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1 © Nokia 2017
Stateful PCE and Segment
Routing
Increasing IP/MPLS network efficiency
Andrew Dolganow
February 2017
Public
2 © Nokia 2017
– Discovers TE resources and topology by
tapping into IGP Segment Routing updates
(IGP, BGP-LS) and collect...
3 © Nokia 2017
PCC-Initiated and PCE-Controlled SR-TE LSP:
Setup
• Once the SR-TE LSP is placed into a no shutdown state
t...
4 © Nokia 2017
PCE-Controlled SR-TE LSP: Failure Recovery
• As Segment Routing has no inherent control plane, it
must rely...
5 © Nokia 2017
Increasing network utilization with PCE control
Public
• PCE can be designed to balance link utilisation an...
6 © Nokia 2017
• Example: Service 1 needs to be routed
disjoined from Service 2 using SPF algorithm
(latency optimization ...
7 © Nokia 2017
Adjacency segment load balancing with PCE
Public
• Multiple adjacencies exist between P1-P2.
• Adj-SID TLV ...
8 © Nokia 2017
AS 100
– PeerNode segment for each of its defined peers (R7,
R8, and R9)
– PeerAdj segment for each recursi...
10 © Nokia 2017 Public
Copyright and confidentiality
The contents of this document are proprietary and
confidential proper...
Stateful PCE and Segment Routing
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Stateful PCE and Segment Routing

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Presentation by Andrew Dolganow at APRICOT 2017 on Monday, 1 March 2017.

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Stateful PCE and Segment Routing

