What is one of the configuration errors within an AS that can stop a Cisco IOS-XR router from announcing certain prefixes to its EBGP peers?

Question

Options

• ASome prefixes were mistagged with the no-export BGP community
• BSome prefixes were set with an MED of 0
• CThe outbound BGP route policy only has set actions defined without any pass actions defined
• DThe inbound BGP route policy only has set actions defined without any pass actions defined

• A
  88% (22)
• B
  8% (2)
• D
  4% (1)

Explanation

The BGP 'no-export' well-known community (value 0xFFFFFF01) explicitly instructs a BGP router not to advertise tagged prefixes to any EBGP peers. If an operator accidentally applies the no-export community to prefixes via a route policy or static configuration, those prefixes will be withheld from all external BGP peers even though they exist in the local BGP table. This is a silent error - the router holds the prefix internally but never sends it to EBGP neighbors. Option B (MED of 0) is the default and does not block advertisement. Option C describes an IOS-XR policy issue but pertains to all routes being dropped, not selective prefix suppression. Option D (inbound policy issues) affects what the router accepts, not what it announces.

No community discussion yet for this question.