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Re: about Wedgelayer 3.5 / Fat IP approaches
Another difference is length of the hash of the key, which may
cause some subtle differences. With 64 bit IDs (or, strictly
speaking, ID tags, since the public keys are the actual
identifiers), we can provide an embedded stack name in the AID,
whereas with HITs, we can only provide a mapping between
(truncated) stack name and AIDs. When we have discussed
shortening HITs to accommodate some structure to aid reverse
lookups, there have been concerns raised that 64 bit IDs might
not be strong enough to withstand server farm attacks in the
future (generating different key that hashes to same ID).
If a larger hash is used as the identifier, then the AID with
truncated HIT can be viewed as a slightly less secure
identifier used for support of referrals for non-multi6/HIP
aware apps, which keeps the door open for future HIP-aware
apps to directly use the full IDs.
But there are some cases where the larger ID (that doesn't fit in the
seen by the ULPs) does not help.
Example: busy server receives a context from a client with large ID = X
and AID=P1 | hash(X)
Server later receives a context from a client with large ID = Y
and AID=P1 | hash(Y)
and the hash values are identical.
Even though the multihoming layer can disambiguate the two contexts, it
can not handle both at the same time because the ULP can not tell them
I think that Tom was considering the case were apps have been upgraded
and they are HIP aware (using a new api), so they can actually deal
with the full HIT or even directly with the HI, so they can benefit
from enhanced security.
Thus when a packet would be passed down from the ULP, the multihoming
layer wouldn't know which of the two contexts to use for transmitting
packet. The number of contexts the server can handle before this
collisions is an issue is of course a function of the hash size. With
of hash handling 4 Billion contexts concurrently would imply about .5
probability that two have the same hash, but the prefixes would most
different so that the AIDs would be different.