  1. 1. 1 © Nokia 2017 Stateful PCE and Segment Routing Increasing IP/MPLS network efficiency Andrew Dolganow February 2017 Public
  2. 2. 2 © Nokia 2017 – Discovers TE resources and topology by tapping into IGP Segment Routing updates (IGP, BGP-LS) and collecting link statistics (Telemetry/IPFIX) – Accepts requests from nodes or management systems for computing paths (using the Path Computation Element Protocol [PCEP]). – Communicates with PCEs in other domains/areas for multi-domain/area path computation (Hierarchical PCE). – Regularly re-optimises and downloads path (re-)placement to nodes given measured real- time traffic demand, LSP statistics, and network-state. – Supports TE tunnelinhg like RSVP and Segment Routing Traffic engineering with stateful PCE server Public Stateful PCE State & Stat Collection Network Topology Disovery Control session manager Northbound I/F Network Telemetry/Ipfix IGP/BGP-LS PCEP/OF/BGP- FS PCEP Databases Path computation and re-optimization engine
  3. 3. 3 © Nokia 2017 PCC-Initiated and PCE-Controlled SR-TE LSP: Setup • Once the SR-TE LSP is placed into a no shutdown state the PCC sends a Path Computation Request (PCReq) to the PCE. • The PCE responds with a Path Computation Reply (PCRep), which if successful carries an SR-ERO object with the hops of the LSP – If the PCE is unable to compute a path it will return a PCRep with a NO-PATH object together with a NI (Nature of Issue) field and a NO-PATH-VECTOR TLV listing the reason for the negative reply. • The PCC instantiates the SR-TE LSP and responds with a Path Computation LSP State Report (PCRpt) indicating the operational state of the LSP and delegating the LSP to the PCE. P1 192.0.2.43 Node-SID 20043 P2 P3 P4 PE4 PE3 192.0.2.13 Node-SID 20013 192.0.2.223 Node-SID 20223 192.0.2.222 Node-SID 20222 192.0.2.19 Node-SID 20019 192.0.2.28 Node-SID 20028 PCC PCE PCReq PCRep PCRpt Adj-SIDs Public
  4. 4. 4 © Nokia 2017 PCE-Controlled SR-TE LSP: Failure Recovery • As Segment Routing has no inherent control plane, it must rely on other mechanisms to detect a downstream failure of the LSP • The PCE is aware of the domain-wide topology, so it will be made aware of topology changes (through IGP listening or BGP-LS). • If the PCE is active it is therefore able to re-route delegated LSPs around network failures. • Upon detection of the topology change, the PCE computes a new path for the affected LSP(s) and sends a Path Computation Update (PCUpd) message containing an SR-ERO with a newly computed post-convergence path. P1 192.0.2.43 Node-SID 20043 P2 P3 P4 PE4 PE3 192.0.2.13 Node-SID 20013 192.0.2.223 Node-SID 20223 192.0.2.222 Node-SID 20222 192.0.2.19 Node-SID 20019 192.0.2.28 Node-SID 20028 PCC PCE PCUpd PCRpt • The PCC instantiates the new path and responds with a Path Computation LSP State Report (PCRpt) containing the SR-ERO, a Reported-Route object (RRO) listing the actual hops, an LSP object listing the admin/operational state of the LSP, together with Metric and Bandwidth objects. Public
  5. 5. 5 © Nokia 2017 Increasing network utilization with PCE control Public • PCE can be designed to balance link utilisation and network utilisation goals with orthogonal objectives: ‒ Efficiency: Consume as little total network bandwidth as possible to optimise cost. ‒ Balance: Avoid overloading any links to avoid congestion and deadlock situations. .• The optimal balance can be determined by introducing a factor a determining the degree for considering alternate paths. An α of 0 corresponds to shortest path (min-hop) and an α of ∞ to the least congested path (min-max). 0α = ¥=α ¥££ α0 LinkUtilization NetworkUtilization • One example: a 59-node network, 30,000 requests 1-10G Gb/s, Bell Labs STAR algorithm yields: ‒ 99.92% of path requests are accepted ‒ The same requests yield 87% of path request acceptance by CSPF
  6. 6. 6 © Nokia 2017 • Example: Service 1 needs to be routed disjoined from Service 2 using SPF algorithm (latency optimization through cost) instead of STAR • Programming behavior - PCEP includes a ‘path-profile’ object - A path-profile represents a policy (i.e. a list of path parameters) that a PCC may present to PCE to influence path computation • Plane to use • Algorithm to use • Etc. - A Profile/template is configured in TE controller corresponding to a supported path-profile indicating how the PCE TE controller should perform the path calculation - Paths are computed and returned to PCC via PCEP Improving path placement grnaularity with PCE Path Profile PCE TE controller PCReq (path- profile=1) ... Path Profile configuration PCEP Msg Public PE1 P1 PE3 Node-SID 30 Node-SID 10 P2 P5 P6 P3 P4 P7 P8 Red Plane Anycast SID 100 Blue Plane Anycast SID 200 PE2 Node-SID 20 PE3 Node-SID 40 Service 1 Service 2
  7. 7. 7 © Nokia 2017 Adjacency segment load balancing with PCE Public • Multiple adjacencies exist between P1-P2. • Adj-SID TLV provides the capability to load- balance across multiple adjacencies. – P1 advertises individual Adj-SIDs for the link A (1001) weight X, and link B(1002) with weight Y. – P1 also advertises an Adj-SID for the adjacency set (1003). • By default PCE returns. To PE1 segment list {200, 1003, 800}. Node-SID 200 gets the traffic to P1 whilst Adj-SID 1003 load- balances the traffic to P2 on a weighted X:Y basis. • Based on link monitoring, PCE can use either Adj SID of link A or Adj SID of link B in PCRep to a PCReq or PCUpd foran existing path to rebalance adjacencies Weighted load- balancing on P1-P2 links Node-SID 300 PE1 P1 P2 PE2 Node-SID 200Node-SID 100 Packet 800 Link A Link B Node-SID 800 Packet 800 Packet Link Adj-SID Adj-Set Weight 10G 1001 1003 1 40G 1002 1003 4 Both 1003 - - 1003 200 800 Swap 800 to 800 Pop {200, 1003} PCC PCE PCRep/PCUp dPCRpt1001 200 800 1002 200 800
  8. 8. 8 © Nokia 2017 AS 100 – PeerNode segment for each of its defined peers (R7, R8, and R9) – PeerAdj segment for each recursive interface to a multi-hop peer (R9) – PeerSet segment to a set of peers (R7 & R8 [AS200]). • BGP-LS session established between EPE-enabled border router (R1) and the EPE controller: – R1 advertises PeerNode, PeerAdj, and PeerSet SIDs using SR extensions to BGP-LS and programmes FIB. • EPE controller programmes source-routes from ingress routers to EBGP peers using i.e. FlowSpec/OpenFlow/BGP SR TE policy; ie: – 80% traffic to AS 300 with segment list {100, 1005}. – 20% traffic to AS 200 with segment list {100, 1006}. – Prefix <NLRI/Length> segment list {100, 1003} – Prefix <NLRI/Length> segment list {100, 1004} Egress Peer Engineering (EPE) R2 1001 300 • Egress Peer Engineering (EPE) defines three BGP Peering SIDs, that allow for programming of source- routed inter-domain paths; PeerNodeSID, PeerAdjSID, and PeerSetSID. • R1 is an EPE-enabled egress router and allocates the following: Incoming Label Operation Outgoing Interface 1001 POP Link to R7 1002 POP Link to R8 1003 POP Upper link to R9 1004 POP Lower link to R9 1005 POP Load-balance on any link to R9 1006 POP Load-balance on any link to R7 or R8 R1 AS 200 AS 300 R7 R8 R9 EPE controller BGP-LS Node-SID 100 CoarseGranular Public
  9. 9. 10 © Nokia 2017 Public Copyright and confidentiality The contents of this document are proprietary and confidential property of Nokia. This document is provided subject to confidentiality obligations of the applicable agreement(s). This document is intended for use of Nokia’s customers and collaborators only for the purpose for which this document is submitted by Nokia. No part of this document may be reproduced or made available to the public or to any third party in any form or means without the prior written permission of Nokia. This document is to be used by properly trained professional personnel. Any use of the contents in this document is limited strictly to the use(s) specifically created in the applicable agreement(s) under which the document is submitted. The user of this document may voluntarily provide suggestions, comments or other feedback to Nokia in respect of the contents of this document ("Feedback"). Such Feedback may be used in Nokia products and related specifications or other documentation. Accordingly, if the user of this document gives Nokia Feedback on the contents of this document, Nokia may freely use, disclose, reproduce, license, distribute and otherwise commercialize the feedback in any Nokia product, technology, service, specification or other documentation. Nokia operates a policy of ongoing development. Nokia reserves the right to make changes and improvements to any of the products and/or services described in this document or withdraw this document at any time without prior notice. The contents of this document are provided "as is". Except as required by applicable law, no warranties of any kind, either express or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose, are made in relation to the accuracy, reliability or contents of this document. NOKIA SHALL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENT or for any loss of data or income or any special, incidental, consequential, indirect or direct damages howsoever caused, that might arise from the use of this document or any contents of this document. This document and the product(s) it describes are protected by copyright according to the applicable laws. Nokia is a registered trademark of Nokia Corporation. Other product and company names mentioned herein may be trademarks or trade names of their respective owners.

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