3com 3031 Instruccion De Instalación
Integrated IS-IS Overview
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Figure 134 IS-IS topology
Route Leak
Generally speaking, an IS-IS area can also be called a Level-1 area. Internal routes
are managed by Level-1 routers. All Level-2 routers form a Level-2 area. Thus, an
IS-IS routing domain may contain multiple Level-1 areas but only one Level-2 area.
are managed by Level-1 routers. All Level-2 routers form a Level-2 area. Thus, an
IS-IS routing domain may contain multiple Level-1 areas but only one Level-2 area.
A Level-1 IS-IS node cannot be connected directly to a different Level-1 IS-IS node.
Level-1 to Level-1 communication must pass through a Level-2 IS-IS node.
Level-1 to Level-1 communication must pass through a Level-2 IS-IS node.
Routing information inside a Level-1 area is advertised to the Level-2 area via
Level-1-2 routers. Therefore, Level-2 routers know routing information in the
entire IS-IS routing domain. However, Level-2 routers do not advertise the routes
of Level-1 routers to which they are not directly connected, nor the routes of the
Level-2 backbone by default. Therefore, Level-1 routers do not know outside
routing information, which may make them unable to choose the best route to a
destination address outside their local area.
Level-1-2 routers. Therefore, Level-2 routers know routing information in the
entire IS-IS routing domain. However, Level-2 routers do not advertise the routes
of Level-1 routers to which they are not directly connected, nor the routes of the
Level-2 backbone by default. Therefore, Level-1 routers do not know outside
routing information, which may make them unable to choose the best route to a
destination address outside their local area.
ES
Routing Domain Boundary
IS-IS Area
End system
Subnetwork Path
Level 1 IS-IS Routing
Level 2 IS-IS Routing
Interdomain Routing
Intermediate system
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IS
Area 1
Area 2
Area 3
Routing Domain 1
Routing Domain 2
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IS
ES
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