PCEP extensions for Distribution of Link-State and TE InformationHuawei TechnologiesDivyashree Techno Park, WhitefieldBangaloreKarnataka560066Indiadhruv.ietf@gmail.comHuawei TechnologiesHuawei Bld., No.156 Beiqing Rd.Beijing100095Chinapengshuping@huawei.comSamsung ElectronicsSeoulSouth Koreayounglee.tx@gmail.comEricssonTorshamnsgatan,48StockholmSwedendaniele.ceccarelli@ericsson.com
Routing
PCE Working GroupIn order to compute and provide optimal paths, Path Computation
Elements (PCEs) require an accurate and timely Traffic Engineering
Database (TED). Traditionally this TED has been obtained from a link
state (LS) routing protocol supporting traffic engineering extensions.This document extends the Path Computation Element Communication
Protocol (PCEP) with Link-State and TE Information. 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 when, and only when, they
appear in all capitals, as shown here.
In Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS), a Traffic Engineering Database (TED) is used in computing
paths for connection oriented packet services and for circuits. The
TED contains all relevant information that a Path Computation
Element (PCE) needs to perform its computations. It is important
that the TED be 'complete and accurate' each time the PCE performs a
path computation.In MPLS and GMPLS, interior gateway routing protocols (Interior Gateway Protocol (IGPs)) have
been used to create and maintain a copy of the TED at each node
running the IGP. One of the benefits of the PCE architecture
is the use of computationally more sophisticated path
computation algorithms and the realization that these may need
enhanced processing power (not necessarily available at each node).Section 4.3 of describes the potential load of the TED on
a network node and proposes an architecture where the TED is
maintained by the PCE rather than the network nodes. However, it
does not describe how a PCE would obtain the information needed to
populate its TED. PCE may construct its TED by participating in the
IGP ( and for MPLS-TE; and
for GMPLS). An alternative mechanism is offered by BGP-LS . 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
IGP, but also the set of active paths and their reserved resources
for its computations. Path Computation Client (PCC) can delegate the rights to modify the LSP
parameters to an Active Stateful PCE. This requires PCE to quickly
be updated on any changes in the topology/TED, so that PCE can
meet the need for updating LSPs effectively and in a timely manner.
The fastest way for a PCE to be updated on TED changes is via a
direct session with each network node and with incremental update
from each network node with only the attributes that gets modified. describes the setup, maintenance and teardown of
PCE-initiated LSPs under the stateful PCE model, without the need
for local configuration on the PCC, thus allowing for a dynamic
network that is centrally controlled and deployed. This model
requires timely topology and TED update at the PCE. describes the specifications for the Path Computation
Element Communication Protocol (PCEP). PCEP specifies the
communication between a PCC and a PCE, or between two PCEs based on the PCE
architecture .This document describes a mechanism by which link-state and TE
information can be collected from networks and shared with PCE
using the PCEP itself. This is achieved using a new PCEP message format.
The mechanism is applicable to physical and virtual links as well as
further subjected to various policies.A network node maintains one or more databases for storing link-state
and TE information about nodes and links in any given area. Link attributes
stored in these databases include: local/remote IP addresses, local/remote interface identifiers, link metric and TE metric, link
bandwidth, reservable bandwidth, per CoS class reservation state,
preemption and Shared Risk Link Groups (SRLG). The node's PCEP
process can retrieve topology from these databases and distribute
it to a PCE, either directly or via another PCEP Speaker, using
the encoding specified in this document.Further describes Hierarchical-PCE architecture,
where a parent PCE maintains a domain
topology map. To build this domain topology map, the child PCE can carry
the border nodes and inter-domain link information to the parent PCE using
the mechanism described in this document. Further as described in
, the
child PCE can also transport abstract Link-State and
TE information from child PCE to a Parent PCE using the mechanism
described in this document to build an abstract topology at the parent PCE. describe LSP
state synchronization between PCCs and PCEs in case of stateful PCE. This
document does not make any change to the LSP state synchronization process.
