OSPF Route Summarization参考.ppt

Configuring OSPF OSPF Route Summarization Benefits of Route Summarization Minimizes number of routing table entries Localizes impact of a topology change Reduces LSA type 3 and 5 flooding and saves CPU resources Using Route Summarization Interarea summary link carries mask. One or more entries can represent several subnets. Configuring Route Summarization Route Summarization Configuration Example at ABR Route Summarization Configuration Example at ASBR Default Routes in OSPF A default route is injected into OSPF as an external LSA type 5. Default route distribution is not on by default; use the default-information originate command under the OSPF routing process. Configuring OSPF Default Routes Default Route Configuration Example Summary Route summarization improves CPU utilization, reduces LSA flooding, and reduces routing table sizes. The area range command is used to summarize at the ABR. The summary-address command is used to summarize at the ASBR. Default routes can be used in OSPF to prevent the need for a specific route to all destination networks. The benefits include a much smaller routing table and LSDB, with complete reachability. OSPF uses the default-information originate command to inject a default route. The IS-IS Protocol Introducing IS-IS and Integrated IS-IS Routing Uses for IS-IS Routing Large ISPs Stable protocol Originally deployed by ISPs because U.S. government mandated Internet support of OSI and IP IS-IS Routing IS = router. IS-IS was originally designed as the IGP for the Connectionless Network Service (CLNS), part of the OSI protocol suite. The OSI protocol suite layer 3 protocol is the Connectionless Network Protocol (CLNP). IS-IS uses CLNS addresses to identify routers and build the LSDB. IS-IS Features Link-state routing protocol Supports VLSM Uses Dijkstra’s SPF algorithm; has fast convergence Uses hellos to establish adjacencies and LSPs to exchange link-state information Efficient use of bandwidth, memory, and processor Supports