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Q301. Which OSPF command prevents OSPF from forming neighbor adjacencies on an interface while still allowing the connected network to be advertised?
1) passive-interface
2) shutdown
3) neighbor disable
4) no network
Correct Answer: 1) passive-interface
Explanation:
The OSPF passive-interface command prevents OSPF from sending Hello packets through the specified interface, which means dynamic OSPF neighbor adjacencies cannot form on that interface. However, the network connected to the passive interface can still be advertised through OSPF, making this command useful for user-facing LAN interfaces where no OSPF neighbor should exist. It also reduces unnecessary OSPF traffic and improves security by preventing unexpected devices from attempting to establish adjacencies. The command can be configured globally under the OSPF process and selectively disabled on interfaces that should actively form neighbor relationships.
Q302. In an OSPF broadcast network, which routers are elected to reduce the number of full adjacencies?
1) ABR and ASBR
2) DR and BDR
3) Root and backup root
4) Active and standby routers
Correct Answer: 2) DR and BDR
Explanation:
On OSPF broadcast multiaccess networks such as Ethernet, OSPF elects a Designated Router (DR) and a Backup Designated Router (BDR). The primary purpose is to reduce the number of OSPF adjacencies that would otherwise be required between every router on the segment. Routers establish full adjacencies with the DR and BDR rather than maintaining full relationships with every other router. The DR represents the segment when exchanging certain LSAs, while the BDR provides redundancy if the DR fails. Router priority influences the election, and a higher priority is preferred. A priority of zero prevents a router from becoming DR or BDR.
Q303. What is the primary purpose of increasing the OSPF reference bandwidth?
1) To reduce Hello packet frequency
2) To change router IDs automatically
3) To provide more accurate cost calculations on high-speed links
4) To disable ECMP
Correct Answer: 3) To provide more accurate cost calculations on high-speed links
Explanation:
OSPF calculates interface cost using bandwidth relative to a reference bandwidth. The default reference bandwidth was designed for older network speeds, so modern high-speed interfaces can all receive the same cost if the reference bandwidth is not adjusted. Increasing the reference bandwidth allows OSPF to distinguish between interfaces such as 1-Gbps, 10-Gbps, and higher-speed links. The change should normally be applied consistently across all routers participating in the OSPF domain. Otherwise, different routers may calculate different path costs, potentially producing unexpected routing decisions. The command commonly used is auto-cost reference-bandwidth.
Q304. Which OSPF network type normally performs a DR/BDR election?
1) Point-to-point
2) Loopback
3) Broadcast
4) Point-to-multipoint
Correct Answer: 3) Broadcast
Explanation:
OSPF uses different network types depending on the characteristics of the underlying interface. A broadcast network, such as a typical Ethernet segment, supports a DR and BDR election because multiple routers can share the same Layer 2 segment. The DR reduces the number of full OSPF adjacencies and manages certain LSA exchanges for the segment. Point-to-point networks do not require a DR or BDR because only two routers participate in the relationship. Point-to-multipoint networks also do not normally use DR/BDR elections. Understanding OSPF network types is important when troubleshooting adjacency formation and differences in neighbor states.
Q305. Which EIGRP feature allows a router to use multiple paths when their metrics are unequal?
1) Split horizon
2) Variance
3) Stub routing
4) Summarization
Correct Answer: 2) Variance
Explanation:
EIGRP supports unequal-cost load balancing through the variance feature. By default, EIGRP normally installs equal-cost paths when multiple feasible paths exist. Variance allows the router to install additional feasible paths whose metrics are higher than the best path, provided they satisfy the appropriate EIGRP feasibility requirements. The variance value acts as a multiplier of the best metric. For example, a variance of 2 permits eligible routes with metrics up to two times the minimum metric. This feature can improve traffic distribution and redundancy, but administrators should ensure that the alternate paths are actually feasible successors and that the resulting traffic distribution is appropriate for the network.
Q306. What is required for an EIGRP route to qualify as a feasible successor?
1) Its reported distance must be less than the successor’s feasible distance
2) Its administrative distance must be zero
3) Its metric must always equal the successor’s metric
4) It must be learned through an external protocol
Correct Answer: 1) Its reported distance must be less than the successor’s feasible distance
Explanation:
EIGRP uses the feasibility condition to determine whether an alternate route can safely become a feasible successor. The reported distance, also called the advertised distance, from the neighboring router must be less than the current successor’s feasible distance. This condition helps guarantee that the alternate path does not contain a routing loop. A feasible successor is particularly valuable because it can be installed quickly if the primary successor becomes unavailable, without requiring the router to perform a new route computation. If no feasible successor exists, EIGRP may need to query neighbors and potentially enter an Active state while searching for an alternate path.
Q307. Which EIGRP feature helps limit query propagation and improve scalability?
1) EIGRP stub
2) BGP confederation
3) OSPF NSSA
4) Route reflection
Correct Answer: 1) EIGRP stub
Explanation:
EIGRP stub routing helps limit the scope of EIGRP queries by informing neighboring routers that the stub router should not normally be used as a transit path for unknown destinations. This is particularly useful at branch offices, where the router may have only a few routes and should not be expected to provide alternate transit paths for the rest of the network. Limiting query propagation helps reduce unnecessary control-plane activity and can improve convergence in larger EIGRP deployments. EIGRP stub does not simply stop routing advertisements; instead, the router can advertise selected route types while restricting how it participates in route queries.
