PCE for BIER-TE Path
draft-chen-pce-bier-te-path-03
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Huaimo Chen , Mike McBride , Aijun Wang , Gyan Mishra , Yisong Liu , Yanhe Fan , Lei Liu , Xufeng Liu | ||
| Last updated | 2022-04-18 | ||
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draft-chen-pce-bier-te-path-03
Network Working Group H. Chen
Internet-Draft M. McBride
Intended status: Standards Track Futurewei
Expires: October 20, 2022 A. Wang
China Telecom
G. Mishra
Verizon Inc.
Y. Liu
China Mobile
Y. Fan
Casa Systems
L. Liu
Fujitsu
X. Liu
Volta Networks
April 18, 2022
PCE for BIER-TE Path
draft-chen-pce-bier-te-path-03
Abstract
This document describes extensions to Path Computation Element (PCE)
communication Protocol (PCEP) for supporting Bit Index Explicit
Replication (BIER) Traffic Engineering (TE) paths.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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."
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This Internet-Draft will expire on October 20, 2022.
Copyright Notice
Copyright (c) 2022 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminologies . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview of PCE for BIER-TE . . . . . . . . . . . . . . . . . 5
2.1. Example BIER-TE Topology with PCE . . . . . . . . . . . . 5
2.2. A Brief Flow of PCEP Messages for a BIER-TE Path . . . . 6
2.3. Procedures on Ingress . . . . . . . . . . . . . . . . . . 8
3. Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . 9
3.1. BIER-TE Path Capability . . . . . . . . . . . . . . . . . 9
3.2. Extensions to SRP . . . . . . . . . . . . . . . . . . . . 10
3.2.1. SRP Object Flag Field . . . . . . . . . . . . . . . . 10
3.2.2. Reuse of Multicast Flow Specification TLV . . . . . . 11
3.3. Ingress Node Object . . . . . . . . . . . . . . . . . . . 11
3.4. Objective Functions . . . . . . . . . . . . . . . . . . . 13
3.5. BIER-TE Path Subobject . . . . . . . . . . . . . . . . . 14
3.6. BIER-TE Path Subobject in ERO . . . . . . . . . . . . . . 15
3.7. BIER-TE Path Subobject in RRO . . . . . . . . . . . . . . 15
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. BIER-TE Path Creation . . . . . . . . . . . . . . . . . . 16
4.2. BIER-TE Path Update . . . . . . . . . . . . . . . . . . . 17
4.3. BIER-TE Path Deletion . . . . . . . . . . . . . . . . . . 17
5. The PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 17
5.1. The PCRpt Message . . . . . . . . . . . . . . . . . . . . 17
5.2. The PCUpd Message . . . . . . . . . . . . . . . . . . . . 18
5.3. The PCInitiate Message . . . . . . . . . . . . . . . . . 18
5.4. The PCReq Message . . . . . . . . . . . . . . . . . . . . 18
5.5. The PCRep Message . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6.1. PST for BIER-TE Path . . . . . . . . . . . . . . . . . . 19
6.2. PCE-BIER-TE-Path Capability sub-TLV . . . . . . . . . . . 19
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6.3. SRP Object Flag Field . . . . . . . . . . . . . . . . . . 19
6.4. Ingress Node Object . . . . . . . . . . . . . . . . . . . 20
6.5. OF Code Points . . . . . . . . . . . . . . . . . . . . . 20
6.6. PCEP BIER-TE Path Subobjects . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
[I-D.ietf-bier-te-arch] introduces Bit Index Explicit Replication
(BIER) Traffic/Tree Engineering (BIER-TE). It is an architecture for
per-packet stateless explicit point to multipoint (P2MP) multicast
path/tree and based on the BIER architecture defined in [RFC8279].
A Bit-Forwarding Ingress Router (BFIR) in a BIER-TE domain receives
the information or instructions from a controller such as a stateful
PCE about which multicast flows/packets are mapped to which P2MP
paths. The multicast flows/packets are indicated by multicast and
source addresses. The paths are represented by BitPositions or say
BitStrings. After receiving the information or instructions, the
ingress node/router encapsulates the multicast packets with the
BitPositions for the corresponding P2MP paths, replicates and
forwards the packets with the BitPositions along the P2MP paths.
[RFC8231] describes a set of extensions to PCEP to provide stateful
control. A stateful PCE has access to not only the information
carried by the network's Interior Gateway Protocol (IGP) but also the
set of active paths and their reserved resources. The additional
state allows the PCE to compute constrained paths while considering
individual paths and their interactions.
