Hi, One overall clarification -
The notion that PCEP extensions replaces other protocol is not the right way to look at the issue here. It should be looked at in complementary terms *only*. There are some other points that some have made on the overarching principle. Let me try to summarize them from my point of view - (1) Use of Yang based mechanism (NetConf/RestConf/gRPC/gNMI) instead, develop solution based on yang only. Well to me that sounds like moving functionality that exist in PCEP to Yang (and isn't that the issue that has been pointed out for these PCEP extensions!). Note that, I would never argue against developing solution based on Yang, as IMHO both should co-exist and have different considerations involved. W.r.t binary in yang based solutions, though it is possible, it is not something that is implemented or available right now in NetConf/RestConf where as PCEP extensions have been implemented/tested, and moreover having multiple SBI options is good :) (2) The functionality already exist in other protocols, and creating choice would lead to operation-issues. I think it was pointed out by Adrian, we already have multiple protocols doing similar things today - - OSPF-TE, ISIS-TE, BGP-LS, Yang based solutions (NetConf/RestConf/gRPC) for TED - PCEP, Yang based solutions (NetConf/RestConf/gRPC) for path setup - BGP-FlowSpec, Yang based solutions (NetConf/RestConf/gRPC) for flow This PCEP proposals in question, did not create these choices, they exist already and adding PCEP in the mix does not change that. --- Some of the arguments for not taking on this work could be applied to various other works that IETF has taken on in recent past :), looks like we apply the principles selectively. IMHO if there exist deployments where the work makes sense, then it should be explored. If there are implementations that exist or are planned, and if there are a volunteers from multiple organizations who would like to continue to work on it, and if it does no harm - the work should continue. There have been experiments, Hackathon and Bits-n-Bytes effort that showcased interest. There have been presentations from operators on how they plan to deploy and use these functionalities. There are implementation reports as well. --- Jon's mail asked the question where do we stop? My answer would be - - at "configuration" - at use of PCEP for work beyond TE - kitchen sink (as Jeff put it) - harm to the network (non-backward compatible etc) - incompatible with framework in TEAS The work proposed in PCEP falls well under the umbrella of acceptable PCEP extensions IMHO. Regards, Dhruv From: Pce [mailto:[email protected]] On Behalf Of Jonathan Hardwick Sent: 20 July 2017 20:52 To: [email protected] Cc: [email protected] Subject: [Pce] PCEP as an SDN controller protocol? Dear PCE WG The purpose of this email is to initiate a discussion about whether we want to extend PCEP to allow it to replace the functions that are traditionally provided by the routing and signalling protocols. Originally, PCEP was designed with the goal of providing a distributed path computation service. In recent years we have extended that mission, and added path modification and path instantiation capabilities to PCEP. This has added capabilities to PCEP that would traditionally have been performed by the network management plane. We are now starting to discuss proposals to add more capabilities to PCEP - capabilities that are traditionally part of routing and signalling. There were three examples of this in the PCE working group meeting this week. * The PCECC proposal, which extends PCEP's path instantiation capability so that the PCE can provision a path end-to-end by touching each hop along the path. This replaces the function already provided by RSVP-TE. * The PCEP-LS proposal, which extends PCEP to allow link state and TE information to be communicated from the network to the PCE. This replaces the link state flooding function provided by the IGPs, or BGP-LS. * The PCECC-SR proposal extends PCEP to allow device-level configuration to be communicated between the network and the PCE, such as SRGBs, prefix SIDs etc. Again, this replaces functions that are already designed into the IGPs. These proposals are taking PCEP in the direction of being a fully-fledged SDN protocol. With these proposals, one can envision a network in which there is no traditional control plane. PCEP is used to communicate the current network state and to program flows. These proposals have their roots in the ACTN and PCECC architectures that are adopted within the TEAS working group. TEAS is very much assuming that this is the direction that we want to take PCEP in. However, there are two procedural issues, as I see it. 1. We have not had an explicit discussion in the PCE WG about whether we want to take PCEP in this direction. We have had a few lively debates on specific cases, like PCEP-LS, but those cases represent the "thin end of the wedge". If we start down this path then we are accepting that PCEP will replace the functions available in the traditional control plane. We need to test whether there is a consensus in the working group to move in that direction. 2. We do not currently have a charter that allows us to add this type of capability to PCEP. Depending on the outcome of discussion (1), we can of course extend the charter. This email is to initiate the discussion (1). So, please reply to the mailing list and share your thoughts on whether PCEP should be extended in this direction, and how far we should go. I am hoping to get more than just "yes" or "no" answers to this question (although that would be better than no answer). I would like to hear justifications for or against. Such as, which production networks would run PCEP in place of a traditional control plane? Why is it not desirable to solve the problems in those networks with the traditional control plane? What harm could this do? What would be the operational problems associated with adding these functions to PCEP? Many thanks Jon
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