Pfx

Functions to make working with prefixes easier, especially IP prefixes (IPv4 and IPv6).

Pfx defines a prefix as a struct with a number of bits and a maximum maxlen length. Hence a Pfx struct represents some domain-specific value, like an IPv4/6 address or network, a MAC address, a MAC OUI range or something completely different.

A Pfx struct can be created with Pfx.new/2 using:

a bitstring/0 and a non_neg_integer/0 for the maximum length,
a Pfx.t/0 and a non_neg_integer/0 for a (new) maximum length.

This allows for the creation of any sort of prefix.

Use Pfx.new/1 to create a prefix struct from:

a Pfx.ip_address/0,
a Pfx.ip_prefix/0, or
a binary/0, a string in IPv4 CIDR, IPv6, EUI-48 or EUI-64 format

This creates a IPv4, IPv6, EUI-48 or an EUI-64 prefix. Other means to create prefixes include Pfx.from_mac/1 and Pfx.from_hex/1.

Several functions, like Pfx.unique_local?/1 are more IP oriented, and are included along with the more generic Pfx functions (like Pfx.cut/3) in order to have one module to rule them all.

Functions generally accept either a Pfx.t/0, a Pfx.ip_address/0, a Pfx.ip_prefix/0 or a binary and yield their result in the same fashion:

iex> hosts("10.10.10.0/30")
["10.10.10.0", "10.10.10.1", "10.10.10.2", "10.10.10.3"]

iex> hosts({{10, 10, 10, 0}, 30})
[
  {{10, 10, 10, 0}, 32},
  {{10, 10, 10, 1}, 32},
  {{10, 10, 10, 2}, 32},
  {{10, 10, 10, 3}, 32}
]

iex> hosts(%Pfx{bits: <<10, 10, 10, 0::6>>, maxlen: 32})
[
  %Pfx{bits: <<10, 10, 10, 0>>, maxlen: 32},
  %Pfx{bits: <<10, 10, 10, 1>>, maxlen: 32},
  %Pfx{bits: <<10, 10, 10, 2>>, maxlen: 32},
  %Pfx{bits: <<10, 10, 10, 3>>, maxlen: 32},
]

# adopt representation of first argument
iex> band({10, 10, 10, 1}, "255.255.255.0")
{10, 10, 10, 0}

iex> multicast?("ff00::1")
true

# MAC OUI prefix
iex> keep("aa:bb:cc:dd:ee:ff", 24)
"AA-BB-CC-00-00-00/24"

# get IPv4 from a IPv4 compatible IPv6 address
iex> cut("::1.2.3.4", -1, -32)
"1.2.3.4"

Validity

The Pfx.new/2 function will silently clip the provided bits-string to maxlen-bits when needed, since a Pfx struct named pfx is valid, iff:

bit_size(pfx.bits) <= pfx.maxlen, and where
pfx.maxlen is a non_neg_integer/0

Keep that in mind when instantiating directly or updating a Pfx, otherwise functions will choke on it.

Same goes for Pfx.ip_address/0 representations, which must be a valid :inet.ip_address(), representing either an IPv4 or IPv6 address through a tuple of four 8-bit wide numbers or eight 16-bit wide numbers.

If used as the first element in a Pfx.ip_prefix/0 tuple, the second element is interpreted as the mask, used to clip the bitstring when creating the Pfx struct. For example: {{1, 1, 1, 0}, 24} is the same as 1.1.1.0/24. IPv4 masks must be in range 0..32 and IPv6 masks in range 0..128. The resulting Pfx will have its maxlen set to 32 for IPv4 tuples and 128 for IPv6 tuples.

Last but not least, binaries are interpreted as either an IPv4 in CIDR-notation, an IPv6 address/prefix, an EUI-48 or EUI-64 formatted string.