To compute and initiate BIER-TE P2MP paths, the stateful PCE needs to
be extended. For a BIER-TE P2MP path, some new state information
will be stored and maintained, which includes the BitPositions,
multicast group and multicast source for the path. The PCE gets the
egresses of the path, the same multicast group and source from the
egresses when each of the egresses reports to the PCE that it
receives a multicast join with the multicast group and source. With
this information, the PCE finds an ingress for the path, computes the
path from the ingress to the egresses that has the optimal
BitPositions and satisfies the constraints, and then initiates the
BIER-TE path at the ingress of the path through sending the ingress
the BitPositions of the path, multicast group and source in a PCEP
message such as PCInitiate. After receiving the message, the ingress
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creates a forwarding entry that imports the packets with the
multicast group/address and source into the BIER-TE path (i.e.,
encapsulates the packets with a BIER-TE header having the
BitPositions of the path), and then reports the status of the path to
the PCE in a PCEP message such as PCRpt.
[I-D.chen-pce-bier] describes part of the solution for this, which is
mainly the BIER-ERO subobject used for P2MP paths.
This document proposes a comprehensive solution for computing and
establishing BIER-TE P2MP paths.
1.1. Terminologies
The following terminologies are used in this document.
PCE: Path Computation Element
PCEP: PCE communication Protocol
PCC: Path Computation Client
CE: Customer Edge
PE: Provider Edge
BIER: Bit Index Explicit Replication.
BIER-TE: BIER Traffic/Tree Engineering.
BFR: Bit-Forwarding Router.
BFIR: Bit-Forwarding Ingress Router.
BFER: Bit-Forwarding Egress Router.
BFR-id: BFR Identifier. It is a number in the range [1,65535].
BFR-NBR: BFR Neighbor.
BFR-prefix: An IP address (either IPv4 or IPv6) of a BFR.
BIRT: Bit Index Routing Table. It is a table that maps from the BFR-
id (in a particular sub-domain) of a BFER to the BFR-prefix of
that BFER, and to the BFR-NBR on the path to that BFER.
BIFT: Bit Index Forwarding Table.
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LSP-DB: Label Switching Path DataBase.
TED: Traffic/Tree Engineering DataBase.
2. Overview of PCE for BIER-TE
This section briefly describes PCE for BIER-TE and illustrates some
details through a simple example BIER-TE topology.
2.1. Example BIER-TE Topology with PCE
An example BIER-TE topology for a BIER-TE domain with a PCE is shown
in Figure 1. There are 8 nodes/BFRs A, B, C, D, E, F, G and H in the
domain. Nodes/BFRs A, H, E, F and D are BFIRs (i.e., ingress nodes)
or BFERs (i.e., egress nodes). There is a connection (i.e., PCE
session) between the PCE and the PCC running on each of the possible
ingress and egress nodes in the domain. Note that some of
connections and the PCC on each node are not shown in the figure.
+------------------------------------+
| PCE |
+------------------------------------+
/ ... \
/ \
/ 4' 17' 18' \
/ /-----------( G )----------( H )
/ / 19'\_______ 12'/4
/ / _______)____/
/ / / (_____
/ /3' / \
/ 1' 2' / 5' 6' /11' 13' 20'\
(CE) --- ( A )--------( B )------------( C )------------( D )
5 \7' \15' 14' 1
\ \
\8' 9' 10' \16'
( E )------------( F )
3 2
Figure 1: Example BIER-TE Topology with PCE
Nodes/BFRs D, F, E, H and A are BFERs (or BFIRs) and have local decap
adjacency BitPositions 1, 2, 3, 4, and 5 respectively. For
simplicity, these BPs are represented by (SI:BitString), where SI = 0
and BitString is of 8 bits. BPs 1, 2, 3, 4, and 5 are represented by
1 (0:00000001), 2 (0:00000010), 3 (0:00000100), 4 (0:00001000) and 5
(0:00010000) respectively.
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The BitPositions for the forward connected adjacencies are
represented by i', where i is from 1 to 20. In one option, they are
encoded as (n+i), where n is a power of 2 such as 32768. For
simplicity, these BitPositions are represented by (SI:BitString),
where SI = (6 + (i-1)/8) and BitString is of 8 bits. BitPositions i'
(i from 1 to 20) are represented by 1'(6:00000001), 2'(6:00000010),
3'(6:00000100), 4'(6:00001000), 5'(6:00010000), 6'(6:00100000),
7'(6:01000000), 8'(6:10000000), 9'(7:00000001), 10'(7:00000010), . .
. , 16'(7:10000000), 17'(8:00000001), 18'(8:00000010), . . . ,
20'(8:00001000).
For a link between two nodes X and Y, there are two BitPositions for
two forward connected adjacencies. These two forward connected
adjacency BitPositions are assigned on nodes X and Y respectively.
The BitPosition assigned on X is the forward connected adjacency of
Y. The BitPosition assigned on Y is the forward connected adjacency
of X.
