v0.2.5

ADDED:
* num-addrs subcommand, to get the number of hosts/addresses in a given
  prefix length
* get-net subcommand, to more easily get a single subnet from either the
  beginning or the end of a prefix. (MUCH FASTER than CIDR-splitting!)

ACKNOWLEDGEMENTS

@@ -0,0 +1,8 @@
+The "IPv6 Segment Reference Diagram" output as rendered in the `table`
+subcommand is from:
+	https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing
+as fetched on April 07, 2025.
+It is licensed under Creative Commons "CC BY-SA 4.0";
+see:
+	https://creativecommons.org/licenses/by-sa/4.0/
+	https://creativecommons.org/licenses/by-sa/4.0/legalcode.en)

README.adoc

@@ -39,7 +39,7 @@ A tool to assist in design of segregate/segment/split/subnet networks.
 ** For IPv4 addresses, it will be `true` if it is an APIPA (_Automatic Private IP Addressing_) address ({rfc}3927[RFC 3927^]) (in the `169.254.0.0/16` range).
 * `First` and `Last` refer to the first and last "usable" ("host"/assignable) addresses in a subnet/network.
 ** Note that for IPv6, the first address (`x::`) in a subnet *may* or *may not* be assignable/"usable". If it is assigned to a device, that device *must* be a router for anycast. See {rfc}4291#section-2.6.1[RFC 4291 § 2.6.1^] for details. In the interest of convenience, `subnetter` will report this address as *not usable/addressable* in ranges for this reason as it is technically not a "host" address.
-** Note that for IPv6, some subnetting calculators erroneously report the last address for /64's (e.g. `x:ffff:ffff:ffff:ffff/64`) as usable. They are actually reserved in strictly RFC-compliant networks for EUI-64 reasons (per {rfc}2526[RFC 2526^]). For this reason, *if and only if* a prefix is a /64 *exactly*, `subnetter` will use `x:ffff:ffff:ffff:fffe` as the last host address.
+** Note that for IPv6, some subnetting calculators erroneously report the last address as usable. They are reserved in strictly RFC-compliant networks for anycast reasons (per {rfc}2526[RFC 2526^]). Subnetter follows RFC as closely as possible, and any deviation from RFC is considered a bug -- as such, the last address of IPv6 subnets is considered *not usable/addressable*.
 ** There are additional restrictions for /64 subnets, but they fall earlier in the range. These are *not explicitly excluded* in the usable host range, nor are they excluded from the total host count.
 * Private networks ({rfc}1918[RFC 1918^]), ULA prefixes ({rfc}4193[RFC 4193^]), and documentation prefixes ({rfc}3849[RFC 3849^], {rfc}5737[RFC 5737^], {rfc}9637[RFC 9637^]) are treated as "normal" networks (in that it is allowed to subnet them).
 * Various other reserved IPv4 and IPv6 addresses/networks will print warnings with their corresponding RFC(s) (unless `-R`/`--allow-reserved` is specified) if they are specified as/included in the initial prefix/network. ({rfc}6890[RFC 6890^] and its update via {rfc}8190[RFC 8190^] are useful summaries.) Note that for checking to function, an Internet connection is required as it pulls it directly from IANA live to ensure the data is accurate to standards. This may be cached locally if `-c`/`--cache-reservations` is specified, in which case a locally-cached copy will be used if present and populated then used if not.
@@ -50,7 +50,7 @@ A tool to assist in design of segregate/segment/split/subnet networks.
 **** If the `XDG_CACHE_HOME` environment variable is not present...
 ***** On macOS, an explicit fallback of `~/Library/Caches/subnetter/` will be used. (To my knowledge/understanding, this is the standard user cache directory and cannot be changed.) This usually evaluates to `/Users/<username>/Library/Caches/subnetter/`.
 ***** On all others, an explicit fallback of `~/.cache/subnetter` will be used.
-****** On most non-macOS \*NIX-like systems , this is usually `/home/<username>/.cache/subetter/`, provided normal user homes. On http://p9f.org/[Plan9^] platforms (e.g. https://9p.io/plan9/index.html[Plan 9 4th Ed.^], https://9front.org/[9front^], http://9legacy.org/[9legacy^]), the `/env/home` environment variable (`$home`) will be used, the `./lib/` subdirectory under there (which typically/should already exist) will be appended to it, and that appended with `./cache/subnetter/` (this usually evaluates to `/usr/<username>/lib/cache/subnetter/`).
+****** On most non-macOS/*NIX-like systems , this is usually `/home/<username>/.cache/subetter/`, provided normal user homes. On http://p9f.org/[Plan9^] platforms (e.g. https://9p.io/plan9/index.html[Plan 9 4th Ed.^], https://9front.org/[9front^], http://9legacy.org/[9legacy^]), the `/env/home` environment variable (`$home`) will be used, the `./lib/` subdirectory under there (which typically/should already exist) will be appended to it, and that appended with `./cache/subnetter/` (this usually evaluates to `/usr/<username>/lib/cache/subnetter/`).
 *** For Windows systems...
 **** If https://learn.microsoft.com/en-us/windows/win32/shell/knownfolderid#constants[the `LOCALAPPDATA` environment variable^] is present, it will be `%LOCALAPPDATA%\Cache\subnetter\` (or `${env:LOCALAPPDATA}\Cache\subnetter\` in Powershell syntax). This usually evaluates to `C:\Users\<username>\AppData\Local\Cache\subnetter\`.
 
@@ -61,3 +61,5 @@ This program in general draws inspiration from `ipcalc` (http://jodies.de/ipcalc
 The `table` subcommand is inspired by `iptab` from https://metacpan.org/pod/Net::IP[Perl Net-IP^].
 
 Additional notes for certain contexts are primarily taken from https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing[the Wikipedia article on _Classless Inter-Domain Routing_^] (as of _Jan 28, 2025_).
+
+Reservations are pulled/cached directly from the IANA registries (https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml[IPv4^], https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml[IPv6^]).

TODO

@@ -1 +1,7 @@
 - add table rendering for reserved networks?
+
+- when checking/rendering reserved networks, currently the footnotes aren't returned.
+-- netsplit.IANARegistryFootnote
+-- encapsulated in the IANARegistry.Footnotes
+
+- add new interface, Getter? different formatting?

cmd/subnetter/_tpl/check.tpl

@@ -1,2 +1,2 @@
-{{- /*gotype: subnetter/cmd/subnetter.ReservedResults*/ -}}
+{{- /*gotype: r00t2.io/subnetter/cmd/subnetter.ReservedResults*/ -}}
 {{- $opts := . -}}

cmd/subnetter/_tpl/table.tpl

@@ -1,4 +1,4 @@
-{{- /*gotype: subnetter/cmd/subnetter.TableArgs*/ -}}
+{{- /*gotype: r00t2.io/subnetter/cmd/subnetter.TableArgs*/ -}}
 {{- $opts := . -}}
 {{- $numRows := 0 -}}
 {{- if not $opts.NoIpv4 }}
@@ -47,13 +47,268 @@ IPV4:
 {{- end }}
 
 {{- if not $opts.NoIpv6 }}
-
 	{{- if $opts.Plain }}
 IPV6:
 	{{- else }}
 {{ bold "IPv6:"}}
 	{{- end }}
+	{{- if not $opts.NoIpv6Seg }}
 		{{- if $opts.Plain }}
+	IPv6 Segment Reference Diagram:
+			{{- if $opts.VertSeg }}
+
+		Example:	2001:0db8:0123:4567:89ab:cdef:1234:5678
+				{{- if not $opts.VertInvert }}
+		2								4
+		0								8
+		0								12
+		1								16
+		:
+			0							20
+			d							24
+			b							28
+			8							32
+			:
+				0						36
+				1						40
+				2						44
+				3						48
+				:
+					4					52
+					5					56
+					6					60
+					7					64
+					:
+						8				68
+						9				72
+						a				76
+						b				80
+						:
+							c			84
+							d			88
+							e			92
+							f			96
+							:
+								1		100
+								2		104
+								3		108
+								4	 	112
+								:
+									5	116
+									6	120
+									7	124
+									8	127 or 128
+				{{- else }}
+		4 ____ 2
+		8 ____ 0
+		12 ___ 0
+		16 ___ 1
+		   ___ :
+		20 _____ 0
+		24 _____ d
+		28 _____ b
+		32 _____ 8
+		   _____ :
+		36 _______ 0
+		40 _______ 1
+		44 _______ 2
+		48 _______ 3
+		   _______ :
+		52 _________ 4
+		56 _________ 5
+		60 _________ 6
+		64 _________ 7
+		   _________ :
+		68 ___________ 8
+		72 ___________ 9
+		76 ___________ a
+		80 ___________ b
+		   ___________ :
+		84 _____________ c
+		88 _____________ d
+		92 _____________ e
+		96 _____________ f
+		   _____________ :
+		100 ______________ 1
+		104 ______________ 2
+		108 ______________ 3
+		112 ______________ 4
+		    ______________ :
+		116 ________________ 5
+		120 ________________ 6
+		124 ________________ 7
+		127 ________________ (8)
+		128 ________________ (8)
+				{{- end }}
+			{{- else }}
+
+		2001:0db8:0123:4567:89ab:cdef:1234:5678
+		|||| |||| |||| |||| |||| |||| |||| ||||
+		|||| |||| |||| |||| |||| |||| |||| |||128
+		|||| |||| |||| |||| |||| |||| |||| |||127
+		|||| |||| |||| |||| |||| |||| |||| ||124
+		|||| |||| |||| |||| |||| |||| |||| |120
+		|||| |||| |||| |||| |||| |||| |||| 116
+		|||| |||| |||| |||| |||| |||| |||112
+		|||| |||| |||| |||| |||| |||| ||108
+		|||| |||| |||| |||| |||| |||| |104
+		|||| |||| |||| |||| |||| |||| 100
+		|||| |||| |||| |||| |||| |||96
+		|||| |||| |||| |||| |||| ||92
+		|||| |||| |||| |||| |||| |88
+		|||| |||| |||| |||| |||| 84
+		|||| |||| |||| |||| |||80
+		|||| |||| |||| |||| ||76
+		|||| |||| |||| |||| |72
+		|||| |||| |||| |||| 68
+		|||| |||| |||| |||64
+		|||| |||| |||| ||60
+		|||| |||| |||| |56
+		|||| |||| |||| 52
+		|||| |||| |||48
+		|||| |||| ||44
+		|||| |||| |40
+		|||| |||| 36
+		|||| |||32
+		|||| ||28
+		|||| |24
+		|||| 20
+		|||16
+		||12
+		|8
+		4
+			{{- end }}
+		{{- else }}
+	{{ bold "IPv6 Segment Reference Diagram:" }}
+			{{- if $opts.VertSeg }}
+
+		{{ bold "Example:"}}	2001:0db8:0123:4567:89ab:cdef:1234:5678
+				{{- if not $opts.VertInvert }}
+		2								4
+		0								8
+		0								12
+		1								16
+		:
+			0							20
+			d							24
+			b							28
+			8							32
+			:
+				0						36
+				1						40
+				2						44
+				3						48
+				:
+					4					52
+					5					56
+					6					60
+					7					64
+					:
+						8				68
+						9				72
+						a				76
+						b				80
+						:
+							c			84
+							d			88
+							e			92
+							f			96
+							:
+								1		100
+								2		104
+								3		108
+								4	 	112
+								:
+									5	116
+									6	120
+									7	124
+									8	127 or 128
+				{{- else }}
+		4 ━━━━ 2
+		8 ━━━━ 0
+		12 ━━━ 0
+		16 ━━━ 1
+		   ━━━ :
+		20 ━━━━━ 0
+		24 ━━━━━ d
+		28 ━━━━━ b
+		32 ━━━━━ 8
+		   ━━━━━ :
+		36 ━━━━━━━ 0
+		40 ━━━━━━━ 1
+		44 ━━━━━━━ 2
+		48 ━━━━━━━ 3
+		   ━━━━━━━ :
+		52 ━━━━━━━━━ 4
+		56 ━━━━━━━━━ 5
+		60 ━━━━━━━━━ 6
+		64 ━━━━━━━━━ 7
+		   ━━━━━━━━━ :
+		68 ━━━━━━━━━━━ 8
+		72 ━━━━━━━━━━━ 9
+		76 ━━━━━━━━━━━ a
+		80 ━━━━━━━━━━━ b
+		   ━━━━━━━━━━━ :
+		84 ━━━━━━━━━━━━━ c
+		88 ━━━━━━━━━━━━━ d
+		92 ━━━━━━━━━━━━━ e
+		96 ━━━━━━━━━━━━━ f
+		   ━━━━━━━━━━━━━ :
+		100 ━━━━━━━━━━━━━━ 1
+		104 ━━━━━━━━━━━━━━ 2
+		108 ━━━━━━━━━━━━━━ 3
+		112 ━━━━━━━━━━━━━━ 4
+		    ━━━━━━━━━━━━━━ :
+		116 ━━━━━━━━━━━━━━━━ 5
+		120 ━━━━━━━━━━━━━━━━ 6
+		124 ━━━━━━━━━━━━━━━━ 7
+		127 ━━━━━━━━━━━━━━━━ (8)
+		128 ━━━━━━━━━━━━━━━━ (8)
+				{{- end }}
+			{{- else }}
+
+		{{ bold "2001:0db8:0123:4567:89ab:cdef:1234:5678" }}
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃128
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃127
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃124
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃120
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ 116
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃112
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃108
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃104
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ 100
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃96
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃92
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃88
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ 84
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃80
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃76
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃72
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃┃ 68
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃┃64
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃┃60
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ ┃56
+		┃┃┃┃ ┃┃┃┃ ┃┃┃┃ 52
+		┃┃┃┃ ┃┃┃┃ ┃┃┃48
+		┃┃┃┃ ┃┃┃┃ ┃┃44
+		┃┃┃┃ ┃┃┃┃ ┃40
+		┃┃┃┃ ┃┃┃┃ 36
+		┃┃┃┃ ┃┃┃32
+		┃┃┃┃ ┃┃28
+		┃┃┃┃ ┃24
+		┃┃┃┃ 20
+		┃┃┃16
+		┃┃12
+		┃8
+		4
+			{{- end }}
+		{{- end }}
+	{{- end }}
+
+
+	{{- if $opts.Plain }}
+
 	CIDR:
 	{{- else }}
 	{{ bold "CIDR:" }}

