use IO::Socket::INET;
my $sock = IO::Socket::INET->new(Proto=>shift);
print "sock=$sock\n";

on 5.8.4
perl -w test.pl tcp = ok
perl -w test.pl udp = ok
perl -w test.pl icmp = ok

on 5.8.6
perl -w test.pl tcp = ok
perl -w test.pl udp = ok
perl -w test.pl icmp = NO