Cisco 300-510 Exam Dumps & Practice Test Questions
Question 1:
After updating the IP address on a Cisco IOS XR router, you find that the new address cannot be pinged. What is the likely configuration step you overlooked?
A. Apply the configuration with the commit command
B. Revert to the previous configuration
C. Integrate the new settings using a merge command
D. Save the active configuration to memory
Answer: A
Explanation:
On a Cisco IOS XR router, configuration changes are made in a candidate configuration area and do not affect the active, running configuration until they are explicitly committed. This behavior differs from traditional IOS, where changes typically take effect immediately. After entering configuration commands in IOS XR, they are staged and stored temporarily until a commit command is issued. Only after this command is executed do the changes become part of the router's operational configuration.
If you change the IP address of an interface but forget to issue the commit command, the change remains in the staging area and is not applied. Consequently, the interface does not receive the new IP address, and any attempt to ping the new address will fail, as the change has not been activated on the device.
Option A is the correct choice because applying the configuration with the commit command is the essential step required to make the new IP address take effect. Until that step is completed, the router continues to operate with its previously active configuration, and the new address will be non-functional.
Option B, reverting to the previous configuration, is not necessary unless the current changes are causing issues. In this case, the issue is that the change has not been applied, not that it needs to be undone. Option C, integrating the new settings using a merge command, does not apply in IOS XR in this context. Merging is more relevant in configuration management systems or versioning, not for making configuration changes active. Option D, saving the active configuration to memory (e.g., using copy running-config startup-config in IOS), is important for persistence across reboots but has no effect on making the configuration live. The configuration must first be committed before it can be saved.
Therefore, the most likely reason why the new IP address cannot be pinged is that the administrator forgot to commit the changes, leaving them in the candidate configuration.
Question 2:
Which two of the following statements accurately describe route reflector behavior? (Select two.)
A. Routes learned from non-client peers are forwarded to both clients and other non-client peers
B. Routes received from non-client peers are shared with the route reflector cluster and OSPF neighbors
C. A router discards iBGP routes that list its own router ID in the originator-ID attribute
D. Routes from route reflector clients are advertised to both other clients and non-clients
E. A route with a different cluster ID in the cluster-list is dropped by the route reflector
Answer: C, D
Explanation:
Route reflectors are used in BGP (specifically iBGP) to reduce the number of peer-to-peer connections required in a full mesh topology. They allow certain iBGP-learned routes to be reflected to other iBGP peers under controlled conditions, avoiding the typical iBGP rule that iBGP routes must not be advertised to other iBGP peers.
Option C is correct. A router discards iBGP routes that contain its own router ID in the originator-ID attribute. This mechanism is used to prevent routing loops in a route reflector environment. The originator-ID is inserted by the route reflector to identify the original source of the route, and if that same router sees a route with its own ID, it knows it is a looped advertisement and discards it.
Option D is also correct. A route reflector advertises routes received from a client to both non-client peers and other clients. This behavior is what allows route reflectors to break the iBGP full-mesh rule. Without it, clients would not be able to learn routes from each other unless they were fully meshed. Reflecting routes from one client to others ensures proper route dissemination.
Option A is incorrect. A route reflector does not forward routes learned from non-client peers to other non-client peers. This is to maintain iBGP’s original rule: iBGP-learned routes must not be passed to other iBGP peers unless they are clients. Only routes from clients are reflected to all peers. This limits loops and maintains routing integrity.
Option B is misleading. Routes received from non-client peers may be shared with clients (if certain criteria are met), but not with the entire cluster or with OSPF neighbors, since BGP and OSPF are separate routing protocols with no automatic redistribution between them. Any such redistribution must be configured explicitly.
Option E is incorrect. A route with a different cluster ID in the cluster-list is not automatically dropped. Instead, route reflectors use the cluster-list attribute to detect loops in the route reflector hierarchy. If the router sees its own cluster ID in the list, then it discards the route. Merely having a different cluster ID does not cause the route to be dropped.
Therefore, the accurate descriptions of route reflector behavior are C and D.
Question 3:
Which two statements are true regarding how multicast IP addresses map to MAC addresses? (Select two.)