cmd/subnetter/args.go

@@ -2,11 +2,14 @@ package main
 
 type Args struct {
 	Version         verArgs         `command:"version" alias:"v" description:"Show version information." validate:"omitempty"`
-	SplitCIDR       SplitCIDRArgs   `command:"split-cidr" alias:"se" description:"Split a network into as many equal subnets of prefix size N as possible." validate:"omitempty"`
+	GetPfx          GetPfxArgs      `command:"get-net" alias:"gn" description:"Get a single subnet from a network at either the beginning or end. (You'll probably want to enable -r/--no-remaining.)" validate:"omitempty"`
-	SplitHost       SplitHostArgs   `command:"split-hosts" alias:"sh" description:"Split a network into N total number of hosts *per subnet* as cleanly/evenly as possible. (VERY easy to run out of memory for IPv6 prefixes; be sure to specify very small network!)" validate:"omitempty"`
+	SplitCIDR       SplitCIDRArgs   `command:"split-cidr" alias:"sc" description:"Split a network into as many equal subnets of prefix size N as possible. (This may have issues/take a very long time if you are splitting a very large network into many very small subnets.)" validate:"omitempty"`
+	SplitHost       SplitHostArgs   `command:"split-hosts" alias:"sh" description:"Split a network into N total number of hosts *per subnet* as cleanly/evenly as possible." validate:"omitempty"`
 	SplitSubnets    SplitSubnetArgs `command:"split-nets" alias:"sn" description:"Split a network into N number of subnets as cleanly as possible." validate:"omitempty"`
-	VLSM            VLSMArgs        `command:"vlsm" alias:"sv" description:"Use VLSM (Variable-Length Subnet Masks) to split a network into differently sized subnets." validate:"omitempty"`
+	VLSM            VLSMArgs        `command:"split-vlsm" alias:"sv" alias:"vlsm" description:"Use VLSM (Variable-Length Subnet Masks) to split a network into differently sized subnets." validate:"omitempty"`
-	ExplicitNetwork XNetArgs        `command:"net" alias:"xn" description:"Print information about an explicit network address." validate:"omitempty"`
+	ExplicitNetwork XNetArgs        `command:"net" alias:"xn" alias:"net" description:"Print information about an explicit network address." validate:"omitempty"`
+	NumAddrs        NAddrArgs       `command:"num-addrs" alias:"na" alias:"addrs" description:"Return the number of addresses/hosts in a given network size. (This saves needing to lookup from the table subcommand.)" validate:"omitempty"`
+	NumNets         NNetArgs        `command:"num-nets" alias:"nn" alias:"nets" description:"Return the number of subnets of a given size that can fit into a given network size. This is MUCH, MUCH FASTER than splitting (if you do not need addressing)." validate:"omitempty"`
 	Parse           ParseArgs       `command:"parse" alias:"p" alias:"read" alias:"convert" description:"Parse/convert output from a previous subnetter run." validate:"omitempty"`
 	Table           TableArgs       `command:"table" alias:"t" alias:"tab" alias:"tbl" description:"Show prefix summaries (by default both IPv4 and IPv6)." validate:"omitempty"`
 	Check           CheckArgs       `command:"reserved" alias:"r" description:"Check if a subnet is reserved per IANA/RFC." validate:"omitempty"`
@@ -16,7 +19,7 @@ type verArgs struct {
 	DetailVersion bool `short:"V" long:"detail" description:"Print detailed version info and exit."`
 }
 
-type common struct {
+type commonBase struct {
 	cacheArgs
 	SuppressRemaining bool   `short:"r" long:"no-remaining" description:"Don't show leftover/unallocated/remaining space."`
 	Plain             bool   `short:"p" long:"plain" description:"Show plain output instead of unicode (only used if -f/--format=pretty)."`
@@ -26,13 +29,17 @@ type common struct {
 	AllowReserved     bool   `short:"R" long:"allow-reserved" description:"If specified, do not warn about reserved IP addresses/networks."`
 	reservedArgs
 	AllowHostNet bool `short:"H" long:"allow-host" description:"If specified, do not warn about host bits. Host bits are always removed for subnetting (as otherwise there would be errors); this is only used only for output."`
+}
+
+type common struct {
+	commonBase
 	Network Net `positional-args:"yes" required:"true" description:"The network/parent prefix to operate on." validate:"required"`
 }
 
 type reservedArgs struct {
 	NoRecursive    bool `short:"u" long:"no-recursive" description:"Don't show reservations that are children subnets of the subnet(s). Only if -f/--format=pretty, always false for other formats."`
-	NoRevRecursive bool `short:"U" long:"no-rev-recursive" description:"Don't show reservations that are parents of the subnet(s). Only if -f/--format=pretty, always false for other formats."`
+	NoRevRecursive bool `short:"U" long:"no-rev-recursive" description:"Don't show reservations that are parents of the subnet(s) -- you almost definitely don't want to suppress this. Only if -f/--format=pretty, always false for other formats."`
-	NoPrivate      bool `short:"e" long:"no-private" description:"Consider private subnets of the subnet(s) to be reserved. If you are subnetting private address space, you probably want to leave this disabled. Only if -f/--format=pretty, always true otherwise."`
+	NoPrivate      bool `short:"e" long:"no-private" description:"Consider private subnets to be reserved. If you are subnetting private address space, you probably want to leave this disabled. Only if -f/--format=pretty, always true otherwise."`
 }
 
 type splitArgs struct {
@@ -44,8 +51,32 @@ type cacheArgs struct {
 	DoResCache bool   `short:"c" long:"cache-reservations" env:"SBNTR_RSVCACHE" description:"Enable caching/cache lookup for reservation data."`
 }
 
-type ParseArgs struct {
+type GetPfxArgs struct {
+	Position string `short:"P" long:"position" choice:"first" choice:"last" default:"first" description:"The position of the subnet within the network." validate:"required,oneof=first last"`
+	Prefix   uint8  `short:"s" long:"size" required:"true" description:"Prefix length/network size in bits (as CIDR number)." validate:"required"`
 	splitArgs
+}
+
+type NAddrArgs struct {
+	Isv6          bool `short:"6" long:"v6" description:"If the prefix given is <=32, specify this flag to indicate that it is an IPv6 prefix and not IPv4. (If it is >32, it is automatically treated as an IPv6 prefix for obvious reasons.)"`
+	InclNetAddr   bool `short:"N" long:"incl-net" description:"If specified, include the network address in the count."`
+	InclBcastAddr bool `short:"B" long:"incl-bcast" description:"If specified, include the broadcast/reserved broadcast address in the count."`
+	Size          struct {
+		PrefixSize uint8 `positional-arg-name:"<prefix length>" required:"1" validate:"lte=128"`
+	} `positional-args:"yes" required:"1" validate:"required"`
+}
+
+type NNetArgs struct {
+	Verbose   bool `short:"v" long:"verbose" description:"Be verbose (more ideal for logging)."`
+	NoV6Check bool `short:"6" long:"no-v6" description:"If specified, do not indicate if the subnetting is IPv6 only (true) or not (false; dual-stack/IPv4 supported)."`
+	Sizes     struct {
+		SubnetSize  uint8 `positional-arg-name:"<subnet prefix>" required:"1" validate:"lte=128,gtefield=NetworkSize"`
+		NetworkSize uint8 `positional-arg-name:"<parent prefix>" required:"1" validate:"lte=128,ltefield=SubnetSize"`
+	} `positional-args:"yes" required:"2" validate:"required"`
+}
+
+type ParseArgs struct {
+	commonBase
 	InFile string `short:"i" long:"input" default:"-" description:"Input file to parse. Default is '-' (for STDIN)." required:"true" validate:"required,filepath|eq=-"`
 }
 
