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flowlet_switching

README.md

Flowlet Switching


                          +--+
             +------------+s2+------------+
             |            +--+            |
             |                            |
             |                            |
             |            +--+            |
             |        +---+s3+----+       |
          +--+--+     |   +--+    |    +--+--+
+--+      |     +-----+           +----+     |     +--+
|h1+------+ s1  |                      | s6  +-----+h2|
+--+      |     +-----+           +----+     |     +--+
          +--+--+     |   +--+    |    +--+--+
             |        +---+s4+----+       |
             |            +--+            |
             |                            |
             |                            |
             |            +--+            |
             +------------+s5+------------+
                          +--+

Introduction

In the ECMP example, we used a very basic (but widely used) technique to load balance traffic across multiple equal cost paths. ECMP works very well when it has to load balance many small flows with similar sizes (since it randomly maps them to one of the possible paths). However, real traffic does not look as described above, real traffic is composed by many small flows, but also but very few that are quite bigger. This makes ECMP suffer from a well-known performance problem such as hash collisions, in which few big flows end up colliding in the same path. In this example use state and information provided by the simple_switch's standard_metadata to fix the collision problem of ECMP, by implementing flowlet switching on top.

Flowlet switching leverages the burstness of TCP flows to achieve a better load balancing. TCP flows tend to come in bursts (for instance because a flow needs to wait to get window space). Every time there is gap which is big enough (i.e., 50ms) between packets from the same flow, flowlet switching will rehash the flow to another path (by hashing an ID value together with the 5-tuple).

For more information about flowlet switching check out this paper

How to run

Run the topology:

sudo p4run

or

sudo python network.py

Monitor all the interfaces connecting s1 to the 4 middle switches. You can use tshark, tcpdump:

sudo tshark -i s1-eth2

(Do the same with the other three interfaces s1-eth3, s1-eth4 and s1-eth5).

Use the send script. The script will send TCP packets with the same 5-tuple but it will wait some time between them. Thus, since each packet will belong to different flowlet they will be hashed to different output ports.

mx h1
python send.py 10.0.6.2 <num_packets> <sleep_between_packets>