Software Defined Networking (SDN)

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Occasional Contributor I

Can SDN work with Openflow and STP ?

Hello community!

 

I have a question regarding the SDN topology. When I enable openflow on 4 switches, the topology does not show the path between them. I am guessing that it is because MSTP is enabled. I strongly believe that the path between switches will be shown once the STP of the VLAN within openflow is disabled. Have someone experienced something like this before? 

 

If the answer is yes, my switches are configured to be "stand-alone" but if the STP is disable on the openflow VLAN, how can we be 100% sure that my network will be loop-free if my controllers fail? 

 

 

Aruba Employee

Re: Can SDN work with Openflow and STP ?

Hey cquirozb,

 

OpenFlow should operate correctly with STP, when they're configured properly to coordinate. The VAN SDN controller discovers links between switches (and therefore the topology) by generating packets from ports with a state 'live' in the OpenFlow Monitor -> Ports screen. I would assume that these ports are not reported by the switch as 'live' due to MSTP. The topology shown by the VAN SDN controller should match the L2 broadcast domain. Therefore if the links are not shown, I wouldn't expect L2 connectivity to work either.

 

For your VAN SDN controller, do you have ControllerManager.hybrid.mode configured to 'true' or 'false'? If the setting is 'true', then the VAN SDN controller will rely upon traditional switching to form a loop-free topology (either via wiring, STP, etc). This is the setting recommended when using OpenFlow as an overlay to add functionality to an existing traditional network.

 

If the setting is 'false', then the VAN SDN controller will take control of all forwarding on the OpenFlow-enabled vlans (including loop resolution). This setting should be used in a new deployment where you'd like to write custom apps to control packet forwarding.

 

I wrote the attached whitepaper a few years ago to explain the difference between hybrid and pure OpenFlow. The content is still relevant, it's just the branding (HP vs HPE Aruba) that is not current.

 

Shaun

Occasional Contributor I

Re: Can SDN work with Openflow and STP ?

Hello Shaun! 

 

Thank you for your answer.

 

Indeed, I have them working on hybrid mode and the ports shown "live" and I saw switches on "Openflow Topology". Nevertheless, I wasn't able to see the lines between them. All I saw was my swtiches but without any lines connecting them. This is maybe because of MSTP? 

 

Carlos Quiroz

Aruba Employee

Re: Can SDN work with Openflow and STP ?

Hi Carlos,

 

I think the best way to identify root cause is to use the OpenFlow Monitor to view the control plane activity. When a switch connects to the controller or a port comes up, you should see a message like this in the OpenFlow monitor. This is what instructs the switch to send a link-discovery packet:

 

{ofm:[V_1_3,PACKET_OUT,110,5361463],acts=[{Act:[OUTPUT,len=16],port=0x1(1),maxLen=65535(NO_BUFFER)}],frameSize=70,packet=[[ETHERNET, LLDP], dst=01:80:c2:00:00:0e, src=70:10:6f:86:67:7f]}

 

From the directly connected switch, you should see a similar message for PACKET_IN, but I'm guessing you won't see that since the link isn't being discovered.

 

I've attached another whitepaper (also relevant, but using out-of-date HP branding) which explains some of the caveats to link discovery. Of particular note would be page 4, where some of the Comware differences are explained in regard to how vlan tagging/trunking is handled.

 

Shaun

Occasional Contributor I

Re: Can SDN work with Openflow and STP ?

Hello Shaun! 

 

Thank you very much for all the information that you provided me!!

 

I did a deep research to find out if it was possible to do the configuration in a different way since we were working with a VLAN that was not assign to any port but the trunks. I think that we cannot untagged VLANs over a trunk port on HP switches (Correct me if Im wrong since I am more a Cisco guy). Also, the requirement to untagged the VLAN of switches was complicated since we have tons of switches. So, I started to reach out for people who had previous experience with HP SDN controller and found out that we could do something on the controller to tag the BPDU packets. Here is the command that was given to me: 

 

curl  --header "X-Auth-Token: <Auth Token> " --header "Content-Type:application/json" -ksS --request POST --url https://<Controller IP>/sdn/v2.0/net/devices/<DPID of the device>/linkDiscoveryVlan/<Openflow-vlan-ID>

 

In my case, I have to use the following: 

 

curl  --header "X-Auth-Token: e08a33a5f86949638f8493e48898ceb2 " --header "Content-Type:application/json" -ksS --request POST --url https://10.213.194.52:8443/sdn/v2.0/net/devices/<00:01:2c:23:3a:34:1e:4d>/linkDiscoveryVlan/<2307>

 

I have to say that thanks to the docummentation that you provided me I got into the right direction to find the solution of the problem. 

 

I hope this could be helpful for someone else!

 

Thanks a lot Mr.! 

 

 

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