@@ -55,13 +86,15 @@ type SplitCIDRArgs struct {
 }
 
 type SplitHostArgs struct {
+	InclNetAddr   bool `short:"N" long:"incl-net" description:"If specified, -n/--num-hosts is interpreted to include the network address in the count."`
+	InclBcastAddr bool `short:"B" long:"incl-bcast" description:"If specified, -n/--num-hosts is interpreted to include the broadcast/reserved broadcast address in the count."`
 	Strict        bool `short:"t" long:"strict" description:"If specified, an error will occur if the number of hosts/assignable addresses in a subnet is not exactly -n/--num-hosts."`
 	Hosts         uint `short:"n" long:"num-hosts" required:"true" description:"Number of hosts (usable addresses) per subnet." validate:"required"`
 	splitArgs
 }
 
 type SplitSubnetArgs struct {
-	Strict  bool `short:"t" long:"strict" description:"If specified, an error will occur if the number of possible equally-sized subnets is not exactly -n/--num-nets."`
+	Strict  bool `short:"t" long:"strict" description:"If specified, an error will occur if the number of subnets is not exactly -n/--num-nets."`
 	NumNets uint `short:"n" long:"num-nets" required:"true" description:"Number of networks." validate:"required"`
 	splitArgs
 }
@@ -73,6 +106,9 @@ type TableArgs struct {
 	NoV4Mask   bool `short:"M" long:"no-mask" description:"Do not include netmasks for IPv4."`
 	NoIpv6     bool `short:"4" long:"ipv4" description:"Only show IPv4 table(s)."`
 	NoIpv4     bool `short:"6" long:"ipv6" description:"Only show IPv6 table(s)."`
+	NoIpv6Seg  bool `short:"D" long:"no-ipv6-seg" description:"Do not show the IPv6 Segment Reference Diagram (ignored if -4/--ipv4 is specified)."`
+	VertSeg    bool `short:"V" long:"vert-ipv6-seg" description:"If specified, display the IPv6 Segment Reference Diagram vertically-aligned instead of horizontally."`
+	VertInvert bool `short:"I" long:"vert-invert" description:"When printing a vertical-aligned IPv6 Segment Reference Diagram, flip so the prefix length is on the left. This takes up less width and is recommended for smaller terminals, and may be easier to read in general."`
 }
 
 type CheckArgs struct {
@@ -89,7 +125,10 @@ type XNetArgs struct {
 
 type VLSMArgs struct {
 	Asc      bool `short:"A" long:"ascending" description:"If specified, place smaller networks (larger prefixes) at the beginning. You almost assuredly do not want to do this."`
-	Sizes []uint8 `short:"s" long:"size" required:"true" description:"Prefix lengths. May be specified multiple times." validate:"required"`
+	Explicit bool `short:"O" long:"explicit-order" description:"If specified, ignore -A/--ascending and do no reordering of prefix sizes whatsoever, instead using the order given. This is EXTREMELY suboptimal and can lead to drastic addressing waste."`
+	// Custom type for now; see https://github.com/jessevdk/go-flags/issues/245
+	// Sizes    []uint8 `short:"s" long:"size" required:"true" description:"Prefix lengths. May be specified multiple times." validate:"required"`
+	Sizes []vlsmSize `short:"s" long:"size" required:"true" description:"Prefix lengths. May be specified multiple times or as a comma-delimited list." validate:"required"`
 	splitArgs
 }
 

cmd/subnetter/errs.go

@@ -5,5 +5,6 @@ import (
 )
 
 var (
+	ErrBadFmt error = errors.New("unknown output format")
 	errBadNet error = errors.New("bad inet/addr family/version")
 )

cmd/subnetter/funcs.go

@@ -10,15 +10,14 @@ import (
 	"net"
 	"net/netip"
 	"os"
-	`sort`
+	"sort"
 	"strings"
 	"time"
 
 	"github.com/goccy/go-yaml"
-	"github.com/projectdiscovery/mapcidr"
 	"go4.org/netipx"
-	"subnetter/netsplit"
+	"r00t2.io/subnetter/netsplit"
-	`subnetter/version`
+	"r00t2.io/subnetter/version"
 )
 
 func printHostPrefix(label string, pfx *netip.Prefix, verb, indent int, indentStr string) (out string) {
@@ -159,8 +158,8 @@ func printMask(label string, pfx netip.Prefix, verb, indent int, indentStr strin
 	fmt.Fprintf(sb, "%sBits:\t\t%d\n", pre2, pfx.Bits())
 	fmt.Fprintf(sb, "%sFirst:\t\t%s\n", pre2, first.String())
 	fmt.Fprintf(sb, "%sLast:\t\t%s\n", pre2, last.String())
-	fmt.Fprintf(sb, "%sAddresses:\t%d\n", pre2, mapcidr.CountIPsInCIDR(true, true, netipx.PrefixIPNet(pfx.Masked())))
+	fmt.Fprintf(sb, "%sAddresses:\t%d\n", pre2, netsplit.NumAddrsPfx(pfx.Masked(), true, true))
-	fmt.Fprintf(sb, "%sHosts:\t\t%d\n", pre2, mapcidr.CountIPsInCIDR(false, false, netipx.PrefixIPNet(pfx.Masked())))
+	fmt.Fprintf(sb, "%sHosts:\t\t%d\n", pre2, netsplit.NumAddrsPfx(pfx.Masked(), false, false))
 	if verb >= 2 {
 		fmt.Fprintf(sb, "%sExpanded:\t%s\n", pre2, netsplit.MaskExpand(mask, pfx.Addr().Is6()))
 		fmt.Fprintf(sb, "%sHex:\t\t0x%s\n", pre2, mask.String())
@@ -236,7 +235,9 @@ func printNets(orig *netip.Prefix, origNet *net.IPNet, nets []*netip.Prefix, rem
 
 	if args == nil {
 		args = &common{
+			commonBase: commonBase{
 				Separator: "\n",
+			},
 		}
 	}
 	fmts = sectFmts[args.Plain]
@@ -399,7 +400,9 @@ func printNets(orig *netip.Prefix, origNet *net.IPNet, nets []*netip.Prefix, rem
 
 		// Remaining
 		if !args.SuppressRemaining {
-			if verb >= 1 {
+			if verb <= 0 {
+				fmt.Println("#")
+			} else {
 				fmt.Println()
 				fmt.Println(sectSep1)
 				fmt.Println("Remaining/Left Over/Unallocated:")
@@ -471,7 +474,180 @@ func printNets(orig *netip.Prefix, origNet *net.IPNet, nets []*netip.Prefix, rem
 	return
 }
 
-func printReserved(nets []*netip.Prefix, remaining *netipx.IPSet, args *common) (err error) {
+func printReserved(records map[netip.Prefix]*netsplit.IANAAddrNetResRecord, origNet netip.Prefix, plain bool, fmtType string) (err error) {
+
+	var b []byte
+	var idx int
+	var pfx netip.Prefix
+	var rec *netsplit.IANAAddrNetResRecord
+	var sortedKeys []netip.Prefix
+	var sb = new(strings.Builder)
+
+	switch fmtType {
+	case "json":
+		if b, err = json.MarshalIndent(records, "", "  "); err != nil {
+			return
+		}
+		fmt.Println(string(b))
+		return
+	case "xml":
+		if b, err = xml.MarshalIndent(records, "", "  "); err != nil {
+			return
+		}
+		fmt.Println(string(b))
+		return
+	case "yml", "yaml":
+		if b, err = yaml.Marshal(records); err != nil {
+			return
+		}
+		fmt.Println(string(b))
+		return
+	}
+
+	if fmtType != "pretty" {
+		err = ErrBadFmt
+		return
+	}
+
+	if records == nil || len(records) == 0 {
+		fmt.Println("No IANA/IETF/RFC-reserved subnet(s) found.")
+		return
+	}
+
+	sortedKeys = make([]netip.Prefix, len(records))
+	idx = 0
+	for pfx, _ = range records {
+		sortedKeys[idx] = pfx
+		idx++
+	}
+	sort.SliceStable(
+		sortedKeys,
+		func(i, j int) (isBefore bool) {
+			isBefore = (netipx.ComparePrefix(sortedKeys[i], sortedKeys[j])) <= 0
+			return
+		},
+	)
+
+	fmt.Fprintf(sb, "= %s =\n", origNet.String())
+	for _, pfx = range sortedKeys {
+		rec = records[pfx]
+		fmt.Fprint(sb, sectFmts[plain][0]+"\n")
+		// Name
+		fmt.Fprintf(sb, "Reservation Name:\t%s\n", rec.Name)
+		fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Networks
+		fmt.Fprint(sb, "\tCanonical Reserved Networks:")
+		if rec.Networks != nil {
+			fmt.Fprint(sb, "\n")
+			for _, recPfx := range rec.Networks.Prefixes {
+				fmt.Fprint(sb, "\t\t"+sectFmts[plain][2]+"\n")
+				fmt.Fprintf(sb, "\t\t%s\n", recPfx.String())
+				// TODO: Print footnotes/refs!
+			}
+		} else {
+			fmt.Fprint(sb, "\t(N/A)\n")
+		}
+		fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Reference/Specification
+		fmt.Fprint(sb, "\tSpecification:")
+		if rec.Spec != nil {
+			fmt.Fprint(sb, "\n")
+			for _, line := range strings.Split(rec.Spec.Text, "\n") {
+				fmt.Fprint(sb, "\t\t"+line+"\n")
+			}
+			if rec.Spec.References != nil {
+				fmt.Fprintf(sb, "\t\t%s\n", sectFmts[plain][2])
+				for rIdx, recref := range rec.Spec.References {
+					if recref != nil {
+						fmt.Fprintf(sb, "\t\t[%d] (%s) %s\n", rIdx, recref.Type, recref.Reference)
+					}
+				}
+			}
+		} else {
+			fmt.Fprint(sb, "\t(None)\n")
+		}
+		fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Allocated (always present)
+		fmt.Fprintf(sb, "\tAllocated:\t%s\n", time.Time(rec.Allocation).String())
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Updated
+		fmt.Fprint(sb, "\tUpdated:\t")
+		if rec.Updated != nil {
+			fmt.Fprintf(sb, "%s\n", time.Time(*rec.Updated).String())
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Termination
+		fmt.Fprint(sb, "\tTerminated:\t")
+		if rec.Termination != nil {
+			fmt.Fprintf(sb, "%s\n", time.Time(*rec.Termination).String())
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Source
+		fmt.Fprint(sb, "\tValid Source:\t\t\t")
+		if rec.Source != nil {
+			if rec.Source.Applicable != nil && !bool(*rec.Source.Applicable) {
+				fmt.Fprint(sb, "(N/A)\n")
+			} else {
+				fmt.Fprintf(sb, "%v\n", bool(*rec.Source.Evaluated))
+			}
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Destination
+		fmt.Fprint(sb, "\tValid Destination:\t\t")
+		if rec.Dest != nil {
+			if rec.Dest.Applicable != nil && !bool(*rec.Dest.Applicable) {
+				fmt.Fprint(sb, "(N/A)\n")
+			} else {
+				fmt.Fprintf(sb, "%v\n", bool(*rec.Dest.Evaluated))
+			}
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Forwardable
+		fmt.Fprint(sb, "\tForwardable:\t\t\t")
+		if rec.Forwardable != nil {
+			if rec.Forwardable.Applicable != nil && !bool(*rec.Forwardable.Applicable) {
+				fmt.Fprint(sb, "(N/A)\n")
+			} else {
+				fmt.Fprintf(sb, "%v\n", bool(*rec.Forwardable.Evaluated))
+			}
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Globally reachable
+		fmt.Fprint(sb, "\tGlobally Routable/Reachable:\t")
+		if rec.GlobalReach != nil {
+			if rec.GlobalReach.Applicable != nil && !bool(*rec.GlobalReach.Applicable) {
+				fmt.Fprint(sb, "(N/A)\n")
+			} else {
+				fmt.Fprintf(sb, "%v\n", bool(*rec.GlobalReach.Evaluated))
+			}
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+		// fmt.Fprint(sb, "\t"+sectFmts[plain][1]+"\n")
+		// Reserved by Protocol
+		fmt.Fprint(sb, "\tReserved by Protocol:\t\t")
+		if rec.ProtoReserved != nil {
+			if rec.ProtoReserved.Applicable != nil && !bool(*rec.ProtoReserved.Applicable) {
+				fmt.Fprint(sb, "(N/A)\n")
+			} else {
+				fmt.Fprintf(sb, "%v\n", bool(*rec.ProtoReserved.Evaluated))
+			}
+		} else {
+			fmt.Fprint(sb, "(N/A)\n")
+		}
+	}
+
+	fmt.Print(sb.String())
 
