350-401 · topic practice
Practise ENCOR 350-401 Bgp practice questions — original exam-style scenarios with answer choices, explanations, and analysis of common mistakes.
Courseiva uses original exam-style practice questions designed for learning and revision. The goal is to understand the concepts, recognise exam patterns, and improve through explanations — not memorise copied exam dumps.
What the exam tests
BGP questions usually test path selection attributes (AS-PATH, LOCAL_PREF, MED), eBGP vs iBGP rules, and why a route may be received but not used.
Watch out for
Practice set
20 questions · select your answer, then reveal the explanation
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Device hostname, vendor, model, OS version, serial number
Interface name, description, IP address, status, speed
BGP neighbor IP, remote AS, state, uptime
LLDP neighbor device ID, port ID, platform
Power supply, fan, temperature status
Drag steps to the numbered slots on the right, or tap a step then tap a slot.
Drag steps to the numbered slots on the right, or tap a step then tap a slot.
Trap 1: Weight
Incorrect. Weight is preferred with the highest value, not the lowest.
Trap 2: Local Preference
Incorrect. Local preference is preferred with the highest value.
Trap 3: AS Path Length
Incorrect. AS path length is preferred with the shortest length (lowest number of ASes), but it is not a single value attribute like MED.
Weight
Why wrong: Incorrect. Weight is preferred with the highest value, not the lowest.
Local Preference
Why wrong: Incorrect. Local preference is preferred with the highest value.
MED (Multi-Exit Discriminator)
Correct. MED is a metric that is preferred with the lowest value.
AS Path Length
Why wrong: Incorrect. AS path length is preferred with the shortest length (lowest number of ASes), but it is not a single value attribute like MED.
Trap 1: The AS-path contains the local AS number.
This is incorrect. While an AS-path containing the local AS number can cause routes to be rejected due to loop prevention, the typical symptom is routes not being received at all or being marked as invalid, not the specific 'received but not valid' status. The most common cause for 'not valid' is next-hop unreachability.
Trap 2: BGP synchronization is enabled.
This is incorrect. BGP synchronization is a legacy feature that requires the route to be in the IGP before it is advertised. In modern networks, synchronization is disabled by default. Even if enabled, it affects advertisement, not the validity of received routes in the BGP table.
Trap 3: The maximum-prefix limit has been exceeded.
This is incorrect. Exceeding the maximum-prefix limit typically causes the BGP session to reset or routes to be withdrawn, not to be marked as 'not valid' in the BGP table. Routes would likely be removed entirely, not just marked invalid.
The AS-path contains the local AS number.
Why wrong: This is incorrect. While an AS-path containing the local AS number can cause routes to be rejected due to loop prevention, the typical symptom is routes not being received at all or being marked as invalid, not the specific 'received but not valid' status. The most common cause for 'not valid' is next-hop unreachability.
The next-hop IP address is not reachable.
Correct. For a BGP route to be considered valid and installed in the routing table, the next-hop IP address must be reachable via an IGP or static route. If the next hop is not reachable, the route will appear in the 'show ip bgp' output but be marked as not valid.
BGP synchronization is enabled.
Why wrong: This is incorrect. BGP synchronization is a legacy feature that requires the route to be in the IGP before it is advertised. In modern networks, synchronization is disabled by default. Even if enabled, it affects advertisement, not the validity of received routes in the BGP table.
The maximum-prefix limit has been exceeded.
Why wrong: This is incorrect. Exceeding the maximum-prefix limit typically causes the BGP session to reset or routes to be withdrawn, not to be marked as 'not valid' in the BGP table. Routes would likely be removed entirely, not just marked invalid.
Drag steps to the numbered slots on the right, or tap a step then tap a slot.
Drag a concept onto its matching description — or click a concept then click the description.
Carries IPv4 VPN routes with MPLS labels across the provider core
Carries IPv6 VPN routes with MPLS labels across the provider core
Carries global IPv4 unicast routes (non-VPN)
Carries global IPv6 unicast routes (non-VPN)
Carries Layer 2 VPN information such as pseudowires and VPLS
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Trap 1: A route reflector client must be fully meshed with all other…
Incorrect: Route reflector clients do not need to be fully meshed; they only peer with the route reflector.
Trap 2: The route reflector modifies the AS_PATH attribute to prevent loops.
Incorrect: Route reflectors do not modify AS_PATH; they use the CLUSTER_LIST and ORIGINATOR_ID attributes for loop prevention.
Route reflectors allow iBGP speakers to advertise routes learned from other iBGP speakers without requiring a full mesh.
Correct: This is the primary purpose of route reflectors; they relax the full mesh requirement.
A route reflector client must be fully meshed with all other clients in the same cluster.