For example, for the link between nodes B and C in the figure, two
forward connected adjacency BitPositions 5' and 6' are assigned to
two ends of the link. BitPosition 5' is assigned on node B to B's
end of the link. It is the forward connected adjacency of node C.
BitPosition 6' is assigned on node C to C's end of the link. It is
the forward connected adjacency of node B.
2.2. A Brief Flow of PCEP Messages for a BIER-TE Path
For a BIER-TE Path to transport the packets with a given multicast
group/address and source in a BIER-TE domain, a sequence of PCEP
messages are exchanged between the PCE for the domain and the PCEs
for the domains containing the source, and between the PCE for the
domain and the PCCs running on the BFERs/BFIRs of the domain.
Suppose that each of nodes H, D and F receives a multicast join with
a same multicast group/address and source, which are MGa and MSa
respectively. For simplicity, assume that the multicast source MSa
is in the left domain containing the CE in Figure 1. The following
is a brief flow of PCEP messages for computing and creating a BIER-TE
Path to transport the packets to H, D and F.
At first, the PCC running on each of nodes H, D and F sends the PCE a
PCEP message such as PCRpt. The message contains the multicast group
and source (i.e., MGa and MSa), which reports to the PCE that the
node receives a multicast join with MGa and MSa. Note that a PCEP
message is sent to the PCE from the PCC on a node to report that the
node leaves when the node receives a multicast leave with MGa and
MSa.
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After receiving the PCEP messages from nodes H, D and F reporting
multicast join with MGa and MSa, the PCE for the domain containing
these nodes determines that nodes H, D and F are the egress nodes of
a BIER-TE path since they have the same multicast group and source.
Second, the PCE for the domain sends a PCEP message such as PCReq to
each of the PCEs for the domains that may contain the multicast
source. This message requests the PCE (that may contain the source)
to find an ingress node for the BIER-TE path having egress nodes H, D
and F. The message contains the multicast group and source (i.e.,
MGa and MSa). For example, the PCE for the BIER-TE domain sends the
PCEP message to the PCE (called PCE-L) for the left domain containing
CE (note that this PCE is not shown in the figure).
After receiving the PCEP message requesting to find an ingress node,
the PCE (e.g., PCE-L) for the domain containing the multicast source
computes the ingress node that is reachable from the source with
minimum cost (e.g., ingress node A). The PCE for the domain without
the source can not find any ingress node.
Third, the PCE for the domain with the source sends the PCE for the
BIER-TE domain a PCEP message such as PCRep with the ingress node.
The PCE for the domain without the source sends the PCE for the BIER-
TE domain a PCEP message such as PCRep with NO INGRESS FOUND.
After receiving the PCEP message with the ingress node, the PCE for
the BIER-TE domain computes a P2MP path from the ingress node (e.g.,
A) to the egress nodes (e.g., H, D and F). The path has the optimal
BitPositions and satisfies the constraints. The optimal BitPositions
means the BitPositions for the path has the minimum number of bit
sets and the minimum bit distance.
Fourth, the PCE for the BIER-TE domain sends a PCEP message such as
PCInitiate to the PCC on the ingress node (e.g., A) for the ingress
to create a BIER-TE path to transport the packets for the given
multicast group and source. The message contains the BitPositions
for the path, the multicast group and source.
After receiving the PCEP message with the path, the PCC on the
ingress (e.g., A) creates the BIER-TE path, i.e., a forwarding entry
that imports the packets with the multicast group/address and source
into the BIER-TE path (i.e., encapsulates the packets with a BIER-TE
header having the BitPositions of the path).
And then the PCC on the ingress sends the PCE a PCEP message such as
PCRpt reporting the status of the path to the PCE.
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After receiving the PCEP message with the status of the path, the PCE
for the domain updates the information about the path accordingly.
2.3. Procedures on Ingress
This section introduces the procedures for the ingress node of a P2MP
path to get the BitPositions representing the explicit P2MP path from
the ingress node to its egress nodes from the PCE.
Suppose that node A in Figure 1 wants to have an explicit P2MP path
from ingress node A to egress nodes H and F. The path satisfies a
set of constraints. In one case, the PCC running on ingress node A
sends a request for the path to the PCE. The request contains the
set of constraints, objective functions, the ingress node and the
egress nodes. After receiving the request, the PCE computes an
explicit P2MP path, which satisfies the constraints and is from the
given ingress node to the egress nodes. While computing the path,
the PCE will optimize the BitPositions of the path. That is that,
for a given length of BitString, the path computed uses the minimum
number of BitStrings (i.e., bit sets) and satisfies the constraints.
