Enable IPv6

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Important.png Note: 0.25 allows users the option of connecting to mythbackend via IPv6. To be clear, enabling IPv6 isn't required for successful operation of MythTV.

This Wiki shows how to activate IPv6. It is part of significant changes in the way MythTV binds to sockets which should be transparent to users.

IPv6 Configuration

Interfaces typically have multiple IPv6 addresses. For help picking the right one, see #Which IPv6 address should be used?.

If IPv6 is known to be working, just complete the following. Otherwise, see #Basics.

Stop all frontends and backends.

Using mythtv-setup on the master backend, go to the General page and enter the address of choice.

The configuration of someone who just upgraded to 0.25 will look like this:

Local Backend
    IP address:   192.168.1.123
    IPv6 address: ::1

Master Backend
    IP address: 192.168.1.123

Change it to look like this:

Local Backend
    IP address:   192.168.1.123
    IPv6 address: fd01:a:b:1::123

Master Backend
    IP address: fd01:a:b:1::123

The existing IPv4 address shouldn't be removed, as some services still require it.

The pre 0.25 convention that requires both Local Backend and Master Backend addresses to be the same in order for a backend to be considered a master backend still applies. It has been expanded to allow for the Master Backend address to equal either the Local IPv4 or IPv6 Backend address.

Some (non MythTV) programs require their IPv6 addresses enclosed in brackets ([]) or the addition of a trailing percent sign and Zone Index (e.g. %eth0.) Neither of these should be used with MythTV.

Use mythtv-setup to configure any slave backends with their own IPv6 addresses.

Restart the backend(s).

Which IPv6 address should be used?

The most likely choice is a Unique Local Address (ULA.) Use ULA's if all access to the backend will be within a LAN.

Note that even though ULAs are global addresses, no self respecting router will pass them out on the internet, much like IPv4 Private Network addresses (e.g. 192.168.1.123.)

Use a search engine and look for: 'Unique Local Address generator' to find a site that will create ULAs correctly like this, for example.

For details on constructing ULAs see RFC 4193.

MythTV must have a globally routeble IPv6 address (e.g. 2001:db8::1) configured only if it is necessary to run MythTV from a frontend/slave over the internet.

Site Local (fec0::/10) addresses were deprecated in 2004.

Host (::1) addresses are only useful for a stand alone system.

Since all Link Local addresses have the same prefix (fe80::/10), they require a Zone Index (e.g. %eth0) for routing and shouldn't be used. MythTV will automatically ignore these addresses.

To list currently assigned IPv6 addresses, type: ifconfig | grep inet6

inet6 addr: ::1/128 Scope:Host
inet6 addr: fe80::222:22ff:fe22:2222/64 Scope:Link
inet6 addr: fd01:a:b:1::123/64 Scope:Global
inet6 addr: 2001:db8::123/64 Scope:Global

In the above, the 3rd address is probably the best choice. It is also probably one that must be assigned manually.

If the desired address doesn't exist, use the configuration tool provided with the host's distribution to add it.

Entries in /etc/hosts (DHCP, router etc.) are optional. The following is an example for one host:

192.168.1.123              masterbe.local    masterbe
fd01:a:b:1::123            masterbe.local    masterbe
2001:db8::123              masterbe.local    masterbe

Back to #IPv6 Configuration

Basics

Verify that IPv6 is active on each MythTV host.

If ssh, for example, is known to work, a simple test (run from the master backend) is:

for HOST in <list all frontend and slave backends here>
do  ssh -6 $HOST hostname
done

If the test works for all frontends and slave backends, IPv6 can be added to MythTV.

If the above fails, see the following section.