 	return
 }
@@ -485,7 +661,7 @@ func printSplitErr(e *netsplit.SplitErr) {
 	os.Stderr.WriteString("\n!! ERROR !!!\n")
 
 	os.Stderr.WriteString("\t" + e.Wrapped.Error() + "\n")
-	os.Stderr.WriteString("\nnetwork Iteration Details\n(when error was encountered):\n\n")
+	os.Stderr.WriteString("\nNetwork Iteration Details\n(when error was encountered):\n\n")
 	if e.Nets == nil {
 		os.Stderr.WriteString("Nets:\t\t\t(N/A)\n")
 	} else {
@@ -494,7 +670,7 @@ func printSplitErr(e *netsplit.SplitErr) {
 			fmt.Fprintf(os.Stderr, "\t%s\n", n.String())
 		}
 	}
-	if e.Remaining == nil {
+	if e.Remaining == nil || e.Remaining.Prefixes() == nil || len(e.Remaining.Prefixes()) == 0 {
 		os.Stderr.WriteString("Remaining:\t\t(N/A)\n")
 	} else {
 		os.Stderr.WriteString("Remaining:\n")
@@ -503,7 +679,7 @@ func printSplitErr(e *netsplit.SplitErr) {
 		}
 	}
 	if e.LastSubnet == nil {
-		os.Stderr.WriteString("Last Subnet:\t\t(N/A)")
+		os.Stderr.WriteString("Last Subnet:\t\t(N/A)\n")
 	} else {
 		fmt.Fprintf(os.Stderr, "Last Subnet:\t\t%s\n", e.LastSubnet.String())
 	}

cmd/subnetter/funcs_tpl.go

@@ -10,9 +10,8 @@ import (
 	`strings`
 
 	`github.com/TwiN/go-color`
-	`github.com/projectdiscovery/mapcidr`
 	`go4.org/netipx`
-	`subnetter/netsplit`
+	`r00t2.io/subnetter/netsplit`
 )
 
 // renderHdr renders a header. Note that the first line does *not* include the indent, but subsequent ones do.
@@ -423,8 +422,8 @@ func tplTablePrefixes(ipVer uint8, indent string, plain bool) (out string, err e
 			return
 		}
 		dummyNet = netipx.PrefixIPNet(rows[idx].NetPrefix.Masked())
-		rows[idx].Addresses = mapcidr.CountIPsInCIDR(true, true, dummyNet)
+		rows[idx].Addresses = netsplit.NumAddrsNet(dummyNet, true, true)
-		rows[idx].Hosts = mapcidr.CountIPsInCIDR(false, false, dummyNet)
+		rows[idx].Hosts = netsplit.NumAddrsNet(dummyNet, false, false)
 	}
 
 	colFields, colTitles, colSizes = sizeStructs(rows)

cmd/subnetter/funcs_vlsmargs.go

@@ -0,0 +1,26 @@
+package main
+
+/*
+	AllSizes returns a properly parsed and consolidated slice
+	of all specified sizes, as it takes two valid syntaxes (`-s 32 -s 32`, `-s 32,32`)
+	that can be mixed together.
+*/
+func (v *VLSMArgs) AllSizes() (sizes []uint8, err error) {
+
+	var sizeSlice []uint8
+
+	if v == nil {
+		return
+	}
+	if v.Sizes == nil || len(v.Sizes) == 0 {
+		return
+	}
+	for _, s := range v.Sizes {
+		if sizeSlice, err = s.Sizes(); err != nil {
+			return
+		}
+		sizes = append(sizes, sizeSlice...)
+	}
+
+	return
+}

cmd/subnetter/funcs_vlsmsize.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	`strconv`
+	`strings`
+)
+
+// Sizes returns a parsed/split slice of uint8s from a vlsmSize.
+func (v *vlsmSize) Sizes() (sizes []uint8, err error) {
+
+	var s []string
+	var u uint64
+
+	if v == nil {
+		return
+	}
+	s = strings.Split(string(*v), ",")
+	for idx, i := range s {
+		s[idx] = strings.TrimSpace(i)
+	}
+
+	sizes = make([]uint8, len(s))
+
+	// No validation is performed since we don't have access to the addr inet family; that's up to the parsers.
+	for idx, i := range s {
+		if u, err = strconv.ParseUint(i, 10, 8); err != nil {
+			return
+		}
+		sizes[idx] = uint8(u)
+	}
+
+	return
+}

cmd/subnetter/main.go

@@ -3,17 +3,18 @@ package main
 import (
 	"bytes"
 	"errors"
-	`fmt`
+	"fmt"
 	"io"
 	"log"
+	`math/big`
 	"net"
 	"net/netip"
 	"os"
 	"strings"
 
 	"go4.org/netipx"
-	"subnetter/netsplit"
+	"r00t2.io/subnetter/netsplit"
-	`subnetter/version`
+	"r00t2.io/subnetter/version"
 
 	"github.com/jessevdk/go-flags"
 	"r00t2.io/sysutils/paths"
@@ -26,14 +27,19 @@ func main() {
 	var pfx *net.IPNet
 	var resPfx *netip.Prefix
 	var origPfx netip.Prefix
+	var vlsmSizes []uint8
 	var splitter netsplit.NetSplitter
 	var cmnArgs common
 	var nets []*netip.Prefix
 	var remaining *netipx.IPSet
 	var buf *bytes.Buffer
 	var res *netsplit.StructuredResults
+	var numNets uint
+	var numAddrs *big.Int
+	var v6Only bool
 	var noStrict bool
 	var strictErr error
+	var reservations map[netip.Prefix]*netsplit.IANAAddrNetResRecord
 	var splitErr *netsplit.SplitErr = new(netsplit.SplitErr)
 	var parser *flags.Parser = flags.NewParser(args, flags.Default)
 
@@ -65,6 +71,9 @@ func main() {
 			return
 		}
 	case "net":
+		if err = validate.Struct(args.ExplicitNetwork); err != nil {
+			log.Panicln(err)
+		}
 		if origPfx, err = netip.ParsePrefix(args.ExplicitNetwork.Network.Network); err != nil {
 			log.Panicln(err)
 		}
@@ -77,9 +86,69 @@ func main() {
 			log.Panicln(err)
 		}
 		return
+	case "num-addrs":
+		if err = validate.Struct(args.NumAddrs); err != nil {
+			log.Panicln(err)
+		}
+		if args.NumAddrs.Size.PrefixSize > 32 {
+			args.NumAddrs.Isv6 = true
+		}
+		if numAddrs, err = netsplit.NumAddrsIn(args.NumAddrs.Size.PrefixSize, args.NumAddrs.Isv6, args.NumAddrs.InclNetAddr, args.NumAddrs.InclBcastAddr); err != nil {
+			log.Panicln(err)
+		}
+		fmt.Println(numAddrs.String())
+		return
+	case "num-nets":
+		if err = validate.Struct(args.NumNets); err != nil {
+			log.Panicln(err)
+		}
+		if numNets, v6Only, err = netsplit.NumNets(
+			args.NumNets.Sizes.SubnetSize,
+			args.NumNets.Sizes.NetworkSize,
+		); err != nil {
+			log.Panicln(err)
+		}
+		if !args.NumNets.Verbose {
+			fmt.Printf("%d\n", numNets)
+			if !args.NumNets.NoV6Check {
+				fmt.Println(v6Only)
+			}
+		} else {
+			fmt.Printf("Network Size:\t\t\t%d\n", args.NumNets.Sizes.NetworkSize)
+			fmt.Printf("Subnet Size:\t\t\t%d\n", args.NumNets.Sizes.SubnetSize)
+			fmt.Printf("Number of Subnets:\t\t%d\n", numNets)
+			if !args.NumNets.NoV6Check {
+				fmt.Printf("Subnetting is IPv6-Only:\t%v\n", v6Only)
+			}
+		}
+		return
 	case "reserved":
-		// TODO
+		if err = validate.Struct(args.Check); err != nil {
+			log.Panicln(err)
+		}
+		if origPfx, err = netip.ParsePrefix(args.Check.Network.Network); err != nil {
+			log.Panicln(err)
+		}
+		nets = make([]*netip.Prefix, 1)
+		nets[0] = new(netip.Prefix)
+		*nets[0] = origPfx
+		if err = netsplit.SetCachePath(args.Check.CacheDir); err != nil {
+			log.Panicln(err)
+		}
+		if err = netsplit.EnableCache(args.Check.DoResCache); err != nil {
+			log.Panicln(err)
+		}
+		if reservations, err = netsplit.CheckReserved(nets, !args.Check.NoRevRecursive, !args.Check.NoRecursive, !args.Check.NoPrivate); err != nil {
+			log.Panicln(err)
+		}
+		if err = printReserved(reservations, origPfx, args.Check.Plain, args.Check.Fmt); err != nil {
+			log.Panicln(err)
+		}
+		return
 	case "table":
+		if err = validate.Struct(args.Table); err != nil {
+			log.Panicln(err)
+		}
 		// Account for a weird redundant CLI condition.
 		if args.Table.NoIpv4 && args.Table.NoIpv6 {
 			args.Table.NoIpv6 = false
@@ -92,6 +161,9 @@ func main() {
 		os.Stdout.Write(buf.Bytes())
 		return
 	case "parse":
+		if err = validate.Struct(args.Parse); err != nil {
+			log.Panicln(err)
+		}
 		if strings.TrimSpace(args.Parse.InFile) == "-" {
 			buf = new(bytes.Buffer)
 			if _, err = io.Copy(buf, os.Stdin); err != nil {
@@ -116,7 +188,12 @@ func main() {
 			origPfx = *resPfx
 		}
 		pfx = netipx.PrefixIPNet(origPfx.Masked())
-		cmnArgs = args.Parse.common
+		cmnArgs = common{
+			commonBase: args.Parse.commonBase,
+			Network: Net{
+				Network: res.Original.String(),
+			},
+		}
 		if err = printNets(&origPfx, pfx, nets, remaining, &cmnArgs, res.GetSplitter()); err != nil {
 			log.Panicln(err)
 		}
@@ -132,12 +209,26 @@ func main() {
 			These are all handily-dandily enclosed in a `common` struct type.
 		*/
 		switch parser.Active.Name {
+		case "get-net": // Not a *true* splitter, per se; splitting is required but only for functional reasons.
+			if err = validate.Struct(args.GetPfx); err != nil {
+				log.Panicln(err)
+			}
+			cmnArgs = args.GetPfx.common
+			splitter = &netsplit.PrefixGetter{
+				Pos:          args.GetPfx.Position,
+				PrefixLength: args.GetPfx.Prefix,
+				BaseSplitter: new(netsplit.BaseSplitter),
+			}
+			noStrict = false
+			strictErr = netsplit.ErrBadNumHosts // dummy
 		case "split-hosts":
 			if err = validate.Struct(args.SplitHost); err != nil {
 				log.Panicln(err)
 			}
 			cmnArgs = args.SplitHost.common
 			splitter = &netsplit.HostSplitter{
+				InclNetAddr:   args.SplitHost.InclNetAddr,
+				InclBcastAddr: args.SplitHost.InclBcastAddr,
 				NumberHosts:   args.SplitHost.Hosts,
 				Strict:        args.SplitHost.Strict,
 				BaseSplitter:  new(netsplit.BaseSplitter),
@@ -165,14 +256,18 @@ func main() {
 				PrefixLength: args.SplitCIDR.Prefix,
 				BaseSplitter: new(netsplit.BaseSplitter),
 			}
-		case "vlsm":
+		case "split-vlsm":
 			if err = validate.Struct(args.VLSM); err != nil {
 				log.Panicln(err)
 			}
 			cmnArgs = args.VLSM.common
+			if vlsmSizes, err = args.VLSM.AllSizes(); err != nil {
+				log.Panicln(err)
+			}
 			splitter = &netsplit.VLSMSplitter{
 				Ascending:     args.VLSM.Asc,
-				PrefixLengths: args.VLSM.Sizes,
+				Explicit:      args.VLSM.Explicit,
+				PrefixLengths: vlsmSizes,
 				BaseSplitter:  new(netsplit.BaseSplitter),
 			}
 		default:

cmd/subnetter/types.go

@@ -1,11 +1,11 @@
 package main
 
 import (
-	`math/big`
+	"math/big"
-	`net`
+	"net"
 	"net/netip"
 
