PCE WG Quan Xiong
Internet-Draft Shuangping Zhan
Intended status: Standards Track ZTE Corporation
Expires: September 12, 2019 Fangwei Hu
Individual
March 11, 2019
PCEP extensions for SR-MPLS-TP
draft-xiong-pce-pcep-extension-sr-tp-03
Abstract
This document proposes a set of extensions to PCEP for Transport
Profile of SR-MPLS (SR-MPLS-TP) networks and defines a mechanism to
create the bi-directional SR tunnel with PCE.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. The SR-MPLS-TP Architecture with PCE . . . . . . . . . . . . 3
2.1. SR Path SID Allocation . . . . . . . . . . . . . . . . . 5
2.2. Associated Bi-directional SR tunnel . . . . . . . . . . . 6
3. PCEP extensions for SR-MPLS-TP . . . . . . . . . . . . . . . 7
3.1. ERO extension . . . . . . . . . . . . . . . . . . . . . . 8
3.2. E bit in LSP object . . . . . . . . . . . . . . . . . . . 9
3.3. Processing Rules . . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
7. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The Path Computation Element Communication Protocol (PCEP) defined in
[RFC5440] provides mechanisms for Path Computation Elements (PCEs) to
perform path computations in response to Path Computation Clients
(PCCs) requests.
[I-D.ietf-pce-segment-routing] proposes extensions to PCEP that allow
a stateful PCE to compute Traffic Engineering (TE) paths in segment
routing (SR) networks. But it is applicable to Multi-protocol Label
Switching (MPLS) networks refered as to SR-MPLS. In the context of
the Transport Profile of SR-MPLS, referred to in this document as SR-
MPLS-TP, a Path Segment uniquely identifies an SR path in a specific
context. It is required to extend the PCEP protocol to meet the new
requirements for SR-MPLS-TP services. One of the requirements is the
bidirectional SR tunnel described in
[I-D.ietf-spring-mpls-path-segment].
This document proposes a set of extensions to PCEP for SR-MPLS-TP
networks and defines a mechanism to create the bidirectional SR
tunnel with PCE.
1.1. 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 [RFC2119].
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1.2. Terminology
The terminology is defined as [RFC5440],
[I-D.ietf-pce-segment-routing] and
[I-D.ietf-spring-mpls-path-segment].
MPLS-TP: MPLS transport profile.
SR: Segment Routing.
SR-MPLS: Segment routing over MPLS data plane.
SR-MPLS-TP: Transport Profile of SR-MPLS.
2. The SR-MPLS-TP Architecture with PCE
As described in [I-D.ietf-spring-mpls-path-segment], in transport
networks, the centralized controller may calculate the end to end SR
paths, and creates the ordered segment list. The centralized
controller may be replaced to PCE as the Figure 1 shown. The PCE can
calculate the SR paths and a SR path can be initiated by PCE or PCC.
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|
|
V
+---+--+
+--------------+ PCE +---------------+
| +---+--+ |
+-------|-------------------------------------|--------+
| | SR network | |
| | | |
| +---+--+ +---+--+ +---+--+ |
| | A +-----------+ B +-----------+ C + |
| +------+ +------+ +------+ |
| |
+------------------------------------------------------+
Ingress Node: Egress Node:
Reverse Path Label Forward Path Label
(Incoming Label) (Outgoing Label)
SR Label Stacks:
+--------------------+ +--------------------+
| Label A | | Label C |
+--------------------+ +--------------------+
| ... | | ... |
+--------------------+ +--------------------+
| Label C | | Label A |
+--------------------+ +--------------------+
| Forward Path Label | | Reverse Path Label |
+--------------------+ +--------------------+
Figure 1 The SR-MPLS-TP Architecture with PCE
It is required to support bidirectional SR tunnel to meet the
requirement of SR-MPLS-TP networks. A label named path segment at
both ends of the paths was defined to identify the direction of the
SR paths as defined in [I-D.ietf-spring-mpls-path-segment]. It
mainly aims to bind two unidirectional SR paths to a single
bidirectional tunnel.
As the Figure 1 shown, the forward and reverse directions of the
bidirectional SR tunnel are identified by the forward and reverse
path label respectively. For the ingress node, the forward path
label shall be added to the bottom of the label stack and the reverse
path label shall be configured to the data plane as incoming label
for the SR LSP. And for the egress node, the reverse path label need
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to be the last one label of the label stack and the forward path
label shall be used as outgoing label.
