The document discusses transitioning traditional networks to Software-Defined Networking (SDN) by utilizing existing routing protocols. It highlights the challenges of managing legacy networks and proposes a framework that allows SDN controllers to program routers using standardized routing messages instead of traditional configurations. The approach enables advanced traffic management and routing capabilities while maintaining compatibility with existing protocols, thus simplifying the deployment of SDN functionalities in conventional network infrastructures.

3. Enabling SDN in old school networks
with Software-Controlled Routing Protocols
ONS research track
Laurent Vanbever
March, 4 2014
Princeton University
Joint work with
Stefano Vissicchio (University of Louvain)

4. How do you go from a traditional network …
a SDN-enabled one?
Traditional

5. SDN-enabled
How do you go from a traditional network
to a SDN-enabled one?
Traditional

6. Well… not easily
Deploying SDN requires to upgrade network …
devices
management systems
operators
challenging, time-consuming and therefore costly

7. Wouldn’t it be great to manage
an existing network “à la SDN”?

8. Wouldn’t it be great to manage
an existing network “à la SDN”?
what does it mean?

9. Cisco Juniper Alcatel
Control-Plane
Data-Plane
Control-Plane
Data-Plane
Control-Plane
Data-Plane
Cisco IOS Juniper JunOS Alcatel TimOS
Instead of configuring your existing network
using configuration “languages”…

10. Cisco Juniper Alcatel
Control-Plane
Data-Plane
Control-Plane
Data-Plane
Control-Plane
Data-Plane
SDN Controller
Forwarding entries
(Floodlight, OpenDaylight,…)
… program it using your favorite SDN controller!

11. Cisco Juniper Alcatel
Control-Plane
Data-Plane
Control-Plane
Data-Plane
Control-Plane
Data-Plane
SDN Controller
How can a SDN controller program
forwarding entries in a router?
? ? ?

12. It uses an API that any router can understand
(hint: not OpenFlow)
Cisco Juniper Alcatel
Control-Plane
Data-Plane
Control-Plane
Data-Plane
Control-Plane
Data-Plane
SDN Controller
? ? ?

13. Routing protocols are good candidates for such an API
e.g., shortest-path routing
nearly all routers out there speak OSPF
all routers must speak the same language
Routing protocols…
messages are standardized
behaviors are well-defined and understood
implementations are widely available

14. How does it work?

15. Forwarding
Paths
Routing
Messages
MPLS
OSPF
BGP
A routing protocol takes routing messages as input
and computes forwarding paths as output

16. h(x)
g(x)
f(x)
Forwarding
Paths
Routing
Messages
A routing protocol is therefore a function
from routing messages to forwarding paths

17. Forwarding
Paths
SDN controller output
h(x)
g(x)
f(x)
Routing
Messages
Forwarding paths are produced
by the SDN controller
Known

18. Routing
Messages
Forwarding
Paths
Known
(Dijkstra, BGP Decision Process…)
Functions are given by the
routing protocol specification
h(x)
g(x)
f(x)

19. Inverse functions
Forwarding
Paths
Routing
Messages
Given a path and a function, our framework computes
corresponding routing messages by inverting the function
h(x)
g(x)
f(x)

20. IGP
BGP
Input
Network topology
Received routes
Type
Dijkstra
Decision process
Algorithm
Link-State
Path-Vector
The type of input to be computed depends on
the routing protocol(s) running in the network

21. IGP
BGP
Input
Network topology
Received routes
Type
Dijkstra
Decision process
Algorithm
Link-State
Path-Vector
The type of input to be computed depends on
the routing protocol(s) running in the network

22. IGP
BGP
Input
Network topology
Received routes
Type
Dijkstra
Decision Process
Algorithm
Link-State
Path-Vector

23. steer traffic on non-shortest paths
create ECMP paths (on a per-destination basis)
provision backup paths
SDN-controlled IGP enables to
in a centralized manner, on existing networks
SDN-controlled IGP enables advanced SDNish
TE functionalities, on top of a distributed protocol

24. 3
10
1
1
A B
C D
destinationsource
traffic flow
Consider this network where
a source sends traffic to 2 destinations

25. 3
10
1
1
A B
C D
desired
3
10
1
1
A B
C D
initial
As congestion appears on the (C,D) link, operators
might want to divert the orange flow to A

26. 3
10
1
1
A B
C D
impossible to achieve by
reweighing the IGP links
desired
3
10
1
1
A B
C D
initial
Moving only the orange flow to A is impossible
with an IGP as both destinations are connected to D

27. 3
1
1
A B
C D
virtual node
1
10
SDN-controlled IGP can move the orange flow by adding
a virtual node announcing the orange destination
V1
Traffic sent to V1 by C is physically sent to A

28. Theorem
A SDN-enabled IGP is powerful
A SDN-enabled IGP can make the routers use
any set of non-contradictory paths

29. Theorem
A SDN-enabled IGP is powerful
A SDN-enabled IGP can make the routers use
any set of non-contradictory paths

30. Theorem
A SDN-enabled IGP is powerful
any path is loop-free
paths are consistent
(e.g. [s1, a, b, d] and
[s2, b, a, d] are inconsistent)
(e.g., [s1, a, b, a, d] is not possible)
A SDN-enabled IGP can make the routers use
any set of non-contradictory paths

31. Given a physical topology and a set of path requirements,
a linear program computes an optimized virtual topology
physical
topology
+
paths requirements Integer
Linear Program
minimize topology size
[ RA, RB, RC, RD ]
ECMP(
[ RX, RY, RZ ],
[ RX, RW, RZ ])
[ RI, RJ, RK ], backup
[ RI, RL, RK ]
Optimizer
virtual
topology

32. Simplify controller implementation
most of the heavy work is still done by the routers
Maintain operators’ mental model
good old protocols running, easier troubleshooting
Facilitate SDN deployment
SDN controller can program routers and SDN switches
SDN-controlled routing enables to realize parts
of the SDN promises today, on an existing network

33. ONS research track
Laurent Vanbever
March, 4 2014
www.vanbever.eu
Enabling SDN in old school networks
with Software-Controlled Routing Protocols