path: root/libs/luci-lib-ip/src/ip.luadoc

--- LuCI IP calculation and netlink access library.
module "luci.ip"

---[[
Construct a new luci.ip.cidr instance and autodetect the address family.
Throws an error if the given strings do not represent a valid address or
if the given optional netmask is of a different family.
@class function
@sort 1
@name new
@param address	String containing a valid IPv4 or IPv6 address, optionally
with prefix size (CIDR notation) or netmask separated by slash.
@param netmask	String containing a valid IPv4 or IPv6 netmask or number
containing a prefix size in bits (`0..32` for IPv4,
`0..128` for IPv6). Overrides mask embedded in the first argument
if specified. (optional)
@return A `luci.ip.cidr` object representing the given
address/mask range.
@usage `addr = luci.ip.new("10.24.0.1/24")
addr = luci.ip.new("10.24.0.1/255.255.255.0")
addr = luci.ip.new("10.24.0.1", "255.255.255.0")        -- separate netmask
addr = luci.ip.new("10.24.0.1/24", 16)                  -- override netmask

addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/64")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/ffff:ffff:ffff:ffff::")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17", "ffff:ffff:ffff:ffff::")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/64", 128) -- override netmask`
@see IPv4
@see IPv6
]]

---[[
Construct a new IPv4 luci.ip.cidr instance.
Throws an error if the given string does not represent a valid IPv4 address or
if the given optional netmask is of a different family.
@class function
@sort 2
@name IPv4
@param address	String containing a valid IPv4, optionally with prefix size
(CIDR notation) or netmask separated by slash.
@param netmask	String containing a valid IPv4 netmask or number
containing a prefix size between `0` and `32` bit.
Overrides mask embedded in the first argument if specified. (optional)
@return A `luci.ip.cidr` object representing the given IPv4 range.
@usage `addr = luci.ip.new("10.24.0.1/24")
addr = luci.ip.new("10.24.0.1/255.255.255.0")
addr = luci.ip.new("10.24.0.1", "255.255.255.0")        -- separate netmask
addr = luci.ip.new("10.24.0.1/24", 16)                  -- override netmask`
@see IPv6
]]

---[[
Construct a new IPv6 luci.ip.cidr instance.
Throws an error if the given string does not represent a valid IPv6 address or
if the given optional netmask is of a different family.
@class function
@sort 3
@name IPv6
@param address	String containing a valid IPv6, optionally with prefix size
(CIDR notation) or netmask separated by slash.
@param netmask	String containing a valid IPv4 netmask or number
containing a prefix size between `0` and `128` bit.
Overrides mask embedded in the first argument if specified. (optional)
@return A `luci.ip.cidr` object representing the given IPv6 range.
@usage `addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/64")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/ffff:ffff:ffff:ffff::")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17", "ffff:ffff:ffff:ffff::")
addr6 = luci.ip.new("fe80::221:63ff:fe75:aa17/64", 128) -- override netmask`
@see IPv4
]]

