| PCE Working Group | D. Dhody |
| Internet-Draft | U. Palle |
| Intended status: Experimental | Huawei Technologies |
| Expires: July 3, 2015 | R. Casellas |
| CTTC | |
| December 30, 2014 |
Standard Representation of Domain-Sequence
draft-ietf-pce-pcep-domain-sequence-07
The ability to compute shortest constrained Traffic Engineering Label Switched Paths (TE LSPs) in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across multiple domains has been identified as a key requirement. In this context, a domain is a collection of network elements within a common sphere of address management or path computational responsibility such as an Interior Gateway Protocol (IGP) area or an Autonomous System (AS). This document specifies a standard representation and encoding of a Domain-Sequence, which is defined as an ordered sequence of domains traversed to reach the destination domain to be used by Path Computation Elements (PCEs) to compute inter-domain constrained shortest paths across a predetermined sequence of domains . This document also defines new subobjects to be used to encode domain identifiers.
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This Internet-Draft will expire on July 3, 2015.
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A PCE may be used to compute end-to-end paths across multi-domain environments using a per-domain path computation technique [RFC5152]. The backward recursive path computation (BRPC) mechanism [RFC5441] also defines a PCE-based path computation procedure to compute inter-domain constrained path for (G)MPLS TE LSPs. However, both per-domain and BRPC techniques assume that the sequence of domains to be crossed from source to destination is known, either fixed by the network operator or obtained by other means. Also for inter-domain point-to-multi-point (P2MP) tree computation, [RFC7334] assumes the domain-tree is known in priori.
The list of domains (Domain-Sequence) in point-to-point (P2P) or a domain tree in point-to-multipoint (P2MP) is usually a constraint in inter-domain path computation procedure. A PCE determines the next PCE to forward the request based on the Domain-Sequence. In a multi-domain path computation, a Path Computation Client (PCC) MAY indicate the sequence of domains to be traversed using the Include Route Object (IRO) defined in [RFC5440].
When the sequence of domains is not known in advance, the Hierarchical PCE (H-PCE) [RFC6805] architecture and mechanisms can be used to determine the Domain-Sequence.
This document defines a standard way to represent and encode a Domain-Sequence in various scenarios including P2P LSP, P2MP LSP, and use of H-PCE.
The Domain-Sequence (the set of domains traversed to reach the destination domain) is either administratively predetermined or discovered by some means like H-PCE.
[RFC5440] defines the Include Route Object (IRO) and the Explicit Route Object (ERO). [RFC5521] defines the Exclude Route Object (XRO) and the Explicit Exclusion Route Subobject (EXRS). The use of Autonomous System (AS) (albeit with a 2-Byte AS number) as an abstract node representing a domain is defined in [RFC3209], this document specifies new subobjects to include or exclude domains including IGP area or an Autonomous Systems (4-Byte as per [RFC6793]).
Further, the domain identifier may simply act as delimiter to specify where the domain boundary starts and ends in some cases.
This is a companion document to Resource ReserVation Protocol - Traffic Engineering (RSVP-TE) extensions for the domain identifiers [DOMAIN-SUBOBJ].
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].
The following terminology is used in this document.
[RFC4726] and [RFC4655] define domain as a separate administrative or geographic environment within the network. A domain may be further defined as a zone of routing or computational ability. Under these definitions a domain might be categorized as an AS or an IGP area. Each AS can be made of several IGP areas. In order to encode a Domain-Sequence, it is required to uniquely identify a domain in the Domain-Sequence. A domain can be uniquely identified by area-id or AS number or both.
A Domain-Sequence is an ordered sequence of domains traversed to reach the destination domain.
A Domain-Sequence can be applied as a constraint and carried in a path computation request to PCE(s). A Domain-Sequence can also be the result of a path computation. For example, in the case of H-PCE [RFC6805] Parent PCE MAY send the Domain-Sequence as a result in a path computation reply.
In a P2P path, the domains listed appear in the order that they are crossed. In a P2MP path, the domain tree is represented as a list of Domain-Sequences.
A Domain-Sequence enables a PCE to select the next domain and the PCE serving that domain to forward the path computation request based on the domain information.
A PCC or PCE MAY add an additional constraint covering which Boundary Nodes (ABR or ASBR) or Border links (Inter-AS-links) MUST be traversed while defining a Domain-Sequence.
Thus a Domain-Sequence MAY be made up of one or more of -
Consequently, a Domain-Sequence can be used:
Domain-Sequence MAY appear in PCEP messages, notably in -
As per [RFC5440], IRO (Include Route Object) can be used to specify that the computed path MUST traverse a set of specified network elements or abstract nodes.
