Maximum length of the textual representation of an IPv6 address

Question

I want to store the data returned by   SERVER  REMOTE ADDR   in PHP into a DB field  pretty simple task  really  The problem is that I can t find any proper information about the maximum length of the textual representation of an IPv6 address  which is what a webserver provides through   SERVER  REMOTE ADDR      I m not interested in converting the textual representation into the 128 bits the address is usually encoded in  I just want to know how many characters maximum are needed to store any IPv6 address returned by   SERVER  REMOTE ADDR

User · Answer

I think  Deepak answer in this link is more close to correct answer  Max length for client ip address  So correct size is 45 not 39  Sometimes we try to scrounge in fields size but it seems to better if we prepare enough storage size

User · Answer

On Linux  see constant INET6 ADDRSTRLEN  include  lt arpa inet h gt   see man inet ntop   On my system  header  in h      define INET6 ADDRSTRLEN 46   The last character is for terminating NULL  as I belive  so the max length is 45  as other answers

User · Answer

Answered my own question       IPv6 addresses are normally written as eight groups of four hexadecimal digits  where each group is separated by a colon        So that s 39 characters max

User · Answer

Watch out for certain headers such as HTTP X FORWARDED FOR that appear to contain a single IP address   They may actually contain multiple addresses  a chain of proxies I assume    They will appear to be comma delimited - and can be a lot longer than 45 characters total - so check before storing in DB

User · Answer

45 characters   You might expect an address to be  0000 0000 0000 0000 0000 0000 0000 0000      8   4   7   39   8 groups of 4 digits with 7   between them   But if you have an IPv4-mapped IPv6 address  the last two groups can be written in base 10 separated by    eg     ffff 192 168 100 228   Written out fully   0000 0000 0000 0000 0000 ffff 192 168 100 228       6   4   5    1    4   3   3    29   1   15   45   Note  this is an input display convention - it s still a 128 bit address and for storage it would probably be best to standardise on the raw colon separated format  i e   0000 0000 0000 0000 0000 ffff c0a8 64e4  for the address above

User · Answer

As indicated a standard ipv6 address is at most 45 chars  but an ipv6 address can also include an ending   followed by a  scope  or  zone  string  which has no fixed length but is generally a small positive integer or a network interface name  so in reality it can be bigger than 45 characters   Network interface names are typically  eth0    eth1    wlan0   so choosing 50 as the limit is likely good enough

[ip] Maximum length of the textual representation of an IPv6 address?

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