Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 4 IS-IS Configuration
4-6
Area 1
L2
Area 3
Area 2
L1
L1
L1/L2
L2
L1/L2
L1
Area 4
Figure 4-3
IS-IS topology
Note:
The IS-IS backbone does not need to be a specific Area.
Both the IS-IS Level-1 and Level-2 routers use the SPF algorithm to generate the
Shortest Path Tree (SPT).
III. Interface routing hierarchy type
You can configure the routing type for each interface. For a Level-1-2 router, one
interface may establish Level-1 adjacency with a router, and another one may establish
Level-2 adjacency with another router. You can limit the adjacency type by configuring
the routing hierarchy on the interface. For example, the level-1 interface can only
establish Level-1 adjacency, while the level-2 interface can only establish Level-2
adjacency.
By having this function, you can prevent the Level-1 hello packets from propagating to
the Level-2 backbone through the Lever-1-2 router. This can result in bandwidth
saving.
IV. Route leaking
An IS-IS routing domain is comprised of only one Level-2 area and multiple Level-1
areas. A Level-1 area is connected with the Level-2 area rather than other Level-1
areas.
The routing information of the Level-1 area is sent to the Level-2 area through the
Level-1-2 router. Therefore, the Level-2 router knows the routing information of the
entire IS-IS routing domain but does not share the information with the Level-1 area by
default.
