Regular expression that matches valid IPv6 addresses

Question

I m having trouble writing a regular expression that matches valid IPv6 addresses  including those in their compressed form  with    or leading zeros omitted from each byte pair      Can someone suggest a regular expression that would fulfill the requirement   I m considering expanding each byte pair and matching the result with a simpler regex

User · Answer

Just matching local ones from an origin with square brackets included. I know it's not as comprehensive but in javascript the other ones had difficult to trace issues primarily that of not working, so this seems to get me what I needed for now. extra capitals A-F aren't needed either.

^\[([0-9a-fA-F]{1,4})(\:{1,2})([0-9a-fA-F]{1,4})(\:{1,2})([0-9a-fA-F]{1,4})(\:{1,2})([0-9a-fA-F]{1,4})(\:{1,2})([0-9a-fA-F]{1,4})\]

Jinnko's version is simplified and better I see.

User · Answer

It is difficult to find a regular expression which works for all IPv6 cases  They are usually hard to maintain  not easily readable and may cause performance problems  Hence  I want to share an alternative solution which I have developed  Regular Expression  RegEx  for IPv6 Separate from IPv4   Now you may ask that  This method only finds IPv6  how can I find IPv6 in a text or file   Here are methods for this issue too   Note  If you do not want to use IPAddress class in  NET  you can also replace it with my method  It also covers mapped IPv4 and special cases too  while IPAddress does not cover    class IPv6       public List lt string gt  FindIPv6InFile string filePath                Char ch          StringBuilder sbIPv6   new StringBuilder            List lt string gt  listIPv6   new List lt string gt             StreamReader reader   new StreamReader filePath           do                       bool hasColon   false              int length   0               do                               ch    char reader Read                     if  IsEscapeChar ch                       break                     Check the first 5 chars  if it has colon  then continue appending to stringbuilder                 if   hasColon  amp  amp  length  lt  5                                        if  ch                                                       hasColon   true                                            sbIPv6 Append ch ToString                                       else if  hasColon    if no colon in first 5 chars  then dont append to stringbuilder                                       sbIPv6 Append ch ToString                                        length                   while   reader EndOfStream                if  hasColon  amp  amp   listIPv6 Contains sbIPv6 ToString     amp  amp  IsIPv6 sbIPv6 ToString                                   listIPv6 Add sbIPv6 ToString                                sbIPv6 Clear               while   reader EndOfStream           reader Close            reader Dispose             return listIPv6             public List lt string gt  FindIPv6InText string text                StringBuilder sbIPv6   new StringBuilder            List lt string gt  listIPv6   new List lt string gt              for  int i   0  i  lt  text Length  i                          bool hasColon   false              int length   0               do                               if  IsEscapeChar text length   i                        break                     Check the first 5 chars  if it has colon  then continue appending to stringbuilder                 if   hasColon  amp  amp  length  lt  5                                        if  text length   i                                                        hasColon   true                                            sbIPv6 Append text length   i  ToString                                       else if  hasColon    if no colon in first 5 chars  then dont append to stringbuilder                                       sbIPv6 Append text length   i  ToString                                        length                   while  i   length    text Length                if  hasColon  amp  amp   listIPv6 Contains sbIPv6 ToString     amp  amp  IsIPv6 sbIPv6 ToString                                   listIPv6 Add sbIPv6 ToString                                i    length              sbIPv6 Clear                       return listIPv6             bool IsEscapeChar char ch                if  ch         amp  amp  ch      r   amp  amp  ch      n   amp  amp  ch    t                         return false                     return true             bool IsIPv6 string maybeIPv6                IPAddress ip          if  IPAddress TryParse maybeIPv6  out ip                         return ip AddressFamily    AddressFamily InterNetworkV6                    else                       return false