# IPv4
iex> new("1.2.3.4")
%Pfx{bits: <<1, 2, 3, 4>>, maxlen: 32}

iex> new({1, 2, 3, 4})
%Pfx{bits: <<1, 2, 3, 4>>, maxlen: 32}

iex> new("1.2.3.0/24")
%Pfx{bits: <<1, 2, 3>>, maxlen: 32}

iex> new({{1, 2, 3, 0}, 24})
%Pfx{bits: <<1, 2, 3>>, maxlen: 32}

# IPv6
iex> new("acdc:1975::")
%Pfx{bits: <<0xACDC::16, 0x1975::16, 0::96>>, maxlen: 128}

iex> new({44252, 6517, 0, 0, 0, 0, 0, 0})
%Pfx{bits: <<0xACDC::16, 0x1975::16, 0::96>>, maxlen: 128}

# EUI-48
iex> new("00-88-88-88-88-88")
%Pfx{bits: <<0, 0x88, 0x88, 0x88, 0x88, 0x88>>, maxlen: 48}

iex> new("0088.8888.8888")
%Pfx{bits: <<0, 0x88, 0x88, 0x88, 0x88, 0x88>>, maxlen: 48}

# EUI-64
iex> new("02-88-88-FF-FE-88-88-88")
%Pfx{bits: <<0x02, 0x88, 0x88, 0xFF, 0xFE, 0x88, 0x88, 0x88>>, maxlen: 64}

iex> new("0288.88FF.FE88.8888")
%Pfx{bits: <<0x02, 0x88, 0x88, 0xFF, 0xFE, 0x88, 0x88, 0x88>>, maxlen: 64}

Ancient tradition

Pfx.new/1 accepts CIDR-strings which are ultimately processed using erlang's :inet.parse_address which, at the time of writing, still honors the ancient linux tradition of injecting zero's (rather than appending them) when presented with less than four IPv4 digits in a CIDR string.

# "d" -> "0.0.0.d"
iex> new("10") |> format()
"0.0.0.10"

iex> new("10/8") |> format()
"0.0.0.0/8"

# "d1.d2" -> "d1.0.0.d2"
iex> new("10.10") |> format()
"10.0.0.10"

iex> new("10.10/16") |> format()
"10.0.0.0/16"

# "d1.d2.d3" -> "d1.d2.0.d3"
iex> new("10.10.10") |> format()
"10.10.0.10"

iex> new("10.10.10/24") |> format()
"10.10.0.0/24"

Bottom line: never go short, you may be unpleasantly surprised.

EUI-64's

Since a string is first parsed as an IP prefix, EUI-64's like "11:22:33:44:55:66:77:88" will come out as an IPv6 prefix with their maxlen property set to 128. So, when parsing EUI's that might use ':'-s as punctuation, use Pfx.from_mac/1, which also supports the tuple formats. Like Pfx.new/1, this function always returns a Pfx.t/0-struct.

# new/1 parses EUI-64's like these correctly:
iex> new("1122.3344.5566.7788")
%Pfx{bits: <<0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88>>, maxlen: 64}

iex> new("11-22-33-44-55-66-77-88")
%Pfx{bits: <<0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88>>, maxlen: 64}

# but new/1 turns this valid EUI-64 into IPv6 due to ':'-punctuation used:
iex> new("01:02:03:04:05:06:07:08")
%Pfx{bits: <<0x1::16, 0x2::16, 0x3::16, 0x4::16, 0x5::16, 0x6::16, 0x7::16, 0x8::16>>, maxlen: 128}

# in this case, use from_mac/1
iex> from_mac("01:02:03:04:05:06:07:08")
%Pfx{bits: <<0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8>>, maxlen: 64}

# and supports digit-styled EUI's
iex> from_mac({0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8})
%Pfx{bits: <<0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8>>, maxlen: 64}

# from {{digits}, len}, keeping first 3 bytes
iex> from_mac({{0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8}, 24})
%Pfx{bits: <<0x1, 0x2, 0x3>>, maxlen: 64}

Enumeration

A Pfx.t/0 implements the Enumerable protocol:

iex> for ip <- %Pfx{bits: <<1, 2, 3, 0::6>>, maxlen: 32}, do: ip
[
  %Pfx{bits: <<1, 2, 3, 0>>, maxlen: 32},
  %Pfx{bits: <<1, 2, 3, 1>>, maxlen: 32},
  %Pfx{bits: <<1, 2, 3, 2>>, maxlen: 32},
  %Pfx{bits: <<1, 2, 3, 3>>, maxlen: 32},
]

String.Chars

Pfx.t/0 implements the String.Chars protocol with some defaults for prefixes that formats prefixes with:

maxlen: 32 as an IPv4 CIDR string,
maxlen: 48 as a EUI-48 address string and
maxlen: 64 as a EUI-64 address string
maxlen: 128 as an IPv6 string

Other maxlen's will simply come out as a series of 8-bit numbers joined by "." followed by /num_of_bits. The latter is omitted if equal to pfx.bits length.

