Transcript Net-Centric 2016 - Old Dog Consulting

Net-Centric 2016
The Path Computation Element as a
Centralized Controller in advanced
SDN Operations
Adrian Farrel : Old Dog Consulting
[email protected]
www.isocore.com/2016
Net-Centric 2016
Agenda
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Remember - What is a PCE?
What does SDN look like?
The role of PCE in SDN
The implications of putting PCE at the centre
What could we do with a “PCE-Based Centralized
Controller”
• What would it take?
• Why would we do it?
• Who is doing it?
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PCE Refresher
• Well, do we really need a PCE refresher?
• History
• Origins
• A mechanism to provide inter-domain paths
• A tool to offload path computation in MPLS systems
• Rapid developments
• Path computation for all connection oriented systems
• MPLS-TE, GMPLS, MPLS-TP, …
• Server functionality
• Receives path computation requests
• Sends responses
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A Functional Entity
• PCE is a functional component
• It can be embedded in other components
• It can be a stand-alone sever
• It’s just a things that computes paths
LSR
TED
PCE
PCE server
NMS
TED
TED
LSR
PCC
NMS
PCE
PCE
PCC
Signalling
engine
PCE server
PCE co-located in the LSR
PCC
PCE in the NMS
PCE in a dedicated server
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Developments Over Time
• It was a request/response server
• “Please compute a path” / “Here is your answer”
• Stateful PCE is valuable
• Coordinate with other LSPs in the system
• Delegated control
• PCE sends “suggested” updates when the network
changes
• PCE-Initiated LSPs
• PCE sends unsolicited LSP setup “requests”
• All these features become important for SDN
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What is Software Defined Networking?
• Let’s not re-open this debate (please!)
• Centralized control
• Especially of end-to-end services
• Network convergence
• Converged services and infrastructure
• Network “abstraction”
• Partitioning of resources
• Network automation
• Application-to-network relationship
• Provides access to the forwarding plane of network devices
• Momentum being driven for commercial benefits
• Rapidly provide cool services at lower prices
• Reduce OPEX and simplify network operations
• Enable better monitoring and diagnostics
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Some Popular SDN Architectures
Application/Service Requester
PCE
Orchestrator
Controller
Controller
Controller
PCE
TED
Applications
PCE
Controller
Application Service Coordinator
TED
TED
PCE
ABNO Controller
Choices
I2RS
• Lots of pictures
• Most show some form of path
computation being performed
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Provisioning Manager
Choices
Controllers
PCEP
OAM
Handler
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Why is PCE at the Centre?
• This is really simple
• Its all about coordination of network resources
• Centralization avoid contention
• And its all about traffic engineering
• Centralization aids planning and optimization
• And it uses complex and intensive algorithms
• May be best to offload from the “dumb” network
• And it can benefit from large databases
• Network capabilities
• Traffic demands and intentions
• Telemetrics
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What Does it Mean To Be At the Centre?
PCE-Based Centralized Control
• PCE is there in all the pictures
• That means PCE is central to the decision-making
processes
• From there on it is a labelling function
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Controllers/Orchestrators/OSS use PCE
PCE-enabled Controllers/Orchestrators/OSS
PCE-based Controllers/Orchestrators/OSS
PCE-based Central Controller
PCE as a Central Controller
• This is mainly semantics
• A lot of it is about how you build software and how you market
product
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Some Useful Functions
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Answer computation enquiries (already supported)
Modify an LSP that is already in place (stateful PCE)
Cause an LSP to be set up (PCE-initiated LSPs)
Say what an LSP is for
Apply to other technologies
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Deterministic networking
Time-sliced channel hopping (IEEE 802.15.4e)
Segment Routing
Service Function Chaining
PCEP as an SDN Southbound Interface – Static LSPs
LSP stitching as a hybrid use case
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Traffic Classification – What is The LSP For?
• When a TE-LSP is set up, the head end needs to know
how to use it
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What traffic to send on the LSP
Whether it is a virtual link
Whether to advertise it in the IGP
What bits of this information to signal to the tail end
What to do with traffic received on an LSP
• PCEP allows an Active PCE to set up or modify LSPs
• But we have no way to tell the head end how to use the LSP
• This is because of history
• It used to be the LER that made the request of the PCE, so it knew
why it wanted the LSP
• This function is presumably necessary
• But it is currently missing
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But LSPs Are Used Today – How?