User · Answer

From  IPv6 regex       A  0-9a-f  1 4    1 1    0-9a-f  1 4   1 6  Z     A  0-9a-f  1 4    1 2    0-9a-f  1 4   1 5  Z     A  0-9a-f  1 4    1 3    0-9a-f  1 4   1 4  Z     A  0-9a-f  1 4    1 4    0-9a-f  1 4   1 3  Z     A  0-9a-f  1 4    1 5    0-9a-f  1 4   1 2  Z     A  0-9a-f  1 4    1 6    0-9a-f  1 4   1 1  Z     A   0-9a-f  1 4    1 7      Z     A    0-9a-f  1 4   1 7  Z     A    0-9a-f  1 4    6   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3   Z     A   0-9a-f  1 4    5  0-9a-f  1 4   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3   Z     A  0-9a-f  1 4    5   0-9a-f  1 4   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A  0-9a-f  1 4    1 1    0-9a-f  1 4   1 4   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A  0-9a-f  1 4    1 2    0-9a-f  1 4   1 3   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A  0-9a-f  1 4    1 3    0-9a-f  1 4   1 2   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A  0-9a-f  1 4    1 4    0-9a-f  1 4   1 1   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A   0-9a-f  1 4    1 5      25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z     A    0-9a-f  1 4   1 5   25 0-5  2 0-4  d  0-1   d  d     25 0-5  2 0-4  d  0-1   d  d   3  Z

User · Answer

I generated the following using python and works with the re module  The look-ahead assertions ensure that the correct number of dots or colons appear in the address   It does not support IPv4 in IPv6 notation   pattern         d 1 3    d 1 3    d 1 3    d 1 3         25 0-5   12  0-4  0-9  1 5-9  0-9   1-9   0-9       4           0-9a-f  0 4    2 7  0-9a-f  0 4                                          w   w   w   w   w   w   w   w                 0-9a-f  4   1-9a-f  0-9a-f  0 3    0 8          0-9a-f  1 4          0 6      result   re match pattern  ip  if result  result group 0

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InetAddressUtils has all the patterns defined  I ended-up using their pattern directly  and am pasting it here for reference   private static final String IPV4 BASIC PATTERN STRING               0-9   1-9  0-9  1 0-9  2  2 0-4  0-9  25 0-5       3        initial 3 fields  0-255 followed by               0-9   1-9  0-9  1 0-9  2  2 0-4  0-9  25 0-5        final field  0-255  private static final Pattern IPV4 PATTERN       Pattern compile       IPV4 BASIC PATTERN STRING          private static final Pattern IPV4 MAPPED IPV6 PATTERN      TODO does not allow for redundant leading zeros         Pattern compile      fF  4      IPV4 BASIC PATTERN STRING          private static final Pattern IPV6 STD PATTERN       Pattern compile                 0-9a-fA-F  1 4    0-9a-fA-F  1 4   7       private static final Pattern IPV6 HEX COMPRESSED PATTERN       Pattern compile                   0-9A-Fa-f  1 4    0-9A-Fa-f  1 4   0 5           0-6 hex fields                                      0-9A-Fa-f  1 4    0-9A-Fa-f  1 4   0 5            0-6 hex fields

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If you use Perl try Net  IPv6Addr  use Net  IPv6Addr   if  defined Net  IPv6Addr  is ipv6  ip address       print  Looks like an ipv6 address n       NetAddr  IP  use NetAddr  IP   my  obj   NetAddr  IP- gt new6  ip address     Validate  IP  use Validate  IP qw is ipv6    if  is ipv6  ip address       print  Looks like an ipv6 address n

User · Answer

Try this small one-liner  It should only match valid uncompressed compressed IPv6 addresses  no IPv4 hybrids                                a-f0-9      a-f0-9  1 4             7           a-f0-9  1 4        a-f0-9  1 4          a-f0-9  1 4       1 2   1 6   a-f0-9  1 4

User · Answer

I m not an Ipv6 expert but I think you can get a pretty good result more easily with this one      0-9A-Fa-f  0 4    2 7   0-9A-Fa-f  1 4     25 0-5  2 0-4  0-9   01   0-9  0-9           4      to answer  is a valid ipv6  it look like ok to me  To break it down in parts    forget it  I ve omitted the unspecified one      since  there is no use to have  unpecified adress  in my database    the beginning     0-9A-Fa-f  0 4    2 7   lt -- match the compressible part  we can translate this as  between 2 and 7 colon who may have heaxadecimal number between them   followed by   0-9A-Fa-f  1 4    lt -- an hexadecimal number  leading 0 omitted  OR   25 0-5  2 0-4  0-9   01   0-9  0-9           4   lt -- an Ipv4 adress

