| Network Working Group | F. Zhang, Ed. |
| Internet-Draft | Q. Zhao |
| Intended status: Standards Track | Huawei |
| Expires: January 15, 2013 | O. Gonzalez de Dios, Ed. |
| Telefónica I+D | |
| R. Casellas | |
| CTTC | |
| D. King | |
| Old Dog Consulting | |
| July 16, 2012 |
Extensions to Path Computation Element Communication Protocol (PCEP) for Hierarchical Path Computation Elements (PCE)
draft-zhang-pce-hierarchy-extensions-02
The Hierarchical Path Computation Element (H-PCE) architecture, defined in the companion framework document [I-D.ietf-pce-hierarchy-fwk], facilitates to obtain optimum end-to-end, multi-domain paths when the sequence of domains is not known in advance. Such H-PCE architecture allows the selection of an optimum domain sequence and, through the use of a hierarchical relationship between domains, derive the optimum end-to-end path.
This document defines the Path Computation Element Protocol (PCEP) extensions for the purpose of implementing Hierarchical PCE procedures which are described the aforementioned document.
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[I-D.ietf-pce-hierarchy-fwk] describes a Hierarchical PCE (H-PCE) architecture which can be used for computing end-to-end paths for inter-domain MPLS Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs). In the hierarchical PCE architecture, the parent PCE can compute a multi-domain path based on the domain connectivity information and each child PCE is able to compute the intra-domain path based on its domain topology information. The end-to-end domain path computing procedures can be abstracted as follows:
Alternatively, the parent PCE, instead of building the complete end-to-end path, can reply with the sequence of domains and later standard procedures, like BRPC, can be applied.
This document defines the PCEP extensions for the purpose of implementing Hierarchical PCE procedures, which are described in [I-D.ietf-pce-hierarchy-fwk].
The document also uses a number of editor notes to describe options and alternative solutions. These options and notes will be removed before publication once agreement is reached.
This document uses the terminology defined in [RFC4655], [RFC5440] and the additional terms defined in section 1.4 of [I-D.ietf-pce-hierarchy-fwk].
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].
This section compiles the set of requirements of the extensions needed in the PCEP protocol to support the H-PCE archicture and procedures.
The PCReq messages are used by a PCC or PCE to make a path computation request to a PCE. In order the achieve the full functionality of the H-PCE procedures, some extensions are needed in the pcReq messages:
As described in section 5.8.1 of [I-D.ietf-pce-hierarchy-fwk], the H-PCE architecture will introduce new request qualifications as follows:
To meet the above requirements, the PCEP PCReq message should be extended.
For inter-domain path computation, there are two new objective functions which are defined in section 1.3.1 and 5.1 of [I-D.ietf-pce-hierarchy-fwk]:
During the PCEP session establishment procedure, the parent PCE needs to be capable of indicating the objective functions (OF) capability in the Open message. This information can be, in turn, announced by child PCEs and used for selecting the PCE when a PCC want a path that satisfies a certain inter-domain objective function.
When a PCC requests a PCE to compute an inter-domain path, the PCC needs also to be capable of indicating the new objective functions for inter-domain path. Note that a given PCE may act as a regular PCE and as a parent PCE.
For the reasons described above, new OF codes need to be defined for the new inter-domain objective functions. Then the PCE can notify its new inter-domain objective functions to the PCC by carrying them in the OF-list TLV which is carried in the OPEN object. The PCC can specify which objective function code to use, which is carried in the OF object when requesting a PCE to compute an inter-domain path.
The proposed solutions may need to differentiate between the OF code that is requested at the parent level and the OF code that is requested at the intra-domain (child) level.
A parent PCE needs to be able to insure homogeneity when applying OF codes for the intra-domain requests.
For inter-domain path computation, there are several path metrics of interest [Editor's note: Current framework only mentions metric objectives. The metric itself should be also defined]:
A PCC may be able to limit the number of domains crossed by applying a limit on the metric.
A parent PCE maintains a domain topology map of the child domains and their interconnectivity, as mentioned in section 4.4 of [I-D.ietf-pce-hierarchy-fwk]. Consequently, a parent PCE maintains a Traffic Engineering Database (TED) for the parent domain.
