Path Computation Element Protocol(PCEP) Extension for RSVP Color

This document defines a new RSVP LSP property, called “color”, that can be exchanged over PCEP. The ‘color’ field can be used as one of the guiding criteria in selecting the LSP as a next hop for service prefixes. While the specific details of how the service prefixes are associated with the appropriate RSVP LSP’s are outside the scope of this specification, the envisioned high level usage of the 'color' field is as follows. The service prefixes are marked with some indication of the type of underlay they need. The underlay LSP's carry corresponding markings, which we refer to as "color" in this specification, enabling an ingress node to associate the service prefixes with the appropriate underlay LSP's. As an example, for a BGP-based service, the originating PE could attach some community, e.g. the Extended Color Community with the service route. A receiving PE could use locally configured policies to associate service routes carrying Extended Color Community 'X' with underlay RSVP LSP's of color 'Y'. While the Extended Color Community provides a convenient method to perform the mapping, the policy on the ingress node is free to classify on any property of the route to select underlay RSVP LSP's of a certain color. The 'color' specified in this draft is mainly used for facilitating underlay selection, and does not have any effect on the constraints used for path computation.

The STATEFUL-PCE-CAPABILITY negotiation message is enhanced to carry the color capability, which allows PCC & PCE to determine how incompatibility should be handled, should only one of them support color. An older implementation that does not recognize the new color TLV would ignore it upon receipt. This can sometimes result in undesirable behavior. For example, if PCE passes color to a PCC that does not understand colors, the LSP may not be used as intended. A PCE that clearly knows the PCC's color capability can handle such cases better, and vice versa. Following are the rules for handling mismatch in color capability. A PCE that has color capability MUST NOT send color TLV to a PCC that does not have color capability. A PCE that does not have color capability can ignore color marking reported by PCC. When a PCC is interacting with a PCE that does not have color capability, the PCC SHOULD NOT report color to the PCE. MUST NOT override the local color, if it is configured, based on any messages coming from the PCE. The actual color value itself is carried in a newly defined TLV in the LSP Object defined in . If a PCC is unable to honor a color value passed in an LSP Update request, the PCC must keep the LSP in DOWN state, and include an LSP Error Code value of "Unsupported Color" [Value to be assigned by IANA] in LSP State Report message. If an RSVP tunnel has multiple LSP's associated with it, the PCE should designate one of the LSP's as primary, and attach the color with that LSP. If PCC receives color TLV for an LSP that it treats as secondary, it SHOULD respond with an error code of 4 (Unacceptable Parameters).

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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type has the value [TO-BE-ASSIGNED-BY-IANA]. Length carries a value of 4. The 'color' field is 4-bytes long, and carries the actual color value. Section 7.1.1 of RFC8231 defines STATEFUL-PCE-CAPABILITY flags. The following flag is used to indicate if the speaker supports color capability: C-bit (TO-BE-ASSIGNED-BY-IANA): A PCE/PCC that supports color capability must turn on this bit.

RSVP LSP's marked with color can also be used for inter-domain service mapping as defined in BGP-CT . In BGP-CT, the mapping community of the service route is used to select a “resolution scheme”, which in turn selects LSP’s of various “transport classes” in the defined order of preference. The ‘color’ field defined in this specification could be used to associate the RSVP LSP with a particular transport class. A colored RSVP LSP can also be exported into BGP-CT for inter-domain classful transport.

This document defines a new TLV for color, and a new flag in capability negotiation, which do not add any new security concerns beyond those discussed in , and . An unauthorized PCE may maliciously associate the LSP with an incorrect color. The procedures described in and can be used to protect against this attack.

IANA is requested to assign code points for the following: Code point for "Color" TLV from the sub-registry "PCEP TLV Type Indicators". C-bit value from the sub-registry "STATEFUL-PCE-CAPABILITY TLV Flag Field". An error code for "Unsupported color" from the sub-registry "LSP-ERROR-CODE TLV Error Code Field".

The authors would like to thank Kaliraj Vairavakkalai, Colby Barth & Natrajan Venkataraman for their review & suggestions, which helped improve this specification.