Re: A common problem with SLAAC in "renumbering" scenarios

[Ole Troan <[e-mail]>]

Mikael,

>> Now, I know there are cases where huge swats of users are moved from one aggregation point in the network to another, where routing would end up very messed up if customer weren’t renumbered, and also that in those cases that flash renumbering is a lot easier to do, but those are typically known events.
> 
> My current ISP has stated that their intention is to make sure people keep the same prefix as long as their HGW is alive, and they even provide a 7 day life time of the lease. So unless your HGW is alive once every 7 days, you get to keep the lease. This makes a lot of sense to me and is a decent tradeoff between different realities.
> 
> Now, there is nothing in the contract that regulates this so they're free to change whenever (and they do in case they need to move people around between aggregation routers, but this is a rare event).
> 
> Trying to demand that ISPs keep the same /56 for the duration of the contract is not going to work because that's not what real life looks like. I'd say we should take the fight about perhaps about lifetimes and definititely about delegation sizes (I still run into people with only /60 or /64), but contract-length stable prefix isn't something I'd advocate to fight for. It's too far out even for me.


“real life looks like”…
Why wouldn’t it? If the ISP has a routed interface directly towards the customer, then having a fixed /56 PD configured on that customer facing interface, that sure looks like real life to me.
Or a fixed mapping of remote-id to a /56 in a DHCP PD database…

Sure, there are ISPs that use DHCP PD servers that allocate from pools. But I have a hard time seeing why that should be easier, cheaper, more managable than a static mapping table.

(and don’t get me wrong, I’m all in favour of making CPEs and hosts more robust. I’m just trying to emphasize the point, that you can hardly blame the CPEs not working well, in a network that’s by some definition misconfigured. I am still on the fence if the way to achieve that is through an IETF document or something else though).

Ole