On Mon, 18 Jan 2010 15:27:30 -0500 Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > On Mon, 2010-01-18 at 15:20 -0500, Jeff Layton wrote: > > On Mon, 18 Jan 2010 14:47:46 -0500 > > Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > > > With the commit of the statd patches over the weekend, we're now > > > positioned to be able to ship IPv6-enabled nfs-utils in distros. There > > > is a potential snag though... > > > > > > Consider this situation: > > > > > > Admin has a Linux server set up. Server has both IPv4 and IPv6 addrs. > > > Both addresses are in DNS. > > > > > > Without an IPv6-enabled nfs-utils, he mounts via IPv4 and all works > > > fine. Now with an IPv6 enabled nfs-utils, mount.nfs prefers the IPv6 > > > addr and the mount fails (or hangs for a long time and then fails, if > > > it's using NFSv4)... > > > > > > While I don't really like it, I think we may need to consider making > > > mount.nfs prefer IPv4 addrs when it can resolve a hostname to both v4 > > > and v6. Otherwise, we run the risk of breaking an awful lot of working > > > setups... > > > > > > > Apologies for the self reply and non-descript initial title. > > > > For discussion purposes, here's a patch to do what I'm thinking of. It > > seems to work and do the right thing. You can still force a mount over > > ipv6 by using the right proto/mountproto options. > > How do other applications deal with this problem? Surely, not every > application out there is having to filter away IPv6 addresses? > > I thought that glibc was by default set up to prefer IPv4 addresses, and > allows you to further configure that using /etc/gai.conf. Why is this > failing? > > Cheers > Trond > At least on my test box (which has no gai.conf set up), IPv6 addrs seem to come first in the list returned by getaddrinfo, and I think that's how it'll turn out for most people. There's a bit of discussion on this in Ulrich's writeup here: http://people.redhat.com/drepper/linux-rfc3484.html (see "The BIG Problem") Though that's sort of orthogonal to the issue. I'm not worried about unreachable IPv6 addresses. The problem is that there is a large installed base of servers that do not support serving NFS over IPv6. Many of those may have IPv6 connectivity set up for other reasons. We don't want clients to start failing to mount them when they get an ipv6-enabled nfs-utils. -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
