Definitive guide to understanding how to formulate an IPv6 address

Question

For fun, I\'d like to better understand the building blocks or elements that are within an IPv6 address.

Here are the basics, from my understanding:

• IPv6 a

Answer 1

Obviously this bit is a typo:

it is possible to use double colons syntax to represent one or more blocks with zeroes. 1:2::6:7 is equivalent to 1:2:3:4:5:6:7:8.

1:2::6:7 means 1:2:0:0:0:0:6:7.

I hadn't heard this before:

double colon may [not appear] within an ip4 dot address.

But I made a test program, and it seems to confirm it.

$ ./testipv6 0:0:0:0:0:0:192.168.0.1
0:0:0:0:0:0:192.168.0.1: OK

$ ./testipv6 0:0:0:0:0:0:192.168::1
0:0:0:0:0:0:192.168::1: ERROR

Otherwise I think everything you said is OK.

---

testipv6.c

#include 
#include 
#include 
#include 

int convert(const char *addr)
{
    struct in6_addr dst;

    return inet_pton(AF_INET6, addr, (void *)&dst);
}

int main(int argc, char **argv)
{
    if (argc == 1) {
        fprintf(stderr, "Usage: testipv6 \n");
        exit(2);
    }

    while (argc > 1) {
        argc--, argv++;
        const char *addr = argv[0];

        if (convert(addr)) {
            printf("%s: OK\n", addr);
        } else {
            printf("%s: ERROR\n", addr);
        }
    }
}