The parent PCE TED may be administratively configured or learnt from information received from the child PCEs. Thus, entities from the child domains (such as the child PCEs) can convey its neighbour information to the parent PCE to maintain the parent TED. One possible option is to use a separate instance of an IGP runnning within the parent domain in which parent and child PCEs establish an IGP adjacency. Alternatively, as mentioned in section 4.8.4 of [I-D.ietf-pce-hierarchy-fwk], a child PCE may forward the its neighbour domain connectivity (inter-domain links or ABRs) to the parent PCE, for example within PCNtf messages or any other mechanisms, without an IGP adjacency.
There are two types of domain borders for providing the domain connectivity information:
The information that would be exchanged for inter-AS TE links includes:
For the ABR, the following information needs to be notified to the parent PCE:
[Editor's Note: Further discussion of the discovery mechanism based on the requirements of section 4.8.4 of [I-D.ietf-pce-hierarchy-fwk] and scope will be discussed in later versions of this document. Note that using PCNtf messages will require PCEP Protocol extensions.]
Parent/Child relationships are likely to be configured. However, as mentioned in [I-D.ietf-pce-hierarchy-fwk] , it helps network operations that the parent PCE indicates its H-PCE capability and that the PCC indicates its intention of using parent PCE capabilities. Thus, during the PCEP session establishment procedure, the child PCE needs to be capable of indicating to the parent PCE whether it requests the parent PCE capability or not. Also, during the PCEP session establishment procedur, the parent PCE needs to be capable of indicating whether its parent capability can be provided or not.
A PCE domain is a single domain with an associated PCE. it is possible for a PCE to manage multiple domains. The PCE domain may be an IGP area or AS.
The PCE ID is an IPv4 and/or IPv6 address that is used to reach the parent/child PCE. It is RECOMMENDED to use an address that is always reachable if there is any connectivity to the PCE.
The PCE ID information and PCE domain identifiers may be provided during the PCEP session establishment procedure or the domain connectivity information collection procedure.
A PCE that is capable of acting as a parent PCE might not be configured or willing to act as the parent for a specific child PCE. This fact could be determined when the child sends a PCReq that requires parental activity (such as querying other child PCEs), and could result in a negative response in a PCEP Error (PCErr) message and indicate the hierarchy PCE error types.
The PCC that asks for an inter-domain path computation is aware of the identity of the destination node by definition. If the PCC also knows the egress domain to which the destination node belongs to, it can supply the information as part of the path computation request. Otherwise, it must be determined by the parent PCE.
The parent PCE can query the child PCEs to obtain the destination domain, using the PCEP Request Qualifiers mentioned before. Alternatively, the child PCEs can forward in PCNtf the set of reachable addresses of the domain. [Editor's note: This point requires further ellaboration]
There are two new OF codes defined here for H-PCE:
There are two OPEN object flags defined here for H-PCE:
The type of Domain-ID TLV is to be assigned by IANA (recommended 7). The length is 8 octets. The format of this TLV is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Domain-ID TLV
Domain Type (8 bits): Indicates the domain type. There are two types of domain defined currently:
Domain ID (32 bits): Indicates an IGP Area ID or AS number.
An AS number may be 2 or 4 bytes long. For 2-byte AS numbers, the AS value is left-padded with 0.
[Editor's note: it may be necessary to support 64 bit domain IDs.]
[Editor's note: draft-dhody-pce-pcep-domain-sequence, section 3.2 deals with the encoding of domain sequences, using ERO-subobjects. Work is ongoing to define domain identifiers for OSPF-TE areas, IS-IS area (which are variable sized), 2-byte and 4-byte AS number, and any other domain that may be defined in the future. It uses RSVP-TE subobject discriminators, rather than new type 1/ type 2. A domain sequence may be encoded as a route object. The "VALUE" part of the TLV could follow common RSVP-TE subobject format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 | Length | AS Id (2 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Alternative Domain-ID TLV
The type of PCE-ID TLV is to be assigned by IANA (recommended 8). The length is 8. The format of this TLV is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// PCE IP Address //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PCE-ID TLV
Address Type (16 bits): Indicates the address type of PCE IP Address. 1 means IPv4 address type, 2 means IPv6 address type.
PCE IP Address: Indicates the reachable address of a PCE.
[Editor's note: [RFC5886] already defines the PCE-ID object. If a semantically equivalent PCE-ID TLV is needed (to avoid modifying message grammars to include the object), it can align with the PCEP object: n any case, the length (4 / 16 bytes) can be used to know whether it is an IPv4 or an IPv6 PCE, the address type is not needed.]
The OF codes defined in this document can be carried in the OF-list TLV of the OPEN object. If the OF-list TLV carries the OF codes, it means that the PCE is capable of implementing the corresponding objective functions. This information can be used for selecting a proper parent PCE when a child PCE wants to get a path that satisfies a certain objective function.
