?– Routing protocols must base their routing decisions on a 32-bit IP address and a pre?¬?x length
that can be up to 32 bits.
?– Routing protocols must carry the pre?¬?x length (subnet mask) with the 32-bit IP address.
Cisco routers manage route summarization in two ways:
?– Sending route summaries: Routing protocols, such as RIP and EIGRP, perform automatic
route summarization across network boundaries. Speci?¬?cally, this automatic summarization
occurs for those routes whose classful network address differs from the major network
address of the interface to which the advertisement is being sent. For OSPF and IS-IS, you
must con?¬?gure manual summarization. For EIGRP and RIP-2, you can disable automatic
route summarization and con?¬?gure manual summarization. Whether routing summarization
is automatic or not depends on the routing protocol. It is recommended that you review the
documentation for your speci?¬?c routing protocols. Route summarization is not always a
solution. You would not use route summarization if you needed to advertise all networks
across a boundary, such as when you have discontiguous networks.
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