[mythtv] Proposed change to Network Communications

Stephen Worthington stephen_agent at jsw.gen.nz
Fri Mar 10 08:50:27 UTC 2017

On Thu, 9 Mar 2017 23:09:26 -0500, you wrote:

>On 03/09/2017 08:29 PM, Stephen Worthington wrote:
>> I have a /56.  Best would be to have an option to set the size of the
>> local IPv6 network.  In the absence of that option, use the subnet
>> size seen on the interface (almost always a /64).  If you limit it to
>> only the link-local subnet, then IPv6 traffic from someone's WiFi that
>> was on a different /64 would be unable to access the MythTV system.
>I have a /64 from Comcast.
>I hope to look up the prefix size from the network settings. I have not 
>yet checked if QT can supply that info. If I cannot get the information 
>I think /64 is a reasonable setting. If your ISP is allocating a smaller 
>prefix, and the code cannot detect it, at worst using /64 may let in 
>some of your neighbors from the same ISP, if they happen to be extreme 
>hackers, know your IP address, etc.

You have prefixes the wrong way around.  A /64 is the standard size
for a minimum subnet, where the rest of the address is made up from
the individual device addresses.  It is like an a.b.c.x address in
IPv4, where the a.b.c designates a subnet of 256 addresses and .x is
used for individual devices on that subnet.  A /56 is a bigger address
space, of 256 /64 subnets.  A /48 is the original recommended
delegation of IPv6 address space to a customer from an ISP (65536 /64
subnets), although many now seem to be using /56 instead.  Allocating
only a single /64 means the customer can not easily create subnets
from their /64 block as most IPv6 software assumes that /64 will be
the smallest subnet size.

>> The same option should probably be available for IPv4 - optionally
>> specify a netmask for the local network.  That way anyone who has a
>> sophisticated network setup where different parts of a 10.x.x.x
>> address space are used for different things (like different sites in a
>> company) can restrict things to just the local part of that network if
>> they want.
>I don't want to add extra settings if possible. I am trying to make 
>setup as simple as possible for the home user. If a company really want 
>to use MythTV on its internal network it probably has hardware firewalls 
>for this kind of thing. These checks are for protecting the home user.

I can agree with keeping things simple.

>Article on why ISP's should give /64. It is not from the register...
>The experts out there can tell me if the article is true, is all wet or 
>garbage. I am not an expert.

That article is not about ISPs allocating a single /64 to a customer -
they should not.  It is about a /64 being way too large for a single
subnet.  There are arguments for and against that, but the decision
was made a long time ago when IPv6 was invented, and changing it now
breaks lots of things, including the SLAAC automatic IPv6 address
assignment system, so it is best to use /64 as the minimum subnet


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