The mechanism described in this document are on top of the existing LSP
state synchronization.The terminology is as per and .The
mechanism specified in this draft is applicable to deployments:
Where there is no IGP or BGP-LS running in the network. Where there is no IGP or BGP-LS running at the PCE to learn link-state and TE information. Where there is IGP or BGP-LS running but with a need for a faster and direct TE and link-state population and convergence at the PCE.
A PCE may receive partial information (say basic TE, link-state) from IGP and other information (optical and impairment) from PCEP.A PCE may receive an incremental update (as opposed to the full (entire) information of the node/link).A PCE may receive full information from both existing mechanism (IGP or BGP-LS) and PCEP.Where there is a need for transporting (abstract) Link-State
and TE information from child PCE to a Parent PCE in H-PCE ;
as well as for Provisioning Network Controller (PNC) to Multi-Domain Service Coordinator
(MDSC) in Abstraction and Control of TE Networks (ACTN) .
Where there is an existing PCEP session between all the nodes and the PCE-based central controller (PCECC) , and the operator would like to use PCEP as a direct south bound interface to all the nodes in the network. This enables operator to use PCEP as single direct protocol between the controller and all the nodes in the network. In this mode all nodes send only the local information.Based on the local policy and deployment scenario, a PCC chooses to send only local information or both local and remote learned information. How a PCE manages the link-state (and TE) information is implementation specific and thus out of scope of this document.The prefix information in PCEP-LS can also help in determining the domain of the tunnel destination in the H-PCE (and ACTN) scenario.
Section 4.5 of describe various mechanisms and procedures that might be used, PCEP-LS provides a simple mechanism
to exchange this information within PCEP. defines three types of
topology abstraction - (1) Native/White Topology; (2) Black Topology;
and (3) Grey Topology. Based on the local policy, the PNC (or child PCE) would share the domain topology to the MDSC (or Parent PCE)
based on the abstraction type. The protocol extensions defined in this document can carry any type of topology abstraction.Following key requirements associated with link-state (and TE) distribution are identified for PCEP:
The PCEP speaker supporting this draft MUST have a mechanism to advertise the Link-State (and TE) distribution capability.PCC supporting this draft MUST have the capability to report the link-state (and TE) information to
the PCE. This MUST include self originated (local) information and also allow remote information
learned via routing protocols. PCC MUST be capable to do the initial bulk sync at
the time of session initialization as well as changes after.A PCE MAY learn link-state (and TE) from PCEP as well as from existing mechanisms like
IGP/BGP-LS. PCEP extensions MUST have a mechanism to link the information
learned via other means. There MUST NOT be any changes to the existing link-state (and TE)
population mechanism
via IGP/BGP-LS. PCEP extension SHOULD keep the properties in a
protocol (IGP or BGP-LS) neutral way, such that an implementation
may not need to know about any OSPF or IS-IS or BGP protocol specifics.It SHOULD be possible to encode only the changes in link-state (and TE) properties
(after the initial sync) in PCEP messages. This leads to faster convergence. The same mechanism SHOULD be used for both MPLS TE as well as GMPLS,
optical and impairment aware properties.The same mechanism SHOULD be used for PCE to PCE Link-state (and TE) synchronization.Several new functions are required in PCEP to support distribution
of link-state (and TE) information. A function can be initiated
either from a PCC towards a PCE (C-E) or from a PCE towards a PCC (E-C).
The new functions are:
Capability advertisement (E-C,C-E): both the PCC and the PCE MUST announce during PCEP session establishment that they support PCEP extensions for distribution of link-state (and TE) information defined in this document.Link-State (and TE) synchronization (C-E): after the session between the PCC and a PCE is initialized, the PCE must learn Link-State (and TE) information before it can perform path computations. In case of stateful PCE it is RECOMMENDED that this operation be done before LSP state synchronization.Link-State (and TE) Report (C-E): a PCC sends a LS (and TE) report to a PCE whenever the Link-State and TE information changes.In this document, we define a new PCEP message called LS Report (LSRpt),
a PCEP message sent by a PCC
to a PCE to report link-state (and TE) information. Each LS Report in a LSRpt message can contain
the node or link properties. An unique PCEP specific LS identifier (LS-ID) is
also carried in the message to identify a node or link and that remains constant for the
lifetime of a PCEP session. This identifier on its own is sufficient
when no IGP or BGP-LS running in the network for PCE to learn link-state (and TE) information.
