Where are data types for yaml file defined?

For instance,

  • ip4_addr <--where is this defined
  • ipv4_source_address

I ask because I am getting netflow records that include some extra mac address fields, and they are turning to junk before getting stashed in elasticsearch. I want to know how to create a custom data type to receive these properly and was thinking I could look at the ip4_addr as an example.