Why wrong: Incorrect: Route reflector clients do not need to be fully meshed; they only peer with the route reflector.
The route reflector can be a client of another route reflector.
Correct: Route reflectors can be hierarchical; a route reflector can be a client of another route reflector in a different cluster.
The cluster ID is used to prevent routing loops in a route reflector environment.
Correct: The cluster ID is added to the CLUSTER_LIST attribute to detect and prevent loops.
The route reflector modifies the AS_PATH attribute to prevent loops.
Why wrong: Incorrect: Route reflectors do not modify AS_PATH; they use the CLUSTER_LIST and ORIGINATOR_ID attributes for loop prevention.
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Well-known mandatory
Well-known discretionary
Optional transitive
Optional non-transitive
Well-known mandatory
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Highest
Highest
Lowest
Lowest
Lowest
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Establishes a BGP session and negotiates capabilities
Advertises new routes or withdraws previously advertised routes
Reports an error condition and closes the BGP session
Periodically sent to keep the BGP session alive
Requests that a peer readvertise its routes
Drag a concept onto its matching description — or click a concept then click the description.
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Trap 1: MED is an optional transitive attribute.
Incorrect: MED is optional non-transitive; it is not passed to other ASes and is used to influence inbound traffic.
Trap 2: ORIGIN is a well-known discretionary attribute used for loop…
Incorrect: ORIGIN is well-known mandatory, not discretionary, and it indicates the origin of the route (IGP, EGP, or incomplete), not used for loop prevention.
Trap 3: NEXT_HOP is an optional non-transitive attribute.
Incorrect: NEXT_HOP is well-known mandatory, not optional non-transitive; it specifies the next-hop IP address to reach a prefix.
AS_PATH is a well-known mandatory attribute.
Correct: AS_PATH is well-known mandatory; it is always included in BGP updates and is used for loop prevention and path selection.
LOCAL_PREF is a well-known discretionary attribute.
Correct: LOCAL_PREF is well-known discretionary; it is recognized by all BGP speakers but may or may not be included in updates, and it influences outbound traffic.
MED is an optional transitive attribute.
Why wrong: Incorrect: MED is optional non-transitive; it is not passed to other ASes and is used to influence inbound traffic.
ORIGIN is a well-known discretionary attribute used for loop prevention.
Why wrong: Incorrect: ORIGIN is well-known mandatory, not discretionary, and it indicates the origin of the route (IGP, EGP, or incomplete), not used for loop prevention.
NEXT_HOP is an optional non-transitive attribute.
Why wrong: Incorrect: NEXT_HOP is well-known mandatory, not optional non-transitive; it specifies the next-hop IP address to reach a prefix.
Trap 1: P routers in the MPLS core must maintain a full routing table for…
Incorrect because P routers only need IGP routes to forward MPLS packets; they do not participate in VPN routing.
Trap 2: CE routers must run MPLS and participate in the label distribution…
Incorrect because CE routers are standard IP routers; they do not run MPLS and exchange only IP routes with the PE.
Trap 3: The MPLS label stack in a Layer 3 VPN always contains exactly one…
Incorrect because the label stack typically has two labels: an IGP label (for transport) and a VPN label (for the egress PE).
PE routers use MP-BGP to exchange VPNv4 routes that include the route distinguisher and the VPN label.
Correct because MP-BGP carries VPNv4 routes (with route distinguisher) and the VPN label in the NLRI, enabling MPLS Layer 3 VPN operation.
P routers in the MPLS core must maintain a full routing table for each customer VRF.
Why wrong: Incorrect because P routers only need IGP routes to forward MPLS packets; they do not participate in VPN routing.
CE routers must run MPLS and participate in the label distribution with the PE router.
Why wrong: Incorrect because CE routers are standard IP routers; they do not run MPLS and exchange only IP routes with the PE.
Each VRF on a PE router maintains a separate routing table and forwarding table per customer.
Correct because a VRF creates an isolated routing and forwarding instance for each customer on the PE.
The MPLS label stack in a Layer 3 VPN always contains exactly one label.
Why wrong: Incorrect because the label stack typically has two labels: an IGP label (for transport) and a VPN label (for the egress PE).
Trap 1: The MPLS core routers (P routers) maintain full VPN routing tables…
Incorrect because P routers only swap MPLS labels and do not maintain VPN routing tables; they are label-switching routers.
Trap 2: Route targets (RT) are used to uniquely identify each customer VPN…
Incorrect because route distinguishers (RD) ensure uniqueness of VPN prefixes, while RTs control route import/export policies.
Customer edge (CE) routers exchange routing information with provider edge (PE) routers using static routing, RIP, OSPF, EIGRP, or BGP.
Correct because PE-CE routing can use any of these protocols, as supported by the provider's configuration.
