for Bit Index Explicit Replication (BIER)
Layer", Work in Progress, Internet-Draft, draft-ietf-bier-
oam-requirements-21, 23 November 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
oam-requirements-21>.
[I-D.ietf-bier-bierin6]
Zhang, Z., Zhang, Z. J., Wijnands, I., Mishra, M. P.,
Bidgoli, H., and G. S. Mishra, "Supporting BIER in IPv6
Networks (BIERin6)", Work in Progress, Internet-Draft,
draft-ietf-bier-bierin6-12, 25 August 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
bierin6-12>.
Contributors' Addresses
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Nobo Akiya
Big Switch Networks
Japan
Email: nobo.akiya.dev@gmail.com
Lianshu Zheng
Individual Contributor
China
Email: veronique_cheng@hotmail.com
Authors' Addresses
Nagendra Kumar
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709
United States of America
Email: naikumar@cisco.com
Carlos Pignataro
North Carolina State University
United States of America
Email: cpignata@gmail.com, cmpignat@ncsu.edu
Mach Chen
Huawei Technologies
Email: mach.chen@huawei.com
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
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