The man page for gethostbyname2(3) says:

     The gethostbyname2() function is an evolution of gethostbyname() which is
     intended to allow lookups in address families other than AF_INET, for ex-
     ample AF_INET6. Currently the af argument must be specified as AF_INET
     else the function will return NULL after having set h_errno to
     NETDB_INTERNAL

This appears to be inaccurate: gethostbyname2("myhost6", AF_INET6)
returns valid results. From looking at the source, it would appear
that the manual is correct only when the resolver looks the name up in
NIS. However, I don't have an NIS server and have not tested this.

Fix: Suggestion: apply the following patch to
/usr/src/lib/libc/net/gethostbyname.3 :
How-To-Repeat: 
* /etc/host.conf should contain:

	hosts

  (and optionally "bind", either before or after "hosts")

* /etc/hosts should contain:

	fec0::a:b:c:d   myhost6 myhost6.my.domain

* Compile ('cc -o foo foo.c') and run the following program:
	#include <stdio.h>
	#include <netdb.h>
	#include <sys/socket.h>

	main()
	{
		struct hostent *he;
		char buf[256];

		he = gethostbyname2("myhost6", AF_INET6);
		if (he == NULL)
		{
			perror("gethostbyname2");
			exit(1);
		}
		if (he->h_addrtype != AF_INET6)
			fprintf(stderr, "h_addrtype != AF_INET6 (%d)\n",
				he->h_addrtype);

		printf("address is [%s]\n",
		       inet_ntop(AF_INET6, he->h_addr_list[0], buf, 256));
	}

  This program prints
	address is [fec0::a:b:c:d]