In case PCE learns some information from PCEP and some
from the existing mechanism, the PCC SHOULD include the mapping of IGP or BGP-LS
identifier to map the information populated via PCEP with IGP/BGP-LS.
See for details.During PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
advertise their support of LS (and TE) distribution via PCEP extensions. A PCEP Speaker
includes the "LS Capability" TLV, described in ,
in the OPEN Object to advertise its support for PCEP-LS extensions.
The presence of the LS Capability TLV in PCC's OPEN Object
indicates that the PCC is willing to send LS Reports with
local link-state (and TE) information. The presence of the
LS Capability TLV in PCE's Open message
indicates that the PCE is interested in receiving LS Reports
with local link-state (and TE) information.The PCEP extensions for LS (and TE) distribution MUST NOT be used if
one or both PCEP Speakers have not included the LS
Capability TLV in their respective OPEN message. If the PCE that
supports the extensions of this draft but did not advertise this
capability, then upon receipt of a LSRpt message from the PCC, it
SHOULD generate a PCErr with error-type 19 (Invalid Operation),
error-value TBD1 (Attempted LS Report if LS
capability was not advertised) and it will
terminate the PCEP session.The LS reports sent by PCC MAY carry the remote link-state (and TE) information
learned via existing means like IGP and BGP-LS
only if both PCEP Speakers set the R (remote) Flag in the
"LS Capability" TLV to 'Remote Allowed (R Flag = 1)'. If this
is not the case and LS reports carry remote link-state (and TE) information, then a
PCErr with error-type 19 (Invalid Operation) and
error-value TBD1 (Attempted LS Report if LS
remote capability was not advertised) and it will
terminate the PCEP session.The purpose of LS Synchronization is to provide a checkpoint-in-time state replica of a PCC's link-state (and TE) database in a PCE. State
Synchronization is performed immediately after the Initialization
phase (see ). In case of stateful PCE
()
it is RECOMMENDED that the LS synchronization should be done
before LSP state synchronization.During LS Synchronization, a PCC first takes a snapshot of the
state of its database, then sends the snapshot to a PCE in a
sequence of LS Reports. Each LS Report sent during
LS Synchronization has the SYNC Flag in the LS Object set to 1.
The end of synchronization marker is a LSRpt message with the SYNC
Flag set to 0 for an LS Object with LS-ID equal to the reserved
value 0. If the
PCC has no link-state to synchronize, it will only send the end of
synchronization marker.Either the PCE or the PCC MAY terminate the session using the PCEP
session termination procedures during the synchronization phase. If
the session is terminated, the PCE MUST clean up state it received
from this PCC. The session re-establishment MUST be re-attempted per
the procedures defined in , including use of a back-off
timer.If the PCC encounters a problem which prevents it from completing the
LS synchronization, it MUST send a PCErr message with error-type TBD2 (LS
Synchronization Error) and error-value 2 (indicating an
internal PCC error) to the PCE and terminate the session.The PCE does not send positive acknowledgments for properly received
LS synchronization messages. It MUST respond with a PCErr message with
error-type TBD2 (LS Synchronization Error) and error-value 1
(indicating an error in processing the LSRpt) if it
encounters a problem with the LS Report it received from the
PCC and it MUST terminate the session.The LS reports can carry local as well as remote link-state (and TE) information depending on the R flag in LS capability
TLV.The successful LS Synchronization sequence is shown in .| (Sync start)
| |
|-----LSRpt, SYNC=1----->|
| . |
| . |
| . |
|-----LSRpt, SYNC=1----->|
| . |
| . |
| . |
| |
|-----LSRpt, SYNC=0----->| (End of sync marker
| | LS Report
| | for LS-ID=0)
| | (Sync done)
]]>The sequence where the PCE fails during the LS Synchronization
phase is shown in .|
| |
|-----LSRpt, SYNC=1----->|
| . |
| . |
| . |
|-----LSRpt, SYNC=1----->|
| |
|---LSRpt,SYNC=1 |
| \ ,-PCErr---|
| \ / |
| \/ |
| /\ |
| / `-------->| (Ignored)
|<--------` |
]]>The sequence where the PCC fails during the LS Synchronization
phase is shown in .|
| |
|-----LSRpt, SYNC=1----->|
| . |
| . |
| . |
|-------- PCErr--------->|
| |
]]>These optimizations are described in .The PCC MUST report any changes in the link-state (and TE) information to the PCE by sending a
LS Report carried on a LSRpt message to the PCE.