-	`subnetter/netsplit`
+	"r00t2.io/subnetter/netsplit"
 )
 
 // subnetResult is only used for human/"pretty" printing.
@@ -96,6 +96,9 @@ type tableFormatter struct {
 	NoBoldTitle     bool
 }
 
+// vlsmSize is a custom type to let us specify multiple sizes as a repeated or consolidated argument.
+type vlsmSize string
+
 type ReservedResults struct {
 	Opts     CheckArgs
 	Reserved map[netip.Prefix]*netsplit.IANAAddrNetResRecord

go.mod

@@ -1,39 +1,29 @@
-module subnetter
+module r00t2.io/subnetter
 
-go 1.23.2
+go 1.24.0
-
-toolchain go1.23.5
 
 require (
 	github.com/TwiN/go-color v1.4.1
-	github.com/davecgh/go-spew v1.1.1
+	github.com/go-playground/validator/v10 v10.25.0
-	github.com/go-playground/validator/v10 v10.24.0
 	github.com/go-resty/resty/v2 v2.16.5
-	github.com/goccy/go-yaml v1.15.16
+	github.com/goccy/go-yaml v1.15.23
 	github.com/jessevdk/go-flags v1.6.1
-	github.com/projectdiscovery/mapcidr v1.1.34
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
-	golang.org/x/mod v0.22.0
+	golang.org/x/mod v0.24.0
+	r00t2.io/goutils v1.8.1
 	r00t2.io/sysutils v1.12.0
 )
 
 require (
-	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/djherbis/times v1.6.0 // indirect
 	github.com/gabriel-vasile/mimetype v1.4.8 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
-	github.com/gorilla/css v1.0.1 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
-	github.com/microcosm-cc/bluemonday v1.0.27 // indirect
+	github.com/stretchr/testify v1.9.0 // indirect
-	github.com/pkg/errors v0.9.1 // indirect
+	golang.org/x/crypto v0.36.0 // indirect
-	github.com/projectdiscovery/blackrock v0.0.1 // indirect
+	golang.org/x/net v0.37.0 // indirect
-	github.com/projectdiscovery/utils v0.4.9 // indirect
+	golang.org/x/sync v0.12.0 // indirect
-	github.com/saintfish/chardet v0.0.0-20230101081208-5e3ef4b5456d // indirect
+	golang.org/x/sys v0.31.0 // indirect
-	golang.org/x/crypto v0.32.0 // indirect
+	golang.org/x/text v0.23.0 // indirect
-	golang.org/x/net v0.34.0 // indirect
-	golang.org/x/sync v0.10.0 // indirect
-	golang.org/x/sys v0.29.0 // indirect
-	golang.org/x/text v0.21.0 // indirect
-	r00t2.io/goutils v1.7.2 // indirect
 )

go.sum

@@ -1,7 +1,5 @@
 github.com/TwiN/go-color v1.4.1 h1:mqG0P/KBgHKVqmtL5ye7K0/Gr4l6hTksPgTgMk3mUzc=
 github.com/TwiN/go-color v1.4.1/go.mod h1:WcPf/jtiW95WBIsEeY1Lc/b8aaWoiqQpu5cf8WFxu+s=
-github.com/aymerick/douceur v0.2.0 h1:Mv+mAeH1Q+n9Fr+oyamOlAkUNPWPlA8PPGR0QAaYuPk=
-github.com/aymerick/douceur v0.2.0/go.mod h1:wlT5vV2O3h55X9m7iVYN0TBM0NH/MmbLnd30/FjWUq4=
 github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -15,57 +13,43 @@ github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/o
 github.com/go-playground/locales v0.14.1/go.mod h1:hxrqLVvrK65+Rwrd5Fc6F2O76J/NuW9t0sjnWqG1slY=
 github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
 github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
-github.com/go-playground/validator/v10 v10.24.0 h1:KHQckvo8G6hlWnrPX4NJJ+aBfWNAE/HH+qdL2cBpCmg=
+github.com/go-playground/validator/v10 v10.25.0 h1:5Dh7cjvzR7BRZadnsVOzPhWsrwUr0nmsZJxEAnFLNO8=
-github.com/go-playground/validator/v10 v10.24.0/go.mod h1:GGzBIJMuE98Ic/kJsBXbz1x/7cByt++cQ+YOuDM5wus=
+github.com/go-playground/validator/v10 v10.25.0/go.mod h1:GGzBIJMuE98Ic/kJsBXbz1x/7cByt++cQ+YOuDM5wus=
 github.com/go-resty/resty/v2 v2.16.5 h1:hBKqmWrr7uRc3euHVqmh1HTHcKn99Smr7o5spptdhTM=
 github.com/go-resty/resty/v2 v2.16.5/go.mod h1:hkJtXbA2iKHzJheXYvQ8snQES5ZLGKMwQ07xAwp/fiA=
-github.com/goccy/go-yaml v1.15.16 h1:PMTVcGI9uNPIn7KLs0H7KC1rE+51yPl5YNh4i8rGuRA=
+github.com/goccy/go-yaml v1.15.23 h1:WS0GAX1uNPDLUvLkNU2vXq6oTnsmfVFocjQ/4qA48qo=
-github.com/goccy/go-yaml v1.15.16/go.mod h1:XBurs7gK8ATbW4ZPGKgcbrY1Br56PdM69F7LkFRi1kA=
+github.com/goccy/go-yaml v1.15.23/go.mod h1:XBurs7gK8ATbW4ZPGKgcbrY1Br56PdM69F7LkFRi1kA=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
-github.com/gorilla/css v1.0.1 h1:ntNaBIghp6JmvWnxbZKANoLyuXTPZ4cAMlo6RyhlbO8=
-github.com/gorilla/css v1.0.1/go.mod h1:BvnYkspnSzMmwRK+b8/xgNPLiIuNZr6vbZBTPQ2A3b0=
 github.com/jessevdk/go-flags v1.6.1 h1:Cvu5U8UGrLay1rZfv/zP7iLpSHGUZ/Ou68T0iX1bBK4=
 github.com/jessevdk/go-flags v1.6.1/go.mod h1:Mk8T1hIAWpOiJiHa9rJASDK2UGWji0EuPGBnNLMooyc=
 github.com/leodido/go-urn v1.4.0 h1:WT9HwE9SGECu3lg4d/dIA+jxlljEa1/ffXKmRjqdmIQ=
 github.com/leodido/go-urn v1.4.0/go.mod h1:bvxc+MVxLKB4z00jd1z+Dvzr47oO32F/QSNjSBOlFxI=
-github.com/microcosm-cc/bluemonday v1.0.27 h1:MpEUotklkwCSLeH+Qdx1VJgNqLlpY2KXwXFM08ygZfk=
-github.com/microcosm-cc/bluemonday v1.0.27/go.mod h1:jFi9vgW+H7c3V0lb6nR74Ib/DIB5OBs92Dimizgw2cA=
-github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
-github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/projectdiscovery/blackrock v0.0.1 h1:lHQqhaaEFjgf5WkuItbpeCZv2DUIE45k0VbGJyft6LQ=
-github.com/projectdiscovery/blackrock v0.0.1/go.mod h1:ANUtjDfaVrqB453bzToU+YB4cUbvBRpLvEwoWIwlTss=
-github.com/projectdiscovery/mapcidr v1.1.34 h1:udr83vQ7oz3kEOwlsU6NC6o08leJzSDQtls1wmXN/kM=
-github.com/projectdiscovery/mapcidr v1.1.34/go.mod h1:1+1R6OkKSAKtWDXE9RvxXtXPoajXTYX0eiEdkqlhQqQ=
-github.com/projectdiscovery/utils v0.4.9 h1:GzYKy5iiCWEZZPGxrtgTOnRTZYiIAiCditGufp0nhGU=
-github.com/projectdiscovery/utils v0.4.9/go.mod h1:/68d0OHGgYF4aW4X7kS1qlFlYOnZxgtFDN85iH732JI=
-github.com/saintfish/chardet v0.0.0-20230101081208-5e3ef4b5456d h1:hrujxIzL1woJ7AwssoOcM/tq5JjjG2yYOc8odClEiXA=
-github.com/saintfish/chardet v0.0.0-20230101081208-5e3ef4b5456d/go.mod h1:uugorj2VCxiV1x+LzaIdVa9b4S4qGAcH6cbhh4qVxOU=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 go4.org/netipx v0.0.0-20231129151722-fdeea329fbba h1:0b9z3AuHCjxk0x/opv64kcgZLBseWJUpBw5I82+2U4M=
 go4.org/netipx v0.0.0-20231129151722-fdeea329fbba/go.mod h1:PLyyIXexvUFg3Owu6p/WfdlivPbZJsZdgWZlrGope/Y=
-golang.org/x/crypto v0.32.0 h1:euUpcYgM8WcP71gNpTqQCn6rC2t6ULUPiOzfWaXVVfc=
+golang.org/x/crypto v0.36.0 h1:AnAEvhDddvBdpY+uR+MyHmuZzzNqXSe/GvuDeob5L34=
-golang.org/x/crypto v0.32.0/go.mod h1:ZnnJkOaASj8g0AjIduWNlq2NRxL0PlBrbKVyZ6V/Ugc=
+golang.org/x/crypto v0.36.0/go.mod h1:Y4J0ReaxCR1IMaabaSMugxJES1EpwhBHhv2bDHklZvc=
-golang.org/x/mod v0.22.0 h1:D4nJWe9zXqHOmWqj4VMOJhvzj7bEZg4wEYa759z1pH4=
+golang.org/x/mod v0.24.0 h1:ZfthKaKaT4NrhGVZHO1/WDTwGES4De8KtWO0SIbNJMU=
-golang.org/x/mod v0.22.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
+golang.org/x/mod v0.24.0/go.mod h1:IXM97Txy2VM4PJ3gI61r1YEk/gAj6zAHN3AdZt6S9Ww=
-golang.org/x/net v0.34.0 h1:Mb7Mrk043xzHgnRM88suvJFwzVrRfHEHJEl5/71CKw0=
+golang.org/x/net v0.37.0 h1:1zLorHbz+LYj7MQlSf1+2tPIIgibq2eL5xkrGk6f+2c=
-golang.org/x/net v0.34.0/go.mod h1:di0qlW3YNM5oh6GqDGQr92MyTozJPmybPK4Ev/Gm31k=
+golang.org/x/net v0.37.0/go.mod h1:ivrbrMbzFq5J41QOQh0siUuly180yBYtLp+CKbEaFx8=
-golang.org/x/sync v0.10.0 h1:3NQrjDixjgGwUOCaF8w2+VYHv0Ve/vGYSbdkTa98gmQ=
+golang.org/x/sync v0.12.0 h1:MHc5BpPuC30uJk597Ri8TV3CNZcTLu6B6z4lJy+g6Jw=
-golang.org/x/sync v0.10.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.12.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
 golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220615213510-4f61da869c0c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.29.0 h1:TPYlXGxvx1MGTn2GiZDhnjPA9wZzZeGKHHmKhHYvgaU=
+golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
-golang.org/x/sys v0.29.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
-golang.org/x/text v0.21.0 h1:zyQAAkrwaneQ066sspRyJaG9VNi/YJ1NfzcGB3hZ/qo=
+golang.org/x/text v0.23.0 h1:D71I7dUrlY+VX0gQShAThNGHFxZ13dGLBHQLVl1mJlY=
-golang.org/x/text v0.21.0/go.mod h1:4IBbMaMmOPCJ8SecivzSH54+73PCFmPWxNTLm+vZkEQ=
+golang.org/x/text v0.23.0/go.mod h1:/BLNzu4aZCJ1+kcD0DNRotWKage4q2rGVAg4o22unh4=
 golang.org/x/time v0.6.0 h1:eTDhh4ZXt5Qf0augr54TN6suAUudPcawVZeIAPU7D4U=
 golang.org/x/time v0.6.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
-r00t2.io/goutils v1.7.2 h1:dJ+pzY/U1yVi2V6eKoxe/4roM+Tb3d0umMEL9Dx4+Lw=
+r00t2.io/goutils v1.8.1 h1:TQcUycPKsYn0QI4uCqb56utmvu/vVSxlblBg98iXStg=
-r00t2.io/goutils v1.7.2/go.mod h1:9ObJI9S71wDLTOahwoOPs19DhZVYrOh4LEHmQ8SW4Lk=
+r00t2.io/goutils v1.8.1/go.mod h1:9ObJI9S71wDLTOahwoOPs19DhZVYrOh4LEHmQ8SW4Lk=
 r00t2.io/sysutils v1.1.1/go.mod h1:Wlfi1rrJpoKBOjWiYM9rw2FaiZqraD6VpXyiHgoDo/o=
 r00t2.io/sysutils v1.12.0 h1:Ce3qUOyLixE1ZtFT/+SVwOT5kSkzg5+l1VloGeGugrU=
 r00t2.io/sysutils v1.12.0/go.mod h1:bNTKNBk9MnUhj9coG9JBNicSi5FrtJHEM645um85pyw=

