From RFC 3986

 IPv6address   =                            6( h16 ":" ) ls32
               /                       "::" 5( h16 ":" ) ls32
               / [               h16 ] "::" 4( h16 ":" ) ls32
               / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
               / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
               / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
               / [ *4( h16 ":" ) h16 ] "::"              ls32
               / [ *5( h16 ":" ) h16 ] "::"              h16
               / [ *6( h16 ":" ) h16 ] "::"

 h16           = 1*4HEXDIG
 ls32          = ( h16 ":" h16 ) / IPv4address
 IPv4address   = dec-octet "." dec-octet "." dec-octet "." dec-octet
 dec-octet     = DIGIT                  ; 0-9
                / %x31-39 DIGIT         ; 10-99
                / "1" 2DIGIT            ; 100-199
                / "2" %x30-34 DIGIT     ; 200-249
                / "25" %x30-35          ; 250-255

This is likely to be incorrect but should still but useful.

 NL     = CR / CRLF
 MASK   = MASK4 / MASK6
 MASK4  = 1*DIGIT         ; max 32 
 MASK6  = 1*DIGIT         ; max 128 
 ASN    = ASN2 / ASN4
 ASN2   = 1*DIGIT         ; max 2^16
 ASN4   = 1*DIGIT         ; max 2^32
 number = 1*DIGIT         ; should split 16 and 32 bits number ...

 configuration =  1*neigbor 1*NL
 neighbor      =  'neighbor' IP '{' NL neighbor_body '}' [ NL ]
 IP            =  IPv4address / IPv6address
 neighbor_body =  [description]
 neighbor_body =/ router-id
 neighbor_body =/ local-address
 neighbor_body =/ local-as
 neighbor_body =/ peer-as
 neighbor_body =/ [ graceful-restart ]
 neighbor_body =/ [ hold-time ]
 neighbor_body =/ static / flow / static flow / flow static
 
 router-id        = 'router-id' IPv4address ';' NL
 local-address    = 'local-address' IP ';' NL
 local-as         = 'local-as' ASN ';' NL
 peer-as          = 'peer-as' ASN ';' NL
 graceful-restart = 'graceful-restart' [ number ] ';' NL
 hold-time        = 'hold-time' [ number ] ';' NL
 static           = 'static' '{' NL 1*static-route '}' NL
 flow             = 'flow' '{' NL 1*flow-route '}' NL
 
 static-route     = 1*single-static | 1*multi-static
 single-static    = 'route' ((IP6Address '/' MASK6)/(IP4Address '/' MASK4)) next-hop [local-preference] [med] [community] [as-path] ';'
 multi-static     = 'route' [1*ALPHA] '{' NL static-group '}' NL
 static-group     = next-hop [ local-preference ';' NL ] [ med ';' NL ] [ community ';' NL] [ as-path ';' ]
 
 next-hop         = 'next-hop' IP 
 local-preference = 'local-preference' number
 med              = 'med' number
 community        = 'community' communities
 communities      =  community_value / '[' 1*community_value ']'
 community_value  =  number
 community_value  =/ ('0x'/'0X') 1*HEXDIG
 community_value  =/ ASN2 ':' ASN2
 as-path          = '[' 1*ASN ']'
 
 flow-route       =  'route' [*ALPHA] '{' NL 'match' '{' NL flow-conditions '}' NL 'then' '{' flow-action '}' NL '}' NL
 
 flow-conditions  = *1source  *1destination *1port *1dport *1sport *1protocol *1packet-length *1fragment *1icmp-type *1icmp-code *1tcp-flags *1dscp
 source           = 'source' IPv4Address '/' MASK4 ';' NL
 destination      = 'destination' IPv4Address '/' MASK4 ';' NL
 port             = 'port' digit-range ';' NL
 dport            = 'destination-port' digit-range ';' NL
 sport            = 'source-port' digit-range ';' NL
 procol           = 'protocol' supported-proto / ('[' 1* supported-proto ']') ';' NL
 supported-proto  = number / 'tcp' / 'udp' /
 packet-length    = 'packet-length' digit-range ';' NL
 fragment         = 'fragment' valid-fragment / ('[' 1* valid-fragment ']') ';' NL
 valid-fragment   = 'first-fragment' / 'last-fragment' / ...
 icmp-type        = 'icmp-type' types / ('[' 1* types ']') ';' NL
 icmp-code        = 'icmp-code' codes / ('[' 1* codes ']') ';' NL
 types            = 'unreachable' / 'echo-request' / 'echo-reply' / ...
 codes            = 'host-unreachable' / 'network-unreachable' / ...
 tcp-flags        = 'tcp-flags' flags / ('[' 1* flags ']') ';' NL
 flags            = 'urgent' / 'rst' / ...
 dscp             = 'dscp' digit-range ';' NL
 
 digit-range      = digit-maths / digit-list

How do you express that compare and number should not be space separated ?

 digit-maths      = digit-math [ '&' digit-maths ]
 digit-math       = compare number
 compare          = '>' / '<' / '=' / '>=' / '<=' 
 digit-list       = '[' 1*number ']'
 
 flow-action      =  'rate-limit' number ';' NL
 flow-action      =  'discard' ';' NL
 flow-action      =  'redirect' ((IP ':' number) / (ASN2 ':' ASN2)) ';' NL