---[[
Determine the route leading to the given destination.
@class function
@sort 4
@name route
@param address	A `luci.ip.cidr` instance or a string containing
a valid IPv4 or IPv6 range as specified by `luci.ip.new()`.
@return <p>Table containing the fields described below.</p>
<table id="routetable">
<tr><th>Field</th><th>Description</th></tr>
<tr><td>`type`<td>
  <p>Route type with one of the following numeric values:</p>
  <table>
  <tr>
	<td>`1`</td>
	<td>`RTN_UNICAST` - Gateway or direct route</td>
  </tr>
  <tr>
	<td>`2`</td>
	<td>`RTN_LOCAL` - Accept locally</td>
  </tr>
  <tr>
	<td>`3`</td>
	<td>`RTN_BROADCAST` -
	    Accept locally as broadcast send as broadcast</td>
  </tr>
  <tr>
	<td>`4`</td>
	<td>`RTN_ANYCAST` -
        Accept locally as broadcast but send as unicast</td>
  </tr>
  <tr>
	<td>`5`</td>
	<td>`RTN_MULTICAST` - Multicast route</td>
  </tr>
  </table>
</td></tr>
<tr>
  <td>`family`</td>
  <td>Number containing the route family, `4` for IPv4 or
      `6` for IPv6</td>
</tr>
<tr>
  <td>`dest`</td>
  <td>Destination `luci.ip.cidr` instance</td>
</tr>
<tr>
  <td>`gw`</td>
  <td>Gateway `luci.ip.cidr` instance (optional)</td>
</tr>
<tr>
  <td>`from`</td>
  <td>Source address `luci.ip.cidr` instance (optional)</td>
</tr>
<tr>
  <td>`src`</td>
  <td>Preferred source `luci.ip.cidr` instance (optional)</td>
</tr>
<tr>
  <td>`dev`</td>
  <td>String containing the name of the outgoing interface</td>
</tr>
<tr>
  <td>`iif`</td>
  <td>String containing the name of the incoming interface (optional)</td>
</tr>
<tr>
  <td>`table`</td>
  <td>Number of the associated routing table (`0..65535`)</td>
</tr>
<tr>
  <td>`proto`</td>
  <td>Number of the associated routing protocol</td>
</tr>
<tr>
  <td>`scope`</td>
  <td>Number describing the scope of the route, most commonly
      `0` for global or `253` for on-link</td>
</tr>
<tr>
  <td>`metric`</td>
  <td>Number describing the route metric (optional)</td>
</tr>
<tr>
  <td>`expires`</td>
  <td>Number of seconds the prefix is valid (IPv6 only, optional)</td>
</tr>
<tr>
  <td>`error`</td>
  <td>Route destination error code (optional)</td>
</tr>
</table>
@usage <ul>
<li>Find default gateway by getting route to Google's public NS server
`rt = luci.ip.route("8.8.8.8")
if rt ~= nil then
	print("gateway is", rt.gw)
end`</li>
<li>Determine IPv6 upstream interface `rt = luci.ip.route("2001::/7")
if rt ~= nil then
	print("ipv6 upstream device is", rt.dev)
end`</li>
</ul>
@see routes
]]

---[[
Fetch all routes, optionally matching the given criteria.
@class function
@sort 5
@name routes
@param filter  <p>Table containing one or more of the possible filter
critera described below (optional)</p><table>
<tr><th>Field</th><th>Description</th></tr>
<tr><td>`family`</td><td>
 Number describing the address family to return - `4` selects
 IPv4 routes, `6` IPv6 ones. Any other value selects both.
</td></tr>
<tr><td>`iif`</td><td>
 String containing the incoming route interface to match.
</td></tr>
<tr><td>`oif`</td><td>
 String containing the outgoing route interface to match.
</td></tr>
<tr><td>`type`</td><td>
 Numeric type to match, e.g. `1` for unicast.
</td></tr>
<tr><td>`scope`</td><td>
 Numeric scope to match, e.g. `253` for onlink.
</td></tr>
<tr><td>`proto`</td><td>
 Numeric protocol to match, e.g. `2` for boot.
</td></tr>
<tr><td>`table`</td><td>
 Numeric routing table to match (`0..65535`).
</td></tr>
<tr><td>`gw`</td><td>
 String containing the gateway address to match. Can be in any notation
 specified by `luci.ip.new()`. Prefix matching is performed when
 comparing the routes, e.g. "192.168.1.0/24" would select routes with gateway
 addresses `192.168.1.1 .. 192.168.1.255`.
</td></tr>
<tr><td>`dest`</td><td>
 String containing the destination to match. Prefix matching is performed.
</td></tr>
<tr><td>`from`</td><td>
 String containing the source address to match. Prefix matching is performed.
</td></tr>
<tr><td>`src`</td><td>
 String containing the preferred source address to match.
 Prefix matching is performed.
</td></tr>
<tr><td>`dest_exact`</td><td>
 String containing the destination to match. Exact matching is performed,
 e.g. `dest = "0.0.0.0/0"` would match <em>any</em> IPv4 route
 while `dest_exact = "0.0.0.0/0"` will <em>only</em> match the
 default route.
</td></tr>
<tr><td>`from_exact`</td><td>
 String containing the source address to match. Exact matching is performed.
</td></tr>
</table>
@param callback  <p>Callback function to invoke for each found route
instead of returning one table of route objects (optional)</p>
@return If no callback function is provided, a table of routes
<a href="#routetable">as specified by `luci.ip.route()`</a>
is returned. If a callback function is given, it is invoked for each route
and nothing is returned.
@see route
@usage <ul>
<li>Find all IPv4 default routes:
`luci.ip.routes({ dest_exact = "0.0.0.0/0" }, function(rt)
	print(rt.type, rt.gw, rt.dev)
end)`</li>
<li>Find all global IPv6 prefixes on the current system:
`luci.ip.routes({ from = "2001::/7" }, function(rt)
	print(rt.from)
end)`</li>
<li>Fetch all IPv4 routes:
`routes = luci.ip.routes({ family = 4 })
for _, rt in ipairs(routes) do
	print(rt.dest, rt.gw, rt.dev)
end`</li>
</ul>
]]