• There are several possibilities
• No-one uses Active PCE
• The problem doesn’t arise
• Active PCE is used only in controlled environments
• Head end always knows what the LSP is for
• Active PCE is used in conjunction with configuration
• The LSP is set up using PCEP
• Some other mechanism tells the head end what to do
• Active PCE is used in conjunction with BGP Flowspec
• Possibly not what BGP Flowspec was designed for
• But it works
• Note that the last two of these seem a waste
• Why separate the functions?
• Could use one protocol for everything
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What Features for “LSP Purposing”?
• Describe:
• How to use the LSP
• What traffic to place on the LSP
• We already have ways of describing traffic flows
• e.g., BGP Flowspec
• How to advertise the LSP
• Does it appear as a link in a topology?
• Which instance, what metric, what bandwidth?
• Compare with RFC 6107
• Extra signalling information
• Other stuff gets signalled to coordinate LSP end points
• Features of “LSP usage”
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Segment Routing
Path Programming and Classification
• Segment routing is a form of
source routing
1st
hop
2nd
hop
3rd
hop
nth
hop
Payload
header
Payload
• A central controller can
• Compute paths through the network
• Instruct the head end about what “stack” to impose
• This is like
• Normal stateful path computation
• Stateful path programming
• Traffic classification
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Further Proposed SR Task
• Labels have to be selected and assigned
• Selection benefits from centralization
• Assignment has competing protocol solutions
PCE allocates Labels
(SID) for node,
Adjacency.
PCEP for label mapping
for node and adjacency.
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4106
payload
4106
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payload
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Static LSPs
• A TE-LSP is a series of “cross connects” and
“resource reservations”
• Familiar in “legacy” transport networks
• Popular with “MPLS-TP”
• MPLS-TE without a control plane
• Order of programming is not important
• Can program in parallel
Incoming interface/label
 Outgoing interface/label
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Static LSPs – PCEP as an SDN SBI
• PCEP allows an active PCE to install LSPs to be
signalled in a TE network
• The “cross-connects” are indicated by the ERO
• An ERO can include label information (GMPLS)
• Incoming label and outgoing label
• LSPs can be short
• A single hop ERO can be just one “cross-connect”
• PCEP is already an SBI for static LSPs
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SBI Thoughts
• The ERO approach is a little ugly
• It might trigger the signalling component to attempt to
do work
• We haven’t worked much on “upstream interface for
head-end LER” in GMPLS or PCEP
• We could add to PCEP specifically for this function
• Not a lot of work
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Claimed Benefit of Central Control and SBI
• Recovery from error cases can result in contention for resources and
signalling storms
• Central control enables prioritisation and optimization
• Comparing apples with apples?
• Central control of signalled LSPs
• Central control with programming of cros-connects
• Contrast with single point of failure
• Consider congestion of management plane
Convergence Time
Number of LSPs
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Source: Huawei Technologies – IETF-94
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LSP Stitching
• LSPs or pseudowires are stitched to form end-to-end
services
• Stitching normally uses configuration
• Some signalling extensions exist
• This is an additional “static LSP” feature
• Adding “cross connect LSPs” to normal LSP setup
ASBR3
ASBR1
CE2
CE1
PE2
PE1
ASBR2
Signaled LSP
ASBR4
Signaled LSP
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Signaled LSP
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Modifications to PCE and PCEP
• Adding traffic classification to an LSP message is “just
another Object”
• We already have experience with BGP Flowspec
• Segment Routing paths are just hop-by-hop paths
• Each hop TLV needs to encode a SID
• Static LSPs are just very short LSPs with no signalling
• Should be possible to use existing messages and objects
• Could add specialist messages
• Bottom line
• Only tweaking PCEP not making radical changes
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Competition with Other Protocols
• Need to be aware of other “competing” protocols
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OpenFlow is an SBI
Netconf/RESTconf with YANG is ubiquitous
BGP is used in many places
Proprietary and legacy protocol usages
• XMPP, TL1, CLI, …
• So why use PCEP?
• Should this talk be about a “PCEP-based Centralized Controller”?
• It’s a question still to be answered, but…
• PCE is at the centre
• It makes sense to add these functions to PCE
• PCE talks PCEP
• Why would you want a PCE to talk multiple protocols?
• But PCE implementations may be configured using Netconf/YANG
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Work in Progress
• The IETF is looking at this stuff
• TEAS working group
• Responsible for traffic Engineering Architecture
• draft-ietf-teas-pce-central-control
“An Architecture for Use of PCE and PCEP in a Network
with Central Control”
• PCE working group
• Responsible for extensions to PCEP
• draft-ietf-pce-segment-routing
PCEP Extensions for Segment Routing
• draft-li-pce-pcep-flowspec
PCEP Extension for Flow Specification
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Questions
[email protected]
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