Metadata in openflow rule

Question

This Question is extension of the following

OpenFlow Rule Metadata

I would like to have this clarified, on my question about Metadata Let us say, I have an Open Flow rules, as below

Cookie=0x8000001, duration=228925.445s, table=17, n_packets=350, n_bytes=32424, priority=10,metadata=0xc000f30000000000/0xffffff0000000000 actions=goto_table:19

I wanted to understand the following

Do we have certain rule/ Algorithm , to determine these Metadata from a Packet.

because the Packet in OVS is actually switched based on Matching Metadata, Is that correct ?? ( At least according to the above flow rule )

• And the Packet itself does not carry the Metadata, then how exactly the packet hitting a flow matched against the Metadata.

  So, If I understood it correctly the Packets those are traversed between the flow-tables, are within the OVS application itself or Handled @OVS Application level, until it had determined Egress Port So in that Case, the MetaData are handled @OVS-Application level, until the Packets is send via Egress Port.

Is this correct??

Finally which Module in ODL is responsible for determine the Metadata, and I would like to understand from the code how exactly it was done.

Answer 1

The OpenFlow metadata field starts with a value of zero for every packets. Tables can then writes to this field and you can match on it in subsequent tables. It is only used to carry information from one table to the next, as explained in the OpenFlow specifications:

Metadata: a maskable register that is used to carry information from one table to the next.