Supporting Explicit Inclusion or Exclusion
of Abstract Nodes for a Subset of P2MP Destinations in Path Computation Element Communication
Protocol (PCEP). Huawei TechnologiesLeela PalaceBangaloreKarnataka560008INDIAdhruv.ietf@gmail.comHuawei TechnologiesLeela PalaceBangaloreKarnataka560008INDIAudayasree.palle@huawei.comHuawei TechnologiesLeela PalaceBangaloreKarnataka560008INDIAvenugopalreddyk@huawei.com
Routing
PCE Working GroupThe ability to determine paths of point-to-multipoint (P2MP) Multiprotocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering Label
Switched Paths (TE LSPs) is one the key requirements for Path Computation Element
(PCE). and describes
these mechanisms for intra and inter domain path computation via PCE(s). This document describes the motivation and PCEP extension for explicitly
specifying abstract nodes for inclusion or exclusion for a subset of destinations
during P2MP path computation via PCE(s).The PCE architecture is defined in .
lay out the requirements for PCEP to support P2MP path computation.
describe an extension to PCEP to compute optimal constrained
intra-domain (G)MPLS P2MP TE LSPs. describes the
mechanism for inter-domain P2MP path computation. Further describes mechanism to specify a list of nodes that can be
used as branch nodes or a list of nodes that cannot be used as branch nodes via Branch
Node Capability (BNC) object. The BNC object is used to specify which nodes have the
capability to act as a branch nodes or which nodes lack the capabilty. It supports IPv4
and IPv6 prefix sub-objects only. This document explains the need to add
the capability to explicitly specify any abstract nodes (not just nodes with branch node
capabiltiy) for inclusion or exclusion for a subset of destinations. describes the core-tree procedure to compute
inter-domain P2MP tree. It assumes that, due to deployment and commercial limitations,
the sequence of domains for a path (the path domain tree) will be known in advance.
For a group of destination which belong to a particular destination domain, the domain-sequence needs
to be encoded separately as described in [DOMAIN-SEQ]. The mechanism, as described in
this document, of explicitly specifying abstract nodes for inclusion or exclusion for
a subset of destinations can be used for this purpose, where abstract nodes are domains. 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 .The following terminology is used in this document.Include Route Object.Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or route based on
a network graph and applying computational constraints.Path Computation Element Protocol.Point-to-MultipointPoint-to-PointRecord Route ObjectResource Reservation ProtocolTraffic Engineering Label Switched Path.Exclude Route Object. describes the core-tree procedure for inter-domain
path computation. The procedure assumes that the sequence of domains for a path (the path domain tree)
will be known in advance due to deployment and commercial limitations (e.g., inter-AS peering agreements).In the below, D1 is the root domain; D5 and D6 are the destination domains.
The ingress is A in domain D1; egresses are X, Y in Domain D6 and Z in Domain D5. In the below, the P2MP tree spans 5 domains. Destination
in D6 (X and Y) would use the domain-sequence: D1-D3-D4-D6; and destination in D5 (Z)
would use the domain-sequence: D1-D3-D4-D5.Since destinations in different destination domain will have different domain sequence
within the domain tree, it requires following encoding-Destination X and Y: D1-D3-D4-D6Destination Z : D1-D3-D4-D5An extension in P2MP Path Computation request is needed to support this.
(Refer )The abstract nodes MAY include (but not limited to) domain subobjects AS number
and IGP Area as described in . also mentions PCE-sequence (i.e. list of PCE for
each domain in the path domain tree). specify PCE-ID object
(used to specify a PCE's IP address)
and <pce-list> (list of PCE or PCE-sequence). Like domain-sequence as explained
above, PCE-sequence
will be different for different destinations and thus should be encoded per
subset of destinations.
describes four possible types of leaves in a P2MP
request encoded in P2MP END-POINTS object.New leaves to add Old leaves to remove Old leaves whose path can be modified/reoptimized Old leaves whose path must be left unchanged only allows to encode a list of nodes that have
(or have not) the branch node capability by using the Branch Node Capability (BNC)
Object. This object apply to all destinations (old and new) in the P2MP tree.For an existing P2MP tree with an overloaded branch node, when adding a set of
new leaves, administrator may want to exclude that particular branch node to balance
the final P2MP tree. This cannot be achieved via the BNC object but by explicitly
excluding a particular node or including a different node, for the P2MP END-POINTS
object for new leaves only.Administrator at the Ingress can exert stronger control by providing explicit
inclusion or exclusion of any abstract nodes (not limited to specifying nodes with
branch node capability) for a group (subset) of destinations and not all destinations. defines Request Message Format and Objects, along with
<end-point-rro-pair-list>. This section introduce the use of <pce-list>, <IRO>
and <XRO> which are added to the <end-point-rro-pair-list>.To allow abstract nodes to be explicitly included or excluded for a subset of
destinations (encoded in one <END-POINTS> object), changes are made as
shown below.The abstract node (encoded as subobject in <IRO> and <XRO>) MAY be
an absolute hop, IP-Prefix, AS or IGP Area. The subobjects are described
in , ,
and .Note that one P2MP Path request can have multiple <END-POINTS> objects and each
P2MP <END-POINTS> object may have multiple destinations, the <pce-list>, <IRO> and <XRO>
is applied for all destinations in one such P2MP <END-POINTS> object.The format of PCReq message is modified as follows:From usage of <end-point-rro-pair-list> is changed
to <end-point-pce-iro-xro-rro-pair-list> in this document. describes Branch Node Capability (BNC) Object which is
different from the use of <IRO> and <XRO> to specify inclusion/exclusion of
abstract nodes for a subset of destinations as described here.<pce-list> can be used to specify the Pce-sequence instead of domain-sequence.A legacy implementation that does not support explicit inclusion or exclusion of
abstract nodes for a subset of P2MP destinations will act according to the procedures
set out in , that is it will find the P2MP Path Request message
out of order with respect to the format specified in .There are no new IANA allocation in this document.PCEP security mechanisms as described in ,
and are applicable for this document.The new explicit inclusion or exclusion of abstract nodes for a subset of P2MP destination
defined in this document allow finer and more specific control of the path computed by a PCE.
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 ,
and are considered more important.Note, however, that the route exclusion 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.Mechanisms defined in this document do not add any new control function/policy requirements
in addition to those already listed in .Mechanisms defined in this document do not imply any new MIB requirements.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 requirements on other protocols in addition
to those already listed in .Mechanisms defined in this document do not have any impact on network operations in addition
to those already listed in .We would like to thank Pradeep Shastry, Suresh babu, Quintin Zhao, Daniel King and Chen Huaimo
for their useful comments and suggestions.PCE-based Computation Procedure To Compute
Shortest Constrained P2MP Inter-domain Traffic Engineering
Label Switched Paths (draft-ietf-pce-pcep-inter-domain-p2mp-procedures)Standard Representation Of Domain Sequence (draft-ietf-pce-pcep-domain-sequence)