User · Answer

This catches the loopback   1  as well and ipv6 addresses   changed    to   and put   inside the first square bracket     a-f0-9        a-f0-9     tested on with ifconfig -a output http   regexr com   Unix or Mac OSx terminal o option returns only the matching output ipv6  including   1  ifconfig -a   egrep -o    a-f0-9        a-f0-9      Get All IP addresses  IPv4 OR IPv6  and print match on unix OSx term  ifconfig -a   egrep -o    0-9  1 3    0-9  1 3    0-9  1 3    0-9  1 3        a-f0-9        a-f0-9

User · Answer

In Scala use the well known Apache Commons validators   http   mvnrepository com artifact commons-validator commons-validator 1 4 1   libraryDependencies     commons-validator     commons-validator     1 4 1    import org apache commons validator routines           Validates if the passed ip is a valid IPv4 or IPv6 address         param ip The IP address to validate      return True if the passed IP address is valid  false otherwise         def ip ip  String    InetAddressValidator getInstance   isValid ip    Following the test s of the method ip ip  String     The  ip  validator  should      return false if the IPv4 is invalid  in       ip  123   must beFalse     ip  255 255 255 256   must beFalse     ip  127 1   must beFalse     ip  30 168 1 255 1   must beFalse     ip  -1 2 3 4   must beFalse         return true if the IPv4 is valid  in       ip  255 255 255 255   must beTrue     ip  127 0 0 1   must beTrue     ip  0 0 0 0   must beTrue          IPv6      see  http   www ronnutter com ipv6-cheatsheet-on-identifying-valid-ipv6-addresses     return false if the IPv6 is invalid  in       ip  1200  AB00 1234  2552 7777 1313   must beFalse         return true if the IPv6 is valid  in       ip  1200 0000 AB00 1234 0000 2552 7777 1313   must beTrue     ip  21DA D3 0 2F3B 2AA FF FE28 9C5A   must beTrue

User · Answer

This will work for IPv4 and IPv6       0-9a-f  0 4    1 7  0-9a-f  1 4    0-9  1 3     3  0-9  1 3

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This regular expression will match valid IPv6 and IPv4 addresses in accordance with GNU C   implementation of regex with REGULAR EXTENDED mode used      s     0-9A-Fa-f  1 4    7   0-9A-Fa-f  1 4         0-9A-Fa-f  1 4    6    0-9A-Fa-f  1 4    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3          0-9A-Fa-f  1 4    5      0-9A-Fa-f  1 4   1 2      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3          0-9A-Fa-f  1 4    4      0-9A-Fa-f  1 4   1 3       0-9A-Fa-f  1 4      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3           0-9A-Fa-f  1 4    3      0-9A-Fa-f  1 4   1 4       0-9A-Fa-f  1 4   0 2    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3           0-9A-Fa-f  1 4    2      0-9A-Fa-f  1 4   1 5       0-9A-Fa-f  1 4   0 3    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3           0-9A-Fa-f  1 4    1      0-9A-Fa-f  1 4   1 6       0-9A-Fa-f  1 4   0 4    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3               0-9A-Fa-f  1 4   1 7       0-9A-Fa-f  1 4   0 5    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9    3               s

User · Answer

Here s what I came up with  using a bit of lookahead and named groups   This is of course just IPv6  but it shouldn t interfere with additional patterns if you want to add IPv4        0-9a-f     0-9a-f       P lt wild gt         0-9a-f               0-9a-f  1 4   1 2   0 6    wild  0-9a-f  0 4   0-9a-f  1 4   0-9a-f  1 4

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Looking at the patterns included in the other answers there are a number of good patterns that can be improved by referencing groups and utilizing lookaheads   Here is an example of a pattern that is self referencing that I would utilize in PHP if I had to       lt hgroup gt    lt hex gt    xdigit    0 4     grab a sequence of up to 4 hex digits                                        and name this pattern for usage later         lt        1 2                     match 1 or 2     characters                                        as long as we can t match 3     amp hgroup  1 6    match our hex group 1 to 6 more times               match an ipv4 address or        lt dgroup gt 2 0-5     2 0-4  1 0 1  0-9   0 1  0-9      3    amp dgroup        match our hex group one last time         amp hex      Note  PHP has a built in filter for this which would be a better solution than this  pattern   Regex101 Analysis

