[mythtv-users] link-local and mythtv

[Stuart Auchterlonie]

On 05/08/15 20:10, Stephen Worthington wrote:
> On Wed, 5 Aug 2015 09:46:25 -0400, you wrote:
> 
>> On Wed, Aug 5, 2015 at 5:07 AM, John Pilkington <J.Pilk at tesco.net> wrote:
>>> Thanks for that, Stephen.  But if I set 127.0.0.1, the TV will display the
>>> UPnP server menu with titles of the recordings, but doesn't show thumbnails
>>> or play recordings.  If I set 169.254.10.241, everything works while the TV
>>> is 'on' but I get complaints or worse when it's in standby.  The only
>>> connection between laptop and TV is an ethernet crossover cable.
>>>
>>> ifconfig, and mythtv-setup, also show a wlan0, the wifi hotspot, but I don't
>>> think I should let myth use that.
>>>
>>> No big deal, but I thought I would ask.
>>
>> You should be able to set up mythtv to listen on 127.0.0.1, then use
>> iptables to NAT the 169.254.10.241 traffic to 127.0.0.1.  You should
>> be able to configure your ethernet device to set this up automatically
>> when the interface is configured.  Then it should just work whenever
>> that interface is available.
>>
>> Eric
> 
> I am not sure that using NAT (not masquerading) rules would work, as
> the lo interface normally runs with a big MTU (mine is showing 65536).
> Any packets larger than the MTU of the ethernet interface (likely
> 1500) would get dropped, which would probably cause some quite hard to
> track down type problems.
> 
> But I have just looked at the ifconfig output for my MythTV box
> (Mythbuntu 14.04), which has static addresses on two ethernet ports
> that are currently unused, with no cable plugged in, and the static
> addresses are visible.  I could have sworn that even static addresses
> disappeared when an interface was down, but maybe something has
> changed since I last looked.  Anyway, if you can assign a static IP
> address to the TV through its settings somewhere, then you can use a
> static IP address on your ethernet interface and have MythTV listen on
> that.  If your TV does not have a setting for a static IP address,
> then you may have to run a DHCP server on the laptop and have it
> assign the TV an appropriate address when it is on.  If the TV only
> does link-local addresses, then you are probably out of luck, but that
> is unlikely.

The linux tcp stack has the property that it'll (by default) accept
packets for an ip address assigned to *any* of it's interfaces.

So you can, in theory, assign the permanent address of the backend to
an alias of the loopback address, and then have the backend bind to
that. Then even if your external interface has a different ip address
things will still be able to talk to the "permanent" address.

Gotta love networking ;-)

By the sounds of it, it's worth running a dhcp client (probably dnsmasq)
on the linux box, so the tv gets a proper ip address.

Cheers
Stuart