Question

A service provider runs a two-level IS-IS domain. Branch routers in a Level 1 area only receive a default route toward the nearest L1/L2 router via the ATT bit, which causes suboptimal exit selection when a specific prefix in another area is actually best reached through a different L1/L2 router. The network engineer wants the L1 routers to make optimal forwarding decisions for a set of important L2 prefixes without converting the entire area to Level 1-2. Which action achieves this?

Accepted Answer

Configure route leaking on the L1/L2 routers to redistribute selected L2 prefixes into Level 1 with the up/down bit set

Answer

Set the overload bit on the L1/L2 routers so L1 routers prefer the closest exit only

Answer

Widen the IS-IS metric style to narrow on the L1 routers so they accept external routes

Answer

Disable the ATT bit on all L1/L2 routers to force full topology flooding into Level 1