http://src.iws.cs.ovgu.de/source/xref/illumos-gate/usr/src/cmd/ipf/tools/ipnat_y.y

N .. decnumber
H .. hexnumber (recognized by a leading '0x')
S .. string
EOL    .. End Of Line or ';'
IPv6   .. IP v6 address
LSB    .. a semicolon separated list of expressions always enclosed in _curly_
          braces.
SN     .. a known service name or port number (see /etc/inet/services etc.)
PN     .. a known protocol name or number incl. 'tcp' and 'udp' (see 
          /etc/inet/protocols etc.)

file:
	[ S '=' S ';' ]*
	[{ map | mapblock | redir } EOL]*

map:
	{ 'map' | 'bimap' }
	S [',' S]								// S == interface name
	{
		addr
		|'from' addr [
			'port' {'='|'!='|'<'|'<='|'>'|'>='} SN
			|'port' SN {'><'|'<>'} SN
		 ]
		 [!]'to' addr [
			'port' {'='|'!='|'<'|'<='|'>'|'>='} SN
			|'port' SN {'><'|'<>'} SN
		 ]
	}
	'->'
	{ addr | 'range' hostname '-' hostname }
	[ 'proxy' 'port' SN S '/' PN
	  |'portmap' {'tcp' |'udp' |'tcp/udp'} { SN':'SN |'auto' } ['sequential']
	  |'icmpidmap' S N':'N
	]
	[mapoptions]

mapblock:
	'map-block'
	S [',' S]								// S == interface name
	addr
	'->'
	addr [N|'auto']							// N == port number
	[mapoptions]

redir:
	 'rdr'
	S [',' S]								// S == interface name
	{
		addr ['port' SN [{'-'|':'} SN]
		|'from' addr [
			'port' {'='|'!='|'<'|'<='|'>'|'>='} SN
			|'port' SN {'><'|'<>'} SN
		 ]
		 [!]'to' addr [
			'port' {'='|'!='|'<'|'<='|'>'|'>='} SN
			|'port' SN {'><'|'<>'} SN
		 ]
		'->'
		hostname ['/' N |',' hostname]
		'port' ['='] SN [PN|'tcp/udp'] [rdroptions]
	}
	|
	{
		addr
		'->'
		hostname ['/' N |',' hostname] [PN|'tcp/udp'] [rdroptions]
	}

addr:
	'any' | hostname ['/' { N['.'N'.'N'.'N] |H |IPv6 } ]
hostname:
	S | N['.'N'.'N'.'N] | [N] IPv6

mapoptions:
	['round-robin'] ['frag'] ['age' N ['/' N]] ['mssclamp' N] ['tag' S]
	[S|N|'tcp'|'udp'|'tcp/udp']

rdroptions:
	['round-robin'] ['frag'] ['age' N ['/' N]] ['sticky'] ['mssclamp' N]
	['proxy' S | 'proxy' 'port' SN S '/' {N |S |'tcp' |'udp'} ]
	['tag' S]