Refer to the exhibit. This network is deployed with all connected links configured to run IS-IS. The routing protocol is enabled globally on each router, and the network engineer expects full routing

Question

Exhibit

Options

• AConfigure all routers to reside in the same area.
• BConfigure R1 and R5 as Level 1/Level 2 routers.
• CConfigure R3 as a Level 1 /Level 2 router.
• DConfigure R5 in the same area as R1.

• A
  78% (29)
• B
  14% (5)
• C
  5% (2)
• D
  3% (1)

Explanation

IS-IS uses a two-level hierarchy: Level 1 (L1) routers share routing information only within their area, and Level 2 (L2) routers share routing information between areas. By default, routers may be configured as L1-only or L2-only. If R1 is in one IS-IS area and R5 is in a different area, and there is no L1/L2 (dual-level) router to leak routes between the areas, R5 will not receive routes originated by R1. The cleanest and simplest resolution - without adding the complexity of L1/L2 boundary routers and inter-area route leaking - is to place all routers in the same IS-IS area (typically area 0 or a single flat area). This eliminates the area boundary problem entirely: all routers become L1 or L2 peers within one area and share full routing tables. Option B (making R1 and R5 L1/L2) partially helps but does not fix the problem unless intermediate routers also handle area boundary properly. Option C (making R3 L1/L2) could help if R3 is the boundary router, but may not be sufficient for all missing routes. Option D placing R5 in R1's area without moving other routers may cause a split topology.

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