Large-Scale IP Network Solutions (CCIE Professional Development)

Using IS-IS Pseudonode

Instead of treating a broadcast network as a fully connected topology, IS-IS treats a broadcast network as a pseudonode with links to each attached system.

Note

To reduce the number of full mesh adjacencies between nodes, multiaccess links are modeled as pseudonodes. As the name implies, this is a virtual node. One of the ISs on the link is designated to be the pseudonode; this node is called the designated intermediate system (DIS). All routers on the broadcast link, including the one elected to be DIS, form adjacencies with the pseudonode instead of forming n^*(n–1) adjacencies with each other in a full mesh.

The DIS is responsible for generating pseudonode link-state packets, for reporting links to all systems on ...