The length is given by the value in BitStrLen field in the PCE-BIER-
TE-Path-Capability sub-TLV. The PCE sends a reply with the path to
the PCC. The reply contains the BitPositions representing the
explicit P2MP path.
For example, assume that the explicit P2MP path computed by the PCE
traverses the link/adjacency from A to B (indicated by BP 2'), the
link/adjacency from B to G (indicated by BP 4') and the link/
adjacency from B to C (indicated by BP 6'), the link/adjacency from G
to H (indicated by BP 18'), and the link/adjacency from C to F
(indicated by BP 16'). This path is represented by {2', 4', 6', 16',
18', 2, 4}, where BitPositions 2 and 4 indicate egress nodes F and H
respectively. The reply sent to the PCC on node A by the PCE
contains the path represented by {2', 4', 6', 16', 18', 2, 4}.
In another case, a request for a P2MP path is from a user or
application. After receiving the request, the PCE finds an ingress
node if no ingress is given, and computes an explicit P2MP path from
the ingress node to the egress nodes and sends the path to the PCC
running on the ingress node.
After receiving the P2MP path, for any packet from CE to be
transported by the path, such as the packet with the multicast
address, the ingress node encapsulates the packet with the
BitPositions representing the path and forwards the packet according
to its BIFT.
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For example, when ingress node A receives the path represented by
BitPositions {2', 4', 6', 16', 18', 2, 4}, it encapsulates every
packet from CE with the multicast address with the BitPositions and
then forwards the packet along the P2MP path according to its BIFT.
A forwards the packet to B according to the forwarding entry for BP
2' in its BIFT.
After receiving the packet from A, B forwards the packet to G and C
according to the forwarding entries for BPs 4' and 6' in B's BIFT
respectively. The packet received by G has path {16', 18', 2, 4}.
The packet received by C has path {16', 18', 2, 4}.
After receiving the packet from B, G sends the packet to H according
to the forwarding entry for BP 18' in G's BIFT.
After receiving the packet from B, C sends the packet to F according
to the forwarding entry for BP 16' in C's BIFT.
Egress node H of the P2MP path receives the packet with BitPosition
4. It decapsulates the packet and pass the payload of the packet to
the packet's NextProto.
Egress node F of the P2MP path receives the packet with BitPosition
2. It decapsulates the packet and pass the payload of the packet to
the packet's NextProto.
3. Extensions to PCEP
This section describes extensions to PCEP.
3.1. BIER-TE Path Capability
During a PCEP session establishment, PCEP Speakers (PCE or PCC)
indicate their ability to support BIER-TE paths. The OPEN object in
the Open message contains the PATH-SETUP-TYPE-CAPABILITY TLV, which
is defined in [RFC8408]. The TLV contains a list of Path Setup Types
(PSTs) and optional sub-TLVs associated with the PSTs. The sub-TLVs
convey the parameters that are associated with the PSTs supported by
a PCEP speaker.
This document defines a new PST value:
* PST = TBD1: Path is setup using BIER-TE.
A new sub-TLV associated with this new PST is defined, which is
called PCE-BIER-TE-Path-Capability sub-TLV. The format of this new
sub-TLV is illustrated in the figure below.
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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 = TBD2 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | SILen | BitStrLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PCE-BIER-TE-Path-Capability sub-TLV
Type - 16 bits: TBD2 is to be assigned by IANA.
Length - 16 bits: 4 is the total length in bytes of the remainder of
the TLV, excluding the Type and Length fields.
SILen (SI Length) - 5 bits: The length in bits of the SI field.
BitStrLen (Bit String Length) - 8 bits: The length in bits of the
BitString field according to [RFC8296]. If k is the length of the
BitString, the value of BitStrLen is log2(k)-5. For example,
BitStrLen = 1 indicates k = 64, BitStrLen = 7 indicates k = 4096.
Reserved - 19 bits: MUST be set to zero by the sender and MUST be
ignored by the receiver.
A PCEP speaker supporting BIER-TE paths includes the new PST and sub-
TLV in the PATH-SETUP-TYPE-CAPABILITY TLV.
3.2. Extensions to SRP
For a PCEP message, when it is used for a BIER-TE path, the SRP
(Stateful PCE Request Parameters) object in the message MUST include
the PATH-SETUP-TYPE TLV defined in [RFC8408]. The TLV MUST contain
the PST = TBD1 for path setup using BIER-TE.
Three contiguous bits in SRP Object Flag Field are defined to
indicate one of the assistant operations for a BIER-TE path. This
three bits field is called AOP (Assistant Operations). In addition,
the Multicast Flow Specification TLV defined in
[I-D.ietf-pce-pcep-flowspec] is re-used in the SRP object for
indicating Multicast Traffic.
