Advanced IP Network Design (CCIE Professional Development)

Core Redundancy

Core redundancy design is generally simplified because all devices should have complete routing information (full reachability). The only exception to this general rule should be the default route used to reach external routing domains (such as the Internet or a corporate partner).

Because all devices have full routing information, there is little chance of a routing loop forming within the core itself under normal circumstances. (Note that running multiple interior routing protocols within the core is not considered a normal circumstance.) It is possible to forward packets along a suboptimal route, but loops with full routing information aren't very likely.

Redundant Core Design

Numerous designs provide redundancy in the core. ...