If other formatting is required, use the Pfx.format/2 function, which takes some options that help shape the string representation for a Pfx struct.

iex> "#{%Pfx{bits: <<10, 11, 12>>, maxlen: 32}}"
"10.11.12.0/24"

iex> "#{new(<<44252::16, 6518::16>>, 128)}"
"acdc:1976:0:0:0:0:0:0/32"

iex> "#{%Pfx{bits: <<0xA1, 0xB2, 0xC3, 0xD4, 0xE5, 0xF6>>, maxlen: 48}}"
"A1-B2-C3-D4-E5-F6"

iex> "#{new(<<1, 2, 3, 4, 5>>, 64)}"
"01-02-03-04-05-00-00-00/40"

# the enumeration example earlier, could also read:
iex> for ip <- new("1.2.3.0/30"), do: "#{ip}"
[
  "1.2.3.0",
  "1.2.3.1",
  "1.2.3.2",
  "1.2.3.3"
]

# or
iex> for ip <- new("1.2.3.0/30"), do: digits(ip, 8) |> elem(0)
[
  {1, 2, 3, 0},
  {1, 2, 3, 1},
  {1, 2, 3, 2},
  {1, 2, 3, 3}
]

Limitations

A lot of Pfx-functions convert the Pfx.bits bitstring to an integer using Pfx.cast/1, before performing some, often Bitwise-related, calculation on them. Luckily Elixir can handle pretty large numbers which seem mostly limited by the available system memory.

Other functions, like Pfx.digits/2 return a tuple with numbers and are so limited by the maximum number of elements in a tuple (~16M+).

So if you're taking this somewhere far, far away, heed these limitations before take off.

Also, everything is done in Elixir with no extra, external dependencies. Usually fast enough, but if you really feel the need for speed, you might want to look elsewhere.

Anyway, enough downplay, here are some more examples.

Examples

# IANA's OUI range 00-00-5e-xx-xx-xx
iex> new("00-00-5e-00-00-00/24")
%Pfx{bits: <<0, 0, 94>>, maxlen: 48}

# IANA's VRRP MAC address range 00-00-5e-00-01-{VRID}
iex> vrrp_mac_range = new("00-00-5e-00-01-00/40")
%Pfx{bits: <<0, 0, 94, 0, 1>>, maxlen: 48}
iex>
iex> vrrp_mac = new("00-00-5e-00-01-0f")
%Pfx{bits: <<0, 0, 94, 0, 1, 15>>, maxlen: 48}
iex>
iex> member?(vrrp_mac, vrrp_mac_range)
true
iex> cut(vrrp_mac, -1, -8) |> cast()
15

iex> new("10.10.10.0/24")
%Pfx{bits: <<10, 10, 10>>, maxlen: 32}

iex> mask("10.10.10.0/25")
"255.255.255.128"

iex> inv_mask("10.10.10.0/25")
"0.0.0.127"

iex> dns_ptr("acdc:1975::b1ba:2021")
"1.2.0.2.a.b.1.b.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.5.7.9.1.c.d.c.a.ip6.arpa"

iex> teredo_decode("2001:0000:4136:e378:8000:63bf:3fff:fdd2")
%{
  server: "65.54.227.120",
  client: "192.0.2.45",
  port: 40000,
  flags: {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
  prefix: "2001:0000:4136:e378:8000:63bf:3fff:fdd2"
}

iex> eui64_encode("0288.8888.8888")
"00-88-88-FF-FE-88-88-88"

Some functions have IP related names (like Pfx.teredo_decode/1, but most of the times functions have generic names, since they apply to all sorts of prefixes, e.g.

iex> partition("10.10.10.0/24", 26)
[ "10.10.10.0/26",
  "10.10.10.64/26",
  "10.10.10.128/26",
  "10.10.10.192/26"
]

iex> new(<<1, 2, 3, 4>>, 32)
...> |> format(width: 1, unit: 8)
"00000001.00000010.00000011.00000100"

iex> from_hex("123456789abcdef")
...> |> keep(20)
%Pfx{bits: <<0x12, 0x34, 0x5::4>>, maxlen: 60}

iex> brot("1.2.3.4", 8)
"4.1.2.3"

Installation

Pfx can be installed by adding pfx to your list of dependencies in mix.exs:

def deps do
  [
    {:pfx, "~> 0.6.0"}
  ]
end

Copyright and License

The source code is licensed under the MIT License.

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