Re: [v6ops] (re)numbering [ULA draft revision #2 Regarding isolated networks]

[Mark ZZZ Smith <[e-mail]>]

Hi Brian,

>________________________________
> From: Brian E Carpenter <[e-mail]>
>To: Mark ZZZ Smith <[e-mail]> 
>Cc: Liubing (Leo) <[e-mail]>; v6ops WG <[e-mail]> 
>Sent: Wednesday, 28 May 2014 12:33 PM
>Subject: (re)numbering [ULA draft revision #2 Regarding isolated networks]
> 
>
>Hi Mark,
>


<snip>

>industry.
>
>> The other reason is that I've actually seen a residential CPE try to swap between global addresses and ULAs. I deal with a number of residential IPv6 CPE vendors in around 2009, and one of them had attempted to support ULAs, but had not done a good job of it. When the global prefix went away because the WAN link failed, the CPE would try to both flush the global prefix by setting a 0 valid liftime (or similar, I can't quite recall) and replace it with a ULA in the RAs on the LAN side. When the WAN link came back, it tried to do the opposite. When I provided feedback to this vendor on this issue and others related to their IPv6 implementation, they just ignored it, unlike the other CPE vendors I was dealing with.
>
>That's horrible.

Certainly was.

While obviously not correct behaviour, I think it shows that internal connectivity should be impervious to external connectivity changes and failures.

RFC1918s have provided that internal connectivity robustness to both home networks and enterprise networks. Of course the drawback is that in IPv4 it is binary - hosts either have RFC1918s or public addresses, so if you have RFC1918s you have to use NAT to access external destinations on the Internet.

Fortunately in IPv6 we can support both ULAs + Globals concurrently, having both independent internal connectivity as well as global connectivity, which is why I think there is a lot of value in a network (home net or enterprise) having ULA addressing for internal reachability, regardless of whether it is isolated or not from the Internet. ULAs reduce external dependencies, and I think doing that increases robustness (sure there is a cost, but everything is a trade-off).

The use case I like to imagine is a home user streaming a video from their NAS to their TV over their internal network. That should use ULAs so that a failure of their Internet connection/Global addressing has no impact on watching their movie. If the movie failed because the Internet connection/global addressing failed, that user will call the ISP's helpdesk. But why should it fail! The home users internal network is fine, it is only external connectivity that has failed. 

People might argue that enterprise networks are different and they are - they're simpler! Enterprise networks have technical staff on hand that can troubleshoot networks and resolve faults. If you can make IPv6 work seamlessly for home networks and their non-technical "operators", you've solved the harder problem. Since enterprise networks also value the same things home networks do - seamless operation, robustness against failure, stable internal connectivity, you've solved most of the enterprise network problems too.

> It doesn't conform to RFC 7084 either, which clearly

>states that "prefix(es) (and ULA prefix if configured...)" must
>be advertised.
>

The precursor to 7084 (6204) was in development at the time, but it wouldn't have helped because they were ignoring our feedback. (Another CPE vendor was much better and almost too keen - they were sending me new software to test within 24 hours after reporting an IPv6 issue.)

Regards,
Mark.