H3C S7500E Series Operation Manual page 364

Operation Manual – IPv4 Routing
H3C S7500E Series Ethernet Switches Chapter 4 IS-IS Configuration
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 Figure 4-4, the same level routers on the same network segment can
establish adjacencies. This is different from OSPF.
Figure 4-4 DIS in the IS-IS broadcast network
The DIS creates and updates pseudonodes as well as their LSP to describe all routers
on the network.
The pseudonode emulates a virtual node on the broadcast network. It is not a real
router. In IS-IS, it is identified by the system ID and one byte Circuit ID (a non zero value)
of the DIS.
4-7