VRF (Virtual Routing and Forwarding) instances are used on PE routers to maintain separate routing tables for each VPN customer.
Correct because VRFs isolate customer routes on the PE, ensuring traffic separation.
MP-BGP (Multiprotocol BGP) is used between PE routers to exchange VPNv4 routes, which include an RD and RT.
Correct because MP-BGP carries VPN-IPv4 prefixes with route distinguishers (RD) and route targets (RT) for VPN membership.
The MPLS core routers (P routers) maintain full VPN routing tables to forward traffic based on customer IP prefixes.
Why wrong: Incorrect because P routers only swap MPLS labels and do not maintain VPN routing tables; they are label-switching routers.
Route targets (RT) are used to uniquely identify each customer VPN across the provider network.
Why wrong: Incorrect because route distinguishers (RD) ensure uniqueness of VPN prefixes, while RTs control route import/export policies.
A network engineer runs the following command on Router R1:
R1# show policy-map control-plane
Control Plane
Service-policy input: CoPP-POLICY
Class-map: BGP-CLASS (match-all) 50 packets, 2500 bytes 5 minute offered rate 500 bps Match: access-group name BGP-ACL police: cir 64000 bps, bc 8000 bytes, be 8000 bytes conformed 50 packets, 2500 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop
Class-map: SNMP-CLASS (match-all) 200 packets, 10000 bytes 5 minute offered rate 2000 bps Match: access-group name SNMP-ACL police: cir 16000 bps, bc 2000 bytes, be 2000 bytes conformed 150 packets, 7500 bytes; actions: transmit exceeded 40 packets, 2000 bytes; actions: drop violated 10 packets, 500 bytes; actions: drop
Class-map: class-default (match-any) 100 packets, 5000 bytes 5 minute offered rate 1000 bps Match: any police: cir 32000 bps, bc 4000 bytes, be 4000 bytes conformed 100 packets, 5000 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop
Based on this output, what can be concluded?
Trap 1: BGP traffic is being dropped because it exceeds the CIR.
BGP shows all 50 packets conformed, so no drops.
Trap 2: All traffic to the control plane is being dropped.
Only SNMP traffic is being partially dropped; BGP and class-default have no drops.
Trap 3: The control-plane policy is applied in the output direction.
The service-policy is input, so it is inbound.
SNMP traffic to the control plane is experiencing drops due to exceeding its policer rate, while BGP traffic is within its rate.
The SNMP class shows 150 conformed and 50 dropped (exceeded+violated), while BGP shows all 50 conformed.
BGP traffic is being dropped because it exceeds the CIR.
Why wrong: BGP shows all 50 packets conformed, so no drops.
All traffic to the control plane is being dropped.
Why wrong: Only SNMP traffic is being partially dropped; BGP and class-default have no drops.
The control-plane policy is applied in the output direction.
Why wrong: The service-policy is input, so it is inbound.
Trap 1: The BGP neighbor is not configured with the password command.
Incorrect because a password is not required for BGP to come up.
Trap 2: The route-target import/export values are incorrect for the…
Incorrect because route-targets affect VPNv4 route distribution, not the BGP session directly.
Trap 3: The engineer forgot to configure the VRF under the BGP router-id.
Incorrect because the router-id is global and not VRF-specific.
The IP address on the interface was removed when the VRF was applied, and it was not reconfigured.
Correct because the ip vrf forwarding command clears the IP address on the interface, requiring it to be re-entered.
The BGP neighbor is not configured with the password command.
Why wrong: Incorrect because a password is not required for BGP to come up.
The route-target import/export values are incorrect for the customer.
Why wrong: Incorrect because route-targets affect VPNv4 route distribution, not the BGP session directly.
The engineer forgot to configure the VRF under the BGP router-id.
Why wrong: Incorrect because the router-id is global and not VRF-specific.
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Trap 1: VRF-lite supports MPLS VPN inter-AS option B.
Incorrect because VRF-lite does not include MPLS functionality.
Trap 2: VRF-lite requires BGP as the routing protocol between VRFs.
Incorrect because VRF-lite can use any routing protocol or static routes.
VRF-lite allows multiple routing instances on a single router using static or dynamic routing protocols.
Correct because VRF-lite supports RIP, EIGRP, OSPF, and static routes per VRF.
VRF-lite does not require MPLS to operate.
Correct because VRF-lite is a pure Layer 3 VPN without label switching.
VRF-lite provides path isolation by maintaining separate forwarding tables.
Correct because each VRF has independent routing and forwarding tables.
VRF-lite supports MPLS VPN inter-AS option B.
Why wrong: Incorrect because VRF-lite does not include MPLS functionality.
VRF-lite requires BGP as the routing protocol between VRFs.
Why wrong: Incorrect because VRF-lite can use any routing protocol or static routes.
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