Presentation at the ManFI workshop Ottawa, 10.05.2015

1. Institute of Computer Science
Chair of Communication Networks
Prof. Dr.-­Ing. P. Tran-­Gia
Investigating the Impact of Network Topology
on the Processing Times of SDN Controllers
Christopher Metter, Steffen Gebert, Stanislav Lange,
Thomas Zinner, Phuoc Tran-­Gia, Michael Jarschel*
www3.informatik.uni-­wuerzburg.de
* Nokia GmbH, Munich

2. Steffen Gebert
2Impact of Network Topology on the Processing Times of SDN Controllers
Metadata
u This paper was presented at the “The Seventh IFIP/IEEE
International Workshop on Management of the Future Internet”
(ManFI), colocated with IM`2015 in Ottawa, Canada.
u http://manfi.org
u Paper author version:
http://www3.informatik.uni-­wuerzburg.de/staff/steffen.gebert/author_versions/conf_510_author_versions.pdf

3. Steffen Gebert
3Impact of Network Topology on the Processing Times of SDN Controllers
Motivation – SDN Architecture
Data PlaneData Plane
C
D
C
D
Control Plane

4. Steffen Gebert
4Impact of Network Topology on the Processing Times of SDN Controllers
Impact of Controller Implementations on Message Processing Times
u Analysis of processing times for a L2 learning switch
§ Switching modules of OpenDayLight (ODL) and Ryu
§ Packet-­in/packet-­out pairs
– e.g., in case of unconnected switches or requests for non-­reachable
destinations
§ Packet-­in-­packet-­out/flow-­mod pairs
– e.g., to set a forwarding path in the flow table to a certain destination
u Topology emulation and packet-­in traffic generation
§ Controlled, low-­rate traffic emulation to reduce waiting times
§ Impact of network topology on the service times
– Unconnected topology (baseline)
– Fat-­tree topology (data center)
– WAN topologies (261 topologies from the Internet Topology Zoo)

5. Steffen Gebert
5Impact of Network Topology on the Processing Times of SDN Controllers
OFCProbe
github.com/lsinfo3/ofcprobe
u Controller performance analysis tool
§ Emulation of virtual OpenFlow-­enabled switches
§ Generate OF messages per switch
§ PCAP file playback
§ Configurable payload IAT distributions
§ Per-­switch statistics collection
C

6. Steffen Gebert
6Impact of Network Topology on the Processing Times of SDN Controllers
Topology Discovery
u Switches are configured to connect to the controller
u Controller has no information about links between switches
??
?
1
2
3
C

7. Steffen Gebert
7Impact of Network Topology on the Processing Times of SDN Controllers
?
Topology Discovery
u Controller injects LLDP packets (Link Layer Discovery Protocol)
u Switches flood them to all ports
?
LLDP
LLDP
PacketOut
(flood)
LLDP
?
1
2
3
C

8. Steffen Gebert
8Impact of Network Topology on the Processing Times of SDN Controllers
C
Topology Discovery
u Other switches receive packets and report packet-­in to controller
u Controller learns topology from information about incoming ports
?
PacketOut
(flood)
LLDP
PacketIn
(port 7)
LLDP
PacketIn
(port 2)
LLDP
Switch Port To Switch
2 2 1
3 7 1
1
2
3
2
7

9. Steffen Gebert
9Impact of Network Topology on the Processing Times of SDN Controllers
Processing Steps of a Controller for Packet-­Ins
1. Data reception
2. Decoding of OpenFlow message and classification
3. Attribute extraction and delegation to application module
4. Module-­specific processing
5. Response generation (e.g., packet-­out / flow-­mod message …)
6. Data transmission
Impact of controller implementation on module-­specific processing?

10. Steffen Gebert
10Impact of Network Topology on the Processing Times of SDN Controllers
Controller
C
Baseline Topology
u 20 switches, 1 host per switch, no connections between switches
u Resulting action in packet-­out message: flood

11. Steffen Gebert
11Impact of Network Topology on the Processing Times of SDN Controllers
Baseline Performance
u Emulated switches generate 16 packet-­ins one after another
u Controller responds with packet-­out message
u Periodic behavior in response times (per switch)
u Higher variation of processing times for ODL (JVM?)
u ODL outperforms Ryu

12. Steffen Gebert
12Impact of Network Topology on the Processing Times of SDN Controllers
C
u 20 switches, represents data center topology
Fat-­Tree

13. Steffen Gebert
13Impact of Network Topology on the Processing Times of SDN Controllers
Packet-­Out: Fat-­Tree
u Bursts of 16 packets are sent from one host to another
u Increased processing times compared to unconnected switches
u Similar average processing times, but high variation and outliers
when using ODL

14. Steffen Gebert
14Impact of Network Topology on the Processing Times of SDN Controllers
Flow-­Mod: Fat-­Tree
u Flow-­mods by utilizing Layer 2 learning switch module
u Processing times for flow-­mods 2-­8 times higher than packet-­outs
u ODL processing times stabilize after ~20 seconds
u Ryu has nearly constant processing times and outperforms ODL

15. Steffen Gebert
15Impact of Network Topology on the Processing Times of SDN Controllers
u Experiment performed on 261 WAN topologies
u CDF shows all measured processing times
u Ryu: Topology has no effect on processing times, flow-­mod
processing slightly slower than packet-­out processing
u ODL: High variation for packet-­out, flow-­mods significantly longer
Internet Topology Zoo – Aggregated Results

16. Steffen Gebert
16Impact of Network Topology on the Processing Times of SDN Controllers
Topology Investigation
u Analysis of the topology impact on the processing times
u Ryu: rather constant behavior, similar processing times for flow-­
mods and packet-­outs
u ODL: high impact of message type, varying processing times

17. Steffen Gebert
17Impact of Network Topology on the Processing Times of SDN Controllers
u Investigation of controller processing times
§ Emulated different network topologies using OFCProbe
§ Time measurements done directly within the controllers
§ Using Layer 2 switch modules (as starting point)
u Benchmarking results:
§ Ryu shows very constant response times
§ ODL faster for packet-­out, Ryu for flow-­mod
u Main take-­aways:
§ Test your own forwarding algorithms using different topologies!
§ OFCProbe now allows importing GraphML topologies
§ Measurement probes available for ODL and Ryu controllers1
1 source code on github.com/lsinfo3 (manfi2015-­perf-­* repos)
Summary

18. Steffen Gebert
18Impact of Network Topology on the Processing Times of SDN Controllers
OFCProbe Architecture
OF Controller
Best Effort
Traffic Generator
OpenFlow Connection Handler Module
Configuration
Communication
Layer
Traffic Generation
Layer
Traffic Generation Module
Statistics
Statistics:
PPS Module
Statistics: RTT
Module
Statistics:
Custom
Module
Interface
Configuration
Packets
Statistics
Implementation
Payload
OF Message
OF Reply
OF ReplyOF Reply