2.1. SR Path SID Allocation
[RFC8402] defined the IGP, BGP, and Binding segments for the SR-MPLS
and SRv6 data planes which can be referred as to Segment Identifier
(SID). And [I-D.ietf-spring-mpls-path-segment] defined a new type of
segment named path segment. So the path segment can also be
identified by SID called SR path SID. The path segment may be
associated with a unidirectional path.
The path SID allocation includes ingress PCC allocated, egress PCC
allocated and PCE allocated in the domain. In case of egress PCC
allocated, the ingress PCC needs to comunicate with PCE to send path
segment request to egress PCC as the Figure 2 shown. When the
ingress PCC requests PCE to compute the SR path with PCReq message,
the PCE needs to request egress PCC to allocate the path SID with the
PCUpd or PCInit message carrying the Tunnel 1 and LSP 1. The egress
PCC needs to identify the allocation function from the initiation
message and should not return back PCErr message when checking the
local address is not equal with the source address of Tunnel 1. This
document defines E bit in section 3.2 carried in LSP object to
indicate the egress PCC operation which may not trigger the LSP
initiation.
When the path SID is allocated by ingress PCC, it need to inform PCE
with the PCRpt message and the latter one sends the notification to
egress PCC with PCUpd or PCInit message carried LSP object which set
the E bit to 1.
When the path SID is allocated by PCE, it need to inform ingress and
egress PCC with PCUpd or PCInit message carrying the Tunnel 1 and LSP
1. But the message sent to egress PCC MUST set the E bit to 1 to
avoid triggering the LSP initiation.
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+------+
| PCE |
+------+
PCReq ^ \ PCUpd/PCInit
Tunnel 1 / \ Tunnel 1
LSP1 / \ LSP1, E=1
/ v
+--------+ LSP1 +-------+
|Ingress |----------->|Egress |
|PCC |<-----------|PCC |
+--------+ LSP2 +-------+
Figure 2 The path SID allocation with PCE
2.2. Associated Bi-directional SR tunnel
As [RFC5654] defined, MPLS-TP MUST support unidirectional, co-routed
bidirectional, and associated bidirectional point-to-point transport
paths. As [RFC8402] defined, segment routing leverages the source
routing paradigm and the sourse node steers a packet through an
ordered segment list along a unidirectional path. So for
bidirectional SR tunnel, the forward and backward directional paths
may be setup by the source node and destination node seperately.
As described in [I-D.ietf-pce-association-bidir], two reverse
unidirectional LSPs can be associated as an associated bidirectional
tunnel which can be initialed by single-sided and double-sided
methods. Based on the discussion above, the associated bidirectional
SR tunnel can only be provisioned on both ingress and egress node
(PCCs).
The Single-sided initiation can be initiated by ingress SR node and
initiate two unidirectional LSPs to headend SR nodes as shown in
Figure 3. The Double-sided initiation can be initiated by PCCs or
PCE as shown in Figure 4 and 5 respectively. The forward and reverse
directional paths can be co-routed or non-corouted. The SR
bidirectional tunnel may follow the same path in the forward and
reverse directions and initiated as a co-routed associated
bidirectional LSP. When the PCE initiated the LSP, the B flag need
to be set to indicate a bi-directional LSP as defined in
[I-D.ietf-pce-pcep-stateful-pce-gmpls].