If a child PCE wants to use the peer PCE as a parent, it can set the parent PCE request bit in the OPEN object carried in the Open message during the PCEP session creation procedure. If the peer PCE does not want to provide the parent function to the child PCE, it must send a PCErr message to the child PCE and clear the parent PCE indication bit in the OPEN object.
If the parent PCE can provide the parent function to the peer PCE, it may set the parent PCE indication bit in the OPEN object carried in the Open message during the PCEP session creation procedure.
The PCE may also report its PCE ID and list of domain ID to the peer PCE by specifying them in the PCE-ID TLV and List of Domain-ID TLVs in the OPEN object carried in the Open message during the PCEP session creation procedure.
Domain Path Request bit (to be assigned by IANA, recommended bit 17): if set it means the child PCE wishes to get the domain sequence.
Destination Domain Query bit (to be assigned by IANA, recommended bit 16): if set it means the parent PCE wishes to get the destination domain ID.
The format of this TLV is defined in Section 3.1.3. This TLV can be carried in an OPEN object to indicate a (list of) managed domains, or carried in a RP object to indicate the destination domain ID when a child PCE responds to the parent PCE's destination domain query by a PCRep message.
[Editors note. In some cases, the Parent PCE may need to allocate a node which is not necessarily the destination node.]
If a child PCE only wants to get the domain sequence for a multi-domain path computation from a parent PCE, it can set the Domain Path Request bit in the RP object carried in a PCReq message. The parent PCE which receives the PCReq message tries to compute a domain sequence for it. If the domain path computation succeeds the parent PCE sends a PCRep message which carries the domain sequence in the ERO to the child PCE . The domain sequence is specified as AS or AREA ERO sub-objects (type 32 for AS [RFC3209] or a to-be-defined IGP area type). Otherwise it sends a PCReq message which carries the NO-PATH object to the child PCE.
The parent PCE can set the Destination Domain Query bit in a PCReq message to query the destination (which is specified in the END-POINTS objects) domain ID from a child PCE. If the child PCE knows the destination(s) domain ID, it sends a PCRep message to the parent PCE and specifies the domain ID in the Domain-ID TLV which is carried in the RP object. Otherwise it sends a PCRep message with a NO-PATH object to the parent PCE.
There are two new metrics defined here for H-PCE:
Because there will not be too many PCEP sessions between the child PCE(s) and parent PCE, it is recommended that the PCEP sessions between them keeping alive all the time . Then the child PCE can report all of the domain connectivity information to the parent PCE when the PCEP session is established successfully. It can also notify the parent PCE to update or delete the domain connectivity information when it detects the changes.
There is a new notification type defined in this document:
IGP in each neighbor domain can advertise its inter-domain TE link capabilities [RFC5316],[RFC5392]. This information can be collected by the child PCEs and forwarded to the parent PCE. PCEP Inter-domain Link TLV is used for carrying the inter-domain TE link attributes for this purpose. Each Inter-domain Link TLV can carry the attributes of one inter-domain link at the most.
The type of Inter-domain Link TLV is to be assigned by IANA (recommended 9). The length is variable. The format of this TLV is defined 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertise Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // sub-TLVS // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Inter-domain Link TLV
Editor's note: evaluate other possibilities regarding the wrapping and encoding (LSAs / LSUs). Other fields may be needed, such as LSA age (max age methods can be used to "withdraw" or remove a link). Sub-TLVs may need to be defined in the context of a Link TLV (top TLV).
Advertise Router ID (32 bits): indicates the router ID which advertises the TE LSA or LSP.
Sub-TLVs: the OSPF sub-TLVs for a TE link which defined in [RFC5392] and other associated OSPF RFCs. It is noted that if the IGP is IS-IS for the child domain the sub-TLVs must be converted to the OSPF sub- TLVs format when sending this information to the parent PCE through PCEP PCNtf message.
Each inter-domain link is identified by the combination of advertise router ID and the link local IP address or link local unnumbered identifier. The PCNtf message which is used for notifying the parent PCE to update or delete a inter-domain link must contain the information identifies a TE link exclusively.
The Inter-domain Node TLV carries only the two adjacent domain ID and the router (IGP ABR) ID.
he type of Inter-domain Node Information TLV is to be assigned by IANA (recommended 10). The length is variable . The format of this TLV is defined 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ABR ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Area ID1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Area ID2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Inter-domain Node TLV
ABR ID (32 bits): indicates the domain border router ID.