Some subobjects are defined in [RFC3209], [RFC3473], [RFC3477] and [RFC4874], but new subobjects related to Domain-Sequence are needed.
The following subobject types are used in IRO.
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
33 Explicit Exclusion (EXRS)
This document extends the above list to support 4-Byte AS numbers and IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
[RFC3209] already defines 2 byte AS number.
To support 4 byte AS number as per [RFC6793] following subobject is defined:
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS-ID (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Since the length and format of Area-id is different for OSPF and ISIS, following two subobjects are defined:
For OSPF, the area-id is a 32 bit number. The subobject is encoded as follows:
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Area Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For IS-IS, the area-id is of variable length and thus the length of the Subobject is variable. The Area-id is as described in IS-IS by ISO standard [ISO10589]. The subobject is encoded as follows:
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 | Area-Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// IS-IS Area ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[RFC5440] describes IRO as an optional object used to specify that the computed path MUST traverse a set of specified network elements. It further state that the L bit of such subobject has no meaning within an IRO. It did not mention if IRO is an ordered or un-ordered list of subobjects.
An update to IRO specification [IRO-UPDATE] makes IRO as an ordered list as well as support for loose bit (L-bit).
The use IRO for Domain-Sequence assumes the updated specification for IRO as per [IRO-UPDATE].
Some subobjects for the IRO are defined in [RFC3209], [RFC3473], [RFC3477], and [RFC4874]; further some new subobjects related to Domain-Sequence are also added in this document as mentioned in Section 3.4.
The subobject type for IPv4, IPv6, and unnumbered Interface ID can be used to specify Boundary Nodes (ABR/ASBR) and Inter-AS-Links. The subobject type for the AS Number (2 or 4 Byte) and the IGP Area are used to specify the domain identifiers in the Domain-Sequence.
The IRO MAY have both intra-domain (from the context of the ingress PCC) and inter-domain (Domain-Sequence) subobjects in a sequence in which they must be traversed in the computed path.
Thus an IRO, comprising of subobjects that represents a Domain-Sequence, define the domains involved in an inter-domain path computation, typically involving two or more collaborative PCEs.
A Domain-Sequence can have varying degrees of granularity. It is possible to have a Domain-Sequence composed of, uniquely, AS identifiers. It is also possible to list the involved IGP areas for a given AS.
In any case, the mapping between domains and responsible PCEs is not defined in this document. It is assumed that a PCE that needs to obtain a "next PCE" from a Domain-Sequence is able to do so (e.g. via administrative configuration, or discovery).
A PCC builds an IRO to encode the Domain-Sequence, so that the cooperating PCEs should compute an inter-domain shortest constrained path across the specified sequence of domains.
For each inclusion, the PCC clears the L-bit to indicate that the PCE is required to include the domain, or sets the L-bit to indicate that the PCC simply desires that the domain be included in the Domain-Sequence.
If a PCE encounters a subobject that it does not support or recognize, it MUST act according to the setting of the L-bit in the subobject. If the L-bit is clear, the PCE MUST respond with a PCErr with Error-Type TBD4 "Unrecognized subobject" and set the Error-Value to the subobject type code. If the L-bit is set, the PCE MAY respond with a PCErr as already stated or MAY ignore the subobject: this choice is a local policy decision.
PCE MUST act according to the requirements expressed in the subobject. That is, if the L-bit is clear, the PCE(s) MUST produce a path that follows the Domain-Sequence in order identified by the subobjects in the path. If the L-bit is set, the PCE(s) SHOULD produce a path along the Domain-Sequence unless it is not possible to construct a path complying with the other constraints expressed in the request.
A successful path computation reported in a path computation reply message (PCRep) MUST include an ERO to specify the path that has been computed as specified in [RFC5440] following the sequence of domains.
In a PCRep, PCE MAY also supply IRO (with Domain-Sequence information) with the NO-PATH object indicating that the set of elements (domains) of the request's IRO prevented the PCEs from finding a path.
Selection of the next domain and the PCE serving that domain is dependent on the domain subobjects (AS and IGP area) in the IRO.
Note that a particular domain in the Domain-Sequence can be identified by :-
The Subobjects representing an internal node, a Boundary Node or an Inter-AS-Link MAY also influence the selection of the path.
The Exclude Route Object (XRO) [RFC5521] is an optional object used to specify exclusion of certain abstract nodes or resources from the whole path.
The following subobject types are defined to be used in XRO as defined in [RFC3209], [RFC3477], [RFC4874], and [RFC5521].