Back to #IPv6 Configuration

What if there's a problem

  • Make sure IPv6 hasn't been disabled either system wide or for the interface MythTV will use. Type:

sysctl -a 2> /dev/null | grep "ipv6.*disable"

net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.lo.disable_ipv6 = 0
net.ipv6.conf.eth0.disable_ipv6 = 0
  • Some distributions keep these options in files under /etc/sysctl.d.
  • Be sure any firewalls have been adjusted to accept the IPv6 addresses being used.
  • If the MythTV configuration is correct, but no IPv6 traffic is seen during, for example recording playback, Master Backend Override may be enabled in mythtv-setup General section and the Master Backend IP address is still set to an IPv4 address.
  • It may take longer for a system to configure addresses on its ethernet interfaces. This could prevent the backend from binding to those addresses and, for example, prevent remote frontend access. Failures like this will show up as critical errors in the backend logs Use tools supplied by the distribution to guarantee interface configuration is complete before starting the backend.

Back to #IPv6 Configuration

Tools and sample output

Warning.png Warning: The output of some tools and in logfiles may expose IPv6 addresses. Some addresses contain a modified MAC address or globally addressable IPv6 addresses. When posting output to a public form, consider camouflaging them.

Additional IPv6 information is available in the logfiles created by mythbackend and mythfrontend if the --loglevel debug option is used.

mythbackend --verbose general --nodblog --quiet \
    --logpath /var/log/mythtv --loglevel debug

IPv6 addresses in the logs don't follow the convention that allows consecutive 0:0s to be represented by ::. So, the address used in this page: fd01:a:b:1::123 will appear as fd01:a:b:1:0:0:0:123. This is not a problem, only a convention used by the underlying Qt code.

These examples are all from a host with mythbackend running and IPv6 configured. MySQL is running and using IPv4. Obviously, these tools can be run on frontends and slave backends.

To make sure mythbackend and mysqld are listening for connections:

sudo netstat -Wpant | egrep '3306|6543'

When the backend is running, but no slave backends/frontends are connected, expect:

tcp   0  0  0.0.0.0:3306            0.0.0.0:*      LISTEN      1198/mysqld     
tcp   0  0  192.168.1.123:6543      0.0.0.0:*      LISTEN      26961/mythbackend
tcp   0  0  127.0.0.1:6543          0.0.0.0:*      LISTEN      26961/mythbackend
tcp6  0  0  fd01:a:b:1::123:6543    :::*           LISTEN      26961/mythbackend
tcp6  0  0  ::1:6543                :::*           LISTEN      26961/mythbackend

With one frontend connected and playing a recording, expect:

tcp   0  0 0.0.0.0:3306           0.0.0.0:*              LISTEN      1384/mysqld     
tcp   0  0 192.168.1.123:6543     0.0.0.0:*              LISTEN      26961/mythbackend
tcp   0  0 127.0.0.1:6543         0.0.0.0:*              LISTEN      26961/mythbackend
tcp   0  0 192.168.1.123:3306     192.168.1.234:56538    ESTABLISHED 1384/mysqld     
tcp   0  0 192.168.1.123:3306     192.168.1.234:56601    ESTABLISHED 1384/mysqld     
tcp   0  0 192.168.1.123:6543     192.168.1.234:42760    ESTABLISHED 26961/mythbackend
tcp   0  0 192.168.1.123:6543     192.168.1.234:42761    ESTABLISHED 26961/mythbackend
tcp   0  0 192.168.10.204:3306    192.168.1.234:56532    ESTABLISHED 1384/mysqld     
tcp6  0  0 fd01:a:b:1::123:6543   fd01:a:b:1::456:36345  ESTABLISHED 26961/mythbackend
tcp6  0  0 fd01:a:b:1::123:6543   fd01:a:b:1::456:36346  ESTABLISHED 26961/mythbackend
tcp6  0  0 ::1:6543               :::*                   LISTEN      26961/mythbackend

If installed, nmap may help diagnose the reason that a connection fails. For example, a firewall could be blocking access.

nmap -P0 -p 6543 -6 --reason someHostName

The expected response is:

PORT     STATE SERVICE REASON
6543/tcp open   mythtv  syn-ack

Back to #IPv6 Configuration