An L1 router has formed an adjacency with an L1-L2 router. Under which condition will the L1-L2 router set the attach bit in its Level 1 link-state PDUs?

Question

Options

• Awhen the L1-L2 router forms an adjacency with another L1 router in the same area
• Bwhen the L1-L2 router forms an adjacency with an L2 router in the same area
• Cwhen the L1-L2 router forms an adjacency with an L2 router in a different area
• Dwhen the L1-L2 router forms an adjacency with an L1 router in a different area

• A
  5% (2)
• B
  10% (4)
• C
  82% (32)
• D
  3% (1)

Explanation

L1 routers use L1/L2 routers as the next hop for the default route 0.0.0.0/0. The L1/L2 routers do not advertise a default route--instead, the L1/L2 routers set the attached bit, which is advertised to the L1 router and causes the L1 router to install a default route with the L1/L2 router as the If an L1/L2 router does not have an L2 adjacency to a different area than its own, the L1/L2 router will not set the attach bit, resulting in the L1 routers not installing a default route. Network Scaling With Bgp Labeled Unicast, Design and Configuration Guide, page 8

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