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
34 SRLG
64 IPv4 Path Key
65 IPv6 Path Key
This document extends the above list to support 4-Byte AS numbers and IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
The new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area MAY also be used in the XRO to specify exclusion of certain domains in the path computation procedure.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS-ID (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
All other fields are consistent with the definition in Section 3.4.
Since the length and format of Area-id is different for OSPF and ISIS, following two subobjects are defined:
For OSPF, the area-id is a 32 bit number. The subobject is encoded as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Area Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
All other fields are consistent with the definition in Section 3.4.
For IS-IS, the area-id is of variable length and thus the length of the subobject is variable. The Area-id is as described in IS-IS by ISO standard [ISO10589]. The subobject is encoded as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Area-Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// IS-IS Area ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
All other fields are consistent with the definition in Section 3.4.
If a PCE that supports XRO and encounters a subobject that it does not support or recognize, it MUST act according to the setting of the X-bit in the subobject. If the X-bit is clear, the PCE MUST respond with a PCErr with Error-Type TBD4 "Unrecognized subobject" and set the Error-Value to the subobject type code. If the X-bit is set, the PCE MAY respond with a PCErr as already stated or MAY ignore the subobject: this choice is a local policy decision.
All the other processing rules are as per [RFC5521].
Explicit Exclusion Route Subobject (EXRS) [RFC5521] is used to specify exclusion of certain abstract nodes between a specific pair of nodes.
The EXRS subobject may carry any of the subobjects defined for inclusion in the XRO, thus the new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area MAY also be used in the EXRS. The meanings of the fields of the new XRO subobjects are unchanged when the subobjects are included in an EXRS, except that scope of the exclusion is limited to the single hop between the previous and subsequent elements in the IRO.
All the processing rules are as per [RFC5521].
The Explicit Route Object (ERO) [RFC5440] is used to specify a computed path in the network. PCEP ERO subobject types correspond to RSVP-TE ERO subobject types as defined in [RFC3209], [RFC3473], [RFC3477], [RFC4873], [RFC4874], and [RFC5520].
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
3 Label
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
33 Explicit Exclusion (EXRS)
37 Protection
64 IPv4 Path Key
65 IPv6 Path Key
This document extends the above list to support 4-Byte AS numbers and IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
The new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area MAY also be used in the ERO to specify an abstract node (a group of nodes whose internal topology is opaque to the ingress node of the LSP). Using this concept of abstraction, an explicitly routed LSP can be specified as a sequence of domains.
In case of Hierarchical PCE [RFC6805], a Parent PCE MAY be requested to find the Domain-Sequence. Refer example in Section 4.6.
The format of the new ERO subobjects is similar to new IRO subobjects, refer Section 3.4.
The examples in this section are for illustration purposes only; to highlight how the new subobjects may be encoded.
In an inter-area path computation where the ingress and the egress nodes belong to different IGP areas within the same AS, the Domain-Sequence MAY be represented using a ordered list of Area subobjects. The AS number MAY be skipped, as area information is enough to select the next PCE.
+-------------------+ +-------------------+
| | | |
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| |
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| |
| |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| | | |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
Figure 1: Inter-Area Path Computation
AS Number is 100.
This could be represented in the <IRO> as:
+---------+ +---------+ +---------+ +---------+ |IRO | |Sub | |Sub | |Sub | |Object | |Object | |Object | |Object | |Header | |Area 2 | |Area 0 | |Area 4 | | | | | | | | | | | | | | | | | +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ |IRO | |Sub | |Sub | |Sub | |Sub | |Object | |Object AS| |Object | |Object | |Object | |Header | |100 | |Area 2 | |Area 0 | |Area 4 | | | | | | | | | | | | | | | | | | | | | +---------+ +---------+ +---------+ +---------+ +---------+
AS is optional and it MAY be skipped. PCE should be able to understand both notations.
In inter-AS path computation, where ingress and egress belong to different AS, the Domain-Sequence is represented using an ordered list of AS subobjects. The Domain-Sequence MAY further include decomposed area information in Area subobjects.
As shown in Figure 2, where AS to be made of a single area, the area subobject MAY be skipped in the Domain-Sequence as AS is enough to uniquely identify the next domain and PCE.
+---------------------------------+
|AS 200 |
| +------+ |
| | | |
+------------------------+ | | | +------+ |
| AS 100 | | +------+ | | |
| +------+ | | +------+ | | |
| | +-+-----+-+ | +------+ |
| | | | | | | |
| +------+ | | +------+ |
| +------+ | | +------+ |
| | | | | | | |
| | | | | | | |
| +------+ | | +------+ |
| | | |
| +------+ | | +------+ |
| | +-+-----+-+ | +------+ |
| | | | | | | | | |
| +------+ | | +------+ | | |
| | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | | | | | | |
| |PCE | | | |PCE | |
| +------+ | | +------+ |
| | | |
+------------------------+ | |
+---------------------------------+
Figure 2: Inter-AS Path Computation
Both AS are made of Area 0.
