Enhanced IGRP Classless Summarization

By default, Enhanced IGRP advertises at the natural classful network boundary for all the Enhanced IGRP internal routes. All external routes are not summarized when advertised across a major network. Before continuing with this discussion, you should understand the difference between internal and external routes in Enhanced IGRP.

Internal routes are routes that are learned from the same autonomous number running on the local router. External routes are routes that are learned from other routing protocols, from IGRP, or from another Enhanced IGRP autonomous system number.

As mentioned earlier, Enhanced IGRP summarizes internal routes at the natural network mask when propagated across a different ...

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