---[[
Fetches entries from the IPv4 ARP and IPv6 neighbour kernel table
@class function
@sort 6
@name neighbors
@param filter  <p>Table containing one or more of the possible filter
critera described below (optional)</p><table>
<tr><th>Field</th><th>Description</th></tr>
<tr><td>`family`</td><td>
 Number describing the address family to return - `4` selects
 IPv4 ARP, `6` select IPv6 neighbour entries. Any other value
 selects both.
</td></tr>
<tr><td>`dev`</td><td>
 String containing the associated interface to match.
</td></tr>
<tr><td>`dest`</td><td>
 String containing the associated address to match. Can be in any notation
 specified by `luci.ip.new()`. Prefix matching is performed when
 comparing the addresses, e.g. "192.168.1.0/24" would select ARP entries
 for `192.168.1.1 .. 192.168.1.255`.
</td></tr>
<tr><td>`mac`</td><td>
 String containing MAC address to match.
</td></tr>
</table>
@param callback  <p>Callback function to invoke for each found neighbour
entry instead of returning one table of neighbour entries (optional)</p>
@return If no callback function is provided, a table of neighbour entries
is returned. If a callback function is given, it is invoked for each entry
and nothing is returned.

A neighbour entry is a table containing the following fields:

<table>
<tr><th>Field</th><th>Description</th></tr>
<tr>
  <td>`family`</td>
  <td>Number containing the neighbour entry family, `4` for IPv4
      ARP or `6` for IPv6 NDP</td>
</tr>
<tr>
  <td>`dev`</td>
  <td>String containing the associated device of the neighbour entry</td>
</tr>
<tr>
  <td>`dest`</td>
  <td>IP address `luci.ip.cidr` instance</td>
</tr>
<tr>
  <td>`mac`</td>
  <td>String containing the associated MAC address</td>
</tr>
<tr>
  <td>`router`</td>
  <td>Boolean "true" if the neighbour entry is a router (IPv6, optional)</td>
</tr>
<tr>
  <td>`proxy`</td>
  <td>Boolean "true" if this is a proxy entry (optional)</td>
</tr>
<tr>
  <td>`incomplete`</td>
  <td>Boolean "true" if the entry is in incomplete state (optional)</td>
</tr>
<tr>
  <td>`reachable`</td>
  <td>Boolean "true" if the entry is in reachable state (optional)</td>
</tr>
<tr>
  <td>`stale`</td>
  <td>Boolean "true" if the entry is stale (optional)</td>
</tr>
<tr>
  <td>`delay`</td>
  <td>Boolean "true" if the entry is delayed (optional)</td>
</tr>
<tr>
  <td>`probe`</td>
  <td>Boolean "true" if the entry is in probe state (optional)</td>
</tr>
<tr>
  <td>`failed`</td>
  <td>Boolean "true" if the entry is in failed state (optional)</td>
</tr>
<tr>
  <td>`noarp`</td>
  <td>Boolean "true" if the entry is not caused by NDP or
      ARP (optional)</td>
</tr>
<tr>
  <td>`permanent`</td>
  <td>Boolean "true" if the entry was statically configured from
      userspace (optional)</td>
</tr>
</table>
@usage <ul>
<li>Find all ARP neighbours in the LAN:
`luci.ip.neighbors({ dest = "192.168.0.0/16" }, function(n)
	print(n.dest, n.mac)
end)`</li>
<li>Find all active IPv6 addresses of host with given MAC:
`luci.ip.neighbors({ family = 6, mac = "00:21:63:75:aa:17" },
	function(n)
		print(n.dest)
	end)`</li>
</ul>
]]