This could be represented in the <IRO> as:
+---------+ +---------+ +---------+
|IRO | |Sub | |Sub |
|Object | |Object AS| |Object AS|
|Header | |100 | |200 |
| | | | | |
| | | | | |
+---------+ +---------+ +---------+
+---------+ +---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object AS| |Object | |Object AS| |Object |
|Header | |100 | |Area 0 | |200 | |Area 0 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
Area subobject is optional and it MAY be skipped. PCE should be able to understand both notations.
As shown in Figure 3, where AS 200 is made up of multiple areas and multiple Domain-Sequence exist, PCE MAY include both AS and Area subobject to uniquely identify the next domain and PCE.
|
| +-------------+ +----------------+
| |Area 2 | |Area 4 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |Area 3 +-++ +--+ +-++ Area 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | Area 0 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|Area 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
AS 100 | AS 200
|
Figure 3: Inter-AS Path Computation
The Domain-Sequence can be carried in the IRO as shown below:
+-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ |IRO | |Sub | |Sub | |Sub | |Sub | |Sub | |Sub | |Object | |Object | |Object | |Object | |Object | |Object | |Object | |Header | |AS 100 | |Area 1 | |AS 200 | |Area 3 | |Area 0 | |Area 4 | | | | | | | | | | | | | | | +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
The combination of both an AS and an Area uniquely identify a domain in the Domain-Sequence.
Note that an Area domain identifier always belongs to the previous AS that appears before it or, if no AS subobjects are present, it is assumed to be the current AS.
If the area information cannot be provided, PCE MAY forward the path computation request to the next PCE based on AS alone. If multiple PCEs are responsible, PCE MAY apply local policy to select the next PCE.
A PCC or PCE MAY add additional constraints covering which Boundary Nodes (ABR or ASBR) or Border links (Inter-AS-link) MUST be traversed while defining a Domain-Sequence. In which case the Boundary Node or Link MAY be encoded as a part of the Domain-Sequence using the existing subobjects.
Boundary Nodes (ABR / ASBR) can be encoded using the IPv4 or IPv6 prefix subobjects usually the loopback address of 32 and 128 prefix length respectively. An Inter-AS link can be encoded using the IPv4 or IPv6 prefix subobjects or unnumbered interface subobjects.
For Figure 1, an ABR to be traversed can be specified as:
+---------+ +---------+ +---------++---------+ +---------+
|IRO | |Sub | |Sub ||Sub | |Sub |
|Object | |Object | |Object ||Object | |Object |
|Header | |Area 2 | |IPv4 ||Area 0 | |Area 4 |
| | | | |x.x.x.x || | | |
| | | | | || | | |
+---------+ +---------+ +---------++---------+ +---------+
For Figure 2, an inter-AS-link to be traversed can be specified as:
+---------+ +---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object AS| |Object | |Object | |Object AS|
|Header | |100 | |IPv4 | |IPv4 | |200 |
| | | | |x.x.x.x | |x.x.x.x | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
A single PCE MAY be responsible for multiple domains; for example PCE function deployed on an ABR. A PCE which can support 2 adjacent domains can internally handle this situation without any impact on the neighbouring domains.
In case of inter-domain P2MP path computation, (Refer [RFC7334]) the path domain tree is nothing but a series of Domain-Sequences, as shown in the below figure:
D1-D3-D6, D1-D3-D5 and D1-D2-D4.
D1
/ \
D2 D3
/ / \
D4 D5 D6
All rules of processing as applied to P2P can be applied to P2MP as well.
In case of P2MP, different destinations MAY have different Domain-Sequence within the domain tree, it requires Domain-Sequence to be attached per destination. (Refer [PCE-P2MP-PER-DEST])
As per [RFC6805], consider a case as shown in Figure 4 consisting of multiple child PCEs and a parent PCE.
