Force getaddrinfo to use IPv4

Question

The man page says:

The getaddrinfo(3) function is not limited to creating IPv4 socket address structures; IPv6 socket address structures can be created if IPv6 support is available. These socket address structures can be used directly by bind(2) or connect(2), to prepare a client or a server socket.

What should I do to force getaddrinfo to not create IPv6 socket address structures?

Is this for a program you're writing? Or are you trying to get an application that calls `getaddrinfo` with `AF_UNSPEC` not to use IPv6? — Gilles 'SO- stop being evil', Aug 16 '12 at 22:58

score 1 · Answer 1 · edited Apr 13 '17 at 12:36

1

Interestingly enough, the first question I ever asked on this site turned out to have an answer you might find useful.

To summarize, the file /etc/gai.conf is used by the getaddrinfo() system call to determine how to respond. For your particular case, adding

precedence ::ffff:0:0/96  100

to the end of the config file should be sufficient.

edited Apr 13 '17 at 12:36

Community

1

answered Aug 16 '12 at 09:39

Shadur

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Thanks for your answer, but in my CentOS 5.5 final, there is no /etc/gai.conf, do I need to create one? – Derui Si Aug 16 '12 at 09:55
Possibly. According to `dpkg` the file is part of the `libc-bin` package, which is pretty deep down the essential packages list in Debian... – Shadur Aug 16 '12 at 10:00

score 1 · Answer 2 · answered Mar 05 '13 at 16:40

According to the manpage for getaddrinfo(), you can pass the address family in the hints parameter, so something like

struct addrinfo hints, *result;
int s;

memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET;        /* or AF_INET6 for ipv6 addresses */
s = getaddrinfo(NULL, "ftp", &hints, &result);
...

I haven't tried this, but the approach seems to be right.

Force getaddrinfo to use IPv4

2 Answers2