June 24, 2013

Debian squeeze => wheezy, IPv?

I pretty much run Debian stable at home for all my servers. KVM, NFS, FW/GW, Myth, etc. A few months ago (probably almost a year) I set up dual stack IPv6 and IPv4 at home and tunnelled over IPv4 to Hurricane Electric. Most things were working fine, I even had one host that was only IPv6 to try certain things out.

Recently I finished upgrading everything from Squeeze to Wheezy. This went well (as it usually does), except for a few odd things that were happening around the network…

Some hosts were missing munin stats, others weren’t automounting NFS. I was seeing permission denied errors in the logs for NFS, and I couldn’t work out why, they were all just working fine only 2 hours ago.

Eventually I worked out that the problem was related to IPv6 DNS lookups. The ordering of lookups of host names had changed to favour AAAA over A records. This meant that things that only had an allow for IPv4 addresses were no longer permitted to see services as they were using the IPv6 interface and not the IPv4 interface.

Adding a few extra lines to exports and munin configuration to add the allowed IPv6 subnets and/or hosts, and everything was working again.

© Greg Cockburn

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