+--------+
| Parent |
| PCE |
+--------+
+-------------------+ +-------------------+
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
Figure 4: Hierarchical PCE
In H-PCE, the Ingress PCE 'PCE(1)' can request the parent PCE to determine the Domain-Sequence and return it in the PCEP response, using the ERO Object. The ERO can contain an ordered sequence of subobjects such as AS and Area (OSPF/ISIS) subobjects. In this case, the Domain-Sequence appear as:
+---------+ +---------+ +---------+ +---------+ |ERO | |Sub | |Sub | |Sub | |Object | |Object | |Object | |Object | |Header | |Area 2 | |Area 0 | |Area 4 | | | | | | | | | | | | | | | | | +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ +---------+ |ERO | |Sub | |Sub | |Sub | |Sub | |Object | |Object AS| |Object | |Object | |Object | |Header | |100 | |Area 2 | |Area 0 | |Area 4 | | | | | | | | | | | | | | | | | | | | | +---------+ +---------+ +---------+ +---------+ +---------+
Instead of a Domain-Sequence, a sequence of PCEs MAY be enforced by policy on the PCC, and this constraint can be carried in the PCReq message (as defined in [RFC5886]).
Note that PCE-Sequence can be used along with Domain-Sequence in which case PCE-Sequence SHOULD have higher precedence in selecting the next PCE in the inter-domain path computation procedures. Note that Domain-Sequence IRO constraints should still be checked as per the rules of processing IRO.
[RFC3209] already describes the notion of abstract nodes, where an abstract node is a group of nodes whose internal topology is opaque to the ingress node of the LSP. It further defines a subobject for AS but with a 2-Byte AS Number.
[DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding new subobjects for IGP Areas and 4-byte AS numbers. These subobjects MAY be included in Explicit Route Object (ERO), Exclude Route object (XRO) or Explicit Exclusion Route Subobject (EXRS) in RSVP-TE.
In any case subobject type defined in RSVP-TE are identical to the subobject type defined in the related documents in PCEP.
The "PCEP Parameters" registry contains a subregistry "PCEP Objects" with an entry for the Include Route Object (IRO), Exclude Route Object (XRO) and Explicit Route Object (ERO). IANA is requested to add further subobjects as follows:
7 ERO
10 IRO
17 XRO
Subobject Type Reference
TBD1 4 byte AS number [This I.D.]
TBD2 OSPF Area ID [This I.D.]
TBD3 IS-IS Area ID [This I.D.]
The "PCEP Parameters" registry contains a subregistry "Error Types and Values". IANA is requested to make the following allocations from this subregistry
ERROR Meaning Reference
Type
TBD4 "Unrecognized subobject" [This I.D.]
Error-Value: type code
This document specifies a standard representation of Domain-Sequence and new subobjects, which MAY be used in inter-domain PCE scenarios as explained in other RFC and drafts. The new subobjects and Domain-Sequence mechanisms defined in this document allow finer and more specific control of the path computed by a cooperating PCE(s). Such control increases the risk if a PCEP message is intercepted, modified, or spoofed because it allows the attacker to exert control over the path that the PCE will compute or to make the path computation impossible. Therefore, the security techniques described in [RFC5440] are considered more important.
Note, however, that the Domain-Sequence mechanisms also provide the operator with the ability to route around vulnerable parts of the network and may be used to increase overall network security.
Several local policy decisions should be made at the PCE. Firstly, the exact behavior with regard to desired inclusion and exclusion of domains must be available for examination by an operator and may be configurable. Second, the behavior on receipt of an unrecognized subobjects with the L or X-bit set should be configurable and must be available for inspection. The inspection and control of these local policy choices may be part of the PCEP MIB module.
A MIB module for management of the PCEP is being specified in a separate document [RFC7420]. That MIB module allows examination of individual PCEP messages, in particular requests, responses and errors. The MIB module MUST be extended to include the ability to view the Domain-Sequence extensions defined in this document.
Mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in [RFC5440].
Mechanisms defined in this document do not imply any new operation verification requirements in addition to those already listed in [RFC5440].
In case of per-domain path computation [RFC5152], where the full path of an inter-domain TE LSP cannot be, or is not determined at the ingress node, a signaling message may use the domain identifiers. The Subobjects defined in this document SHOULD be supported by RSVP-TE. [DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding new subobjects for IGP Areas and 4-byte AS numbers.
Apart from this, mechanisms defined in this document do not imply any requirements on other protocols in addition to those already listed in [RFC5440].
Mechanisms defined in this document do not have any impact on network operations in addition to those already listed in [RFC5440].
We would like to thank Adrian Farrel, Pradeep Shastry, Suresh Babu, Quintin Zhao, Fatai Zhang, Daniel King, Oscar Gonzalez, Chen Huaimo, Venugopal Reddy, Reeja Paul Sandeep Boina and Avantika for their useful comments and suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5440] | Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. |
| [RFC5441] | Vasseur, JP., Zhang, R., Bitar, N. and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", RFC 5441, April 2009. |
| [RFC5521] | Oki, E., Takeda, T. and A. Farrel, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Route Exclusions", RFC 5521, April 2009. |
| [RFC6805] | 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", RFC 6805, November 2012. |