netsplit/conts.go

@@ -5,9 +5,16 @@ import (
 	`net/netip`
 	`sync`
 
+	`github.com/go-playground/validator/v10`
 	`github.com/go-resty/resty/v2`
 )
 
+const (
+	maxBitsv4 uint8 = 32
+	maxBitsv6 uint8 = 128
+	maxBits   uint8 = maxBitsv6
+)
+
 const (
 	cachedirEnvName string = "SBNTR_RSVCACHE_DIR"
 	// https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
@@ -33,8 +40,12 @@ var (
 )
 
 var (
-	// TODO
+	// validate *validator.Validate = validator.New(validator.WithRequiredStructEnabled(), validator.WithPrivateFieldValidation())
-	cacheLock   sync.RWMutex
+	validate *validator.Validate = validator.New(validator.WithRequiredStructEnabled())
+)
+
+var (
+	cacheLock   sync.RWMutex // TODO
 	cacheClient *resty.Client
 	// IPv4: https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml#iana-ipv4-special-registry-1
 	// IPv6: https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml

netsplit/errs.go

@@ -5,9 +5,11 @@ import "errors"
 var (
 	ErrBadBoundary  error = errors.New("subnet does not align on bit boundary")
 	ErrBadNumHosts  error = errors.New("bad number of hosts; cannot split into prefix exactly")
+	ErrBadNumNets   error = errors.New("bad number of nets; cannot split into prefix exactly")
 	ErrBadPrefix    error = errors.New("prefix is invalid")
 	ErrBadPrefixLen error = errors.New("prefix length exceeds maximum possible for prefix's inet family")
 	ErrBadSplitter  error = errors.New("invalid or unknown splitter when containing")
 	ErrBigPrefix    error = errors.New("prefix length exceeds remaining network space")
 	ErrNoNetSpace   error = errors.New("reached end of network space before splitting finished")
+	ErrUnknownPos   error = errors.New("unknown subnet position")
 )

netsplit/funcs.go

@@ -1,9 +1,12 @@
 package netsplit
 
 import (
+	`bytes`
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
+	"math"
+	"math/big"
 	"net"
 	"net/netip"
 	"strings"
@@ -191,6 +194,7 @@ func CheckReserved(nets []*netip.Prefix, revRecursive, recursive, excludePrivate
 				reservations = make(map[netip.Prefix]*IANAAddrNetResRecord)
 			}
 			reservations[*n] = res
+		}
 		if !revRecursive && !recursive {
 			continue
 		}
@@ -204,7 +208,8 @@ func CheckReserved(nets []*netip.Prefix, revRecursive, recursive, excludePrivate
 					reservations = make(map[netip.Prefix]*IANAAddrNetResRecord)
 				}
 				reservations[p] = r
-				} else if recursive && n.Contains(p.Addr()) {
+			}
+			if recursive && n.Bits() < p.Bits() && n.Contains(p.Addr()) {
 				if reservations == nil {
 					reservations = make(map[netip.Prefix]*IANAAddrNetResRecord)
 				}
@@ -212,7 +217,6 @@ func CheckReserved(nets []*netip.Prefix, revRecursive, recursive, excludePrivate
 			}
 		}
 	}
-	}
 
 	return
 }
@@ -221,7 +225,7 @@ func CheckReserved(nets []*netip.Prefix, revRecursive, recursive, excludePrivate
 func Contain(origPfx *netip.Prefix, nets []*netip.Prefix, remaining *netipx.IPSet, splitter NetSplitter) (s *StructuredResults, err error) {
 
 	var rem []netip.Prefix
-	var reserved map[netip.Prefix]*IANAAddrNetResRecord
+	// var reserved map[netip.Prefix]*IANAAddrNetResRecord
 	var sr = StructuredResults{
 		Original: origPfx,
 	}
@@ -274,6 +278,7 @@ func Contain(origPfx *netip.Prefix, nets []*netip.Prefix, remaining *netipx.IPSe
 		}
 	}
 
+	/*
 		if nets != nil {
 			if reserved, err = CheckReserved(nets, true, true, false); err != nil {
 				return
@@ -287,12 +292,120 @@ func Contain(origPfx *netip.Prefix, nets []*netip.Prefix, remaining *netipx.IPSe
 				}
 			}
 		}
+	*/
 
 	s = &sr
 
 	return
 }
 
+/*
+LastSubnetNet returns the last subnet of prefix length pfxLen from network pfx.
+
+lastSubnet will be nil if pfx is nil or invalid.
+*/
+func LastSubnetNet(pfx *net.IPNet, pfxLen uint8) (lastSubnet *net.IPNet, err error) {
+
+	var nPfx netip.Prefix
+	var ok bool
+
+	if pfx == nil {
+		return
+	}
+	if nPfx, ok = netipx.FromStdIPNet(pfx); !ok {
+		return
+	}
+	if !nPfx.IsValid() {
+		return
+	}
+
+	if nPfx, err = LastSubnetPfx(nPfx, pfxLen); err != nil {
+		return
+	}
+	if !nPfx.IsValid() {
+		return
+	}
+
+	lastSubnet = netipx.PrefixIPNet(nPfx)
+
+	return
+}
+
+// LastSubnetPfx is exactly like LastSubnetNet but using netip.Prefix instead.
+func LastSubnetPfx(pfx netip.Prefix, pfxLen uint8) (lastSubnet netip.Prefix, err error) {
+
+	var ok bool
+	var pfxBytes []byte
+	var bitOffset uint
+	var offset *big.Int
+	var ipInt *big.Int
+	var ipBytes []byte
+	var byteLen int
+	var lastNet *net.IPNet
+	var maxBitLen uint8 = maxBitsv4
+
+	if !pfx.IsValid() {
+		return
+	}
+
+	pfx = pfx.Masked()
+
+	if pfx.Addr().Is6() || pfxLen > maxBitsv4 {
+		maxBitLen = maxBitsv6
+	}
+	if pfxLen > maxBitLen {
+		err = ErrBadPrefixLen
+		return
+	}
+	if pfxLen < uint8(pfx.Bits()) {
+		err = ErrBigPrefix
+		return
+	}
+
+	if pfxBytes, err = pfx.Addr().MarshalBinary(); err != nil {
+		return
+	}
+
+	byteLen = pfx.Addr().BitLen() / 8
+	bitOffset = uint(pfxLen - uint8(pfx.Bits()))
+
+	offset = new(big.Int).Lsh(big.NewInt(1), bitOffset)
+	offset.Sub(offset, big.NewInt(1))
+
+	// Cast the prefix (as represented as bytes) into a *big.Int for some number magic.
+	ipInt = new(big.Int).SetBytes(pfxBytes)
+	// Shift to the first "address" in the prefix/mask it.
+	offset.Lsh(offset, uint(pfx.Addr().BitLen()-int(pfxLen)))
+	// Now add the offset to the base network.
+	ipInt.Add(ipInt, offset)
+
+	// If the base address starts at the "0 address" (e.g. 0.0.0.0 or :: etc....),
+	// this can cause some strange behavior when casting the *big.Int to bytes.
+	// So it gets left-null-padded to the appropriate length for the inet family.
+	ipBytes = ipInt.Bytes()
+	if len(ipBytes) < byteLen {
+		ipBytes = append(
+			bytes.Repeat([]byte{0x00}, byteLen-len(ipBytes)),
+			ipBytes...,
+		)
+	}
+
+	// Create an explicit net.IPNet...
+	lastNet = &net.IPNet{
+		IP:   net.IP(ipBytes),
+		Mask: net.CIDRMask(int(pfxLen), pfx.Addr().BitLen()),
+	}
+	// And then make it a netip.Prefix.
+	if lastSubnet, ok = netipx.FromStdIPNet(lastNet); !ok {
+		return
+	}
+	if !lastSubnet.IsValid() {
+		return
+	}
+
+	return
+}
+
 /*
 MaskExpand expands a net.IPMask's string format.
 Like AddrExpand but for netmasks.
@@ -375,6 +488,134 @@ func MaskInvert(mask net.IPMask) (inverted net.IPMask) {
 	return
 }
 
