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Re: [Sidr] Re: S-BGP and IP prefix aggregation
- From: Tony Li
- Date: Fri Dec 02 03:42:58 2005
Advertising an aggregate that is not specifically assigned to you is
known as "proxy aggregation".
An alternative for sbgp design could be that aggregating ASN would
create special self-signing cert for such aggregate block and that
cert would have special attribute(s) indicating list of all sub-
blocks and reference
to all certs that "make" this aggregate block. Then verifying router
in such a case would go through and verify each one of those sub-block
certs (and those sub-block certs would have to be such that they
give permission for announcing the block from that sub-block owner
to aggregating ASN).
William has given a good description of what's required above, but it
needs a further enhancement
in that proxy aggregation will frequently need to happen in several
locations for the aggregate to
have any true impact on routing. In graph theoretic terms, proxy
aggregation must form a
"cut set" topologically around the longer prefixes to contain them
and prevent them from being
distributed throughout the network.
Thus, any security mechanism needs to provide some means for
an entire set of ASes may legitimately be advertising a proxy
aggregate prefix. How one
determines the appropriate set of ASes that are authorized is another
issue that needs to be resolved.