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.

Answer 1

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