Communicating between two openflow instances

[EnasAhmad]

Hi,

I created two OpenFlow instances on a 2930F switch (each with its own VLAN of course ). Is it possible to forward packets from one OpenFlow instance to the other? I am unable to create flow entries that would do that because it says that the output port does not exist. Even if I connect the two VLANs using a physical link (coming out from one VLAN to the other).

Thanks,

Enas

[ShaunWackerly · Accepted solution]

Hi Enas,

When you get a response from the switch that says "Output port does not exist" (in response to a flow-mod or packet-out), what that means is that the port you're attempting to forward to is not a member of the OpenFlow instance that you're attempting to modify.

For instance (pun intended), if you have two OF instances:

• Instance A: vlan 100, which contains ports 1,2 (untagged) and 3 (tagged)
• Instance B: vlan 200, which contains ports 3 (tagged) and 4,5 (untagged)

Then in a flow-mod or packet-out message to instance A, you'll be able to use port 1,2, or 3 as the output port. In a flowmod or packet-out to instance B, you'll be able to use port 3,4 or 5 as the output port. Notice that port 3 is accepted for either instance, because it is tagged on both vlan 100 and 200, so port 3 is a member of both instances.

If you needed to forward a packet from instance A to instance B, then you could (for example) connect port 2 to port 4 with a cable. To send packets from instance A to B, send out port 2 of instance A and they will arrive at port 4 of instance B.. Link-discovery should discover the link between instance A and B going over ports 2 and 4.

Shaun

[EnasAhmad]

Thanks Shaun for the useful information.

I am trying to achieve the second scenario, and I have connected a physical link as you have described between two untagged ports of the two vlans, however, I am still unable to send packets between the two vlans.

 I have read about trunk ports, should I make the two ports of the physical link as trunk ports in order for packets to travel between the vlans ?? 

Thanks,

Enas

[ShaunWackerly]

Hi Enas,

Could you post the output from the switch when "debug openflow" and "debug destination session" are configured (assuming you're using 16.03 firmware)? That should give the specific reason why the flowmod is being rejected. Are you including a vlan tag in the flowmod?

Regarding "trunk" ports, we'll need to clear up ambiguity. The term "trunk" can refer to tagging multiple vlans on the same physical link (vlan tagging) or it can refer to grouping multiple physical links into a single logical link (link aggregation). Based on your description, it sounds like you're referring to link aggregation (which uses the term "trunk" on the HPE Aruba firmware CLI). I don't think that link aggregation / trunking would help in this case, since the main purpose of link aggregation / trunking is to give physical link redundancy and higher bandwidth. In terms of packet forwarding direction, it is identical to a single physical link.

Shaun

[EnasAhmad]

Thank you very much Shaun, reading your post I took a closer look at my flow entries and indeed there was a mistake which is why packets never reached the end host in the second vlan. Now it works perfectly!

Thanks again!

Enas