In this illustration, we see three separate networks of four routers arranged in a triangle. In the left-most network, the left-hand point on the triangle is labeled 1a, the topmost point is labeled 1b, the right-hand point is labeled 1c, and the bottom point is labeled 1d. This network is designated as AS1.

The middle network is positioned in the same way as AS1, except that the routers are labeled 2a, 2b, 2c, and 2d. This network is designated as AS2. Router 1c is connected with router 2a.

The right-most network is positioned in the same way as the previous two, except that the routers are labeled as 3a, 3b, 3c, and 3d. This network is designated as AS3. Router 3d is connected to an unseen subnet, labeled x.