Curious situation - not urgent, but I'd like to know more

[Brian E Carpenter]

On 21/12/2015 03:28, Marc Luethi wrote:
> Hi all
> 
> I suggest to investigate source address selection on the client side,
> while closely following name resolution (assuming this is similar to
> Windows 2012R2's DA implementation, DNS64 is supposed to be at work, here)
> and keeping an eye on the IPv6 routing table.
> 
> In your situation, I would presume that the end system ends up with an RFC
> 4193 address (from the /48 that was initially chosen when DA was set up) on
> its *IP-over-HTTPS* tunneling interface (courtesy of the DA implementation)
> and a global unicast address  the (W)LAN interface, based on the CPE's RAs.
> 
> While things *should* be neat, my experience with Windows 7's way of
> picking source addresses was so bad ("longest match" seemed entirely
> unheard-of), I eventually gave up using RFC 4193 addresses for my internal
> network altogether.
> 
> I repeateadely observed Win7 using its global unicast address(es) to access
> internal ressources, while stubbornly sticking to te RFC4193 source address
> when attempting to talk to addresses on the global IPv6 internet.

Yes. Apparently Win8 is up to date in that respect (i.e. follows RFC6724 not
RFC3484). It would be possible to make Win8 misbehave by changing the default
preferences (https://tools.ietf.org/html/rfc6724#section-10.6).

Conversely, it's possible to make Win7 behave correctly by changing its default
policies to conform to RFC6724. I just found the following site that offers a
script (YMMV, I haven't checked it):
https://sites.google.com/site/jrey42/Home/ipv6/prefixpolicies

But if that is the cause of the original issue, maybe switching off the
ULA prefix would be easier, and nicer than switching off IPv6.

    Brian Carpenter


> 
> cheers
> Marc
> 
> 
> 
> 
> On 19 December 2015 at 22:37, Kurt Buff <kurt.buff at gmail.com> wrote:
> 
>> All,
>>
>> I ran into an interesting situation some months ago which still
>> baffles me, and though I was able to work around it, I expect it will
>> happen again.
>>
>> We implemented MSFT DirectAcess at our company quite some time ago
>> (using 2008R2 and Forefront 2010), and it works extremely well.
>>
>> At least it worked well for everyone until one of the employees got
>> his Comcast connection upgraded, and then DirectAccess didn't work for
>> that employee any more.
>>
>> We proved that if he tethered to his cell phone, that would work, and
>> if he used an SSL VPN client while on his Comcast connect that would
>> work, but DirectAccess would not work at home.
>>
>> Finally, I discovered that his Comcast-installed router was handing
>> our IPv6 addresses on his home LAN. Turning that off enabled
>> DirectAccess to work again.
>>
>> We do not have an assigned IPv6 block from our ISP, though of course
>> MSFT OSes use it, and auto-assign themselves addresses, but for now
>> we're ignoring it.
>>
>> Has anyone run into this problem and solved it - not by turning off
>> iIPv6 address assignment for the home LAN, but really solved it? If
>> so, how did you do that?
>>
>> Would getting and implementing an IPv6 assignment from our ISP cure
>> the problem, or make it worse?
>>
>> I've found little guidance from MSFT about DirectAccess in an IPv6
>> environment, though I admit I haven't been terribly diligent in my
>> searches.
>>
>> Kurt
>>
> 
> 
>