You need to use the Exporter module in your module, and use the constant-holding module in your main program.

package Constants:

use strict;
use vars qw( @ISA @EXPORT_OK );

require Exporter;
@ISA = qw( Exporter );

use constant IP_ADDR = '192.34.56.78';

# and in another file

use Constants qw( IP_ADDR );
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