[erlang-bugs] Connection to IPv6 link local address fails due to missing scope identifier

Raimo Niskanen <>
Wed Oct 13 09:04:30 CEST 2010

On Tue, Oct 12, 2010 at 10:41:19PM +0200, Michael Stapelberg wrote:
> Hi,
> the following proof of concept fails:
>   -module(poc).
>   -export([start/0]).
>   start() ->
>       {ok, Sock} = gen_tcp:connect("fe80::21f:16ff:fe1a:f5b8%eth0", 80, [inet6]),
>       io:fwrite("connect said: ~p~n", [ok]).
> If you strace it using strace -fF -etrace=network erl -s poc, you???ll see the
> following:
>   bind(7, {sa_family=AF_INET6, sin6_port=htons(0), inet_pton(AF_INET6, "::",
>     &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
>   getsockname(7, {sa_family=AF_INET6, sin6_port=htons(36404),
>     inet_pton(AF_INET6, "::", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
>     [28]) = 0
>   connect(7, {sa_family=AF_INET6, sin6_port=htons(80), inet_pton(AF_INET6,
>     "fe80::21f:16ff:fe1a:f5b8", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
>     28) = -1 EINVAL (Invalid argument)
> The problem is the missing scope identifier (sin6_scope_id), which should be 2
> for eth0 in my case (see /proc/net/igmp6 for easily getting the scope id for
> your interfaces).

Scope identifiers are currently not implemented. They are also not quite
portable, especially how you find them out and translate them into the 32-bit
scope ID needed in sockaddr_in6{}.

We need to support as many as possible of Linux, Solaris 8/9/10/..,
Windows XP/Vista/7, MacOS X, FreeBSD, OpenBSD and NetBSD, plus some other
Unix-like OS:es. Most do not have Linux /proc.

We also need to solve our own backwards compatibility problem of representing
IPv6 addresses as 8-tuples of 0..65535 and having _lots_ of code testing
for a term being an IPv6-address simply by checking if it is an 8-tuple.
Somehow we need to squeeze in a scope ID in our representation of IPv6 addresses.

There are also issues to consider regarding how and to what extent the
name resolving functions can/should return scope IDs with accompaning
OS compatibility quirks.

But it _is_ on our todo list...

> To reproduce this test:
>   ??? to test the client side, use nc -6 fe80::21f:16ff:fe1a:f5b8%eth0 80
>   ??? to test the server side, use for example OpenSSH (listens on all
>     interfaces/addresses per default) or Apache.
>   ??? to get your link local address, use ifconfig(1) or "ip a|grep fe80"
> Best regards,
> Michael
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/ Raimo Niskanen, Erlang/OTP, Ericsson AB

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