---[[
Fetch basic device information
@class function
@sort 7
@name link
@param device  String containing the network device to query
@return  If the given interface is found, a table containing the fields
described below is returned, else an empty table.

<table>
<tr><th>Field</th><th>Description</th></tr>
<tr>
  <td>`up`</td>
  <td>Boolean indicating whether the device is in IFF_RUNNING state</td>
</tr>
<tr>
  <td>`type`</td>
  <td>Numeric value indicating the type of the device, e.g. `1`
      for ethernet.</td>
</tr>
<tr>
  <td>`name`</td>
  <td>String containing the name of the device</td>
</tr>
<tr>
  <td>`master`</td>
  <td>If queried device is a bridge port, string containing the name of
      parent bridge device (optional)</td>
</tr>
<tr>
  <td>`mtu`</td>
  <td>Number containing the current MTU of the device</td>
</tr>
<tr>
  <td>`qlen`</td>
  <td>Number containing the TX queue length of the device</td>
</tr>
<tr>
  <td>`mac`</td>
  <td>String containing the link local address of the device in
      dotted hex notation</td>
</tr>
</table>
@usage <ul>
<li>Test whether device br-lan exists:
`print(luci.ip.link("br-lan").name ~= nil)
`</li>
<li>Query MAC address of eth0:
`print(luci.ip.link("eth0").mac)
`</li>
</ul>
]]


--- IP CIDR Object.
-- Represents an IPv4 or IPv6 address range.
-- @cstyle instance
module "luci.ip.cidr"

---[[
Checks whether the CIDR instance is an IPv4 address range

@class function
@sort 1
@name cidr.is4
@see cidr.is6
@return `true` if the CIDR is an IPv4 range, else `false`
]]

---[[
Checks whether the CIDR instance is within the private RFC1918 address space

@class function
@sort 2
@name cidr.is4rfc1918
@return `true` if the entire range of this CIDR lies within one of
	the ranges `10.0.0.0-10.255.255.255`,
	`172.16.0.0-172.31.0.0` or
	`192.168.0.0-192.168.255.255`, else `false`.
@usage `local addr = luci.ip.new("192.168.45.2/24")
if addr:is4rfc1918() then
	print("Is a private address")
end`
]]

---[[
Checks whether the CIDR instance is an IPv4 link local (Zeroconf) address

@class function
@sort 3
@name cidr.is4linklocal
@return `true` if the entire range of this CIDR lies within the range
	the range `169.254.0.0-169.254.255.255`, else `false`.
@usage `local addr = luci.ip.new("169.254.34.125")
if addr:is4linklocal() then
	print("Is a zeroconf address")
end`
]]

---[[
Checks whether the CIDR instance is an IPv6 address range

@class function
@sort 4
@name cidr.is6
@see cidr.is4
@return `true` if the CIDR is an IPv6 range, else `false`
]]

---[[
Checks whether the CIDR instance is an IPv6 link local address

@class function
@sort 5
@name cidr.is6linklocal
@return `true` if the entire range of this CIDR lies within the range
	the `fe80::/10` range, else `false`.
@usage `local addr = luci.ip.new("fe92:53a:3216:af01:221:63ff:fe75:aa17/64")
if addr:is6linklocal() then
	print("Is a linklocal address")
end`
]]