Area ID1 and Area ID2 (32 bits): indicates the two neighbor area IDs.
Editor's note (1): a node may be an inter-domain node for more than just 2 areas, the encoding is wrong, unless we explicitly state that this TLV can be repeated and we give an example. Alternatively, we can use the generic concept of "domain id" as introduced earlier, to avoid the restriction of 4 byte areas only.
Editor's note (2): do we homogenize so we also have a Advertising Router ID? would it be different from the ABR id?
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertise Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ABR ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IS/IS area 1 ... |
.. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IS/IS area 2 ... |
.. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Alternative Inter-domain Node TLV
The format of this TLV is defined in Section 3.1.3. This TLV can be carried in a NOTIFICATION object to indicate the domain ID of the PCE who sends the PCNtf message.
[Editors note: A PCE may be responsible for several domains, it may be beneficial to use a list of TLVs]
The format of this TLV is defined in Section 3.1.4. This TLV can be carried in a NOTIFICATION object to indicate the PCE ID of the PCE who sends the PCNtf message.
The reachability TLV carries information of the set of end-points reachable in a given domain.
The format of the TLV is a list of IPv4 Prefix, IPv6 Prefix, AS and unnumbered Interface ERO subojects, as defined in [RFC3209] and[RFC3477]. This TLV can be carried in a NOTIFICATION object to indicate the reachable end-points of the domain of the PCE who sends the PCNtf message.
[Editor's note]: If the child PCE represents several domains, the reachability TLV should be sent together with a domain_tlv
When a parent PCE establishes a PCEP session with a child PCE successfully, the parent PCE may request the child PCE to report the domain connectivity information. This procedure can be done by sending a PCNtf message from the parent to the child, setting the notification-type to 3 and notification-value to 0 in the NOTIFICATION object.
When a child PCE receives the PCNtf message, it may send all of the domain connectivity information to the parent PCE by the PCNtf message(s). The notification-type is 3 and notification-value is 1 in the NOTIFICATION object. The NOTIFICATION object may carry the inter-domain link TLV and inter-domain node TLV to describe the inter-domain connectivity information. It is noted that if the child PCE does not support this function, it will ignore the received PCNtf message and the parent PCE will not receive the response.
The child PCE can also update the domain connectivity information by re-sending the PCNtf message(s) with the newly information.
When the child PCE detects a deletion of domain connectivity (e.g., the inter-domain link TLV is aged out), it must notify the parent PCE to delete the inter-domain link by sending the PCNtf message. The notification-type is 3 and notification-value is 2 in the NOTIFICATION object.
When a parent PCE establishes a PCEP session with a child PCE successfully, the parent PCE may request the child PCE to report the end-points reachability information of the represented domain. This procedure can be done by sending a PCNtf message from the parent to the child, setting the notification-type to 3 and notification-value to 0 in the NOTIFICATION object.
A new PCEP Error-Type is allocated for hierarchy PCE (to be assigned by IANA, recommended 19):
+------------+------------------------------------------------------+ | Error-Type | Meaning | +------------+------------------------------------------------------+ | 19 | H-PCE error Error-value=1: parent PCE capability | | | cannot be provided | +------------+------------------------------------------------------+
When a specific child PCE sends a PCReq to a peer PCE that requires parental activity and the peer PCE does not want to act as the parent for it, the peer PCE should send a PCErr message to the child PCE and specify the error-type (IANA) and error-value (1) in the PCEP-ERROR object.
TBD.
As per [RFC5226], IANA is requested to create/update the following registries
| Value | Meaning | Reference |
|---|---|---|
| 11 | MBN | This document |
| 12 | MTD | This document |
| 13 | DDR | This document |
| Value | Meaning | Reference |
|---|---|---|
| x | Interdomain Link TLV | This document (section Section 3.3.2) |
| x | Interdomain Node TLV | This document (section Section 3.3.3) |
| Type | Value | Meaning |
|---|---|---|
| DC Notification | 1 | query all of the domain connectivity |
| 2 | update domain connectivity information | |
| 3 | delete domain connectivity information |
| Type | Value | Meaning |
|---|---|---|
| H-PCE Error 19 | 1 | parent PCE capability cannot be provided |
| 2 | TBD | |
| 3 | TBD |
TBD
| [I-D.ietf-pce-hierarchy-fwk] | King, D. and A. Farrel, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS, draft-ietf-pce-hierarchy-fwk-04", June 2012. |