Cengiz Alaettinoglu. SDN Traffic Engineering A Natural Evolution

Transcription

1 Cengiz Alaettinoglu SDN Traffic Engineering A Natural Evolution

2 What is Traffic Engineering (TE)? Minimizes the worst link utilization Alleviates traffic congestion Better/longer use of capital expenditure Routing traffic around congested links Can use shortest as well as non-shortest paths IGP metric tuning, RSVP-TE, segment routing Confidential. Copyright 2014 Packet Design 2

3 Evolution of Traffic Engineering Offline traffic engineering Optimal but not adaptive On device traffic engineering Adaptive but not optimal Software defined networking Best of both worlds, yet simpler; simplicity enabled by Segment routing Push based telemetry SDN Traffic Engineering App Confidential. Copyright 2014 Packet Design 3

4 Offline Traffic Engineering Topology model Traffic demand matrix Optimization algorithm computes routes so that the worst link utilization is minimized Linear-programming Confidential. Copyright 2014 Packet Design 4

5 Pros and Cons of Offline Traffic Engineering Very good link utilization values Network model is hard to keep accurate Traffic demand matrix is hard to compute Optimization algorithm is very slow Hours to days Can not adopt to failures Too many tunnels (N^2) Some paths may be surprisingly long Confidential. Copyright 2014 Packet Design 5

6 On Device Traffic Engineering All routers redistribute available bandwidth of its links Each router Sets up 1-N tunnels to other routers Monitors the utilization of these tunnels (auto-bandwidth) Triggers a re-optimization when utilization changes Uses CSPF (constraint based shortest path first) to compute the paths Signals the path and reserves bandwidth using RSVP Confidential. Copyright 2014 Packet Design 6

7 Pros and Cons of On-Device Traffic Engineering Very good link utilization values Each router is selfish in optimization No network wide optimization Network model is hard to keep accurate Traffic demand matrix is hard to compute Optimization algorithm is very slow Hours to days Can not adopt to failures Too many tunnels (N^2) Some paths may be surprisingly long Impact on IGP, particularly convergence times Race conditions after failures Long-lived FRR RSVP-TE high-state and high-refresh overhead Confidential. Copyright 2014 Packet Design 7

8 Example Deployments Small Medium Large Routers Links Tunnels Majority of the tunnels have very small amount of traffic No TE needed Confidential. Copyright 2014 Packet Design 8

9 Link / Tunnel Distribution Most links carry small number of tunnels Small number of links carry a lot of tunnels Confidential. Copyright 2014 Packet Design 9

10 Lets See What Happens When a Link Fails NNOV-CR1-B M10-CR1-B fails at :04: Carries 327 tunnels 22 head-end routers Head routers get a signal via RSVP-TE and re-optimize Race to available bandwidth Each optimizes for itself They donot know what the other 21 routers need Confidential. Copyright 2014 Packet Design 10

11 5 Routers for 9 tunnels Fail to Find a Path Time Head-end Operation Tunnel Next State :06: VLGD-RGR3 Change Tunnel State RT-VLGD_RGR3-to-M10_CR2A Oper Status: Down :06: VLGD-RGR3 Change Tunnel State nonrt-vlgd_rgr3-to-m10_cr2a Oper Status: Down :07: VLGD-RGR2 Change Tunnel State RT-VLGD_RGR2-to-M10_CR1A Oper Status: Down :07: VLGD-RGR2 Change Tunnel State nonrt-vlgd_rgr2-to-m10_cr1a Oper Status: Down :11: NNOV-RGR1 Change Tunnel State xyz:12389:3456:mvpn:v3456-vgtrk Oper Status: Down :23: ARKH-RGR1 Change Tunnel State RT-ARKH_RGR1-to-M10_CR1A Oper Status: Down :23: ARKH-RGR1 Change Tunnel State nonrt-arkh_rgr1-to-m10_cr1a Oper Status: Down :24: SKTV-RGR2 Change Tunnel State RT-SKTV_RGR2-to-M10_CR1A Oper Status: Down :24: SKTV-RGR2 Change Tunnel State nonrt-sktv_rgr2-to-m10_cr1a Oper Status: Down This can be avoided with a centralized optimization solution! Confidential. Copyright 2014 Packet Design 11

12 An Example Failed Tunnel This tunnel only requests 34Mbps Its shortest IGP path does not have this bandwidth Confidential. Copyright 2014 Packet Design 12

13 Stuck FRR Tunnels What happens when a tunnel fails to optimize and it is FRR protected? FRR is stuck Usually no reservations are made on these paths Confidential. Copyright 2014 Packet Design 13

