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Topic: BGPSwitch
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3.0 Infrastructure

BGP Practice Questions

BGP path selection, attributes, route reflectors, and communities.

One solved question, so you can see how these are marked

Which Cisco-proprietary BGP path-selection value, set locally on a router and never sent to any peer, is evaluated before all other attributes?

Weight

Weight is a Cisco-defined value assigned locally on a router. It is not a BGP path attribute carried in UPDATE messages and is never advertised to neighbors. Higher weight is preferred, and it is checked before Local Preference and every other step.

Every question in the set below is marked like this. The answers stay hidden until you pick one.

All 17 BGP questions in this set

Answers and explanations appear when you work through the set above.

  1. In BGP, which state is entered after the TCP connection succeeds and the local router has sent its OPEN message while awaiting the peer's OPEN?

    • Active
    • Connect
    • OpenSent
    • OpenConfirm

  2. If a Cisco router receives two BGP paths for the same prefix with identical Weight and Local Preference values, which decision criteria is evaluated next?

    • Shortest AS_PATH length (fewest autonomous systems listed)
    • Locally originated (network or aggregate-address)
    • Lowest MED value received from the neighbor AS
    • Lowest BGP router ID of the advertising peer

  3. Which well-known BGP community lets a route be advertised to iBGP peers but stops it from being advertised to any eBGP peer?

    • no-advertise
    • no-export
    • internet
    • gshut

  4. To prevent routing loops, what two BGP path attributes are appended by a BGP Route Reflector when re-advertising reflected routes to client peers?

    • AS_PATH and NEXT_HOP
    • ORIGINATOR_ID and CLUSTER_LIST
    • LOCAL_PREF and WEIGHT
    • COMMUNITY and EXTENDED_COMMUNITY

  5. Which statement correctly describes the behavior of the BGP Multi-Exit Discriminator (MED) attribute?

    • MED is a well-known mandatory attribute that is passed unchanged across every Autonomous System on the Internet.
    • MED is optional non-transitive, sent to eBGP neighbors to suggest the preferred entry point into the AS.
    • Higher MED values are preferred over lower MED values when comparing paths from the same neighboring AS.
    • MED is evaluated before Local Preference, so it overrides the outbound exit choice made inside the AS.

  6. In Policy-Based Routing (PBR), what is the key functional difference between set ip next-hop and set ip default next-hop?

    • set ip next-hop is used only after the routing table lookup fails; set ip default next-hop ignores the routing table entirely.
    • set ip next-hop is applied before the routing table lookup; set ip default next-hop is used only if no explicit route exists.
    • set ip default next-hop applies only to IPv6 traffic, while set ip next-hop applies only to IPv4 traffic.
    • set ip next-hop requires an established BGP peering to the next hop; set ip default next-hop works with any IGP.

  7. What is the default Administrative Distance (AD) for an External BGP (eBGP) route and an Internal BGP (iBGP) route in Cisco IOS XE?

    • eBGP = 20, iBGP = 200
    • eBGP = 110, iBGP = 120
    • eBGP = 90, iBGP = 170
    • eBGP = 20, iBGP = 110

  8. When evaluating candidate BGP paths, which path attribute priority rank is highest according to standard Cisco BGP selection order?

    • Local Preference
    • Weight
    • AS-Path Length
    • Lowest MED

  9. Why does Internal BGP (iBGP) enforce the split horizon rule prohibiting a router from re-advertising routes learned from one iBGP peer to another iBGP peer?

    • To reduce memory use on routers in a full-mesh design by halving the number of stored paths.
    • To prevent loops inside the AS, because iBGP does not add the local AS number to AS_PATH.
    • To keep MPLS label distribution bounded to the routers that run LDP inside the AS.
    • To make the router prefer eBGP-learned routes over iBGP-learned routes for the same prefix.

  10. Which BGP attribute is automatically added by a Route Reflector to identify the originator of a route within the local Autonomous System to prevent loops?

    • Cluster_List
    • Originator_ID
    • AS_Path
    • Extended Community

  11. Which well-known BGP community attribute prevents a route from being advertised to any BGP peer (both eBGP and iBGP)?

    • no-export
    • no-advertise
    • local-AS
    • graceful-shutdown

  12. How does the BGP Local Preference (LOCAL_PREF) attribute affect traffic routing decisions inside an Autonomous System?

    • It tells neighboring ASes which entry point to use when sending traffic into the local AS.
    • It selects the exit path for outbound traffic leaving the AS (higher value preferred).
    • It limits route propagation to the local subnets attached to the advertising router.
    • It is a non-transitive attribute sent to eBGP peers to influence their path choice.

  13. If a BGP router receives two routes for the exact same destination prefix with identical Weight, Local Preference, Originate status, and AS_Path length, which criterion is evaluated next in standard Cisco BGP path selection?

    • Lowest MED (Multi-Exit Discriminator)
    • Lowest Router ID
    • Origin Type (IGP < EGP < Incomplete)
    • Oldest eBGP route

  14. What is the administrative purpose of applying BGP AS-Path Prepending to outgoing route updates sent to an eBGP neighbor?

    • To increase the CPU priority given to incoming BGP updates so the router converges faster.
    • To force internal iBGP peers to drop external default routes learned through that eBGP neighbor.
    • To make the path look longer so other ASes prefer a different entry link for inbound traffic.
    • To replace private AS numbers with the public AS number before routes leave the local AS.

  15. What action does a BGP router take when it receives a route tagged with the well-known NO_EXPORT community attribute?

    • It drops the route immediately and removes it from the BGP table on receipt.
    • It advertises the route to iBGP peers but not to eBGP peers outside the AS.
    • It advertises the route to eBGP peers only and withholds it from iBGP peers.
    • It accepts the route into the BGP table but keeps it out of the IP routing table.

  16. Which characteristic accurately describes the BGP Weight attribute in Cisco IOS/IOS XE devices?

    • It is carried in BGP UPDATE messages and propagated to eBGP peers outside the local Autonomous System.
    • It is Cisco-proprietary and local to the router; higher wins, and it is never sent to any neighbor.
    • Lower Weight values take precedence over higher Weight values during best-path selection.
    • It is exchanged only between iBGP route reflectors and their clients inside the local AS.

  17. Which two BGP attributes are appended by a Route Reflector to prevent routing loops within an iBGP topology?

    • AS_PATH and Multi-Exit Discriminator (MED)
    • ORIGINATOR_ID and CLUSTER_LIST
    • LOCAL_PREF and Community String
    • Weight and Next-Hop Unchanged