Each node and Link would be uniquely identified by a
PCEP LS identifier (LS-ID). The LS reports may carry local as well as
remote link-state (and TE) information depending on the R flag in LS capability
TLV.
In case R flag is set, it MAY also include the mapping of IGP or BGP-LS
identifier to map the information populated via PCEP with IGP/BGP-LS identifiers.More details about LSRpt message are in .A permanent PCEP session (section 4.2.8 of ) MUST be established between a PCE
and PCC supporting link-state (and TE) distribution via PCEP. In the case of session failure,
session re-establishment
is re-attempted as per the procedures defined in
.As defined in , a PCEP message consists of a common header
followed by a variable-length body made of a set of objects that can
be either mandatory or optional. An object is said to be mandatory
in a PCEP message when the object must be included for the message to
be considered valid. For each PCEP message type, a set of rules is
defined that specify the set of objects that the message can carry.
An implementation MUST form the PCEP messages using the object
ordering specified in this document.A PCEP LS Report message (also referred to as
LSRpt message) is a PCEP message sent by a PCC to a PCE to report the
link-state (and TE) information. A LSRpt message can carry more than one LS
Reports (LS object). The Message-Type field of the PCEP common header
for the LSRpt message is set to [TBD3].The format of the LSRpt message is as follows: ::=
Where:
::= []
]]>The LS object is a mandatory object which carries LS information of
a node/prefix or a link. Each LS object has an unique LS-ID as described
in . If the LS
object is missing, the receiving PCE MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=[TBD4] (LS
object missing).A PCE may choose to implement a limit on the LS information a single PCC
can populate. If a LSRpt is received that causes the PCE to exceed
this limit, it MUST send a PCErr message with error-type 19 (invalid
operation) and error-value 4 (indicating resource limit exceeded) in
response to the LSRpt message triggering this condition and SHOULD
terminate the session.If a PCEP speaker has advertised the LS capability on the PCEP
session, the PCErr message MAY include the LS object. If the error
reported is the result of an LS report, then the LS-ID
number MUST be the one from the LSRpt that triggered the error.The format of a PCErr message from is
extended as follows: ::=
( [] ) |
[]
::=[]
::=[ | ]
::=The PCEP objects defined in this document are compliant with the PCEP
object format defined in . The P flag and the I flag of the
PCEP objects defined in this document MUST always be set to 0 on
transmission and MUST be ignored on receipt since these flags are
exclusively related to path computation requests.The TLV and the sub-TLV format (and padding) in this document, is as per section 7.1 of . This document defines a new optional TLV for use in the OPEN
Object.The LS-CAPABILITY TLV is an optional TLV for use in the
OPEN Object for link-state (and TE) distribution via PCEP capability
advertisement. Its format is shown in the following figure:The type of the TLV is [TBD5] and it has a fixed length of 4 octets.The value comprises a single field - Flags (32 bits):
R (remote allowed - 1 bit): if set to 1 by a PCC, the R Flag
indicates that the PCC allows reporting of remote LS information
learned via other means like IGP and BGP-LS; if
set to 1 by a PCE, the R Flag indicates that the PCE is capable of
receiving remote LS information (from the PCC point of view).
The R Flag must be
advertised by both PCC and PCE for LSRpt messages to report
remote as well as local LS information on a PCEP session. The
TLVs related to IGP/BGP-LS identifier MUST be encoded when
both PCEP speakers have the R Flag set.Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.Advertisement of the LS capability implies support of local link-state (and TE)
distribution, as well as the objects, TLVs and
procedures defined in this document.The LS (link-state) object MUST be carried
within LSRpt messages and MAY be carried within PCErr
messages. The LS object contains a set of fields used to specify
the target node or link. It also
contains a flag indicating to a PCE that the LS
synchronization is in progress. The TLVs used with the LS object
correlate with the IGP/BGP-LS encodings.LS Object-Class is TBD6.Four Object-Type values are defined for the LS object so far:
LS Node: LS Object-Type is 1. LS Link: LS Object-Type is 2.LS IPv4 Topology Prefix: LS Object-Type is 3.LS IPv6 Topology Prefix: LS Object-Type is 4.The format of all types of LS object is as follows:Protocol-ID (8-bit): The field provides the source information.
