Mark Constable writes:
On 21/01/11, Sam Varshavchik wrote:> My question is how to configure courier-mta to work with the > above default net.ipv6.bindv6only = 1 setting for when Debian > testing becomes stable and I go to upgrade other servers?The problem is that IPv6-mapped IPv4 addresses are a part of the official IPv6 spec. If you have an IPV6 socket, you are expected to be able to use it to contact IPv4 addresses. RFC 4038, 4.2. Courier's code relies on being able to use IPv6 sockets to connect to either IPv4 or IPv6 addresses. There is no way to configure that an IPv4 socket be used for IPv4 addresses, and IPv6 sockets for IPv6 addresses. Doing something like this requires some code rewriting.Perhaps this could be a heads up that when Debian 6 (squeeze) is released in the next month or so that this will become an issue for Debian stable + courier users. ~ cat /etc/sysctl.d/bindv6only.conf # This sysctl sets the default value of the IPV6_V6ONLY socket option. # # When disabled, IPv6 sockets will also be able to send and receive IPv4 # traffic with addresses in the form ::ffff:192.0.2.1 and daemons listening # on IPv6 sockets will also accept IPv4 connections. # # When IPV6_V6ONLY is enabled, daemons interested in both IPv4 and IPv6 # connections must open two listening sockets. # This is the default behaviour of almost all modern operating systems. net.ipv6.bindv6only = 1 For future googlers, I had to change the above 1 to 0 for courier to work.
One way of mitigating this situation for your specific case, of DNS resolution on localhost, is to append
nameserver ::1In addition to "nameserver 127.0.0.1" in /etc/resolv.conf. If Courier fails to reach 127.0.0.1, it should then try ::1, and succeed.
This won't address, though, outgoing connections. Courier will still try to use IPv6 sockets to connect to IPv4 addresses for sending mail. The only thing that can be done there is to smarthost all outgoing mail, to another IPv6 relay.
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