H3C S3610-28P Operation Manual page 440

Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Since the Level-1 router simply sends the routing information for destinations outside
the area to the nearest Level-1-2 router, this may cause a problem that the best path
cannot be selected.
To solve this problem, route leaking was introduced. The Level-2 router can advertise
the Level-2 routing information to a specified Level-1 area. By having the routing
information of other areas, the Level-1 router can make a better routing choice for the
packets destined outside the area.
4.1.3 IS-IS Network Type
I. Network type
IS-IS supports two network types:
Broadcast network, such as Ethernet, Token-Ring.
Point-to-point network, such as PPP, HDLC.
Note:
For the Non-Broadcast Multi-Access (NBMA) network, such as ATM, you need to
configure point-to-point or broadcast network on its configured subinterfaces. IS-IS
does not run on Point to Multipoint (P2MP) links.
II. DIS and pseudonodes
On an IS-IS broadcast network, a router has to be selected as the Designated
Intermediate System (DIS).
The Level-1 and Level-2 DISs are selected respectively. You can assign different
priorities for different level DIS selections. The higher a router's priority is, the more
likelihood the router becomes the DIS. If there are multiple routers with the same
highest DIS priority, the one with the highest SNPA (Subnetwork Point of Attachment)
address (which is the MAC address on a broadcast network) will be selected. A router
can be the DIS for different levels.
As shown in
establish adjacencies. This is different from OSPF.
Figure 4-4, the same level routers on the same network segment can
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Chapter 4 IS-IS Configuration