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The following will validate IPv4  IPv6  full and compressed   and IPv6v4  full and compressed  addresses         gt    gt   a-f0-9  1 4     gt    1   7           a-f0-9    gt       8      1    gt    1   0 6       2       gt    gt   1    gt    1   5            a-f0-9    6     3       gt    1    gt    1   0 4        25 0-5  2 0-4  0-9  1 0-9  2   1-9   0-9     gt     4   3     iD

User · Answer

Following regex is for IPv6 only  Group 1 matches with the IP      0-9a-fA-F  0 4    1 7  0-9a-fA-F  0 4

User · Answer

It sounds like you may be using Python   If so  you can use something like this   import socket  def check ipv6 n       try          socket inet pton socket AF INET6  n          return True     except socket error          return False  print check ipv6    1     True print check ipv6  foo     False print check ipv6 5        TypeError exception print check ipv6 None     TypeError exception   I don t think you have to have IPv6 compiled in to Python to get inet pton  which can also parse IPv4 addresses if you pass in socket AF INET as the first parameter   Note  this may not work on non-Unix systems

User · Answer

You can use the ipextract shell tools I made for this purpose  They are based on regexp and grep   Usage     ifconfig   ipextract6 fe80  1 lo0   1 fe80  7ed1 c3ff feec dee1 en0

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As stated above  another way to get an IPv6 textual representation validating parser is to use programming  Here is one that is fully compliant with RFC-4291 and RFC-5952  I ve written this code in ANSI C  works with GCC  passed tests on Linux - works with clang  passed tests on FreeBSD   Thus  it does only rely on the ANSI C standard library  so it can be compiled everywhere  I ve used it for IPv6 parsing inside a kernel module with FreeBSD       IPv6 textual representation validating parser fully compliant with RFC-4291 and RFC-5952    BSD-licensed   Copyright 2015-2017 Alexandre Fenyo   include  lt string h gt   include  lt netinet in h gt   include  lt stdlib h gt   include  lt stdio h gt   include  lt ctype h gt   typedef enum   false  true   bool   static const char hexdigits      0123456789abcdef   static int digit2int const char digit      return strchr hexdigits  digit  - hexdigits        This IPv6 address parser handles any valid textual representation according to RFC-4291 and RFC-5952     Other representations will return -1        note that str input parameter has been modified when the function call returns       parse ipv6 char  str  struct in6 addr  retaddr     parse textual representation of IPv6 addresses    str      input arg    retaddr  output arg int parse ipv6 char  str  struct in6 addr  retaddr      bool compressed field found   false    unsigned char   retaddr    unsigned char    retaddr    char   str   str    char  delim     bzero  void    retaddr  sizeof struct in6 addr      if   strlen str     strchr str          NULL     str 0          amp  amp  str 1                    strlen str   gt   2  amp  amp  str strlen str  - 1          amp  amp  str strlen str  - 2           return -1        convert transitional to standard textual representation   if  strchr str              int ipv4bytes 4       char  curp   strrchr str            if  curp    NULL  return -1      char   curp     curp      int i      for  i   0  i  lt  4  i            char  nextsep   strchr  curp              if   curp 0      0      i  lt  3  amp  amp  nextsep    NULL      i    3  amp  amp  nextsep    NULL   return -1        if  nextsep    NULL   nextsep   0        int j        for  j   0  j  lt  strlen  curp   j    if   curp j   lt   0      curp j   gt   9   return -1        if  strlen  curp   gt  3  return -1        const long val   strtol  curp  NULL  10         if  val  lt  0    val  gt  255  return -1        ipv4bytes i    val         curp   nextsep   1            sprintf curp    x 02x  x 02x   ipv4bytes 0   ipv4bytes 1   ipv4bytes 2   ipv4bytes 3              parse standard textual representation   do       if   delim   strchr  str            str     delim    NULL  amp  amp   strlen  str            if  delim    str   str          else if  delim    NULL  return 0        else           if  compressed field found    true  return -1          if  delim    str   strlen str  - 1  amp  amp   retaddr     unsigned char     retaddr   1   return 0          compressed field found   true           str            int cnt   0          char    str          for    str    str     str    if      str            cnt            unsigned char    retaddr   - 2     cnt    unsigned char     retaddr   1           if    retaddr  lt    retaddr  return -1           retaddr     retaddr                else         char hexnum 4     0000         if  delim    NULL  delim   str   strlen str         if  delim -  str  gt  4  return -1        int i        for  i   0  i  lt  delim -  str  i            if   isxdigit  str i    return -1          else hexnum 4 -  delim -  str    i    tolower  str i           str   delim   1           retaddr       digit2int hexnum 0    lt  lt  4    digit2int hexnum 1             retaddr       digit2int hexnum 2    lt  lt  4    digit2int hexnum 3              while   str  lt  str   strlen str      return 0