A. All multicast MAC addresses start with the prefix 0x0100.5E
B. The router performs the IP-to-MAC mapping before sending the packet to the switch
C. Every multicast MAC address ends with 0x0100.5E
D. The mapping method can lead to duplicate MAC addresses, causing unintended packet delivery
E. All destination MAC addresses begin with a byte of all binary 1s
Answer: A, D
Explanation:
Multicast IP addresses are mapped to multicast MAC addresses using a specific algorithm defined by the IEEE and IANA. This is essential for ensuring that Ethernet frames carrying multicast IP packets can be correctly delivered at the data link layer to the intended recipients.
Option A is correct. All multicast MAC addresses used for IPv4 multicast traffic start with the prefix 01:00:5E. This prefix is assigned by the IEEE for multicast use. It identifies the address as a Layer 2 multicast address and ensures that switches and network interface cards (NICs) treat these frames appropriately.
Option D is also correct. The IP-to-MAC mapping process uses only the lower 23 bits of the multicast IP address to form the MAC address. However, since IPv4 multicast addresses are 28 bits in the address space (224.0.0.0/4), this truncation can result in overlapping MAC addresses for different multicast IPs. This overlapping creates the possibility of MAC address collisions, where different multicast IP addresses map to the same MAC address. As a result, a host may receive packets for a multicast group it did not subscribe to, leading to unintended packet delivery.
Option B is incorrect. The IP-to-MAC mapping is not performed solely by the router before sending traffic to the switch. It is primarily used by network devices and interfaces when encapsulating multicast IP packets into Ethernet frames. All multicast receivers on the local segment use this mapping to determine what MAC address to listen for based on the multicast IP address.
Option C is incorrect because not all multicast MAC addresses end with 0x0100.5E. That is a prefix, not a suffix. The remainder of the MAC address depends on the last 23 bits of the multicast IP address, not on a fixed ending.
Option E is incorrect because multicast MAC addresses do not begin with a byte of all binary 1s. Instead, they start with a defined 24-bit prefix (01:00:5E). A byte of all 1s (0xFF) is reserved for special purposes like broadcast, not multicast.
Therefore, the two correct answers are A and D, as they accurately describe how multicast IP addresses map to MAC addresses and the potential implications of the limited bit-mapping mechanism.
Question 4:
You are working with routing policies on a Cisco IOS XR device using the Routing Policy Language (RPL). Which two statements about these policies are accurate? (Select two.)
A. Routing policies only impact BGP routing information
B. Modifying a policy without pasting the full definition will erase the original
C. It's possible to edit specific statements in an existing routing policy
D. Routing policy rules are executed in the order they are listed
E. IOS XR routing policies are configured using route maps
Answer: B, D
Explanation:
In Cisco IOS XR, routing policies are configured using a declarative language called the Routing Policy Language (RPL), which is different from traditional IOS-style route maps. RPL provides a more structured and modular approach to defining routing policies for various protocols including BGP, OSPF, IS-IS, and others.
Option B is correct. One important operational consideration when using RPL is that editing a policy without reapplying the full policy definition will overwrite the existing configuration. This is because RPL does not allow for partial or line-by-line edits of policies directly. If an administrator pastes only a portion of the policy (e.g., only one statement of a multi-statement policy), the rest of the previously configured statements are lost. Therefore, the full definition must be pasted or entered each time changes are made.
Option D is also correct. RPL statements are executed sequentially, in the order they appear in the policy. This ordering is critical because routing decisions are made based on the first match encountered in the policy, and subsequent statements are not evaluated once a condition is satisfied (depending on policy logic). Thus, the order of statements influences the outcome significantly.
Option A is incorrect. Routing policies in IOS XR affect multiple routing protocols, not just BGP. RPL can be used to control route redistribution, filtering, attribute modification, and acceptance or rejection of routes for protocols such as OSPF, IS-IS, RIP, and static routes, in addition to BGP.
Option C is incorrect. Unlike Cisco IOS where individual lines of a route map can be edited, IOS XR's RPL does not support editing specific lines in an existing policy. The entire policy must be redefined and reapplied to make changes.
Option E is incorrect. IOS XR does not use route maps like traditional IOS or IOS XE platforms. Instead, it uses RPL, which offers a more structured syntax and logic model to define route policies.
Thus, the correct answers are B and D, as they reflect the correct behavior and constraints of routing policy management using RPL in IOS XR.
Question 5:
When redistributing BGP routes into OSPF on a Cisco router, what is the default cost assigned to these routes?
