Hello @rathid I believe you are looking at this query
 

/**
 * @intent Gets the min and max MTUs for interfaces on a path
 */

getIface(ifaces, ifaceName) =
  foreach iface in ifaces
  where iface.name == ifaceName
  select iface;

ifaceMtus(path) =
  foreach hop in path.hops
  foreach device in network.devices
  where device.name == hop.deviceName
  foreach iface in device.interfaces
  foreach iface
    in getIface(device.interfaces, hop.egressIfaceName) +
       getIface(device.interfaces, hop.ingressIfaceName)
  where isPresent(iface.mtu)
  select iface.mtu;

@query
getPathMtuInfo(path: Path) =
  foreach mtus in nifaceMtus(path)]
  let minMtu = min(mtus)
  let maxMtu = max(mtus)
  select { "Min MTU": minMtu, "Max MTU": maxMtu, violation: minMtu != maxMtu };

This query is designed to be used as a Path Decorator you can learn more about Decorators here https://fwd.app/docs/enterprise/applications/nqe/nqe_decorators/

When enabled, you will see the decorator below the path indicating the Min, Max and Violation for a path. So to answer your question, In this query you don’t pass anything into that function, it happens automatically in-platform.

 

@rathid The decorators are meant to ingest a bunch of information from a path trace.  Putting that information into the query manually is not very practical.  

A path trace starts with a source and destination ip address, but then once the path is calculated there is a lot of data that is returned about each hop.

The decorator queries are not good for an automated workflow, they are good at showing extra data about a path in the UI.  There is just a lot of data that would have to be passed in if you tried to do it manually.

The decorator format is really good for the decorator feature.  For doing your own MTU check, it is better to use a non-decorator query.

-Tyson