User · Answer

For PHP 5 2  users filter var works great   I know this doesn t answer the original question  specifically a regex solution   but I post this in the hope it may help someone else in the future    is ip4address    filter var  ip  FILTER VALIDATE IP  FILTER FLAG IPV4      FALSE    is ip6address    filter var  ip  FILTER VALIDATE IP  FILTER FLAG IPV6      FALSE

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I was unable to get  Factor Mystic s answer to work with POSIX regular expressions  so I wrote one that works with POSIX regular expressions and PERL regular expressions   It should match    IPv6 addresses zero compressed IPv6 addresses  section 2 2 of rfc5952  link-local IPv6 addresses with zone index  section 11 of rfc4007  IPv4-Embedded IPv6 Address  section 2 of rfc6052  IPv4-mapped IPv6 addresses  section 2 1 of rfc2765  IPv4-translated addresses   section 2 1 of rfc2765    IPv6 Regular Expression      0-9a-fA-F  1 4    7 7  0-9a-fA-F  1 4    0-9a-fA-F  1 4    1 7     0-9a-fA-F  1 4    1 6   0-9a-fA-F  1 4    0-9a-fA-F  1 4    1 5    0-9a-fA-F  1 4   1 2    0-9a-fA-F  1 4    1 4    0-9a-fA-F  1 4   1 3    0-9a-fA-F  1 4    1 3    0-9a-fA-F  1 4   1 4    0-9a-fA-F  1 4    1 2    0-9a-fA-F  1 4   1 5   0-9a-fA-F  1 4      0-9a-fA-F  1 4   1 6        0-9a-fA-F  1 4   1 7     fe80    0-9a-fA-F  0 4   0 4   0-9a-zA-Z  1      ffff  0 1 4   0 1    0 1   25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      3 3  25 0-5   2 0-4  1 0 1  0-9   0 1  0-9     0-9a-fA-F  1 4    1 4    25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      3 3  25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      For ease of reading  the following is the above regular expression split at major OR points into separate lines     IPv6 RegEx     0-9a-fA-F  1 4    7 7  0-9a-fA-F  1 4              1 2 3 4 5 6 7 8   0-9a-fA-F  1 4    1 7                              1                                1 2 3 4 5 6 7     0-9a-fA-F  1 4    1 6   0-9a-fA-F  1 4             1  8             1 2 3 4 5 6  8  1 2 3 4 5 6  8   0-9a-fA-F  1 4    1 5    0-9a-fA-F  1 4   1 2      1  7 8           1 2 3 4 5  7 8  1 2 3 4 5  8   0-9a-fA-F  1 4    1 4    0-9a-fA-F  1 4   1 3      1  6 7 8         1 2 3 4  6 7 8  1 2 3 4  8   0-9a-fA-F  1 4    1 3    0-9a-fA-F  1 4   1 4      1  5 6 7 8       1 2 3  5 6 7 8  1 2 3  8   0-9a-fA-F  1 4    1 2    0-9a-fA-F  1 4   1 5      1  4 5 6 7 8     1 2  4 5 6 7 8  1 2  8  0-9a-fA-F  1 4      0-9a-fA-F  1 4   1 6            1  3 4 5 6 7 8   1  3 4 5 6 7 8  1  8        0-9a-fA-F  1 4   1 7                              2 3 4 5 6 7 8    2 3 4 5 6 7 8   8               fe80    0-9a-fA-F  0 4   0 4   0-9a-zA-Z  1          fe80  7 8 eth0   fe80  7 8 1      link-local IPv6 addresses with zone index     ffff  0 1 4   0 1    0 1    25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      3 3   25 0-5   2 0-4  1 0 1  0-9   0 1  0-9                 255 255 255 255     ffff 255 255 255 255    ffff 0 255 255 255 255   IPv4-mapped IPv6 addresses and IPv4-translated addresses    