3com 3031 Instruccion De Instalación
522
C
HAPTER
41: I
NTEGRATED
IS-IS C
ONFIGURATION
IS-IS-applied link types
IS-IS can operate over point-to-point links, such as PPP and HDLC, or broadcast
links, such as Ethernet and Token-ring. For NBMA (Non-Broadcast Multi-Access)
network, such as ATM and Frame Relay, it is necessary to configure sub-interfaces
and configure the types of sub-interfaces as P2P or broadcast network. IS-IS
cannot operate over point-to-multipoint links.
links, such as Ethernet and Token-ring. For NBMA (Non-Broadcast Multi-Access)
network, such as ATM and Frame Relay, it is necessary to configure sub-interfaces
and configure the types of sub-interfaces as P2P or broadcast network. IS-IS
cannot operate over point-to-multipoint links.
Two-level Structure of
IS-IS Routing Protocol
Two-level structure
In order to support large-scale routing networks, IS-IS adopts a two-level structure
in an RD. A large RD is divided into one or more areas. Intra-area routing is
managed by Level-1 router while inter-area routing is managed by Level-2 router.
in an RD. A large RD is divided into one or more areas. Intra-area routing is
managed by Level-1 router while inter-area routing is managed by Level-2 router.
Level-1 and Level-2
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Level-1 Router
The Level-1 router manages the intra-area routing. Level-1 routers in the same
area form Level-1 peer adjacencies to maintain the LSDB in its own Level-1
area. The LSDB contains the routing information of its area. When a Level-1
router receives a packet whose destination address is in an external area, it will
forward the packet to the nearest Level-2 router.
area form Level-1 peer adjacencies to maintain the LSDB in its own Level-1
area. The LSDB contains the routing information of its area. When a Level-1
router receives a packet whose destination address is in an external area, it will
forward the packet to the nearest Level-2 router.
■
Level-2 Router
The Level-2 router manages the inter-area routing. A Level-2 router forms
Level-2 peer adjacencies with other Level-2 routers to maintain the LSDB of the
Level-2 area. The LSDB contains routing information between areas. All Level-2
routers constitute the backbone network of the routing domain, and are
responsible for communication between different areas. The Level-2 routers in
the routing domain must be successive to ensure the continuity of the
backbone network. Only Level-2 routers can exchange data packets or routing
information with routers outside the routing domain.
Level-2 peer adjacencies with other Level-2 routers to maintain the LSDB of the
Level-2 area. The LSDB contains routing information between areas. All Level-2
routers constitute the backbone network of the routing domain, and are
responsible for communication between different areas. The Level-2 routers in
the routing domain must be successive to ensure the continuity of the
backbone network. Only Level-2 routers can exchange data packets or routing
information with routers outside the routing domain.
■
Level-1-2 Router
A router, which belongs to both a Level-1 area and a Level-2 area, is called a
Level-1-2 router. There is at least one Level-1-2 router in each area, which
connect the area to the backbone network. It maintains two LSDBs: the Level-1
LSDB is used for intra-area routing and the Level-2 LSDB for inter-area routing.
Level-1-2 router. There is at least one Level-1-2 router in each area, which
connect the area to the backbone network. It maintains two LSDBs: the Level-1
LSDB is used for intra-area routing and the Level-2 LSDB for inter-area routing.
The following figure illustrates an IS-IS enabled network, containing both
Routing Domain 1 and Routing Domain 2. Routing Domain 1 includes two
areas, Area 1 and Area 2. Routing Domain 2 only includes one area, Area 3. In
Routing Domain 1, the 3 ISs connected with bold lines formthe backbone of
the Routing Domain. These 3 ISs are all Level-2 routers. The other 4 ISs, which
are not directly connected with bold lines, are Level-1 routers.
Routing Domain 1 and Routing Domain 2. Routing Domain 1 includes two
areas, Area 1 and Area 2. Routing Domain 2 only includes one area, Area 3. In
Routing Domain 1, the 3 ISs connected with bold lines formthe backbone of
the Routing Domain. These 3 ISs are all Level-2 routers. The other 4 ISs, which
are not directly connected with bold lines, are Level-1 routers.