If you are relying on the cable modem to route, any number of things
could be happening there.  One of the cool things with IPv6 is that
the host can *make up* its own host-part of the IP address, as long as
its reasonably random or based on a MAC addr that's "guaranteed" to be
unique.  A host can have multiple IPv6 addresses.  If the gateway
isn't tracking the association between the (local) MAC address and the
IPv6 address, then IPv6 has a degree of obfuscation associated with
it.  But the network part of the address will be unique to your
location.  Some IPv6 addresses can be based on the MAC address, which
used to be the default on Linux, so you should be aware of that.
There are 2^64 addresses to choose from on each network, so the risk
of collisions is very small.

On Wed, Dec 24, 2014 at 9:27 AM, David Madden <[email protected]> wrote:
> On 24-Dec-2014 04:22 , Russell Senior wrote:
>> Typically, in order to get IPv6 from Comcast, your cable modem needs
>> to bridge and your gateway router needs to both support and enable
>> IPv6.
>
> Hmmm, I have Comcast Business at home & work, and on both ends,
> Ethernet-connected machines seem to have picked up IPv6 addresses.  I
> can ping6 in both directions.  However, I can't make TCP connections (or
> else I'm not doing it right...I've tried ssh [pingable-ipv6-address] and
> telnet [pingable-ipv6-address] port).  On my local networks, those work
> between machines, but not between machines at different Comcast locations.)
>
> What would cause ping6 to work, but tcp6 connections to hang?  (Yes, I
> tried disabling firewalls & etc.)  Anything else?
>
> (And is it true that IPv6 addresses are globally unique, even where they
> would have been behind NAT or whatever in IPv4?  Yikes, the copyright
> trolls are gonna have a field day with that!)
>
> Thanks!
> --
> Mersenne Law LLC  ·  www.mersenne.com  ·  +1-503-679-1671
> - Small Business, Startup and Intellectual Property Law -
> 9600 S.W. Oak Street · Suite 500 · Tigard, Oregon  97223
>
>
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