The protocol could be an IGP, BGP-LS or an abstraction algorithm.
In case PCC only provides local information of the PCC,
it MUST use Protocol-ID
as Direct. The following values are defined (some of the initial values are same as
):Flags (24-bit):
S (SYNC - 1 bit): the S Flag MUST be set to 1 on each LSRpt sent
from a PCC during LS Synchronization. The S Flag MUST be set
to 0 in other LSRpt messages sent from the PCC.R (Remove - 1 bit): On LSRpt messages the R Flag indicates that the
node/link/prefix has been removed from the PCC and the PCE SHOULD remove
from its database. Upon receiving an LS Report with
the R Flag set to 1, the PCE SHOULD
remove all state for the node/link/prefix identified by the LS Identifiers
from its database.LS-ID(64-bit): A PCEP-specific identifier for the node or
link or prefix information. A PCC creates an unique LS-ID for
each node/link/prefix that is
constant for the lifetime of a PCEP session. The PCC will
advertise the same LS-ID on all PCEP sessions it maintains at a
given time. All
subsequent PCEP messages then address the node/link/prefix by the LS-ID.
The
values of 0 and 0xFFFFFFFFFFFFFFFF are reserved.Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.TLVs that may be included in the LS Object are described in the
following sections.In case of remote link-state (and TE) population when existing IGP/BGP-LS are
also used, OSPF and IS-IS may run multiple routing protocol instances over
the same link as described in .
See and for more information.
These instances define
independent "routing universe". The 64-bit 'Identifier' field is
used to identify the "routing universe" where the LS object belongs.
The
LS objects representing IGP objects (nodes or links or prefix) from the
same routing universe MUST have the same 'Identifier' value; LS objects
with different 'Identifier' values MUST be considered to be from
different routing universes. The format of the optional ROUTING-UNIVERSE TLV is shown in the following
figure:Below table lists the 'Identifier'
values that are defined as well-known in this draft (same as
).If this TLV is not present the default value 0 is assumed.To allow identification of VPN link, node and prefix information
in PCEP-LS, a Route Distinguisher (RD) is used.
The
LS objects from the
same VPN MUST have the same RD; LS objects
with different RD values MUST be considered to be from
different VPNs. The ROUTE-DISTINGUISHER TLV is defined in as a Flow Specification TLVs with a seperate registry. This
document also adds the ROUTE-DISTINGUISHER TLV with TBD15 in the PCEP TLV registry to be used inside the LS object.To realize ACTN, the MDSC needs to build an multi-domain topology.
This topology is best served, if this is an abstracted view of the
underlying network resources of each domain. It is also important
to provide a customer view of network slice for each customer.
There is a need to control the level of abstraction based on
the deployment scenario and business relationship between the controllers.
Virtual service coordination function in ACTN incorporates customer
service-related knowledge into the virtual network operations in
order to seamlessly operate virtual networks while meeting customer's
service requirements. describes various VN operations
initiated by a customer/application. In this context, there is a
need for associating the abstracted link-state and TE topology with a VN "construct" to
facilitate VN operations in PCE architecture.VIRTUAL-NETWORK-TLV as per
can be included in LS object to identify the link, node and prefix information
belongs to a particular VN.As described in ,
each link is anchored by a pair of Router-IDs that are used by the
underlying IGP, namely, 48-bit ISO System-ID for IS-IS and 32 bit
Router-ID for OSPFv2 and OSPFv3. In case of additional auxiliary
Router-IDs used for TE, these MUST also be included in the link
attribute TLV (see ).It is desirable that the Router-ID assignments inside the Node
Descriptor are globally unique. Some considerations for globally
unique Node/Link/Prefix identifiers are described in
.The Local Node Descriptors TLV contains Node Descriptors for the node
anchoring the local end of the link. This TLV MUST be included in the LS Report
when during a given PCEP session a node/link/prefix is first reported to a PCE.
