On Tue, 2006-07-04 at 19:25 -0400, Michael J Freedman wrote: > We don't really have such information. The problem you bring up is more > an issue of legal route advertisements and is somewhat orthogonal to NATs. > > I assume from the above example that FastWeb probably isn't announcing > 41.0.0.0/8 anymore given its re-allocation; if that is the case, it's > unclear to me how one could really differentiate between the two (when > coming from NATs) without a priori knowledge.
The FastWeb problem actually was not them hijacking an address block (by illegally announcing it to the rest of the world), but rather them allocating those 'reserved' IPs to their private DHCP users who were behind an ISP-wide NAT. That NAT would translate the reserved address to FastWeb's legal address space when the packet exited FastWeb but not otherwise. Basically, instead of 192.168.x.y, they opted to use non-private addresses. Certainly a configuration error (intentional or otherwise). Last I heard, FastWeb did not intend to re-number their private network -- so people in Turin still cannot get to Africa even if the African server is on a public address. One way to detect such errors may be to check if the internal IP is non-private, the external IP is non-private, and they are from address blocks belonging to different (or non-existent) AS's. cheers, -- Saikat
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