Q308. Which BGP attribute is commonly used to influence outbound traffic from an autonomous system?
1) MED
2) Local Preference
3) Originator ID
4) Cluster List
Correct Answer: 2) Local Preference
Explanation:
BGP Local Preference is an important attribute used to influence the path selected for traffic leaving an autonomous system. A higher Local Preference value is preferred, so administrators can use it to make one exit link more attractive than another. Unlike BGP Weight, Local Preference is an attribute that is propagated to other BGP routers within the same autonomous system, making it useful for consistent outbound traffic policy. It is commonly configured using route maps or applied through BGP policy mechanisms. Local Preference primarily controls outbound path selection, whereas MED is generally used to influence how neighboring autonomous systems enter the local network.
Q309. Which BGP origin code represents a route that was learned through an Interior Gateway Protocol?
1) ?
2) e
3) i
4) x
Correct Answer: 3) i
Explanation:
In BGP routing tables, the origin attribute indicates how a network prefix was originally introduced into BGP. The lowercase i represents IGP origin, which is considered the most preferable origin code during BGP route selection. A route with e represents EGP, an older mechanism that is rarely encountered in modern networks. A question mark ? represents an incomplete origin, commonly associated with redistribution into BGP. Origin is only one factor in the BGP best-path decision process, so it does not automatically mean a route with i will always be selected over another route. Other attributes, including Local Preference, AS_PATH, and MED, are evaluated according to the selection process.
Q310. What is the purpose of BGP conditional advertisement?
1) To advertise a route only when specified conditions are met
2) To encrypt BGP updates
3) To replace the BGP AS number
4) To disable route selection
Correct Answer: 1) To advertise a route only when specified conditions are met
Explanation:
BGP conditional advertisement allows a router to advertise certain routes only when defined conditions are satisfied. This can be useful for controlling backup connectivity, implementing specific routing policies, or advertising prefixes based on the presence or absence of another route. Instead of simply advertising a prefix continuously, the router evaluates a condition and determines whether the configured advertisement should occur. This capability can be valuable in multihomed networks where an organization wants a backup route to become visible only when a primary path is unavailable. Proper configuration requires careful consideration of route-policy logic so that the condition accurately reflects the intended network state.
Q311. Which command is useful for checking whether a BGP neighbor is exchanging prefixes and viewing the negotiated session information?
1) show ip ospf interface
2) show ip eigrp topology
3) show ip bgp summary
4) show mpls interfaces
Correct Answer: 3) show ip bgp summary
Explanation:
The show ip bgp summary command provides a concise overview of BGP neighbor relationships and is one of the most useful commands for initial BGP troubleshooting. It displays information such as the local router’s BGP identifier, local AS number, neighboring router addresses, remote AS numbers, message counts, session state, and the number of prefixes received from each neighbor. If the neighbor state is shown as Established, the BGP session has successfully formed. The prefix count can also help identify whether routes are actually being exchanged. When troubleshooting BGP, this command is often followed by more detailed commands such as show ip bgp neighbors.
Q312. In an MPLS Layer 3 VPN, which identifier distinguishes overlapping customer address spaces?
1) Route Distinguisher
2) VLAN ID
3) BGP Weight
4) OSPF Router ID
Correct Answer: 1) Route Distinguisher
Explanation:
An MPLS Layer 3 VPN uses a Route Distinguisher, or RD, to make customer prefixes unique within the provider’s VPNv4 address space. Different customers can use identical private IPv4 address ranges, such as 10.0.0.0/8, without causing ambiguity because the RD is combined with the IPv4 prefix to create a unique VPNv4 route. The RD provides uniqueness but does not determine which VPNs are allowed to import or export routes. That function is handled by Route Targets. Therefore, administrators should distinguish between the RD’s role in making overlapping prefixes unique and the RT’s role in controlling VPN route membership.
Q313. What is the primary purpose of a Route Target in an MPLS L3VPN?
1) To calculate the OSPF cost
2) To control VPN route import and export
3) To assign MPLS labels to interfaces
4) To select the BGP router ID
Correct Answer: 2) To control VPN route import and export
Explanation:
Route Targets are extended BGP communities used in MPLS Layer 3 VPNs to control which VPN routes are exported from and imported into VRFs. When a provider edge router advertises a VPN route, it can attach one or more export Route Targets. A VRF then uses import Route Targets to determine which VPN routes should be installed in that VRF’s routing table. This mechanism enables flexible connectivity models such as full mesh, hub-and-spoke, and shared-services designs. Route Targets should not be confused with Route Distinguishers. The RD creates uniqueness for overlapping prefixes, while RTs control route distribution and VPN membership.
Q314. In an MPLS network, what information does the VPN label primarily identify?