---[[
Checks whether the CIDR instance is an IPv6 mapped IPv4 address

@class function
@sort 6
@name cidr.is6mapped4
@return `true` if the address is an IPv6 mapped IPv4 address in the
	form `::ffff:1.2.3.4`.
@usage `local addr = luci.ip.new("::ffff:192.168.1.1")
if addr:is6mapped4() then
	print("Is a mapped IPv4 address")
end`
]]

---[[
Checks whether this CIDR instance is lower than the given argument.
The comparisation follows these rules:
<ul><li>An IPv4 address is always lower than an IPv6 address</li>
<li>Prefix sizes are ignored</li></ul>

@class function
@sort 7
@name cidr.lower
@param addr A `luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()` to compare against.
@return `true` if this CIDR is lower than the given address,
	else `false`.
@usage `local addr = luci.ip.new("192.168.1.1")
print(addr:lower(addr)) -- false
print(addr:lower("10.10.10.10/24")) -- false
print(addr:lower(luci.ip.new("::1"))) -- true
print(addr:lower(luci.ip.new("192.168.200.1"))) -- true`
@see cidr.higher
@see cidr.equal
]]

---[[
Checks whether this CIDR instance is higher than the given argument.
The comparisation follows these rules:
<ul><li>An IPv4 address is always lower than an IPv6 address</li>
<li>Prefix sizes are ignored</li></ul>

@class function
@sort 8
@name cidr.higher
@param addr A `luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()` to compare against.
@return `true` if this CIDR is higher than the given address,
	else `false`.
@usage `local addr = luci.ip.new("192.168.1.1")
print(addr:higher(addr)) -- false
print(addr:higher("10.10.10.10/24")) -- true
print(addr:higher(luci.ip.new("::1"))) -- false
print(addr:higher(luci.ip.new("192.168.200.1"))) -- false`
@see cidr.lower
@see cidr.equal
]]

---[[
Checks whether this CIDR instance is equal to the given argument.

@class function
@sort 9
@name cidr.equal
@param addr A `luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()` to compare against.
@return `true` if this CIDR is equal to the given address,
	else `false`.
@usage `local addr = luci.ip.new("192.168.1.1")
print(addr:equal(addr)) -- true
print(addr:equal("192.168.1.1")) -- true
print(addr:equal(luci.ip.new("::1"))) -- false

local addr6 = luci.ip.new("::1")
print(addr6:equal("0:0:0:0:0:0:0:1/64")) -- true
print(addr6:equal(luci.ip.new("fe80::221:63ff:fe75:aa17"))) -- false`
@see cidr.lower
@see cidr.higher
]]

---[[
Get or set prefix size of CIDR instance.
If the optional mask parameter is given, the prefix size of this CIDR is altered
else the current prefix size is returned.

@class function
@sort 10
@name cidr.prefix
@param mask Either a number containing the number of bits (`0..32`
	for IPv4, `0..128` for IPv6) or a string containing a valid
	netmask (optional)
@return Bit count of the current prefix size
@usage `local range = luci.ip.new("192.168.1.1/255.255.255.0")
print(range:prefix()) -- 24

range:prefix(16)
print(range:prefix()) -- 16

range:prefix("255.255.255.255")
print(range:prefix()) -- 32`
]]

---[[
Derive network address of CIDR instance.

Returns a new CIDR instance representing the network address of this instance
with all host parts masked out. The used prefix size can be overridden by the
optional mask parameter.

@class function
@sort 11
@name cidr.network
@param mask Either a number containing the number of bits (`0..32`
	for IPv4, `0..128` for IPv6) or a string containing a valid
	netmask (optional)
@return CIDR instance representing the network address
@usage `local range = luci.ip.new("192.168.62.243/255.255.0.0")
print(range:network())                -- "192.168.0.0"
print(range:network(24))              -- "192.168.62.0"
print(range:network("255.255.255.0")) -- "192.168.62.0"

local range6 = luci.ip.new("fd9b:62b3:9cc5:0:221:63ff:fe75:aa17/64")
print(range6:network())               -- "fd9b:62b3:9cc5::"`
]]

---[[
Derive host address of CIDR instance.