+/*
+	NumAddrsIn returns the number of addresses in a given prefix length
+	and inet family.
+
+	If isIpv6 is false, it is assumed to be IPv4 (...duh).
+
+	inclNet and inclBcast have the same meanings as in NumAddrsNet and NumAddrsPfx.
+
+	Note that for the single-host prefix (/32 for IPv4, /128 for IPv6), numAddrs will *always* be 1.
+	For point-to-point prefix (IPv4 /31, IPv6 /127), numAddrs will *ALWAYS* be 2.
+*/
+func NumAddrsIn(pfxLen uint8, isIpv6, inclNet, inclBcast bool) (numAddrs *big.Int, err error) {
+
+	var numBits uint
+	var numRemoved int64
+	var maxBitLen uint8 = maxBitsv4
+
+	if isIpv6 || pfxLen > maxBitsv4 {
+		maxBitLen = maxBitsv6
+	}
+	if pfxLen > maxBitLen {
+		err = ErrBadPrefixLen
+		return
+	}
+	if pfxLen == maxBitLen {
+		numAddrs = big.NewInt(1)
+		return
+	}
+	if (pfxLen + 1) == maxBitLen {
+		numAddrs = big.NewInt(2)
+		return
+	}
+
+	numBits = uint(maxBitLen - pfxLen)
+
+	numAddrs = new(big.Int).Lsh(big.NewInt(1), numBits)
+
+	if !inclNet {
+		numRemoved++
+	}
+	if !inclBcast {
+		numRemoved++
+	}
+	if numRemoved > 0 {
+		_ = numAddrs.Sub(numAddrs, big.NewInt(numRemoved))
+	}
+
+	return
+}
+
+/*
+NumAddrsNet returns the number of IP addresses in a net.IPNet.
+
+The network address is included in the count if inclNet is true, otherwise it is excluded.
+
+The broadcast (or reserved broadcast, in the case of IPv6) address will be included in
+the count if inclBcast is true, otherwise it is excluded.
+
+numAddrs will be nil if pfx is nil or invalid.
+*/
+func NumAddrsNet(pfx *net.IPNet, inclNet, inclBcast bool) (numAddrs *big.Int) {
+
+	var nPfx netip.Prefix
+	var ok bool
+
+	if pfx == nil {
+		return
+	}
+	if nPfx, ok = netipx.FromStdIPNet(pfx); !ok {
+		return
+	}
+	if !nPfx.IsValid() {
+		return
+	}
+
+	numAddrs = NumAddrsPfx(nPfx, inclNet, inclBcast)
+
+	return
+}
+
+// NumAddrsPfx is the exact same as NumAddrsNet but for a net/netip.Prefix instead.
+func NumAddrsPfx(pfx netip.Prefix, inclNet, inclBcast bool) (numAddrs *big.Int) {
+
+	var err error
+
+	if !pfx.IsValid() {
+		return
+	}
+
+	// Since we're dealing with existing prefixes/networks, we should never get an error.
+	if numAddrs, err = NumAddrsIn(uint8(pfx.Bits()), pfx.Addr().Is6(), inclNet, inclBcast); err != nil {
+		// But *somehow* in case we do...
+		panic(err)
+	}
+
+	return
+}
+
+/*
+NumNets returns the number of times prefix size subnet fits into prefix size network.
+
+It will error if network is larger than 128 or if subnet is smaller than network.
+
+This is MUCH more performant than splitting out an actual network into explicit subnets,
+and does not require an actual network.
+*/
+func NumNets(subnet, network uint8) (numNets uint, ipv6Only bool, err error) {
+
+	var x float64
+
+	// network cannot be higher than 128, as that's the maximum for IPv6.
+	if network > maxBits {
+		err = ErrBadPrefixLen
+		return
+	}
+	if subnet < network {
+		err = ErrBigPrefix
+		return
+	}
+	ipv6Only = (network > maxBitsv4) || (subnet > maxBitsv4)
+
+	x = float64(subnet - network)
+
+	numNets = uint(math.Pow(2, x))
+
+	return
+}
+
 // Parse parses b for JSON/XML/YAML and tries to return a StructuredResults from it.
 func Parse(b []byte) (s *StructuredResults, err error) {
 

netsplit/funcs_cache.go

@@ -195,6 +195,7 @@ func SetCachePath(cacheDirPath string) (err error) {
 	}
 
 	if cacheDirPath != oldPath {
+		cacheDir = cacheDirPath
 		if err = os.MkdirAll(cacheDir, cacheDirPerms); err != nil {
 			return
 		}

netsplit/funcs_cidrsplitter.go

@@ -22,6 +22,10 @@ func (c *CIDRSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 		return
 	}
 
+	if err = validate.Struct(c); err != nil {
+		return
+	}
+
 	if base, ok = netipx.FromStdIPNet(c.network); !ok {
 		err = ErrBadBoundary
 		return
@@ -31,7 +35,7 @@ func (c *CIDRSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 		return
 	}
 
-	if c.PrefixLength > uint8(base.Bits()) {
+	if c.PrefixLength < uint8(base.Bits()) {
 		err = ErrBigPrefix
 		return
 	}
@@ -41,6 +45,15 @@ func (c *CIDRSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 		return
 	}
 
+	/*
+		TODO: This is *super* slow for tiny subnets in a large net.
+				For future optimzation, first off benchmark to make sure it makes a difference, but
+				chunk out the network (how to find appropriate length?) of n < x < y, where n is the network pfx len,
+				and goroutine each split into a channel.
+				Because this splits *on CIDR boundaries* and we aren't VLSM-ing, remaining never has to be considered-
+				it'll always be clean splitting.
+				See CIDRSplitter.LenSwitch.
+	*/
 	for {
 		if sub, remaining, ok = remaining.RemoveFreePrefix(c.PrefixLength); !ok {
 			if !sub.IsValid() {
@@ -48,11 +61,11 @@ func (c *CIDRSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 				// We just hit the end of the prefix.
 				break
 			}
+		}
 		subPtr = new(netip.Prefix)
 		*subPtr = sub
 		nets = append(nets, subPtr)
 	}
-	}
 
 	return
 }

netsplit/funcs_hostsplitter.go

@@ -1,11 +1,9 @@
 package netsplit
 
 import (
-	`math/big`
+	"math/big"
-	`net`
 	"net/netip"
 
-	`github.com/projectdiscovery/mapcidr`
 	"go4.org/netipx"
 )
 
@@ -15,52 +13,88 @@ import (
 
 remaining may or may not be nil depending on if the number of hosts can fit cleanly within equal network sizes on boundaries.
 
-	An ErrBadNumHosts will be returned if the number of hosts does not match the *addressable* range in a prefix.
+An ErrBadNumHosts will be returned if the number of hosts does not match the *exact* number of addresses per spec in a prefix.
 */
 func (h *HostSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {
 
+	var pfx netip.Prefix
 	var tgt *big.Int
+	var splitCidr int
 	var hosts *big.Int
-	var sub netip.Prefix
+	var found bool
-	var subPtr *netip.Prefix
+	var cs *CIDRSplitter
-	var split []*net.IPNet
-	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
 
 	if h == nil || h.NumberHosts == 0 || h.BaseSplitter == nil || h.network == nil {
 		return
 	}
 
-	if split, err = mapcidr.SplitIPNetByNumber(h.network, int(h.NumberHosts)); err != nil {
+	if err = validate.Struct(h); err != nil {
 		return
 	}
 
-	tgt = big.NewInt(0)
+	pfx, _ = netipx.FromStdIPNet(h.network)
+	tgt = new(big.Int)
 	tgt.SetUint64(uint64(h.NumberHosts))
 
-	nets = make([]*netip.Prefix, len(split))
+	if NumAddrsPfx(pfx, h.InclNetAddr, h.InclBcastAddr).Cmp(tgt) < 0 {
-	for idx, n := range split {
+		// The number of hosts per-subnet exceeds the number of addresses in the specified network.
-		sub, _ = netipx.FromStdIPNet(n)
+		err = ErrNoNetSpace
-		hosts = mapcidr.CountIPsInCIDR(false, false, n)
+		return
-		if hosts == nil || tgt.Cmp(hosts) != 0 {
+	}
+	/*
+		Iterate up through prefix lengths for the inet family's maximum length, getting larger and larger,
+		until we reach the first prefix that can contain tgt.
+		If we reach h.network.Bits(), we are forced to use that.
+		(Any case otherwise should be handled by the above checks.)
+	*/
+	for splitCidr = pfx.Addr().BitLen(); splitCidr >= pfx.Bits(); splitCidr-- {
+		if hosts, err = NumAddrsIn(uint8(splitCidr), pfx.Addr().Is6(), h.InclNetAddr, h.InclBcastAddr); err != nil {
+			return
+		}
+		if hosts.Cmp(tgt) >= 0 {
+			found = true
+			break
+		}
+	}
+	if !found {
+		// Pragmatically, we should never be able to get to this code.
+		err = ErrNoNetSpace
+		return
+	}
+
+	// Now that we have an appropriate prefix length for splitting, we can offload a huge portion of that to a CIDRSplitter.
+	cs = &CIDRSplitter{
+		PrefixLength: uint8(splitCidr),
+		BaseSplitter: h.BaseSplitter,
+	}
+	if nets, remaining, err = cs.Split(); err != nil {
+		return
+	}
+	// If strict mode is enabled, we then need to match the number of hosts exactly in the subnet.
+	if !h.Strict {
+		return
+	}
+	// First off, if remaining is not nil/empty, that immediately fails strict.
+	if remaining != nil && remaining.Prefixes() != nil && len(remaining.Prefixes()) != 0 {
 		err = &SplitErr{
 			Wrapped:            ErrBadNumHosts,
 			Nets:               nets,
 			Remaining:          remaining,
-				LastSubnet:         &sub,
+			LastSubnet:         nil,
-				RequestedPrefixLen: uint8(sub.Bits()),
+			RequestedPrefixLen: uint8(splitCidr),
 		}
-			ipsb.AddPrefix(sub)
+		return
-		} else {
-			subPtr = new(netip.Prefix)
-			*subPtr = sub
-			nets = append(nets, subPtr)
 	}
 
-		nets[idx] = new(netip.Prefix)
+	// Then we check the cidr we split on, and check its number of hosts.
-		*nets[idx] = sub
+	if hosts.Cmp(tgt) != 0 {
+		err = &SplitErr{
+			Wrapped:            ErrBadNumHosts,
+			Nets:               nets,
+			Remaining:          remaining,
+			LastSubnet:         nil,
+			RequestedPrefixLen: uint8(splitCidr),
 		}
-
-	if remaining, err = ipsb.IPSet(); err != nil {
 		return
 	}
 

netsplit/funcs_prefixgetter.go

@@ -0,0 +1,102 @@
+package netsplit
+
+import (
+	`fmt`
+	`net/netip`
+
+	`go4.org/netipx`
+)
+
+// Split is to conform to a NetSplitter, though a PrefixGetter is *technically* not a splitter.
+func (p *PrefixGetter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {
+
+	var ok bool
+	var base netip.Prefix
+	var vlsmS *VLSMSplitter
+	var addr netip.Addr
+	var maxPfxLen uint8 = maxBitsv4
+	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
+
+	if p == nil || p.PrefixLength == 0 || p.BaseSplitter == nil || p.network == nil {
+		return
+	}
+
+	if err = validate.Struct(p); err != nil {
+		return
+	}
+
+	// If the position is "first", we can simply call a VLSM.
+	if p.Pos == "first" {
+		vlsmS = &VLSMSplitter{
+			Ascending:     false,
+			Explicit:      false,
+			PrefixLengths: []uint8{p.PrefixLength},
+			BaseSplitter:  p.BaseSplitter,
+		}
+		if nets, remaining, err = vlsmS.Split(); err != nil {
+			return
+		}
+		return
+	}
+
+	if p.Pos != "last" {
+		err = ErrUnknownPos
+		return
+	}
+
+	// Otherwise this gets... messy.
+	if base, ok = netipx.FromStdIPNet(p.network); !ok {
+		err = ErrBadBoundary
+		return
+	}
+	if !base.IsValid() {
+		err = ErrBadBoundary
+		return
+	}
+	ipsb = new(netipx.IPSetBuilder)
+	ipsb.AddPrefix(base.Masked())
+
+	// First if it's a single host prefix, ezpz gg no re.
+	if base.Addr().Is6() {
+		maxPfxLen = maxBitsv6
+	}
+	if p.PrefixLength == maxPfxLen {
+		nets = make([]*netip.Prefix, 1)
+		nets[0] = new(netip.Prefix)
+		addr = netipx.PrefixLastIP(base)
+		fmt.Println(addr.String())
+		if *nets[0], err = addr.Prefix(int(p.PrefixLength)); err != nil {
+			return
+		}
+		ipsb.Remove(addr)
+		if remaining, err = ipsb.IPSet(); err != nil {
+			return
+		}
+		return
+	}
+
+	// Otherwise this gets... interesting.
+	/*
+		For IPv4, performance NORMALLY would be "fine" on modern hardware with:
+			1. straight CIDR-splitting
+			2. grabbing the last prefix
+			3. condensing the leading prefixes to a new IPSet
+		But even this can take a long time (see CIDRSplitter.Split comments).
+
+		In almost all cases (unless subnetting like, n+12 prefix length),
+		IPv6 takes WAY too long.
+
+		So use the same function (LastSubnetPfx) for both cases.
+	*/
+	nets = make([]*netip.Prefix, 1)
+	nets[0] = new(netip.Prefix)
+	if *nets[0], err = LastSubnetPfx(base, p.PrefixLength); err != nil {
+		return
+	}
+	ipsb.RemovePrefix(*nets[0])
+	if remaining, err = ipsb.IPSet(); err != nil {
+		return
+	}
+
+	return
+}

netsplit/funcs_subnetsplitter.go

@@ -1,10 +1,9 @@
 package netsplit
 
 import (
-	`net`
+	`math`
 	"net/netip"
 
