Dell S5148F-ON OS10 Enterprise Edition User Guide Release 10.3.2E-R1 - Page 255

Router types

Page 255 highlights

The backbone is the only area with a default area number. You configure all other areas Area ID. If you configure two nonbackbone areas, you must enable the B bit in OSPF. Routers, A, B, C, G, H, and I are the backbone, see Autonomous system areas. • A stub area (SA) does not receive external route information, except for the default route. These areas do receive information from interarea (IA) routes. • A not-so-stubby area (NSSA) can import AS external route information and send it to the backbone as type-7 LSA. • Totally stubby areas are also known as no summary areas. Configure all routers within an assigned stub area as stubby and do not generate LSAs that do not apply. For example, a Type 5 LSA is intended for external areas and the stubby area routers may not generate external LSAs. A virtual link cannot traverse stubby areas. Networks and neighbors As a link-state protocol, OSPF sends routing information to other OSPF routers concerning the state of the links between them. The up or down state of those links is important. Routers that share a link become neighbors on that segment. OSPF uses the hello protocol as a neighbor discovery and keepalive mechanism. After two routers are neighbors, they may proceed to exchange and synchronize their databases, which creates an adjacency. Router types Router types are attributes of the OSPF process-multiple OSPF processes may run on the same router. A router connected to more than one area, receiving routing from a BGP process connected to another AS, acts as both an area border router and an autonomous system border router. Each router has a unique ID, written in decimal format-A.B.C.D. You do not have to associate the router ID with a valid IP address. To make troubleshooting easier, ensure the router ID is identical to the router's IP address. Layer 3 255

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The backbone is the only area with a default area number. You
configure
all other areas Area ID. If you
configure
two nonbackbone areas,
you must enable the B bit in OSPF. Routers, A, B, C, G, H, and I are the backbone, see
Autonomous system areas
.
A stub area (SA) does not receive external route information, except for the default route. These areas do receive information from
interarea (IA) routes.
A not-so-stubby area (NSSA) can import AS external route information and send it to the backbone as type-7 LSA.
Totally stubby areas are also known as no summary areas.
Configure
all routers within an assigned stub area as stubby and do not generate LSAs that do not apply. For example, a Type 5 LSA is
intended for external areas and the stubby area routers may not generate external LSAs. A virtual link cannot traverse stubby areas.
Networks and neighbors
As a link-state protocol, OSPF sends routing information to other OSPF routers concerning the state of the links between them. The up or
down state of those links is important. Routers that share a link become neighbors on that segment. OSPF uses the
hello
protocol as a
neighbor discovery and
keepalive
mechanism. After two routers are neighbors, they may proceed to exchange and synchronize their
databases, which creates an adjacency.
Router types
Router types are attributes of the OSPF process—multiple OSPF processes may run on the same router. A router connected to more than
one area, receiving routing from a BGP process connected to another AS, acts as both an area border router and an autonomous system
border router.
Each router has a unique ID, written in decimal format—A.B.C.D. You do not have to associate the router ID with a valid IP address. To
make troubleshooting easier, ensure the router ID is identical to the router’s IP address.
Layer 3
255