3.2.1. SRP Object Flag Field
The three bits for AOP are bits 27 to 29 (the exact bits to be
assigned by IANA) in the SRP Object Flag Field. The values of AOP
are defined as follows:
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AOP Value Meaning (Assistant Operation)
0x001 (J): Join with Multicast Group and Source
0x010 (L): Leave from Multicast Group and Source
0x011 (I): Ingress node computation
The value of AOP indicates one of the three operations above. When
any of the other values is received, an error MUST be reported.
When the PCC running on an edge node of a BIER-TE domain sends the
PCE for the domain a PCEP message such as PCRpt to report that the
edge node receives a multicast join, the message MUST include a SRP
object with AOP == 0x001 (J).
When the PCC running on an edge node of a BIER-TE domain sends the
PCE for the domain a PCEP message such as PCRpt to report that the
edge node receives a multicast leave, the message MUST include a SRP
object with AOP == 0x010 (L).
When the PCE for the domain sends a PCEP message such as PCReq to
another PCE for requesting to find an ingress node for a BIER-TE
path, the message MUST include a SRP object with AOP == 0x011 (I).
3.2.2. Reuse of Multicast Flow Specification TLV
For a PCE-Initiated BIER-TE path, when a PCE sends a PCC a message
such as PCInitiate message to create a BIER-TE path in a BIER-TE
domain, the message MUST contain a Multicast Flow Specification TLV
in the SRP object. The TLV indicates the multicast traffic that the
BIER-TE path will carry.
When the PCC running on an edge node of a BIER-TE domain sends the
PCE for the domain a PCEP message to report that the edge node
receives a multicast join or leave with a multicast group/address and
source, the message MUST contain a Multicast Flow Specification TLV
in the SRP object. The TLV indicates the multicast group by the
multicast group adress and/or multicast source address.
When the PCE for a BIER-TE domain sends another PCE a PCEP message to
request for finding an ingress node of a BIER-TE path, the message
MUST contain a Multicast Flow Specification TLV in the SRP object.
The TLV indicates the multicast source.
3.3. Ingress Node Object
To represent an ingress node, a new ingress node object is defined.
The format of the new object for IPv4 (OT = 1) is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ObjectClass=TBD| OT=1 |Res|P|I| Object Length (bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress Node IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost to Ingress Node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Ingress Node Object for IPv4
ObjectClass: TBD is to be assigned by IANA.
OT: 1 for IPv4.
Res, P, I and Object Length: Same as those defined in Common Object
Header in [RFC5440].
Ingress Node IPv4 address: Indicates an IPv4 address of an ingress
node.
Cost to Ingress Node: Indicates the cost from the multicast source
to the ingress node.
No optional TLV is defined so far.
The format of the new object for IPv6 (OT = 2) is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ObjectClass=TBD| OT=2 |Res|P|I| Object Length (bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress Node IPv6 address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost to Ingress Node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Ingress Node Object for IPv6
TBD, Res, P, I, Object Length, and Cost to Ingress Node: Same as
those defined in Ingress Node Object for IPv4.
OT: 2 for IPv6.
Ingress Node IPv6 address: Indicates an IPv6 address of an ingress
node.
No optional TLV is defined so far.
3.4. Objective Functions
[RFC5541] defines a mechanism to specify an objective function (OF)
that is used by a PCE when it computes a path. For a BIER-TE path,
the following new OF is defined.
Objective Function Code: TBD8
Name: Minimum Bit Sets (MBS)
Description: Find a path represented by BitPositions that has
the minimum number of bit sets.
Objective Function Code: TBD9
Name: Minimum Bits (MB)
Description: Find a path represented by BitPositions that has
the minimum bit distance. The bit distance of
BitPositions is the distance from the lowest bit
to the highest bit in BitPositions.
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3.5. BIER-TE Path Subobject
A BIER-TE path is represented by the BitPositions for the adjacencies
through which the path traverses. A BitPosition is represented by a
SI:BitString or a number.
A new subobject, called BIER-TE Path subobject (or BIER-TE-ERO
subobject), is defined to contain the information about one or more
BitPositions.
The format of a BIER-TE Path subobject in a ERO is shown in the
figure below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type = TBDa | Length | sub-domain-id | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: BitPositions :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: BIER-TE Path Subobject in ERO
L Flag (1 bit): It indicates whether the subobject represents a
loose-hop in the path.
Type (7 bits): It is to be assigned by IANA. It identifies the BIER
subobject type.
Length (8 bits): It contains the total length of the subobject in
octets. The Length MUST be at least 4.
sub-domain-id: Unique value identifying the BIER sub-domain within
the BIER domain.
MT-ID: Multi-Topology ID identifying the topology that is associated
with the BIER sub-domain.
BitPositions: It MUST be at least one BitPosition.