14 AN SDN APPROACH Confidential. Copyright 2014 Packet Design 14

15 What do We Really Want Real-time model Alleviate congestion especially after a link failure Create as few tunnels as necessary Very small signaling overhead Very small IGP overhead No dynamics due to utilization changes Network wide centralized optimization Confidential. Copyright 2014 Packet Design 15

16 SDN Promises a Solution Segment routing (SR) replaces RSVP Provides uncompromised functionality Simple control plane Push based telemetry for traffic matrices YANG model based SDN Controller is part of the network control plane Has real-time topology Enables manipulating paths on the devices using a standard south bound protocol SDN Traffic Engineering App optimizes paths network wide As few or as many tunnels as policy allows Confidential. Copyright 2014 Packet Design 16

17 Segment Routing Segment routing simplifies IP/MPLS control plane No need to run LDP or RSVP-TE Functionality is not compromised Can forward traffic on none-shortest paths for traffic engineering Detour, bypass FRR (fast re-route) and IP LFA protection Secondary paths SLA conforming service specific paths (e.g. L2/L3 VPNs) SDN programmability Confidential. Copyright 2014 Packet Design 17

18 TE Needs Shortest and Non-shortest Paths SR can Encode Any Path A B V W X Y C D Z 1 Segment (shortest IGP path) Go to Z on shortest path (node segment) A B V W X Y A B V W X Y C C D D Z Z 3 Segments Go to C on shortest path Go to X on link 3 (adjacency segment) Go to Z on shortest path 5 Segments Go to B on shortest path Go to W on shortest path Go to Y on shortest path Go to D on shortest path Go to Z on shortest path Confidential. Copyright 2014 Packet Design 18

19 Push Based Telemetry We Still Need Traffic Demand Matrices How much customer traffic enters the network in Vietnam and Destined to Tokyo Demand does not change based on IGP routing (less ignore BGP for now) Traditionally netflow is used for this and can still be used Push and model based telemetry is has very promising features, including much more real-time view Confidential. Copyright 2014 Packet Design 19

20 YANG Model Pushed by Ingress Routers +--ro traffic-collector +--ro afs +--ro af* [af-name] +--ro counters +--ro prefixes +--ro prefix* +--ro ipaddr? +--ro mask? string string +--ro label? Tc-oper-local-label +--ro base-counter-statistics +--ro transmit-packets-per-second-switched? uint64 +--ro transmit-bytes-per-second-switched? uint64 +--ro count-history* +--ro event-start-timestamp? uint64 +--ro event-end-timestamp? uint64 +--ro transmit-number-of-packets-switched? uint64 +--ro transmit-number-of-bytes-switched? uint64 +--ro is-valid? boolean +--ro traffic-matrix-counter-statistics +--ro transmit-packets-per-second-switched? uint64 +--ro transmit-bytes-per-second-switched? uint64 +--ro count-history* +--ro event-start-timestamp? uint64 +--ro event-end-timestamp? uint64 +--ro transmit-number-of-packets-switched? uint64 +--ro transmit-number-of-bytes-switched? uint64 +--ro is-valid? boolean +--ro prefix? string Similar content to netflow for traffic matrix generation No port/proto level detail OpenConfig standardizes the model Vendor extensions Pushed from the routers Few seconds to minutes Efficient transfer of data Binary encoded using Google ProtoBuf Confidential. Copyright 2014 Packet Design 20

21 Traffic Engineering as an SDN App SDN App manages traffic demand Current as well as future IGP does not have to signal available bandwidth Push based telemetry or netflow based matrices can be generated SDN App computes paths and allocates bandwidth Centralization yields better resource optimization Only creates as many tunnels as necessary SDN App adapts to failures and repairs No race conditions after failures and repairs Segment routing can be used as a simplification SDN controller makes this an abstraction for the APP 21

22 Reducing the N^2 Tunnels Only generated tunnels for traffic going over congested links Tunnels no longer needs to be configured apriori at the routers Only create them if they will have a positive impact Special case: Under normal conditions don t generate any tunnels Under failure conditions generate as necessary Do not create tunnels when IGP path satisfies the constrains These are easy to implement in software but hard to do in each device without a global picture Confidential. Copyright 2014 Packet Design 22

23 Illustration 1 Gbps links Two elephant flows 850Mbps west to east 500Mbps north to south Lots of mice flows Confidential. Copyright 2014 Packet Design 23

24 Concluding Remarks SDN simplifies running a traffic engineered network Magic is in the SDN App on the top This App needs enablers from the infrastructure SDN controllers Segment routing Push based telemetry NetConf/YANG, PCEP and other south bound protocols Confidential. Copyright 2014 Packet Design 24