Lenovo Flex System Fabric CN4093 Application Manual page 426

Typically, an AS will have one or more border routers (peer routers that exchange
routes with other OSPF networks) as well as an internal routing system enabling
every router in that AS to reach every other router and destination within that AS.
When a routing device advertises routes to boundary routers on other autonomous
systems, it is effectively committing to carry data to the IP space represented in the
route being advertised. For example, if the routing device advertises 192.204.4.0/24,
it is declaring that if another router sends data destined for any address in the
192.204.4.0/24 range, it will carry that data to its destination.
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CN4093 Application Guide for N/OS 8.2