For the subobject in a message received from a PCEP session, the
format of the BitPositions in the subobject is determined by the
values of SILen and BitStrLen in the PCE-BIER-TE-Path-Capability sub-
TLV exchanged during the establishment of the session. When both
SILen and BitStrLen are greater than zero, each of the BitPositions
has two parts SI and BitString, where SI occupies SILen bits and
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BitString occupies BitStrLen bits. When both SILen and BitStrLen are
zeros, each of the BitPositions is a number of 16 bits.
For example, when SILen = 8 and BitStrLen = 1 (indicating BitString
is of 64 bits), each BitPosition has a SI of 8 bits and a BitString
of 64 bits. For simplicity, BitString of 8 bits is used below. The
BitPositions for a BIER-TE path are sorted in descending order before
they are put into a BIER-TE path subobject. For BIER-TE path {2',
4', 6', 16', 18', 2, 4}, when its BitPositions are sorted, it is
{18', 16', 6', 4', 2', 4, 2}, which is {18'(8:00000010),
16'(7:10000000), 6'(6:00100000), 4'(6:00001000), 2'(6:00000010), 4
(0:00001000), 2 (0:00000010)}. The BitPositions with the same SI are
stored in one BitString. For example, 6'(6:00100000), 4'(6:00001000)
and 2'(6:00000010) are stored in (SI:BitString) = (6:00101010), where
SI = 6. BIER-TE path {18', 16', 6', 4', 2', 4, 2} is encoded in the
BIER-TE path subobject in the figure below. The path uses four
BitStrings of 8 bits.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Type = TBDa | Length = 10 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 |0 0 0 0 0 0 1 0| 7 |1 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 |0 0 1 0 1 0 1 0| 0 |0 0 0 0 1 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: BIER-TE Path Subobject for a Path
3.6. BIER-TE Path Subobject in ERO
The ERO defined in [RFC5440] may contain a BIER-TE Path subobject for
the BitPositions of a BIER-TE path. The BitPositions in the BIER-TE
Path subobject for the BIER-TE path MUST be in descending order.
When an ERO contains one or more BIER-TE Path subobjects for a BIER-
TE path, the ERO MUST NOT include any other type of subobjects (i.e.,
it MUST include only BIER-TE Path subobjects). The first one is used
and the others are ignored.
3.7. BIER-TE Path Subobject in RRO
A BIER-TE Path Subobject in a RRO (Record Route Object) has the same
format as a BIER-TE Path subobject in a ERO except for L flag. The
former does not have L flag. The format of a BIER-TE Path Subobject
in a RRO is shown in the firgure below.
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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 = TBDa | Length | sub-domain-id | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitPositions |
: :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: BIER-TE Path Subobject in RRO
A PCC may send a PCE a message such as a PCRpt message defined in
[RFC8231]. The message contains a RRO with one BIER-TE Path
subobject having the BitPositions for the actual BIER-TE path that is
used to transport the traffic in the BIER-TE domain. The
BitPositions in the BIER-TE Path subobject for the BIER-TE path MUST
be in descending order.
4. Procedures
This section describes the procedures related to a BIER-TE path.
4.1. BIER-TE Path Creation
For PCC-Initiated BIER-TE path, a PCC MUST delegate the path by
sending a path computation report (PCRpt) message with its demanded
resources to a stateful PCE. Note the PCC MAY use the PCReq/PCRep
before delegating.
Upon receiving the delegation via PCRpt message, the stateful PCE
MUST compute a path based on the network resource availability stored
in the TED.
The stateful PCE will send a PCUpd message for the BIER-TE path to
the PCC. The stateful PCE MUST update its local LSP-DB and TED and
would need to synchronize the information with other PCEs in the
domain.
For PCE-Initiated BIER-TE path, the stateful PCE MUST compute a BIER-
TE path per request from network management systems or applications
automatically based on the network resource availability in the TED
and send a PCInitiate message with the path information to the PCC.
After receiving the PCInitiate message, the PCC creates the BIER-TE
path.
For both PCC-Initiated and PCE-Initiated BIER-TE paths:
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o The stateful PCE MUST update its local LSP-DB and TED with the
paths.
o Upon receiving the PCUpd message or PCInitiate message for the
path from the PCE with a found path, the PCC determines that it is
a BIER-TE path by the PST = TBD1 for path setup using BIER-TE in
the PATH-SETUP-TYPE TLV of the SRP object in the message.
4.2. BIER-TE Path Update
After a BIER-TE path is created in a BIER-TE domain, when some
network events such as a node failure happen on the path (called old
path) or a leaf/egress joins/leaves, the PCE computes a new BIER-TE
path and replaces the old path with the new path. The new path
satisfies the same constraints as the old path.
The PCE sends a PCUpd message to the PCC running on the ingress node.