This function essentially constructs a copy of this CIDR with the prefix size
set to `32` for IPv4 and `128` for IPv6.

@class function
@sort 12
@name cidr.host
@return CIDR instance representing the host address
@usage `local range = luci.ip.new("172.19.37.45/16")
print(range)        -- "172.19.37.45/16"
print(range:host()) -- "172.19.37.45"`
]]

---[[
Derive netmask of CIDR instance.

Constructs a CIDR instance representing the netmask of this instance. The used
prefix size can be overridden by the optional mask parameter.

@class function
@sort 13
@name cidr.mask
@param mask Either a number containing the number of bits (`0..32`
	for IPv4, `0..128` for IPv6) or a string containing a valid
	netmask (optional)
@return CIDR instance representing the netmask
@usage `local range = luci.ip.new("172.19.37.45/16")
print(range:mask())            -- "255.255.0.0"
print(range:mask(24))          -- "255.255.255.0"
print(range:mask("255.0.0.0")) -- "255.0.0.0"`
]]

---[[
Derive broadcast address of CIDR instance.

Constructs a CIDR instance representing the broadcast address of this instance.
The used prefix size can be overridden by the optional mask parameter.

This function has no effect on IPv6 instances, it will return nothing in this
case.

@class function
@sort 14
@name cidr.broadcast
@param mask Either a number containing the number of bits (`0..32`
	for IPv4, `0..128` for IPv6) or a string containing a valid
	netmask (optional)
@return Return a new CIDR instance representing the broadcast address if this
	instance is an IPv4 range, else return nothing.
@usage `local range = luci.ip.new("172.19.37.45/16")
print(range:broadcast())            -- "172.19.255.255"
print(range:broadcast(24))          -- "172.19.37.255"
print(range:broadcast("255.0.0.0")) -- "172.255.255.255"`
]]

---[[
Derive mapped IPv4 address of CIDR instance.

Constructs a CIDR instance representing the IPv4 address of the IPv6 mapped
IPv4 address in this instance.

This function has no effect on IPv4 instances or IPv6 instances which are not a
mapped address, it will return nothing in this case.

@class function
@sort 15
@name cidr.mapped4
@return Return a new CIDR instance representing the IPv4 address if this
	instance is an IPv6 mapped IPv4 address, else return nothing.
@usage `local addr = luci.ip.new("::ffff:172.16.19.1")
print(addr:mapped4()) -- "172.16.19.1"`
]]

---[[
Test whether CIDR contains given range.

@class function
@sort 16
@name cidr.contains
@param addr A `luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()` to test.
@return `true` if this instance fully contains the given address else
	`false`.
@usage `local range = luci.ip.new("10.24.0.0/255.255.0.0")
print(range:contains("10.24.5.1"))  -- true
print(range:contains("::1"))        -- false
print(range:contains("10.0.0.0/8")) -- false

local range6 = luci.ip.new("fe80::/10")
print(range6:contains("fe80::221:63f:fe75:aa17/64"))         -- true
print(range6:contains("fd9b:6b3:c5:0:221:63f:fe75:aa17/64")) -- false`
]]

---[[
Add given amount to CIDR instance. If the result would overflow the maximum
address space, the result is set to the highest possible address.