A PCC sends to a PCE the first LS Report either during State
Synchronization, or when a new node/link/prefix is learned at the PCC.
The value
contains one or more Node Descriptor Sub-TLVs, which
allows specification of a flexible key for any given node/link/prefix
information such that global uniqueness of the node/link/prefix is ensured.This TLV is applicable for all LS Object-Type.The value contains
one or more Node Descriptor Sub-TLVs defined in
.The Remote Node Descriptors contains Node Descriptors for the node
anchoring the remote end of the link. This TLV MUST be included in the LS Report
when during a given PCEP session a link is first reported to a PCE.
A PCC sends to a PCE the first LS Report either during State
Synchronization, or when a new link is learned at the PCC. The length of this TLV is
variable. The value contains
one or more Node Descriptor Sub-TLVs defined in .This TLV is applicable for LS Link Object-Type.The Node Descriptors TLV (Local and Remote) carries one or more Node Descriptor Sub-TLV follows the format of all PCEP TLVs as defined
in , however, the Type values are selected from a new PCEP-LS sub-TLV IANA registry (see ).Type values are chosen so that there can be commonality with BGP-LS . This is possible because the "BGP-LS Node Descriptor, Link
Descriptor, Prefix Descriptor, and Attribute TLVs" registry marks
0-255 as reserved. Thus the space of the sub-TLV values for the Type
field can be partitioned as shown below -
Range |
---------------+---------------------------------------------
0 | Reserved - must not be allocated.
|
1 .. 255 | New PCEP sub-TLV allocated according to the
| registry defined in this document.
|
256 .. 65535 | Per BGP registry defined by
| [I-D.ietf-idr-rfc7752bis].
| Not to be allocated in this registry.
All Node Descriptors TLVs defined for BGP-LS can then be used with PCEP-LS as well. One new PCEP sub-TLVs for Node Descriptor are defined in this document.A new sub-TLV type (1) is allocated for SPEAKER-ENTITY-ID sub-TLV. The length and value field are as per .The Link Descriptors TLV contains Link Descriptors for each link.
This TLV MUST be included in the LS Report
when during a given PCEP session a link is first reported to a PCE.
A PCC sends to a PCE the first LS Report either during State
Synchronization, or when a new link is learned at the PCC. The length of this
TLV is variable. The value contains one or more Link Descriptor Sub-TLVs.The 'Link descriptor' TLVs uniquely identify a link among
multiple parallel
links between a pair of anchor routers similar to
. This TLV is applicable for LS Link Object-Type.All Link Descriptors TLVs defined for BGP-LS can then be used with PCEP-LS as well. No new PCEP sub-TLVs for Link Descriptor are defined in this document.The format and semantics of the 'value' fields in most 'Link
Descriptor' sub-TLVs correspond to the format and semantics of value
fields in IS-IS Extended IS Reachability sub-TLVs, defined in
, and . Although the encodings for 'Link
Descriptor' TLVs were originally defined for IS-IS, the TLVs can
carry data sourced either by IS-IS or OSPF or direct.The information about a link present in the LSA/LSP originated by the
local node of the link determines the set of sub-TLVs in the Link
Descriptor of the link as described in
.The Prefix Descriptors TLV contains Prefix Descriptors uniquely identify an IPv4 or IPv6
Prefix originated by a Node. This TLV MUST be included in the LS Report
when during a given PCEP session a prefix is first reported to a PCE.
A PCC sends to a PCE the first LS Report either during State
Synchronization, or when a new prefix is learned at the PCC. The length of this TLV is
variable. This TLV is applicable for LS Prefix Object-Types for both IPv4 and IPv6.All Prefix Descriptors TLVs defined for BGP-LS can then be used with PCEP-LS as well. No new PCEP sub-TLVs for Prefix Descriptor are defined in this document.This is an optional attribute that is used to
carry node attributes. This TLV is applicable for LS Node Object-Type.All Node Attributes TLVs defined for BGP-LS can then be used with PCEP-LS as well. No new PCEP sub-TLVs for Node Attributes are defined in this document.This TLV is applicable for LS Link Object-Type. The format
and semantics of the 'value' fields in some 'Link Attribute' sub-TLVs
correspond to the format and semantics of the 'value' fields in IS-IS
Extended IS Reachability sub-TLVs, defined in ,
and .