0-9a-fA-F  1 4    1 4     25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      3 3   25 0-5   2 0-4  1 0 1  0-9   0 1  0-9               2001 db8 3 4  192 0 2 33  64 ff9b  192 0 2 33  IPv4-Embedded IPv6 Address       IPv4 RegEx   25 0-5   2 0-4  1 0 1  0-9   0 1  0-9      3 3  25 0-5   2 0-4  1 0 1  0-9   0 1  0-9     To make the above easier to understand  the following  pseudo  code replicates the above   IPV4SEG     25 0-5   2 0-4  1 0 1  0-9   0 1  0-9   IPV4ADDR    IPV4SEG    3 3 IPV4SEG IPV6SEG     0-9a-fA-F  1 4  IPV6ADDR                 IPV6SEG   7 7 IPV6SEG                   1 2 3 4 5 6 7 8             IPV6SEG   1 7                           1                                   1 2 3 4 5 6 7               IPV6SEG   1 6  IPV6SEG                  1  8               1 2 3 4 5 6  8   1 2 3 4 5 6  8             IPV6SEG   1 5   IPV6SEG  1 2            1  7 8             1 2 3 4 5  7 8   1 2 3 4 5  8             IPV6SEG   1 4   IPV6SEG  1 3            1  6 7 8           1 2 3 4  6 7 8   1 2 3 4  8             IPV6SEG   1 3   IPV6SEG  1 4            1  5 6 7 8         1 2 3  5 6 7 8   1 2 3  8             IPV6SEG   1 2   IPV6SEG  1 5            1  4 5 6 7 8       1 2  4 5 6 7 8   1 2  8            IPV6SEG    IPV6SEG  1 6                  1  3 4 5 6 7 8     1  3 4 5 6 7 8   1  8                IPV6SEG  1 7                           2 3 4 5 6 7 8      2 3 4 5 6 7 8    8                            fe80   IPV6SEG  0 4   0-9a-zA-Z  1       fe80  7 8 eth0     fe80  7 8 1   link-local IPv6 addresses with zone index                ffff  0 1 4   0 1    0 1 IPV4ADDR       255 255 255 255    ffff 255 255 255 255    ffff 0 255 255 255 255  IPv4-mapped IPv6 addresses and IPv4-translated addresses              IPV6SEG   1 4  IPV4ADDR                 2001 db8 3 4  192 0 2 33  64 ff9b  192 0 2 33  IPv4-Embedded IPv6 Address                 I posted a script on GitHub which tests the regular expression  https   gist github com syzdek 6086792

User · Answer

The regex allows the use of leading zeros in the IPv4 parts   Some Unix and Mac distros convert those segments into octals   I suggest using 25 0-5  2 0-4  d 1 d d  1-9   d as an IPv4 segment

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Depending on your needs  an approximation like    0-9a-f      may be enough  as with simple log file grepping  for example

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If you want only normal IP-s  no slashes   here        0-9a-f  1 4          0 7    0-9a-f      I use it for my syntax highlighter in hosts file editor application  Works as charm

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A simple regex that will match  but I wouldn t recommend for validation of any sort is this     A-Fa-f0-9  1 4      1 7  A-Fa-f0-9  1 4    Note this matches compression anywhere in the address  though it won t match the loopback address   1   I find this a reasonable compromise in order to keep the regex simple   I successfully use this in iTerm2 smart selection rules to quad-click IPv6 addresses

