Re: Aggregation Implies Provider Dependence // Re: [RRG] ALT's strong aggregation often leads to *very* long paths

[Scott Brim <swb@employees.org>]

The whole scenario still feels specious to me.  To start with, for
redundancy a particular ALT infrastructure node will be
multiply-connected to the aggregation level above it.  This will be
true for sites as well -- they will be multiply-connected to
first-level ALT nodes, whether those ALT nodes are provided by a
site's access provider or not.  There is no single point of ALT
connectivity to hold hostage.  

However, because of aggressive aggregation of routing information,
each node needs to attempt to connect to all next-level aggregators
(above it), or packets might be lost if sent to the "wrong"
aggregator.  So there is some potential vulnerability ... 

... but an ALT node that pretended to have routes to all active EIDs
within a prefix, while simultaneously refusing a connection to a valid
holder of an EID prefix and intentionally blackholing packets to it,
would be seen as a disruptor of the entire system.  However, because
of redundancy, the system can easily defend itself -- higher level ALT
nodes can stop depending on the misbehaving node to route any packets
at all, at least for the including prefix.  This is not an
architecture issue, it's an operations issue.



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