This document discusses implementing equal cost multipath routing (ECMP) in the OpenSDNCore software-defined networking (SDN) controller. It begins with introductions to ECMP and SDN, then outlines problems with routing, communication between controllers and switches, and packet forwarding. It proposes using the arc cutting method to calculate multiple equal cost paths and the OpenFlow FlowMod and GroupMod messages to implement paths on switches. Random and hash-based approaches to packet forwarding across paths are presented and compared. A demo topology is shown, with expected outcomes being successful ECMP implementation, documentation, communication, and experiences gained.

1. UWB
Equal Cost Multipath Routing
in FOKUS OpenSDNCore
Hai Dinh Tuan
Next Generation Networks & Future Internet Technologies Projects

2. • Introduction – ECMP & SDN
• Problems
• Solutions
• Demo
• Remark
Agenda

3. The separation of
control plane (routing
functionalities) and
data plane (forwarding
functionalities)
Introduction - SDN
Source: SDNCentral

4. Shortest path first (SPF) algorithm calculates the single shortest path
from a source node to a destination is used in Link-state protocols
such as OSPF and IS-IS.
Equal Cost Multipath is a Traffic Engineering technique that enables
using several equal cost paths in IP routing
Introduction - ECMP

5. Introduction – ECMP (2)
Which path(s) is used for packet forwarding from A to G?

6. Shortest Path First
Only 1 path {A,D,G} is stored in forwarding table

7. Equal Cost Multipath Routing
Multiple paths {A,D,G}, {A,E,D,G}, {A,E,F,G} are used for forwarding

8. Routing
Problems in this project
IMPLEMENT ECMP IN OPENSDNCORE
Controller-switch
communication
Forwarding
How to calculate all
possible paths
How to implement
all paths in switches
How to choose path
for packet forwarding
Controller Switch

9. Routing Problems

10. “Set each link’s cost along the shortest path to infinite, and run the
shortest path calculation again each time”
Arc cutting method

11. How it works (1)
A single shortest part is discovered by Dijkstra's algorithm as normal

12. How it works (2)
Delete one link of shortest path by setting its weight to infinitive

13. How it works (3)
Execute Dijkstra's algorithm one more time and compare path cost

14. How it works (4)
Delete another link of shortest path

15. How it works (5)
Continue using Dijkstra's algorithm

16. How it works (6)
Finally, multiple equal cost paths are discovered

17. Communication Problems

18. What type of messsages to be transfered between controller
and swiches?
• FlowMod message
• GroupMod message
How to implement all posible paths?
• FlowMod “Add Flow Entry” message
• GroupMod “Add Bucket”message
Message types

19. Forwading Problems

20. Which path selection scheme should be used?
• Random?
• Round Robin?
• Hash-based?
Packet forwarding

21. Which path selection scheme should be used?
• Random
• Round Robin?
• Hash-based
Packet forwarding

22. Random ECMP

23. CONTROLLER SIDE

24. SWITCH SIDE

25. ENTRY LOOKUP OPERATION

26. Hash based ECMP

27. CONTROLLER SIDE

28. SWITCH SIDE

29. ENTRY LOOKUP OPERATION

30. Comparison
Random ECMP Hashed based ECMP
Advantages
Simple, implement only on
the Controller
Deterministic behavior
Work well with any switch
Provides control over
path selection
Disadvantages
Possible congestion
Require more
computing resources
Possible congestion

31. Demo Topology

32. Remark
Expected outcomes Results
Successful implementation of ECMP in OpenSDNCore
Detailed documentation
Efficient communication between supervisor and student
Gather experiences

33. Remark
Expected outcomes Results
Successful implementation of ECMP in OpenSDNCore
Detailed documentation (to be submitted)
Efficient communication between supervisor and student
Gather experiences

34. UWBTHANK YOU
Hai Dinh Tuan
Next Generation Networks & Future Internet Technologies Projects