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+---------+
| PCE |
+---------+
1,PCReq ^ /2,PCInit\ 2,PCInit
Tunnel 1 / / Tunnel 1 \ Tunnel 1
/ / LSP1 \ LSP2
/ v v
+--------+ LSP1 +-------+
|Ingress |----------->|Egress |
|PCC |<-----------|PCC |
+--------+ LSP2 +-------+
Figure 3 PCC-initiated Single-sided Associated Bi-directional LSPs
+---------+
| PCE |
+---------+
1,PCReq ^ /2,PCInit \ ^ 1,PCReq
Tunnel 1 / / Tunnel 1 \ \ Tunnel 1
LSP1 / / LSP1/LSP2 \ \ LSP2
/ v v \
+--------+ LSP1 +-------+
|Ingress |----------->|Egress |
|PCC |<-----------|PCC |
+--------+ LSP2 +-------+
Figure 4 PCC-initiated Double-sided Associated Bi-directional LSPs
+---------+
| PCE |
+---------+
PCInit / \ PCInit
Tunnel 1 / \ Tunnel 1
LSP1 / \ LSP2
v v
+--------+ LSP1 +-------+
|Ingress |----------->|Egress |
|PCC |<-----------|PCC |
+--------+ LSP2 +-------+
Figure 5 PCE-initiated Double-sided Associated Bi-directional LSPs
3. PCEP extensions for SR-MPLS-TP
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3.1. ERO extension
As described in [I-D.ietf-spring-mpls-path-segment], it is required
to support bi-directional tunnel to meet the requirement of SR
networks. But it is the uni-directional tunnel for SR and
engineering traffic network as discussed in
[I-D.ietf-pce-segment-routing]. The SR path is carried in the
Segment Routing Explicit Route Object (SR-ERO), which consists of a
sequence of SR subobjects. This document proposes the extension of
the SR-ERO Subobject to carry the bi-directional tunnel information
as the Figure 6 shown. The subobjects with path SIDs need to be
added to the list of the SR-ERO subobjects.
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 | Length | NT | Flags |R|F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI(variable,optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 Extension of SR-ERO Subobject format
NAI Type (NT) : A new type of NT = 6 is added in this document and it
indicates the type and format of the NAI associated with the path SID
contained in the object body. When NT is set to 6, the format of NAI
field is shown as Figure 7.
R (Reverse Flag -- 1 bit): indicates the SR path direction, when it
is clear, it indicates the forward direction and when it is set, it
indicates the reverse direction.
The definition of other fields is the same with
[I-D.ietf-pce-segment-routing].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 NAI for Path Label information
The format of Path Label information is specified as
[I-D.ietf-spring-mpls-path-segment].
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3.2. E bit in LSP object
The LSP object is defined in [RFC8231]. This document proposes the E
bit in flag field of the LSP object as shown in Figure 8:
E (Egress PCC Operation bit): If the bit is set to 1, it indicates
that the egress PCC operation with PCUpd or PCInit message and no
need to trigger the LSP initiation. A PCE would set the bit to 1 in
SR network to request or inform the path SID information.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PLSP-ID | Flag |E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 The extension of LSP object
3.3. Processing Rules
As discussed in [I-D.ietf-spring-mpls-path-segment], the bi-
directional SR tunnel is created from two binding unidirectional SR
paths. As defined in [RFC8281], the stateful PCE calculates the SR
paths and initiates the bi-directional LSP with PCUpd or PCInit
message.
The B bit in SRP Object MUST be set and the two unidirectional SR
paths may be computed from the forward and reverse direction and sent
to the source and destination PCC respectively in SR-ERO object. The
path labels which binding the paths may be generated in PCE and sent
to the related PCC carried in the bottom of the SR-ERO. When the
PCCs at both ends receiving the PCInit message with the labels in SR-
ERO subobjects, they may forward the packets from bi-directional
tunnel in MPLS-TP networks.
4. Security Considerations
TBD.
5. IANA Considerations
TBD.
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6. Acknowledgements
TBD.
7. Normative References
[I-D.ietf-pce-association-bidir]
Barth, C., Gandhi, R., and B. Wen, "PCEP Extensions for
Associated Bidirectional Label Switched Paths (LSPs)",
draft-ietf-pce-association-bidir-02 (work in progress),
November 2018.
[I-D.ietf-pce-pcep-stateful-pce-gmpls]
Lee, Y., Zhang, F., Casellas, R., Dios, O., and Z. Ali,
"Path Computation Element (PCE) Protocol Extensions for
Stateful PCE Usage in GMPLS-controlled Networks", draft-
ietf-pce-pcep-stateful-pce-gmpls-10 (work in progress),
March 2019.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-16 (work in progress),
March 2019.
[I-D.ietf-spring-mpls-path-segment]
Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
"Path Segment in MPLS Based Segment Routing Network",
draft-ietf-spring-mpls-path-segment-00 (work in progress),
March 2019.
[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>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
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[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>.
[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>.
[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
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan, Hubei 430223
China
Phone: +86 27 83531060
Email: xiong.quan@zte.com.cn
Shuangping Zhan
ZTE Corporation
Liuxian Rd
Shenzhen 518057
China
Phone: +86 755 26773770
Email: zhan.shuangping@zte.com.cn
Fangwei Hu
Individual
Email: hufwei@gmail.com
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