Customer XYZ network consists of an MPLS core. IS-IS running as IGP a pair of BGP route reflectors for route propagation, and a few dozens of MPLS-TE tunnels for specific tactical traffic…

Question

Options

• AIt can be set on a router during the startup process for a fixed period of time
• BNetworks advertised within the LSPs of the respective node will become unreachable
• CIt forces the midpoint MPLS-TE node to reoptimize the primary tunnels going through the OL
• DIt can be set on a router until other interacting protocols have signaled convergence.
• EIt is not recommended on BGP Route Reflectors

• A
  71% (45)
• B
  16% (10)
• C
  8% (5)
• E
  5% (3)

Explanation

The IS-IS Overload Bit (OL bit), when set, signals to other routers not to use this router as a transit hop in SPF calculations, preventing traffic from being forwarded through it while it is not yet ready. A is true: the OL bit can be set at startup for a fixed configurable time period (e.g., 'set-overload-bit on-startup 300'), giving routing protocols time to populate tables before traffic is forwarded through the node. D is true: the OL bit can also be held set until BGP or other interacting protocols signal convergence (e.g., 'set-overload-bit on-startup wait-for-bgp'), which is a common and recommended practice on BGP route reflectors to prevent black-holing traffic before BGP is fully converged. B is false: the router's own directly attached prefixes remain reachable even when the OL bit is set - only transit paths through the router are avoided. C is false: the OL bit does not force MPLS-TE midpoint nodes to reoptimize existing established tunnels; existing RSVP-signaled LSPs remain in place. E is false: using the OL bit on BGP route reflectors is actually a recommended best practice.

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