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finding netmask for "arbitrary" ip address

by jasonl (Novice)
on Nov 28, 2011 at 23:26 UTC ( #940493=perlquestion: print w/ replies, xml ) Need Help??
jasonl has asked for the wisdom of the Perl Monks concerning the following question:

I'm parsing an LDAP record that has an IPv4 address as one attribute, and then a list of IPv4 subnets in <network>/<dotted quad netmask> format as another attribute. I need to be able to first verify that the single IP address is a member of one of the subnets in the list, and then get the netmask of that subnet. Net::Subnet will tell me if it's a member of one of the subnets, but I can't follow the flow well enough to modify it to give me the netmask of the subnet in question (I'm not sure if it's really clever or really poorly-written, but either way I've spent quite a bit of time staring at it and am now hopelessly stuck). I need to be able to run this on any given server, most of which I won't have access to and won't have Net::Subnet installed, so I'm trying to do this internally.

Here is the code I've got so far; it runs as-is and will tell me whether it finds a hit or not, but without being able to grab the netmask, it's not useful. I'm also open to other implementation suggestions, but at this point I'm really curious about how this is actually working (for example, WTF is "return !!0"???). All of the subs outside of main() are from Net::Subnet, but I pared them down to the minimum to get them to do what I needed.

(And to clarify, this is only a POC--the LDAP bits are represented here by $ip, @true, and @false. $ip is a member of @true, but not @false.)

#!/usr/bin/perl -w use strict; use Socket; sub subnet_matcher { @_ > 1 and goto &multi_matcher; my ($net, $mask) = split m[/], shift; return ipv4_matcher($net, $mask); } sub ipv4_matcher { my ($net, $mask) = @_; $net = inet_aton($net); $mask = inet_aton($mask); my $masked_net = $net & $mask; return sub { ((inet_aton(shift) // return !1) & $mask) eq $masked_ +net }; } sub multi_matcher { my @nets = map subnet_matcher($_), @_; return sub { $_->($_[0]) and return 1 for @nets; return !!0; } } sub main { my $ip = "65.181.207.232"; my @true = qw(10.96.2.0/255.255.254.0 10.123.50.0/255.255.255.0 72 +.24.196.0/255.255.255.0 72.24.137.192/255.255.255.192 10.122.50.0/255 +.255.255.0 65.181.207.128/255.255.255.128); my @false = qw(10.96.2.0/255.255.254.0 10.123.50.0/255.255.255.0 7 +2.24.196.0/255.255.255.0 72.24.137.192/255.255.255.192 10.122.50.0/25 +5.255.255.0); my $matcherTrue = subnet_matcher(@true); my $matcherFalse = subnet_matcher(@false); print "matcherTrue = " . ($matcherTrue->($ip) ? "yes\n" : "no\n"); print "matcherFalse = " . ($matcherFalse->($ip) ? "yes\n" : "no\n" +); } main;

