Refer to the exhibit. A service provider is running IS-IS in the core, and all routers use the default IS-IS configuration and reside in the same area. All routers maintain a different 6 bytes for…

Question

Exhibit

Options

• AConfigure all routers to operate as IS-IS Level 1 routers by altering the attached bit to ensure that
• BConfigure routers RS and R3 to operate as Level 1 routers only so that they inject a default
• CConfigure R6 to operate as a Level 1 router only so that it maintains the Level 1 database for all
• DConfigure all routers to operate as IS-IS Level 2 routers so that only a Level 2 database is

• A
  17% (4)
• B
  9% (2)
• C
  4% (1)
• D
  70% (16)

Explanation

In IS-IS, a router operating as Level 1-2 (the default) maintains both a Level 1 (intra-area) and Level 2 (inter-area/backbone) link-state database. The 'attached bit' in a router's LSP signals to Level 1 routers that this L1/L2 router can reach the Level 2 backbone. The problem states that all routers have the same attached bit setting, meaning all are operating as L1/L2 by default. When router R6 was added, it introduced more L1/L2 routers, increasing LSP flooding in the Level 1 domain and causing CPU issues on R3 and RS due to excessive SPF calculations triggered by the larger, constantly updating L1 database. The solution is to configure all routers as Level 2 only. This eliminates the Level 1 database entirely - there is only a single Level 2 database, reducing flooding, SPF frequency, and CPU load. Options A and B involve partial solutions that don't eliminate the underlying L1 database overhead. Option C only changes R6, which doesn't resolve the systemic issue.

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