On 20-apr-2005, at 18:05, Cameron Gray (RIPE Address Policy WG) wrote:
My, now somewhat aging, e-mail to lir-help asked what happens to LIRs that cannot get/justify/plan for 200 /48s their reply was simple: get it off another LIR. This now leads into a problem with routing policies: if /32s are only to be allowed in the backbone, how doe these sub-lir allocations get announced.
Well, there are no rules as to what is and isn't "allowed in the backbone". There is RFC 2772, which provides "6bone backbone routing GUIDELINES" and there are is a remark in the RIR/IANA IPv6 policies that the RIRs will only allocate blocks of /32 and bigger for the benefit of prefix length filtering. (But some root DNS servers have / 48 blocks...) At the end of the day, it's individual ISPs who decide what they allow and don't allow in their routing tables. It's true that if you announce a smaller block than a /32 you'll be filtered in many places. However, this isn't necessarily a problem. For instance, if someone in Asia sends your customer who has a /48 from you and also announces this /48 to another ISP, and the Asian network filters the / 48, the packet will flow towards Europe as per your /32. Then when it gets to Europe, it's pretty likely that the packet will hit an ISP who actually has the /48 in their routing table. After all, what's allowing a few /48s from the people you get drunk with at all those RIPE meetings? If then the link between you and your customer is down the packets still get to the customer. (Obviously if you drop the /32 announcement for whatever reason this is no longer true.) So I would encourage you, your customers and your customer's other ISPs to announce these smaller blocks over regional exchange points. This will give your customers 80% of the advantages of having PI space with only 20% of the downsides. (Note that it would be good if those customers had a bigger block than a /48. Even a /47 would be better, as it's likely that ISPs will leak /48s that shouldn't be announced at some point, which will make others want to filter /48s. But since customers generally don't have bigger blocks than a /48 there is no reason to disallow /47s in anti- leak filters.)