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Re: finding netmask for "arbitrary" ip address
by Khen1950fx (Canon) on Nov 29, 2011 at 02:35 UTC
    In the original, Net::Subnet, there were a couple of typos at lines 41 and 52. Heres the fixed source:
    package Net::Subnet; use strict; use Socket; use Socket6; use base 'Exporter'; our @EXPORT = qw(subnet_matcher subnet_classifier sort_subnets); our $VERSION = '1.02'; sub cidr2mask_v4 { my ($length) = @_; return pack "N", 0xffffffff << (32 - $length); } sub cidr2mask_v6 { my ($length) = @_; my $mask = "\x00" x 16; vec($mask, $_, 1) = 1 for 0 .. ($length - 1); return $mask; } sub subnet_matcher { @_ > 1 and goto &multi_matcher; my ($net, $mask) = split m[/], shift; return $net =~ /:/ ? ipv6_matcher($net, $mask) : ipv4_matcher($net, $mask); } sub ipv4_matcher { my ($net, $mask) = @_; $net = inet_aton($net); $mask = $mask =~ /\./ ? inet_aton($mask) : cidr2mask_v4($mask); my $masked_net = $net & $mask; return sub { ((inet_aton(shift) || return !1) & $mask) eq $masked_ +net }; } sub ipv6_matcher { my ($net, $mask) = @_; $net = inet_pton(AF_INET6, $net); $mask = $mask =~ /:/ ? inet_pton(AF_INET6, $mask) : cidr2mask_v6($ +mask); my $masked_net = $net & $mask; return sub { ((inet_pton(AF_INET6,shift) || return!1) & $mask) eq +$masked_net} } sub multi_matcher { my @v4 = map subnet_matcher($_), grep !/:/, @_; my @v6 = map subnet_matcher($_), grep /:/, @_; return sub { $_->($_[0]) and return 1 for $_[0] =~ /:/ ? @v6 : @v4; return !!0; } } use constant MATCHER => 0; use constant SUBNET => 1; sub subnet_classifier { # MATCHER, SUBNET my @v4 = map [ subnet_matcher($_), $_ ], grep !/:/, @_; my @v6 = map [ subnet_matcher($_), $_ ], grep /:/, @_; return sub { $_->[MATCHER]->($_[0]) and return $_->[SUBNET] for $_[0] =~ /:/ ? @v6 : @v4; return undef; } } sub sort_subnets { my @unsorted; for (@_) { my ($net, $mask) = split m[/]; $mask = $net =~ /:/ ? ($mask =~ /:/ ? inet_pton(AF_INET6, $mask) : cidr2mask_v +6($mask)) : ($mask =~ /\./ ? inet_aton($mask) : cidr2mask_v4($mask)) +; $net = $net =~ /:/ ? inet_pton(AF_INET6, $net) : inet_aton($net); push @unsorted, sprintf "%-16s%-16s%s", ($net & $mask), $mask, + $_; } return map substr($_, 32), reverse sort @unsorted; } 1; __END__ =head1 NAME Net::Subnet - Fast IP-in-subnet matcher for IPv4 and IPv6, CIDR or mas +k. =head1 SYNOPSIS use Net::Subnet; # CIDR notation my $is_rfc1918 = subnet_matcher qw( 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 ); # Subnet mask notation my $is_rfc1918 = subnet_matcher qw( 10.0.0.0/255.0.0.0 172.16.0.0/255.240.0.0 192.168.0.0/255.255.0.0 ); print $is_rfc1918->('192.168.1.1') ? 'yes' : 'no'; # prints "yes" print $is_rfc1918->('8.8.8.8') ? 'yes' : 'no'; # prints "no" # Mixed IPv4 and IPv6 my $in_office_network = subnet_matcher qw( 192.168.1.0/24 2001:db8:1337::/48 ); $x = $in_office_network->('192.168.1.1'); # $x is true $x = $in_office_network->('2001:db8:dead:beef::5'); # $x is false my $classifier = subnet_classifier qw( 192.168.1.0/24 2001:db8:1337::/48 10.0.0.0/255.0.0.0 ); $x = $classifier->('192.168.1.250'); # $x is '192.168.1.0/2 +4' $x = $classifier->('2001:db8:1337::babe'); # $x is '2001:db8:1337 +::/48' $x = $classifier->('10.2.127.1'); # $x is '10.0.0.0/255. +0.0.0' $x = $classifier->('8.8.8.8'); # $x is undef # More specific subnets (smaller subnets) must be listed first my @subnets = sort_subnets( '192.168.0.0/24', # second '192.168.0.1/32', # first '192.168.0.0/16', # third ); my $classifier = subnet_classifier @subnets; =head1 DESCRIPTION This is a simple but fast pure Perl module for determining whether a g +iven IP address is in a given set of IP subnets. It's iterative, and it doesn' +t use any fancy tries, but because it uses simple bitwise operations on strings +it's still very fast. All documented functions are exported by default. Subnets have to be given in "address/mask" or "address/length" (CIDR) +format. The Socket and Socket6 modules are used to normalise addresses, which +means that any of the address formats supported by inet_aton and inet_pton c +an be used with Net::Subnet. =head1 FUNCTIONS =head2 subnet_matcher(@subnets) Returns a reference to a function that returns true if the given IP ad +dress is in @subnets, false it it's not. =head2 subnet_classifier(@subnets) Returns a reference to a function that returns the element from @subne +ts that matches the given IP address, or undef if none matched. =head2 sort_subnets(@subnets) Returns @subnets in reverse order of prefix length and prefix; use thi +s with subnet_matcher or subnet_classifier if your subnet list has overlappin +g ranges and it's not already sorted most-specific-first. =head1 TRICKS =head2 Generating PTR records for IPv6 If you need to classify an IP address, but want some other value than +the original subnet string, just use a hash. You could even use code refer +ences; here's an example of how to generate dynamic reverse DNS records for I +Pv6 addresses: my %ptr = ( '2001:db8:1337:d00d::/64' => sub { my $hostname = get_machine_name(shift); return $hostname =~ /\.