@class function
@sort 17
@name cidr.add
@param amount A numeric value between 0 and 0xFFFFFFFF, a
	`luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()`.
@param inplace If `true`, modify this instance instead of returning
	a new derived CIDR instance.
@return <ul>
	<li>When adding inplace: Return `true` if the addition succeded
	    or `false` when the addition overflowed.</li>
	<li>When deriving new CIDR: Return new instance representing the value of
        this instance plus the added amount or the highest possible address if
	    the addition overflowed the available address space.</li></ul>
@usage `local addr = luci.ip.new("192.168.1.1/24")
print(addr:add(250))         -- "192.168.1.251/24"
print(addr:add("0.0.99.0"))  -- "192.168.100.1/24"

addr:add(256, true)          -- true
print(addr)                  -- "192.168.2.1/24

addr:add("255.0.0.0", true)  -- false (overflow)
print(addr)                  -- "255.255.255.255/24

local addr6 = luci.ip.new("fe80::221:63f:fe75:aa17/64")
print(addr6:add(256))        -- "fe80::221:63f:fe75:ab17/64"
print(addr6:add("::ffff:0")) -- "fe80::221:640:fe74:aa17/64"

addr:add(256, true)          -- true
print(addr)                  -- "fe80::221:63f:fe75:ab17/64

addr:add("ffff::", true)     -- false (overflow)
print(addr)                  -- "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/64"`
]]

---[[
Substract given amount from CIDR instance. If the result would under, the lowest
possible address is returned.

@class function
@sort 18
@name cidr.sub
@param amount A numeric value between 0 and 0xFFFFFFFF, a
	`luci.ip.cidr` instance or a string convertable by
	`luci.ip.new()`.
@param inplace If `true`, modify this instance instead of returning
	a new derived CIDR instance.
@return <ul>
	<li>When substracting inplace: Return `true` if the substraction
	    succeded or `false` when the substraction underflowed.</li>
	<li>When deriving new CIDR: Return new instance representing the value of
        this instance minus the substracted amount or the lowest address if
	    the substraction underflowed.</li></ul>
@usage `local addr = luci.ip.new("192.168.1.1/24")
print(addr:sub(256))         -- "192.168.0.1/24"
print(addr:sub("0.168.0.0")) -- "192.0.1.1/24"

addr:sub(256, true)          -- true
print(addr)                  -- "192.168.0.1/24

addr:sub("255.0.0.0", true)  -- false (underflow)
print(addr)                  -- "0.0.0.0/24

local addr6 = luci.ip.new("fe80::221:63f:fe75:aa17/64")
print(addr6:sub(256))        -- "fe80::221:63f:fe75:a917/64"
print(addr6:sub("::ffff:0")) -- "fe80::221:63e:fe76:aa17/64"

addr:sub(256, true)          -- true
print(addr)                  -- "fe80::221:63f:fe75:a917/64"

addr:sub("ffff::", true)     -- false (underflow)
print(addr)                  -- "::/64"`
]]

---[[
Calculate the lowest possible host address within this CIDR instance.

@class function
@sort 19
@name cidr.minhost
@return Returns a new CIDR instance representing the lowest host address
	within this range.
@usage `local addr = luci.ip.new("192.168.123.56/24")
print(addr:minhost())  -- "192.168.123.1"

local addr6 = luci.ip.new("fd9b:62b3:9cc5:0:221:63ff:fe75:aa17/64")
print(addr6:minhost()) -- "fd9b:62b3:9cc5::1"`
]]

---[[
Calculate the highest possible host address within this CIDR instance.

@class function
@sort 20
@name cidr.maxhost
@return Returns a new CIDR instance representing the highest host address
	within this range.
@usage `local addr = luci.ip.new("192.168.123.56/24")
print(addr:maxhost())  -- "192.168.123.254" (.255 is broadcast)

local addr6 = luci.ip.new("fd9b:62b3:9cc5:0:221:63ff:fe75:aa17/64")
print(addr6:maxhost()) -- "fd9b:62b3:9cc5:0:ffff:ffff:ffff:ffff"`
]]

---[[
Convert CIDR instance into string representation.

If the prefix size of instance is less than 32 for IPv4 or 128 for IPv6, the
address is returned in the form "address/prefix" otherwise just "address".

It is usually not required to call this function directly as CIDR objects
define it as __tostring function in the associated metatable.

@class function
@sort 21
@name cidr.string
@return Returns a string representing the range or address of this CIDR instance
]]