Always wonder what was wrong with a prefix? Wondering which ISP's are not able to reach you and where it stops? GRH (Ghost Router Hunter *1) now has a new utility for doing prefix comparisons (*2). This feature was requested by Daniel Rösen for the purpose of comparing: 2001:5000::/21 with 2001:650::/32 (*3). Which are originated from the same ASN, but as the /21 is filtered at some places, have different or no paths to the participants (*4) that provide routes to GRH and many more ISP"s around the world. This utility thus allows you to see which participants of GRH do have the routes in question and the difference in the paths towards those participants. This allows a very quick view where a prefix is not accepted, most possibly of misconfigured filters. People who don't have, for instance, 2001:5000::/21 in their BGP, please figure out where the filtering is wrongly applied by looking at the utility and applying the current set of recommended filters, available from: http://www.space.net/~gert/RIPE/ipv6-filters.html It is good to see that ISP's have prefix filtering, but they really should update them. Though I'd rather see no prefix filtering but that they do RPF filtering on their customers. When you have (near) 0 IPv6 prefixes in your BGP, then you better start catching on ;) At the moment of writing you should have at least IPv6 499 prefixes, as then you have all the allocated, and currently announced, TLA's in your router, if you have less you are missing a number of them. For interested ISP's, GRH signup is, of course, free and can be done through the website (*5), the more peers join, the better the statistics of all the GRH utilities will be. Also, if you, like Daniel, miss a good utility, don't hesitate to bring it up. I would also like to thank all the already participating ISP's for providing their tables which have made it able to fix a large number of problems already over the almost 2 years GRH has been running. Last but not least, thanks to Daniel Rösen for the brilliant idea. Greets, Jeroen *1 = http://www.sixxs.net/tools/grh/ *2 = http://www.sixxs.net/tools/grh/compare/ *3 = http://www.sixxs.net/tools/grh/compare/?a=2001:5000::/21&b=2001:650::/32 *4 = http://www.sixxs.net/tools/grh/participants/ *5 = http://www.sixxs.net/tools/grh/signup/