
Configuring IP Services
7-6 117356-A Rev. A
OSPF Router Types
OSPF defines three router types: internal routers, border routers, and boundary
routers.
A router with interfaces to networks in one area only is considered to be an area
internal router. Internal routers flood each area with complete routing information
about changes that occur within the area. In Area 0.0.0.1, for example, R4, R5,
and R6 are internal routers.
A router with an interface to the backbone network and interfaces to one or more
additional areas is considered to be a border router. Each border router connects
one or more areas to the backbone. In F
igure 7-1, R3, R8, and R11 are border
routers. Using the backbone, border routers ensure that AS external routes (ASEs)
and summaries of routing information for all areas are distributed throughout the
AS.
A router configured with BGP, RIP, or another protocol to receive information
about external routes and OSFP to inject this information into an OSPF AS is
considered to be an OSPF boundary router.
AS External Routes
OSPF considers the following routes to be AS external (ASE) routes:
• A route to a destination outside the AS
• A static route
• A default route
• A route derived by RIP
• A directly connected network not running OSPF
In F
igure 7-1, for example, routers R1 and R2 are boundary routers that use BGP
and EGP to connect the backbone to external ASs. R7 in Area 0.0.0.1 is also a
boundary router, connecting the area to an external RIP network. R14 in Area
0.0.0.3 connects the area to an external AS via BGP.
Comentarios a estos manuales