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
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
From: Pce [mailto:pce-boun...@ietf.org] On Behalf Of Jonathan Hardwick
Sent: 20 July 2017 20:52
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
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?
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