1) The customer’s VPN/VRF forwarding context
2) The physical Ethernet port
3) The BGP autonomous system number
4) The OSPF area number
Correct Answer: 1) The customer’s VPN/VRF forwarding context
Explanation:
In an MPLS Layer 3 VPN, the VPN label identifies the appropriate VPN forwarding context on the provider edge router. A typical packet may carry an outer transport label used to reach the egress PE and an inner VPN label that tells the egress PE which VRF should process the packet. This label separation allows the MPLS core to transport traffic without needing customer-specific routing information in every P router. The transport label is concerned with reaching the appropriate provider edge, while the VPN label provides the information necessary for final customer-specific forwarding. This separation is fundamental to scalable MPLS VPN architecture.
Q315. Which DMVPN component provides the Next Hop Resolution Protocol service for spoke routers?
1) NHRP NHS
2) BGP route reflector
3) OSPF DR
4) MPLS PE
Correct Answer: 1) NHRP NHS
Explanation:
In a traditional DMVPN design, the hub router commonly acts as the NHRP Next Hop Server, or NHS. Spoke routers register their public tunnel addresses with the NHS, allowing the hub to maintain mappings between tunnel addresses and NBMA addresses. These mappings are then used to help establish dynamic spoke-to-spoke communication depending on the DMVPN phase and routing design. The NHRP NHS is therefore a central component of the DMVPN control mechanism. In Phase 1, traffic generally passes through the hub, while later DMVPN phases can use NHRP information to create more direct spoke-to-spoke forwarding paths.
Q316. Which DMVPN technology allows multiple remote sites to share a single multipoint GRE tunnel interface?
1) IPsec transport mode
2) mGRE
3) GRE point-to-point
4) L2TP
Correct Answer: 2) mGRE
Explanation:
Multipoint GRE, or mGRE, allows a single tunnel interface to communicate dynamically with multiple remote tunnel endpoints. This capability is a fundamental component of DMVPN because it avoids the need to manually configure a separate point-to-point GRE tunnel for every spoke relationship. NHRP works alongside mGRE to resolve tunnel addresses to the appropriate NBMA addresses. IPsec can then provide encryption for the GRE traffic. The combination of mGRE, NHRP, and IPsec provides a scalable framework for dynamic VPN connectivity. Without mGRE, a large hub-and-spoke network would require many individually configured GRE tunnel interfaces, creating significant administrative overhead.
Q317. Which IPsec mode encrypts the entire original IP packet and adds a new outer IP header?
1) Transport mode
2) Tunnel mode
3) Access mode
4) Routing mode
Correct Answer: 2) Tunnel mode
Explanation:
IPsec tunnel mode encapsulates the original IP packet inside a new IP packet. The original packet, including its original IP header, is protected, and a new outer IP header is added for routing across the network. This makes tunnel mode especially suitable for site-to-site VPNs, where traffic travels between private networks through an untrusted intermediate network. In contrast, transport mode primarily protects the payload of the original IP packet while retaining the original IP header. Tunnel mode is widely used by IPsec VPN gateways because it provides a clear separation between the protected internal packet and the public addressing used to transport the VPN packet.
Q318. Which QoS component defines the conditions used to classify traffic into a traffic class?
1) class-map
2) route-map
3) crypto-map
4) access-map
Correct Answer: 1) class-map
Explanation:
In Cisco MQC-based QoS configuration, a class-map defines the criteria used to identify and classify traffic. It can match characteristics such as access control lists, DSCP values, IP precedence, protocols, or other supported packet attributes. The resulting traffic class can then be referenced by a policy-map, where actions such as marking, policing, shaping, queuing, or bandwidth allocation are configured. This separation between classification and policy action makes QoS configuration modular and easier to manage. The class map answers the question of which traffic belongs to a class, while the policy map determines what treatment that traffic receives.
Q319. Which DSCP value is commonly associated with Expedited Forwarding for voice traffic?
1) AF11
2) CS1
3) EF
4) BE
Correct Answer: 3) EF
Explanation:
Expedited Forwarding, or EF, is commonly used for latency-sensitive traffic such as voice media. EF is represented by DSCP value 46 and is designed to receive low-delay, low-jitter treatment when the network is properly configured for QoS. Voice traffic is sensitive to packet delay, jitter, and loss, so placing voice packets into an appropriate priority queue can improve call quality during congestion. However, simply marking packets as EF does not guarantee priority treatment. Network devices must also be configured to recognize the marking and apply the intended queuing policy. QoS should therefore be designed as an end-to-end strategy rather than relying only on packet markings.
Q320. Which HSRP feature allows a router with a higher priority to become active after it becomes available again?
1) Authentication
2) Preemption
3) Object tracking
4) Load balancing
Correct Answer: 2) Preemption
Explanation:
HSRP preemption allows a router with a higher configured HSRP priority to take over the Active role when it becomes available again. Without preemption, a router that originally had the higher priority may remain in a standby or other state after recovering from an outage, depending on the current HSRP state. Enabling preemption ensures that the preferred router can reclaim the Active role according to the configured priority. This is useful when administrators want a specific router to be the normal gateway because it has better connectivity or resources. HSRP object tracking can also modify priority based on interface or tracked-object status, but preemption controls whether the higher-priority router actually retakes the Active role.