how to use $ns create-trace type file src dst op

The correct syntax of “$ns create-trace Drop file s0 d0” would be like the following one :

$ns create-trace Drop $outfile $s0 $d0

Where
$file is the file descriptor ( which we initiated like this : set outfile [open out.dat w]

$s0 is the source node
$d0 is the destination node