Although the encodings for 'Link Attribute' TLVs were originally
defined for IS-IS, the TLVs can carry data sourced either by IS-IS or
OSPF or direct.All Link Attributes TLVs defined for BGP-LS can then be used with PCEP-LS as well. No new PCEP sub-TLVs for Link Attributes are defined in this document.This TLV is applicable for LS Prefix Object-Types for both IPv4 and IPv6.
Prefixes are learned from the IGP (IS-IS or OSPF) or BGP topology with a set
of IGP attributes (such as metric, route tags, etc.). This section describes the
different attributes related to the IPv4/IPv6 prefixes. Prefix
Attributes TLVs SHOULD be encoded in the LS Prefix Object.All Prefix Attributes TLVs defined for BGP-LS can then be used with PCEP-LS as well. No new PCEP sub-TLVs for Prefix Attributes are defined in this document.One of the key objective of PCEP-LS is to encode
and carry only the impacted attributes of a Node, a Link or a Prefix.
To accommodate this requirement, in case of a removal of an attribute,
the sub-TLV MUST be included with no 'value' field and length=0
to indicate that the attribute is removed. On receiving a sub-TLV
with zero length, the receiver removes the attribute from the database. An absence of a sub-TLV that was included earlier MUST be interpreted as no change.The main source of LS (and TE) information is the IGP, which is not active on
inter-AS links. In some cases, the IGP may have information of
inter-AS links (, ). In other cases, an
implementation SHOULD provide a means to inject inter-AS links into
PCEP. The exact mechanism used to provision the inter-AS links is
outside the scope of this document.This document extends PCEP for LS (and TE) distribution including a new
LSRpt message with a new object and TLVs. Procedures and protocol extensions
defined in this document do not effect the overall PCEP security model.
See , .
Tampering with the LSRpt message
may have an effect on path computations at PCE. It also provides adversaries
an opportunity to eavesdrop and learn sensitive information and plan
sophisticated attacks on the network infrastructure. The PCE implementation
SHOULD provide mechanisms to prevent strains created by network flaps and
amount of LS (and TE) information. Thus it is suggested
that any mechanism used for securing the transmission of other PCEP
message be applied here as well. As a general precaution, it is
RECOMMENDED that these PCEP extensions only be activated on
authenticated and encrypted sessions belonging to the same
administrative authority.Further, as stated in , PCEP implementations SHOULD support the
TCP-AO and not use TCP MD5 because of TCP MD5's known
vulnerabilities and weakness. PCEP also support Transport Layer Security (TLS)
as per the recommendations and best current practices
in .All manageability requirements and considerations listed in
apply to PCEP protocol extensions defined in this document. In
addition, requirements and considerations listed in this section
apply.A PCE or PCC implementation MUST allow configuring the PCEP-LS
capabilities as described in this document.A PCC implementation SHOULD allow configuration to suggest if
remote information learned via routing protocols should be reported or not.An implementation SHOULD allow the operator to specify the maximum
number of LS data to be reported.An implementation SHOULD also allow the operator to create abstracted
topologies that are reported to the peers and create different
abstractions for different peers.An implementation SHOULD allow the operator to configure a 64-bit
identifier for Routing Universe TLV.An implementation SHOULD allow the operator to view the LS
capabilities advertised by each peer. To serve this purpose, the PCEP YANG module
can be extended to include advertised
capabilities.An implementation SHOULD also provide the statistics:
Total number of LSRpt sent/received, as well as per neighbourNumber of errors received for LSRpt, per neighbourTotal number of locally originated Link-State InformationThese statistics should be recorded as absolute counts since system
or session start time. An implementation MAY also enhance this
information by recording peak per-second counts in each case.An operator SHOULD define an import policy to limit inbound LSRpt
to "drop all LSRpt from a particular peers" as well provide means to
limit inbound LSRpts.Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in ".