-	`github.com/projectdiscovery/mapcidr`
 	"go4.org/netipx"
 )
 
@@ -22,15 +21,16 @@ func (s *SubnetSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet,
 	var ok bool
 	var pfxLen int
 	var base netip.Prefix
-	var sub netip.Prefix
+	var vlsm *VLSMSplitter
-	var subPtr *netip.Prefix
-	var split []*net.IPNet
-	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
 
 	if s == nil || s.BaseSplitter == nil || s.network == nil || s.NumberSubnets == 0 {
 		return
 	}
 
+	if err = validate.Struct(s); err != nil {
+		return
+	}
+
 	if base, ok = netipx.FromStdIPNet(s.network); !ok {
 		err = ErrBadBoundary
 		return
@@ -40,65 +40,48 @@ func (s *SubnetSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet,
 		return
 	}
 
-	if split, err = mapcidr.SplitIPNetIntoN(s.network, int(s.NumberSubnets)); err != nil {
+	// Previously, this used (github.com/projectdiscovery/mapcidr).SplitIPNetIntoN.
-		return
+	// It no longer does: https://github.com/projectdiscovery/mapcidr/issues/628
-	}
+	// I am Noticing.
 
-	for _, n := range split {
+	// First the number of bits needed is calculated.
-		if sub, ok = netipx.FromStdIPNet(n); !ok {
+	pfxLen = int(math.Ceil(math.Log2(float64(s.NumberSubnets))))
-			// We bail early on this error.
+	// And this is then added to the original prefix length to get the new prefix size.
-			err = &SplitErr{
+	pfxLen = pfxLen + base.Bits()
-				Wrapped:            ErrBadBoundary,
+	// I don't know how this would happen, but it'd be bad if it did.
-				Nets:               nets,
+	if pfxLen < base.Bits() {
-				Remaining:          remaining,
+		err = ErrBigPrefix
-				LastSubnet:         subPtr,
-				RequestedPrefixLen: 0,
-			}
-			err = ErrBadBoundary
 		return
 	}
-		if sub.String() == base.String() {
+	// Likewise.
-			continue
+	if base.Addr().Is6() {
-		}
+		ok = pfxLen <= int(maxBitsv6)
-		if pfxLen == 0 {
-			pfxLen = sub.Bits()
-			if nets == nil {
-				nets = make([]*netip.Prefix, 0)
-			}
-			subPtr = new(netip.Prefix)
-			*subPtr = sub
-			nets = append(nets, subPtr)
 	} else {
-			if sub.Bits() != pfxLen {
+		ok = pfxLen <= int(maxBitsv4)
-				if err == nil {
-					// Return this err but don't return early; wait for the populate.
-					err = &SplitErr{
-						Wrapped:            ErrNoNetSpace,
-						Nets:               nets,
-						Remaining:          remaining,
-						LastSubnet:         subPtr,
-						RequestedPrefixLen: uint8(pfxLen),
 	}
-				}
+	if !ok {
-				ipsb.AddPrefix(sub)
+		err = ErrBadPrefix
-			} else {
-				subPtr = new(netip.Prefix)
-				*subPtr = sub
-				nets = append(nets, subPtr)
-			}
-		}
-	}
-
-	if remaining, err = ipsb.IPSet(); err != nil {
 		return
 	}
 
-	if len(nets) < int(s.NumberSubnets) {
+	// We can now VLSM.
-		err = &SplitErr{
+	vlsm = &VLSMSplitter{
-			Wrapped:   ErrNoNetSpace,
+		// Ascenting and Explicit are pointless to set as all defined sizes are the same.
-			Nets:      nets,
+		Ascending:     false,
-			Remaining: remaining,
+		Explicit:      false,
+		PrefixLengths: make([]uint8, s.NumberSubnets),
+		BaseSplitter:  s.BaseSplitter,
 	}
+	for i := 0; i < int(s.NumberSubnets); i++ {
+		vlsm.PrefixLengths[i] = uint8(pfxLen)
+	}
+
+	if nets, remaining, err = vlsm.Split(); err != nil {
+		return
+	}
+
+	if s.Strict && remaining != nil && remaining.Prefixes() != nil && len(remaining.Prefixes()) > 0 {
+		err = ErrBadNumNets
 		return
 	}
 

netsplit/funcs_vlsmsplitter.go

@@ -2,7 +2,7 @@ package netsplit
 
 import (
 	"net/netip"
-	"sort"
+	`sort`
 
 	"go4.org/netipx"
 )
@@ -21,7 +21,15 @@ func (v *VLSMSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 	var base netip.Prefix
 	var sub netip.Prefix
 	var subPtr *netip.Prefix
-	var ipsb = new(netipx.IPSetBuilder)
+	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
+
+	if v == nil || v.PrefixLengths == nil || len(v.PrefixLengths) == 0 || v.BaseSplitter == nil || v.network == nil {
+		return
+	}
+
+	if err = validate.Struct(v); err != nil {
+		return
+	}
 
 	if err = ValidateSizes(v.network, v.PrefixLengths...); err != nil {
 		return
@@ -38,10 +46,7 @@ func (v *VLSMSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 		But, as I expected, netipx ftw again.
 	*/
 
-	if v == nil || v.PrefixLengths == nil || len(v.PrefixLengths) == 0 || v.BaseSplitter == nil || v.network == nil {
+	if !v.Explicit {
-		return
-	}
-
 		sort.SliceStable(
 			v.PrefixLengths,
 			func(i, j int) (isBefore bool) { // We use a reverse sorting by default so we get larger prefixes at the beginning.
@@ -53,6 +58,7 @@ func (v *VLSMSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, e
 				return
 			},
 		)
+	}
 
 	pfxLen, _ = v.network.Mask.Size()
 	pfxLen8 = uint8(pfxLen)

netsplit/types.go

@@ -31,7 +31,16 @@ type NetSplitter interface {
 
 // BaseSplitter is used to encapsulate the "parent" network to be split.
 type BaseSplitter struct {
-	network *net.IPNet
+	network *net.IPNet `validate:"required"`
+}
+
+// PrefixGetter is a "pseudo-splitter"; it splits according to a given prefix but only returns a specfic subnet (either the first or the last).
+type PrefixGetter struct {
+	// Pos is the position in BaseSplitter.network for the selected PrefixLength.
+	Pos string `json:"pos" xml:"pos,attr" yaml:"Position" validate:"required,oneof=first last"`
+	// PrefixLength specifies the CIDR/prefix length of the subnet.
+	PrefixLength uint8 `json:"prefix" xml:"prefix,attr" yaml:"network Prefix Length" validate:"required,lte=128"`
+	*BaseSplitter
 }
 
 /*
@@ -40,7 +49,11 @@ It attemps to split the network into as many networks of size PrefixLength as cl
 */
 type CIDRSplitter struct {
 	// PrefixLength specifies the CIDR/prefix length of the subnets to split out.
-	PrefixLength  uint8 `json:"prefix" xml:"prefix,attr" yaml:"network Prefix Length"`
+	PrefixLength uint8 `json:"prefix" xml:"prefix,attr" yaml:"network Prefix Length" validate:"required,lte=128"`
+	// TODO: See CIDRSplitter.Split for future optimization using this.
+	// LenSwitch specifies the threshold bit offset after which (inclusive) it switches from a repeated prefix removal to manual recursive binary split.
+	// If 0, 12 is the default.
+	// LenSwitch uint8 `json:"switch_at" xml:"switchAt,attr" yaml:"Switch Offset Threshold"`
 	*BaseSplitter `json:"net" xml:"net,omitempty" yaml:"network,omitempty"`
 }
 
@@ -50,7 +63,11 @@ It attempts to evenly distribute addresses amoungs subnets.
 */
 type HostSplitter struct {
 	// NumberHosts is the number of hosts to be placed in each subnet to split out.
-	NumberHosts uint `json:"hosts" xml:"hosts,attr" yaml:"Number of Hosts Per Subnet"`
+	NumberHosts uint `json:"hosts" xml:"hosts,attr" yaml:"Number of Hosts Per Subnet" validate:"required"`
+	// InclNetAddr, if true, specifies that NumberHosts includes the network address.
+	InclNetAddr bool `json:"net_addr" xml:"netAddr,attr,omitempty" yaml:"Network Address Included,omitempty"`
+	// InclBcastAddr, if true, specifies that NumberHosts includes the broadcast address.
+	InclBcastAddr bool `json:"bcast_addr" xml:"bcast,attr,omitempty" yaml:"Broadcast Address Included,omitempty"`
 	// Strict, if true, will return an error from Split if the network cannot split into subnets of NumberHosts-addressable networks exactly.
 	Strict        bool `json:"strict" xml:"strict,attr,omitempty" yaml:"Strictly Equal Hosts Per Subnet"`
 	*BaseSplitter `json:"net" xml:"net,omitempty" yaml:"network,omitempty"`
@@ -62,7 +79,7 @@ as cleanly as poossible.
 */
 type SubnetSplitter struct {
 	// NumberSubnets indicates the number of subnets to split the network into.
-	NumberSubnets uint `json:"nets" xml:"nets,attr" yaml:"Number of Target Subnets"`
+	NumberSubnets uint `json:"nets" xml:"nets,attr" yaml:"Number of Target Subnets" validate:"required"`
 	// Strict, if true, will return an error from Split if the network sizes cannot split into equally-sized networks.
 	Strict        bool `json:"strict" xml:"strict,attr,omitempty" yaml:"Strictly Equal Subnet Sizes"`
 	*BaseSplitter `json:"net" xml:"net,omitempty" yaml:"network,omitempty"`
@@ -78,9 +95,16 @@ type VLSMSplitter struct {
 		(ascending order) instead of larger networks/smaller prefixes (descending order).
 		You almost assuredly do not want to do this.
 	*/
-	Ascending bool
+	Ascending bool `json:"asc,omitempty" xml:"asc,attr,omitempty" yaml:"Ascending Order,omitempty"`
+	/*
+		Explicit, if true, will ignore Ascending completely and split in the explicit order of PrefixLengths.
+
+		This has the potential to be *extremely* wasteful of addressing space as the resulting blocks are
+		VERY unoptimized.
+	*/
+	Explicit bool `json:"explicit,omitempty" xml:"explicit,attr,omitempty" yaml:"Explicit Ordering,omitempty"`
 	// PrefixLengths contains the prefix lengths of each subnet to split out from the network.
-	PrefixLengths []uint8 `json:"prefixes" xml:"prefixes>prefix" yaml:"Prefix Lengths"`
+	PrefixLengths []uint8 `json:"prefixes" xml:"prefixes>prefix" yaml:"Prefix Lengths" validate:"required,dive,lte=128"`
 	*BaseSplitter `json:"net" xml:"net,omitempty" yaml:"network,omitempty"`
 }