| 9.5 | Configure BGP to Interact with IGPs | ||
| 9.5.3 | Injecting information statically into BGP |
|
Today, injecting information statically
into BGP has proven to be the most effective in ensuring route stability.
Of course, this method also has drawbacks. To statically inject
information into BGP, 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.
If, for example, the route is advertised to the Internet from a single point, then advertising a route that is actually down is not a big issue. 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 black-holing the traffic. If problems inside the AS prevent the border router from being able to reach the network it is advertising, traffic to that destination will be dropped, even though it could have been reached from some other entry point. The actual advertisement of the static route can be done with either of the methods described in the "Injecting Information Dynamically into BGP" section. Advertisement can be done by redistributing all the static routes via the redistribute command or a subset of the static routes via the network command. The latter method enables a more controlled route injection because redistribution might cause some unwanted static routes to be sent via BGP.
|