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
. Mechanisms defined in this document do not imply any new requirements
on other protocols.Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in . This document requests IANA actions to allocate code points for the
protocol elements defined in this document.IANA created a registry for "PCEP Messages". Each PCEP message has a
message type value. This document defines a new PCEP message value.This document defines the following new PCEP Object-classes and
Object-values:This document requests that a new sub-registry, named "LS Object
Protocol-ID Field", is created within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the Flag field of the LSP
object. New values are to be assigned by Standards Action .
Further, this document also requests that a new sub-registry, named "LS Object
Flag Field", is created within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the Flag field of the LSP
object.New values are to be assigned by Standards Action .
Each bit should be tracked with the following qualities:
Bit number (counting from bit 0 as the most significant bit)Capability descriptionDefining RFCThe following values are defined in this document:IANA is requested to make the following allocation in the "PCEP-ERROR
Object Error Types and Values" registry.This document defines the following new PCEP TLVs.This document specifies the PCEP-LS Sub-TLVs. IANA
is requested to create an "PCEP-LS Sub-TLV Types"
sub-registry for the sub-TLVs
carried in the PCEP-LS TLV (Local and Remote Node Descriptors TLV,
Link Descriptors TLV, Prefix Descriptors TLV, Node Attributes TLV,
Link Attributes TLV and Prefix Attributes TLV. Allocations from this registry are to be made according to the following assignment policies :IANA is requested to pre-populate this registry with values defined in this
document as follows, taking the new values from the range 1 to 251:This section contains the global table of all TLVs in LS object defined
in this document.The PCEP-LS protocol extensions as described in this I-D
were implemented and tested for a variety of applications. Apart from the below implementation, there exist other experimental implementations done for optical networks.The PCEP-LS has been implemented as part of IETF97 Hackathon and Bits-N-Bites demonstration. The use-case demonstrated was DCI use-case of ACTN architecture in which to show the following scenarios:
- connectivity services on the ACTN based recursive hierarchical SDN/PCE platform that has the three tier level SDN controllers (two-tier level MDSC and PNC) on the top of the PTN systems managed by EMS. - Integration test of two tier-level MDSC: The SBI of the low level MDSC is the YANG based Korean national standards and the one of the high level MDSC the PCEP-LS based ACTN protocols.- Performance test of three types of SDN controller based recovery schemes including protection, reactive and proactive restoration. PCEP-LS protocol was used to demonstrate quick report of failed network components. Huawei (PNC, MDSC) and SKT (MDSC) implemented PCEP-LS during Hackathon and IETF97 Bits-N-Bites demonstration. The demonstration was ONOS-based ACTN architecture in which to show the following
capabilities:
Both packet PNC and optical PNC (with optical PCEP-LS extensions) implemented PCEP-LS on its SBI as well as its NBI (towards MDSC).SKT orchestrator (acting as MDSC) also supported PCEP-LS (as well as RestConf) towards packet and optical PNCs on its SBI.Further description can be found at
and the code at .This document borrows some of the structure and text from the
.
Thanks to Eric Wu, Venugopal Kondreddy, Mahendra Singh Negi,
Avantika, and Zhengbin Li for the reviews.Thanks to Ramon Casellas for his comments and suggestions based on his implementation experience.These examples are for illustration purposes only to show how the new
PCEP-LS message could be encoded. They are not meant to be an exhaustive
list of all possible use cases and combinations.Each node (PCC) in the network chooses to provide its own local node
and link information, and in this way PCE can build the full link-state and
TE information.A designated node(s) in the network will provide its own local node as well as
all learned remote information, and in this way PCE can build the full link-state and
TE information.As described in , the same LS Node and Link objects will be
generated with a difference that it would be a designated router say RTA that generate all
this information.As per Hierarchical-PCE , Parent PCE
builds an abstract domain topology map with each domain as an abstract node
and inter-domain links as an abstract link. Each child PCE may provide
this information to the parent PCE. Considering the example in
figure 1 of , following LS object
will be generated:Further the exact border nodes and abstract internal path between
the border nodes may also be transported to the Parent PCE to enable
ACTN as described in
using the similar LS node and link objects encodings.