use warnings;
use strict;

my @routers = ( "R1", "R2", "R3" );
my %interfaces =  (
	R1R0  => 1, R1R6  => 2,
	R2R0  => 3, R2R6  => 1,
	R3R61 => 2, R3R62 => 3,
);

for my $r (@routers) {
	my @ifs = grep {/^\Q$r\E\D/} keys %interfaces;
	for my $i (@ifs) {
		print "Router $r Interface $i\n";
	}
}