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Today, injecting information statically into
BGP has proven to be the most effective means to ensure route stability. Of course, this method also has drawbacks. To statically inject
information into BGP, the IGP routes (or aggregates) that need to be
advertised to other peers are manually defined as static routes. This
ensures that these routes will never disappear from the IP routing table
and hence will always be advertised. Because administrators are often
uncomfortable advertising routes to networks that might be down or
unreachable, the appropriateness of injecting information statically
depends on the particular situation.
For example, if the route is advertised to the
Internet from a single point, then advertising a route that is actually
down is essentially moot. Hosts trying to access that destination will
fail, regardless of whether the route is advertised. On the other hand, if
a route is advertised to the Internet from multiple points, then
advertising the route statically at all times might end up creating a
black hole for traffic. If problems inside the AS prevent the border
router from being capable of reaching the network that it is advertising,
traffic to that destination will be dropped, even though it could have
been reached from some other entry point.
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