v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space (IPv6-MW)]

Nathan Ward nanog at daork.net
Thu Feb 5 01:38:29 UTC 2009

On 5/02/2009, at 2:28 PM, Matthew Moyle-Croft wrote:

> Anthony Roberts wrote:
>> I don't think there's any need for the ISP's routers to advertise  
>> all the
>> prefixes they delegate. They'll advertise the /48 or whatever it  
>> is, and
>> then delegate chunks out of that.
> My apologies for not being clear:
> As I posted just before in reply to MarkA - I'm hoping that for the  
> MAJORITY of customers that I can use PD and dynamic /64s (or  
> whatever) local to a BRAS.
> My FEAR is that people ("customers") are going to start assuming  
> that v6 means their own static allocation (quite a number are  
> assuming this).   This means that I have a problem with routing  
> table size etc if I have to implement that.

In my opinion, if they want static, they get business grade services,  
and get a /48. Or maybe a /56 over DSL perhaps.

And they pay more for it.

Otherwise they get PD like everybody else. The ability is there *now*  
for you to manage this expectation and say to customers that they are  
dynamic. Exploit it.

> I'm still not convinced though that, given DHCPv6 is going to be a  
> reality for DNS assignment etc, that stateless autoconfig is needed  
> and thus /64 doesn't have to be the smallest we assign.

Dynamic PD requires SLAAC, unless your customers have say 30s DHCPv6  
lease times on their DHCPv6 servers.

DSL reconnects, gets new IPv6 prefix, sends RA messages internally,  
hosts renumber and mark the existing prefix as deprecated until it  

The alternative is waiting for hosts to do a DHCPv6 query to get a new  
address. That is sub-optimal.

Nathan Ward

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