[Sidr] Re: S-BGP and IP prefix aggregation

Fri Dec 2 08:41:37 UTC 2005

>
> 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).
>

Advertising an aggregate that is not specifically assigned to you is  
known as "proxy aggregation".
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  
indicating that
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  
interesting administrative
issue that needs to be resolved.

Tony