1. Router A double-link connects L2 switch. Two interfaces of router A are interface A1 and interface A2. Router B double-link connects L2 switch. Two interfaces of router A are interface B1 and interface B2.
2. The interface of the router enables circuit-level level-2 and circuit-type p2p.
3. Log records Adjacency up/down frequently.
Change the type of interface circuit:
1. Change circuit-type of router interface as broadcast-type.
2. Change circuit-type of one interface as broadcast-type. e.g. change circuit-type of interface A1 of router A as broadcast-type. Change circuit-type of interface B1 of router B as broadcast-type.
In this topology, the interface of router A can receive Hello packet sent by two interfaces of router B. But local circuit identifier of these two packets is different. A1 of router A, B1 and B2 of router B have possibility to set up Adjacency. When circuit-type of ISIS is p2p, there must be one Adjacency. A1 of router A and B1 and B2 of router B frequently set up Adjacency. New Adjacency overwrites old Adjacency. Adjacency is instable.
Not use point-to-point circuit-type in broadcast network.