The message contains the information about the new BIER-TE path.
After receiving the message, the PCC overwrites (or replaces) the
BIER-TE path with the new BIER-TE path.
4.3. BIER-TE Path Deletion
For a BIER-TE path that has been created in a BIER-TE domain, after
receiving a request for deleting the path from a user or application,
the PCE MUST send a PCInitiate or PCUpd message to the PCC running on
the ingress node of the path to remove the path.
5. The PCEP Messages
5.1. The PCRpt Message
The Path Computation State Report (PCRpt) message is a PCEP message
sent by a PCC to a PCE to report the status of one or more LSPs, as
per [RFC8281]. Each LSP State Report in a PCRpt message contains the
actual LSP's path, bandwidth, operational and administrative status,
etc. An LSP Status Report carried in a PCRpt message is also used in
delegation or revocation of control of an LSP to/from a PCE.
In the case of a BIER-TE path, a PATH-SETUP-TYPE TLV with PST = TBD1
for path setup using BIER-TE MUST be carried in the SRP object in the
PCRpt message. A BIER-TE path in the message is represented by a
BIER-TE path subobject.
In addition, a PCRpt message is sent from the PCC running on an edge
node to the PCE to report that the edge node as leaf/egress joins/
leaves to/from a multicast group and source.
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5.2. The PCUpd Message
The Path Computation Update Request (PCUpd) message is a PCEP message
sent by a PCE to a PCC to update LSP parameters on one or more LSPs,
as per [RFC8281]. In the case of a BIER-TE path, a PATH-SETUP-TYPE
TLV with PST = TBD1 for path setup using BIER-TE MUST be carried in
the SRP object in the PCUpd message. Each BIER-TE path Update
Request in a PCUpd message contains all parameters that a PCE wishes
to be set for a given BIER-TE path. A BIER-TE path in the message is
represented by a BIER-TE path subobject.
5.3. The PCInitiate Message
The LSP Initiate Request (PCInitiate) message is a PCEP message sent
by a PCE to a PCC to trigger LSP instantiation or deletion, as per
[RFC8281]. In the case of a BIER-TE path, a PATH-SETUP-TYPE TLV with
PST = TBD1 for path setup using BIER-TE MUST be carried in the SRP
object in the PCInitiate message. A BIER-TE path in the message is
represented by a BIER-TE path subobject. The multicast packets to be
transported by the BIER-TE path is specified by the Multicast Flow
Specification TLV included in the SRP object.
5.4. The PCReq Message
The Path Computation Request (PCReq) message is a PCEP message sent
by a PCC to a PCE to request a path computation [RFC5440], and it may
contain the LSP object [RFC8231] to identify the LSP for which the
path computation is requested. In the case of a BIER-TE path, a
PATH-SETUP-TYPE TLV with PST = TBD1 for path setup using BIER-TE MUST
be carried in the SRP object in the PCReq message.
In addition, a PCReq message is sent from the PCE (as a PCC) for the
BIER-TE domain to another PCE for the domain that may contain the
multicast source for a BIER-TE path in order to find an ingress node
for the BIER-TE path.
5.5. The PCRep Message
The Path Computation Reply (PCRep) message is a PCEP message sent by
a PCE to a PCC in reply to a path computation request [RFC5440], and
it may contain the LSP object [RFC8231] to identify the LSP for which
the path is computed. A PCRep message can contain either a set of
computed paths if the request can be satisfied or a negative reply if
not. A negative reply may indicate the reason why no path could be
found. In the case of a BIER-TE path, a PATH-SETUP-TYPE TLV with PST
= TBD1 for path setup using BIER-TE MUST be carried in the SRP object
in the PCRep message. Each of the computed paths in the message is
represented by a BIER-TE path subobject.
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In addition, a PCRep message is sent from the PCE for the domain that
may contain the multicast source for a BIER-TE path to the PCC (i.e.,
the PCE for the BIER-TE domain) in response to the request for
finding an ingress node for the BIER-TE path. A PCRep message can
contain either a set of ingress nodes represented by ingress node
objects if the request can be satisfied or a negative reply if not.