$/ ? $hostname : "$hostname.example +.org."; }, '2001:db8:1337:babe::/64' => sub { my $hostname = get_machine_name(shift); return $hostname =~ /\.$/ ? $hostname : "$hostname.example +.net."; }, '::/0' => sub { (my $ip = shift) =~ s/:/x/g; return "$ip.unknown.example.com."; }, ); my $classifier = subnet_classifier sort_subnets keys %ptr; while (my $ip = readline) { # We get IP adresses from STDIN and return the hostnames on ST +DOUT print $ptr{ $classifier->($ip) }->($ip), "\n"; } =head2 Matching ::ffff:192.168.1.200 IPv4 subnets only match IPv4 addresses. If you need to match IPv4-mapp +ed IPv6 addresses, i.e. IPv4 addresses with C<::ffff:> stuck in front of them, + simply remove that part before matching: my $matcher = subnet_matcher qw(192.168.1.0/22); $ip =~ s/^::ffff://; my $boolean = $matcher->($ip); Alternatively, translate the subnet definition to IPv6 notation: C<1.2 +.3.0/24> becomes C<::ffff:1.2.3.0/120>. If you do this, hexadecimal addresses s +uch as C<::ffff:102:304> will also match, but IPv4 addresses without C<::ffff +:> will no longer match unless you include C<1.2.3.0/24> as well. my $matcher = subnet_matcher qw(::ffff:192.168.1.0/118 192.168.1.0 +/22); my $boolean = $matcher->($ip); =head1 CAVEATS No argument verification is done; garbage in, garbage out. If you give + it hostnames, DNS may be used to resolve them, courtesy of the Socket and + Socket6 modules. =head1 AUTHOR Juerd Waalboer <juerd#@tnx.nl> =head1 LICENSE This library is free software; you can redistribute it and/or modify i +t under the same terms as Perl itself.
    ========================================================
    Now, after manually installing with the new source:
    !/usr/bin/perl -slw use strict; use warnings; use Net::Subnet; my $is_rfc1918 = subnet_matcher qw( 10.96.2.0/255.255.254.0 10.123.50.0/255.255.255.0 72.24.196.0/255.255.255.0 72.24.137.192/255.255.255.192 10.122.50.0/255.255.255.0 ); print $is_rfc1918->('10.96.2.0') ? 'yes' : 'no';
    Outputs:
    yes
Re: finding netmask for "arbitrary" ip address
by Plankton (Priest) on Nov 29, 2011 at 06:12 UTC
    I am not sure I understand the problem you are trying to solve, but if you just want to figure out if a given ip address is within a subnet it is easier if you convert the ip address, and network addresses and broadcast addresses from a quad 4 representation to an integer. Then do something like this ...
    #!/usr/bin/perl -w use Socket; use strict; my %subnets = ( '10.96.2.0/255.255.254.0' => { start => 174064128, end => 174064639 } , '10.123.50.0/255.255.255.0' => { start => 175845888, end => 175846143 } , '72.24.196.0/255.255.255.0' => { start => 1209582592, end => 1209582847 } , '72.24.137.192/255.255.255.192' => { start => 1209567680, end => 1209567743 } , '10.122.50.0/255.255.255.0' => { start => 175780352, end => 175780607 } , '65.181.207.128/255.255.255.128' => { start => 1102434176, end => 1102434303 } ); my $ip = shift; my $int = unpack("N",inet_aton(shift||$ip)); for my $subnet ( keys %subnets ) { if ( $subnets{$subnet}{'start'} <= $int && $int <= $subnets{$subnet}{'end'} ) { print "$ip ($int) is in subnet $subnet (" . $subnets{$subnet}{'start'} . ", " . $subnets{$subnet}{'end'} . ") \n"; } }
    I used ipcalc to work out the network address and broadcast address and script I wrote, quad2int.pl, to convert those IP to integer.
Re: finding netmask for "arbitrary" ip address
by TJPride (Pilgrim) on Nov 29, 2011 at 12:58 UTC
    I could probably solve this problem if I knew how subnet masks worked and factored into this. Can you give a few examples of input data and desired output? I'm good with algorithms but don't know much about networking.
SOLVED Re: finding netmask for "arbitrary" ip address
by jasonl (Novice) on Dec 07, 2011 at 16:35 UTC

    Here's what I ended up doing; it does require Socket.pm, but from what I've seen so far that looks pretty standard. It uses inet_aton to convert ip, net, and mask to structs, &s them to compare, then returns the mask when it finds a hit.

    use Socket; sub findMask { my ($ip, $nets) = @_; my ($net, $mask) = (); foreach my $i (@$nets) { ($net, $mask) = split(m[/], $i); my $netBin = inet_aton($net); my $maskBin = inet_aton($mask); my $maskedNet = ($netBin & $maskBin); if (((inet_aton($ip)) & $maskBin) eq $maskedNet) { return "$mask"; } } ## no match return -1; }

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