Brain Goo » networking

Linux HOWTO Enable Miltucast Ping (ICMP) Replies (Echo)

admin — Thu, 21 Apr 2011 17:50:07 +0000

The 2.6 Linux kernel does not respond to multicast ICMP Echo requests by default. This is a setting in /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

Test it:

# cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
1
#

Set it to 0 for ping replies:

# echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
0
#

Perl code to find an IP A in subnet B/C

admin — Tue, 05 Jun 2007 22:14:39 +0000

my $ip = '1.2.3.4';
my $block1 = '1.2.3.0/27';

if(checkip($ip, $block1)) {
    print STDOUT "$ip is in $block1\n";
}
else {
    print STDOUT "$ip is not in $block1\n";
}

sub checkip() {
    my $ip = shift;
    my $block = shift;

    @ip1 = split(/\./, $ip);
    $ip1 = $ip1[0] * 2**24 + $ip1[1] * 2**16 + $ip1[2] * 2**8 + $ip1[3];
    my @temp = split(/\//, $block);

    $ip2 = $temp[0];
    my $netmask = $temp[1];

    @ip2 = split(/\./, $ip2);
    $ip2 = $ip2[0] * 2**24 + $ip2[1] * 2**16 + $ip2[2] * 2**8 + $ip2[3];

    if( $ip1 >> (32-$netmask) == $ip2 >> (32-$netmask) ) {
            return 1;
    }
    return 0;
}