6. IANA Considerations
6.1. PST for BIER-TE Path
IANA is requested to allocate a new code point within registry "PCEP
Path Setup Types" under "Path Computation Element Protocol (PCEP)
Numbers" as follows:
+==========+=============================+=================+
| Value | Description | Reference |
+==========+=============================+=================+
| TBD1 (2) | Path is setup using BIER-TE | This document |
+----------+-----------------------------+-----------------+
6.2. PCE-BIER-TE-Path Capability sub-TLV
IANA is requested to allocate a new code point within registry "PATH-
SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators" under "Path
Computation Element Protocol (PCEP) Numbers" as follows:
+===========+=============================+=================+
| Value | Meaning | Reference |
+===========+=============================+=================+
| TBD2 (1) | PCE-BIER-TE-Path Capability | This document |
+-----------+-----------------------------+-----------------+
6.3. SRP Object Flag Field
IANA is requested to allocate the following bits in the "SRP Object
Flag Field" subregistry under the "Path Computation Element Protocol
(PCEP) Numbers" registry:
+=========+===============================+=================+
| Value | Description | Reference |
+=========+===============================+=================+
| 27-29 | Assistant Operations for Path | This document |
+---------+-------------------------------+-----------------+
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6.4. Ingress Node Object
IANA is requested to allocate the following Object-Class Value in the
"PCEP Objects" subregistry under the "Path Computation Element
Protocol (PCEP) Numbers" registry:
+==================+========+===============+=============+
|Object-Class Value|Name |Object-Type |Reference |
+==================+========+===============+=============+
| TBD (45) |INGRESS |0: Reserved |This document|
| | |1: IPv4 Address|This document|
| | |2: IPv6 Address|This document|
| | |3-15:Unassigned| |
+------------------+--------+---------------+-------------+
6.5. OF Code Points
IANA is requested to allocate the following Objective Function Code
Points in the "Objective Function" subregistry under the "Path
Computation Element Protocol (PCEP) Numbers" registry:
+============+=============================+=================+
| Code Point | Name | Reference |
+============+=============================+=================+
| TBD8 (18) | Minimum Bit Sets (MBS) | This document |
+------------+-----------------------------+-----------------+
| TBD9 (19) | Minimum Bit Distance (MBD) | This document |
+------------+-----------------------------+-----------------+
6.6. PCEP BIER-TE Path Subobjects
This document defines a new subobject, called PCE BIER-TE Path (or
BIER-TE-ERO) subobject, for PCEP ERO object. It also defines a new
subobject, called PCE BIER-TE Path (or BIER-TE-RRO) subobject, for
PCEP RRO object. The code points of the subobjects for the objects
are maintained under ERO and RRO objects in the RSVP Parameters
registry.
IANA is requested to allocate a code point under "Subobject type - 20
EXPLICIT_ROUTE - Type 1 Explicit Route" within registry "Resource
Reservation Protocol (RSVP) Parameters" for PCEP BIER-TE path
subobject as follows:
+===========+=============================+=================+
| Value | Name | Reference |
+===========+=============================+=================+
| TBDa (63) | PCEP BIER-TE Path | This document |
+-----------+-----------------------------+-----------------+
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IANA is requested to allocate a code point under "Subobject type - 21
ROUTE_RECORD - Type 1 Explicit Route" within registry "Resource
Reservation Protocol (RSVP) Parameters" for PCEP BIER-TE path
subobject as follows:
+===========+=============================+=================+
| Value | Name | Reference |
+===========+=============================+=================+
| TBDa (63) | PCEP BIER-TE Path | This document |
+-----------+-----------------------------+-----------------+
7. Security Considerations
TBD
8. Acknowledgements
The authors would like to thank Dhruv Dhody, and others for their
comments to this work.
9. References
9.1. Normative References
[I-D.ietf-bier-te-arch]
Eckert, T., Menth, M., and G. Cauchie, "Tree Engineering
for Bit Index Explicit Replication (BIER-TE)", draft-ietf-
bier-te-arch-12 (work in progress), January 2022.
[I-D.ietf-pce-pcep-flowspec]
Dhody, D., Farrel, A., and Z. Li, "Path Computation
Element Communication Protocol (PCEP) Extension for Flow
Specification", draft-ietf-pce-pcep-flowspec-13 (work in
progress), October 2021.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
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[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541,
DOI 10.17487/RFC5541, June 2009,
<https://www.rfc-editor.org/info/rfc5541>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
[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>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[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>.
[RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying Path Setup Type in PCE Communication
Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
July 2018, <https://www.rfc-editor.org/info/rfc8408>.
9.2. Informative References
[I-D.chen-pce-bier]
Chen, R., Zhang, Z., Chen, H., Dhanaraj, S., Qin, F., and
A. Wang, "PCEP Extensions for BIER-TE", draft-chen-pce-
bier-09 (work in progress), July 2021.
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[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA
USA
Email: Huaimo.chen@futurewei.com
Mike McBride
Futurewei
Email: michael.mcbride@futurewei.com
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring MD 20904
USA
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
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Yanhe Fan
Casa Systems
USA
Email: yfan@casa-systems.com
Lei Liu
Fujitsu
USA
Email: liulei.kddi@gmail.com
Xufeng Liu
Volta Networks
McLean, VA
USA
Email: xufeng.liu.ietf@gmail.com
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