DevoFlow: Scaling Flow Management for High Performance Networks

Transcription

1 DevoFlow: Scaling Flow Management for High Performance Networks SDN Seminar David Sidler

2 Smart, handles everything Controller Control plane Data plane Dump, forward based on rules Existing hardware can be used David Sidler

3 Possible bottlenecks Controller, addressed by others Traffic between switches and controllers Switches Original goal of SDN: Full control & visibility over all flows to compute optimal flow rules Performance vs Optimal flow rules David Sidler

4 3 Key Goals of DevoFlow Keep flows in the data-plane Maintain enough visibility over network flows Simplify design and implementation of fast switches David Sidler

5 Why is performance an issue? Overheads in OpenFlow David Sidler

6 OpenFlow - Intrinsic Overheads Installs 2N flow rules Controller N-switch path, N=4 2N + 4 extra packets per flow => N bytes to/from controller N=4: 670bytes Internet: on average 20 packets per flow Datacenter: median flow has 1KB of payload David Sidler

7 Overhead I Flow Setup Latency overhead Arrival rate: ~30/s Controller 17Mbit/s For 40 servers: 1200 flows to controller 238 * 1200 = 285Mbit/s - Wimpy CPU -low bw btw CPU and ASIC Excluding: Flows from other switches Statistics gathering David Sidler

8 Overhead II Gathering Flow Stats Push-based: Only indicates creation or time-out of a flow Pull-based: Required Frequency: 500ms Measured: 5600 entries: ~1s 3200 entries: ~500ms Top of rack switch can contain ~78K entires => 15s David Sidler

9 Flow Setup vs. Stats Gathering David Sidler

10 Other Overheads Switch state size Wildcard rules require TCAMs (expensive) OpenFlow matches against multiple fields Controller Requirement for scalable controllers, related work David Sidler

11 Overhead - Summary Switch CPUs are wimpy Bandwidth between control & data plane limited Flow setup and statistics gathering are competing for bandwidth Controller need to be scalable Switches require more state size (larger TCAMs) David Sidler

12 DevoFlow David Sidler

13 Devolving control Rule Cloning Wilcard rules TCAM Exact match rules packet Lookup Clone & insert rule IP SRC IP DEST PORT SRC PORT DST PROT TCP IP SRC IP DEST PORT SRC PORT DST PROT * * * 80 TCP David Sidler

14 Devolving control Local Actions Multipath support on clone pick an output port according to probability distribution Wildcard: More State space required IP SRC IP DEST PORT SRC PORT DST PROT Output * * * 80 TCP 1(20), 2(10), 3(70) Exact: IP SRC IP DEST PORT SRC PORT DST PROT Output TCP 3 Rapid re-routing install fallback rules in case of link failure David Sidler

15 Efficient statistics collection Sampling sflow Triggers and reports threshold-based trigger detect elephant flows Approximate counters top-k flow (bytes) David Sidler

16 Evaluation Traffic to Controller David Sidler

17 Evaluation Flow Table Entries David Sidler

18 Evaluation Throughput n: number of servers part in shuffle phase (128MB) k: number of connections to other servers David Sidler

19 Evaluation Revisiting Overheads Overhead of installing a flow rule? Overhead is the same, but less rules are installed Traffic between data and control plane? Reduced efficient statistics gathering & less flow setups Switch state size? depends Scalability of the controller? Reducing load, other work on this David Sidler

20 DevoFlow Discussion Baseline a single switch, HP 5406zl Requires new switch hardware costs? Rule Cloning, Multipath, Triggers, Approx. counters Which of this functionality is required? What is the impact? Which overheads remain? Graceful switch from OpenFlow to DevoFlow? Evaluation on actual hardware instead of simulation David Sidler