This fork of Open vSwitch [1] implements stochastic switching for packets. Open vSwitch switches offer an option to split flows travelling through a switch, which can be used to implement link load balancing.
The problem is that this option is based on a hash of a limited set of header fields [2]. As most header fields remain constant in any given communication session, flows will be forwarded to the same link for the entirety of their session. When simulating load balancing using the hash method, a very large number of flows are required to ensure proper balancing. This scales very poorly for simulators.
Stochastic Packet Switching is a quick-and-dirty method to solve this issue. It implements stochastic switching in the dp_hash method of Open vSwitch switches [2].
This version is based off Salahuddin's Stochastic Switching [3] with code rewritten for Open vSwitch v2.15.0.
Copy ofproto-dpif-xlate.c to the ovs/ofproto directory, then follow the installation instructions on the Open vSwitch website [1]. Clone this repository with the following command.
git clone --recurse-submodules git://github.com/tanner-andrulis/stochastic-ovs.git
The quick-install script installs on Linux systems with default options. Quick install is tested and working on the Mininet v2.3.0 [5] virtual machine.
To run quick install, issue:
sudo -s git clone --recurse-submodules git://github.com/tanner-andrulis/stochastic-ovs.git chmod -R 700 stochastic-ovs cd stochastic-ovs ./quick-install
Open vSwitch daemon can be started as usual.
sudo -s export PATH=$PATH:/usr/local/share/openvswitch/scripts ovs-ctl stop ovs-ctl start
Buckets are set to use stochastic switching by using the default dp_hash selection method. As this is the default selection method for Open vSwitch routers, creating any select group will default to stochastic switching [4].
To force a dp_hash / stochastic selection method, ensure the following is in your group declaration.
type=select,selection_method=dp_hash
This exercise is modified from Salahuddin's exercise [3]. This exercise involves building a topology where two hosts can communicate with each other over two paths. To ensure packets are split properly, paths are set with weights of 65 and 35, and an iperf session is used to generate a large number of packets. Finally, packets are counted by Mininet to check that they are being forwarded in the proper porportions.
Ensure Mininet [5] and Python3 [6] are installed. Then, start the Open vSwitch daemon if it is not started already.
sudo -s export PATH=$PATH:/usr/local/share/openvswitch/scripts ovs-ctl stop ovs-ctl start
Run the Python script located in the examples directory. This script builds the exercise topology and starts Mininet.
cd example ./build_topology.py
Run the Bash script in the examples directory. This script creates the two flows for packets to traverse. Pay special attention to line 3 of script.sh. This line invokes stochastic switching.
sh ./add_flows.sh
Open an Xterm window for host h0 and h9.
xterm h0 h9
*In the Xterm window for host h9* start an iperf server session to receive and respond to UDP packets from host h0.
iperf -s -u -i 1
*In the Xterm window for host h0* start an iperf client session to send UDP packets to host h9 for ten seconds.
iperf -c 10.0.9.2 -u -i 1 -b 50M -t 10
*In the original Mininet window* check the number of packets sent on ports 4 and 5 for switch s7. Switch s7 is the separation point for the two flows; we should see that port 4 sends around 35% of the total packets, while port 5 sends 65%.
sh ovs-ofctl dump-ports s7 -O OpenFlow15
Stochastic OVS incurs a considerable overhead compared to standard Open vSwitch. For a much faster equivalent with negligible overhead, see https://github.com/tanner-andrulis/Weighted-Tunnels
All sites accessed 6/22/2021
| [1] | (1, 2) Website at https://www.openvswitch.org/ and Github at https://github.com/openvswitch/ovs |
| [2] | (1, 2) Field list section can be found in the ovs-fields section of the Open vSwitch man pages https://www.openvswitch.org/support/dist-docs/ |
| [3] | (1, 2) https://github.com/saeenali/openvswitch/ |
| [4] | Additionally, if you're running OpenFlow versions before 15, dp_hash is the only option available. OpenFlow versions can be specified in the command line call to add groups, e.g. "ovs-ofctl -O OpenFlow15" |
| [5] | (1, 2) http://mininet.org/ |
| [6] | https://www.python.org/downloads/ |
Below is copied from the Open vSwitch license, and covers all in the ovs/ directory. All other files are licensed under Apache 2 as well.
The following is a summary of the licensing of files in this distribution. As mentioned, Open vSwitch is licensed under the open source Apache 2 license. Some files may be marked specifically with a different license, in which case that license applies to the file in question.
Files under the datapath directory are licensed under the GNU General Public License, version 2.
File build-aux/cccl is licensed under the GNU General Public License, version 2.
The following files are licensed under the 2-clause BSD license. include/windows/getopt.h lib/getopt_long.c lib/conntrack-tcp.c
The following files are licensed under the 3-clause BSD-license include/windows/netinet/icmp6.h include/windows/netinet/ip6.h lib/strsep.c
Files under the xenserver directory are licensed on a file-by-file basis. Refer to each file for details.
Files lib/sflow*.[ch] are licensed under the terms of either the Sun Industry Standards Source License 1.1, that is available at: http://host-sflow.sourceforge.net/sissl.html or the InMon sFlow License, that is available at: http://www.inmon.com/technology/sflowlicense.txt