New Ghost Route Hunter Utility: Prefix Compare

[Nanog: Yes, this is message has operational content, at least, in
Europe IPv6 is operational :wink: | excuses for the crosspost, the
message-id's should be the same, thus configure your filters...]

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

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 :wink: 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.


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