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Beware  In Java  the use of InetAddress and related classes  Inet4Address  Inet6Address  URL  may involve network trafic  E g  DNS resolving  URL equals  InetAddress from string    This call may take long and is blocking   For IPv6 I have something like this  This of course does not handle the very subtle details of IPv6 like that zone indices are allowed only on some classes of IPv6 addresses  And this regex is not written for group capturing  it is only a  matches  kind of regexp   S - IPv6 segment    0-9a-f  1 4   I - IPv4         25 0-5  2 0-4  0-9   01   0-9  1 2      3    25 0-5  2 0-4  0-9   01   0-9  1 2    Schematic  first part matches IPv6 addresses with IPv4 suffix  second part matches IPv6 addresses  last patrt the zone index           S   0 5   S   S   0 4    S   2   S   0 3    S   3   S   0 2    S   4   S      S   5     S   6    I           S  1 7    S      S  1 6     S   2      S  1 5     S   3      S  1 4     S   4      S  1 3     S   5      S  1 2     S   6      S     S   7     S   7 S         0-9a-z       And here the might regex  case insensitive  surround with what ever needed like beginning end of line  etc                   0-9a-f  1 4    0 5    0-9a-f  1 4       0-9a-f  1 4    0 4       0-9a-f  1 4    2      0-9a-f  1 4    0 3       0-9a-f  1 4    3      0-9a-f  1 4    0 2       0-9a-f  1 4    4      0-9a-f  1 4          0-9a-f  1 4    5        0-9a-f  1 4    6          25 0-5  2 0-4  0-9   01   0-9  1 2      3     25 0-5  2 0-4  0-9   01   0-9  1 2                0-9a-f  1 4   1 7     0-9a-f  1 4            0-9a-f  1 4   1 6        0-9a-f  1 4    2           0-9a-f  1 4   1 5        0-9a-f  1 4    3           0-9a-f  1 4   1 4        0-9a-f  1 4    4           0-9a-f  1 4   1 3        0-9a-f  1 4    5           0-9a-f  1 4   1 2        0-9a-f  1 4    6           0-9a-f  1 4         0-9a-f  1 4    7        0-9a-f  1 4    7  0-9a-f  1 4          0-9a-z

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Regexes for ipv6 can get really tricky when you consider addresses with embedded ipv4 and addresses that are compressed  as you can see from some of these answers   The open-source IPAddress Java library will validate all standard representations of IPv6 and IPv4 and also supports prefix-length  and validation of such    Disclaimer  I am the project manager of that library   Code example           try               IPAddressString str   new IPAddressString    1                IPAddress addr   str toAddress                if addr isIPv6      addr isIPv6Convertible                      IPv6Address ipv6Addr   addr toIPv6                                use address           catch AddressStringException e                  e getMessage has validation error

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Using Ruby  Try this                       3   3   3    dA-F  1 4      dA-F  1 4   3   b   2  5     dA-F  1 4   3   b     2  2     2 0-4  1 d  1-9    d 25 0-5      b  4   z i

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I d have to strongly second the answer from Frank Krueger   Whilst you say you need a regular expression to match an IPv6 address  I m assuming what you really need is to be able to check if a given string is a valid IPv6 address  There is a subtle but important distinction here   There is more than one way to check if a given string is a valid IPv6 address and regular expression matching is only one solution   Use an existing library if you can  The library will have fewer bugs and its use will result in less code for you to maintain   The regular expression suggested by Factor Mystic is long and complex  It most likely works  but you should also consider how you d cope if it unexpectedly fails  The point I m trying to make here is that if you can t form a required regular expression yourself you won t be able to easily debug it   If you have no suitable library it may be better to write your own IPv6 validation routine that doesn t depend on regular expressions  If you write it you understand it and if you understand it you can add comments to explain it so that others can also understand and subsequently maintain it   Act with caution when using a regular expression whose functionality you can t explain to someone else

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In Java  you can use the library class sun net util IPAddressUtil   IPAddressUtil isIPv6LiteralAddress iPaddress

[regex] Regular expression that matches valid IPv6 addresses

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