software-defined networking & OpenFlow

Question

I'm trying to dive into these new concepts, SDN and OpenFlow. One thing that is not clear to me, is how the traditional routing (OSPF, BGP etc.) done in SDN, or it is completely gone and replaced with some lightweight mechanisms instead?

I would appreciate any hints, links to get better understanding on this. Thanks!

Mark

Oxidase

Answer 1

In the SDN world the controller sets up the data plane in each router and switch to ensure flows are forwarded in some desirable way. The controller needs to be given the logic to make these routing decisions. If you would like to use a traditional mechanism such as OSPF you can install something like RouteFlow on your controller (https://sites.google.com/site/routeflow/). Alternatively though you may decide to use some other more relevant or desirable mechanism. SDN opens up a new world of possibilities.

For example imagine you have two routes between two locations. One route is extremely expensive to run but is also low latency and gets the traffic across more quickly. the other route is longer and has higher latency however it is very cheap to run. You may decide that you want to route specific traffic flows via one path rather than another. Eg. your bosses traffic takes the fast route (so he doesn't beat you up all the time) but your colleagues traffic takes the slower route (after all he did steal the cookies you left on your desk!). Or, your email traffic takes the slower route and your trading/real time application traffic takes the fast route.

Eight

Answer 2

With SDN, each switch/router basically becomes a "dumb" device that only does what it is told to do. A centralized SDN server will have all the required information about the whole network to be able to determine and configure the required routing/switching tables for all switches/routers involved.

Therefore, I guess the answer to your question is that the traditional dynamic routing will not be done in SDN.

Craniotomy

@wooki919, thanks for comment. I was also thinking that many of current complex routing protocols would go away in SDN world, however think about virtualization, as one of applications of SDN, and it is not obvious that dynamic routing won't be necessary, i.e. VMs might be running in different data centers on physically separate networks, so routing (OSPF, RIP) still would be in need. Am I wrong ? – Oxidase

Yes of course a form of dynamic routing will be needed. What I meant was the 'traditional' form of dynamic routing that involves each router communicating routing information with one another will no longer need to happen. Also the new dynamic routing that occurs on the SDN server will (hopefully) be far more sophisticated than RIP/OSPF/BGP, taking into account multiple factors at the same time (e.g. hop count, capacity, etc) to minimize congestion. If congestion can't be avoided then SDN could even automatically apply user defined QoS as needed. – Craniotomy

I don't think SDN and OpenFlow enabled Networking makes "switch/router basically becomes a "dumb" device" instead make more intelligent and more Learning based system, which can revolutionize the networking architecture. Beside there are 2 flavour of switches available - 1. Pure OF Switch(Only OF) and 2. Hybrid OF Switch (OF enabled- which support OF protocol in addition to the tradition way of interactions and protocols) – Johnette

Answer 3

In SDN, controllers are used to provide functionality to the openflow switches(dumb).

Consider these two parts,

1) Controllers: These are the programs that run on any device with the logic may be l2/l3 and make the switches connected to it according to the algorithms defined in the controller. There are some controller APIs like POX,NOX,PYRETIC, FLOODLIGHT on different languages, in market that you can implement to write your own controller.

2) Switches: The controllers control the switches. Fine! But how? There must be some protocol that is used to provide communication between them, this is what we call OpenFlow Protocol. The controller implements the functionality say OSPF/BGP using the controller's API and the openFlow API together.

Finally this is the structure that comes in imagination.

Controller(at some IP say 192.168.56.101) providing OSPF/firewall/URL filtering or any functionality to the openflow switches >> OpenFlow Switch or switches(dumb) used for connectivity of hosts >> then there is/are Host(s): that are normally linux based if you use mininet emulator.

Darelldarelle

As a summarized answer , yes OSPF/BGP functionality is written using these controllers APIs I mentioned in my post. Check RouteFlow for OSPF/BGP , it uses third party tools to achieve this purpose. sites.google.com/site/routeflow/home – Darelldarelle

Answer 4

Routing does take place with SDN, yet it is centralized on a so-called controller. Most legacy routing protocols are heavy just because of the requirement to synchronize a distributed database of routing tables across the network infrastructure. With SDN, the routing process becomes a simple application that handles a centralized database. The controller then transmit routing tables to network equipment ...

Woodson

Answer 5

About the resources part ,

I am not advertising or endorsing per say, but Nick Feamster(from Georgia Tech) has been offering SDN course on coursera. The contents is quite neat. Also, search for few interviews conducted by Nick and many renowned personalities from SDN space talk about various issues.

PS: I am not advertising as such, I took the course and got quite clear understanding about SDN.

Hosbein

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