In this illustration, we see a series of hosts and routers-there are eight hosts and seven total routers, and each router is numbered. Routers 1, 3, 5 and 6 form a square with R1 at top left, R3 at bottom left, R5 at bottom right, and R6 at top right. Each of these routers connects to the next. R2 is to the left of the square and connects with R1 and R3. R4 is below the square and connects with R3 and R5. R7 is to the right of the square and connects to R5. R1, R2, R6, and R7 all connect to two hosts, one shaded gray and one shaded blue. The blue host connected to R1 is labeled "H1." The blue host connected to R2 is labeled "H2." The blue host connected R6 is labeled "H4." The blue host connected R7 is labeled H3. R1, R2, R6, and R7 are all shaded light blue, while R3, R4, and R5 are dark blue. A key at the bottom of the figure identifies R2 as a leaf router and R3 as a core router. A light blue arrow points from H1 to R1, to R3. A light blue arrow points from H2 to R2 to R3. A dark blue arrow points from R3 to R4 to R5. A light blue arrow points from R5 to R6 to H4. And a light blue arrow points from R5 to R7 to H3.