A. 20
B. 1
C. Infinite
D. Determined automatically
Answer: A
Explanation:
When BGP routes are redistributed into OSPF on a Cisco router, they are treated as external routes, and by default, Cisco assigns them a metric (cost) of 20. These are specifically classified as Type 2 External (E2) routes, which means they retain a fixed external cost (default: 20), and internal OSPF metrics do not influence route selection among them—only the external metric does.
This default value of 20 allows the redistributed BGP routes to be considered for OSPF route calculations, while still keeping them less preferred than internal OSPF routes, which typically have lower costs calculated based on bandwidth. The reasoning behind this default is to discourage OSPF from preferring BGP-learned routes unless specifically intended, preserving OSPF’s integrity as an IGP.
Option B, the cost of 1, is incorrect and represents the default cost for some directly connected OSPF routes, not redistributed BGP routes. Option C, Infinite, would mean the routes are unreachable or unusable, which is not the case with Cisco’s default redistribution behavior. Option D, "Determined automatically," is misleading because the metric is not dynamically determined; it is statically set to 20 by default unless manually overridden using the metric keyword during redistribution configuration.
Administrators can override the default behavior using the redistribute bgp <ASN> subnets metric <value> command under the OSPF routing process configuration. However, if no metric is specified, the default remains at 20.
Thus, the correct answer is A, as this reflects Cisco’s default redistribution metric for BGP routes into OSPF.
Question 6:
In a Segment Routing (MPLS data-plane) deployment, which two control-plane components must be configured on every core router to allow traffic-engineering paths computed by an SR-PCE? (Choose 2.)
A. Advertise the SRGB (Segment-Routing Global Block) range in OSPF or IS-IS
B. Enable BGP-LS session toward the PCE for topology export
C. Configure IGP Flexible-Algorithm 128 on every node
D. Define Adj-SID (Adjacency Segment IDs) for all core interfaces manually
E. Activate BFD for SR-TE on the head-end to track liveness
Answer: A, B
Explanation:
In Segment Routing (SR) deployments using the MPLS data plane, the control plane plays a critical role in enabling path computation and forwarding based on segments advertised via the IGP. When deploying SR-TE (Segment Routing Traffic Engineering) with a centralized Path Computation Element (PCE), especially a stateful SR-PCE, there are two essential control-plane requirements on all core routers to enable end-to-end traffic engineering:
Option A is correct. Each router in the core must advertise its SRGB (Segment Routing Global Block) via the IGP (either OSPF or IS-IS). The SRGB is a range of labels that are locally significant for interpreting Prefix SIDs. When routers advertise Prefix SIDs, they include the index (offset), which is interpreted relative to the SRGB. The SR-PCE relies on this consistent advertisement across the IGP topology to calculate valid segment lists for traffic-engineered paths. Without SRGB advertisement, SID-to-label resolution cannot occur correctly, which would prevent SR-TE paths from being programmed.
Option B is also correct. The PCE needs access to the IGP topology to perform centralized computation of paths. This is typically achieved by establishing a BGP-LS (Link-State) session from routers (or a route reflector) to the PCE. BGP-LS exports the IGP topology, including node SIDs, link SIDs, and SRGB ranges, to the PCE. This topology feed is crucial for the PCE to compute optimal segment lists based on constraints like latency, bandwidth, or administrative policies.
Option C, configuring Flexible Algorithm 128, is unrelated to standard SR-TE path computation and refers to a different type of policy routing supported in some newer IGP extensions. It's not required for SR-PCE operation. Option D, manually defining Adj-SIDs for all core interfaces, is unnecessary in most cases, as these are typically automatically generated and advertised by the IGP when Segment Routing is enabled. Option E, enabling BFD (Bidirectional Forwarding Detection) on the head-end, is a useful feature for liveness detection but is not required by the SR-PCE for control-plane operation.
Therefore, the two essential components that must be configured on every core router to support an SR-PCE are A and B.
Question 7
A service provider runs a single-area IS-IS with multiple levels of hierarchy. To reduce flooding while still maintaining loop-free connectivity,
Which two IS-IS features can be applied on intermediate routers? (Choose 2.)
A. LSP-refresh-interval tuning to 90 seconds
B. Mesh-group blocked on broadcast interfaces
C. Overload-bit set with ignore-lsp-errors
D. Partial-SPF (incremental SPF) calculation
E. IS-IS Route Leaking between level 1 and level 2
Answer: B, D
Explanation:
IS-IS is a link-state routing protocol that, in large topologies or flat single-area designs, may lead to excessive flooding of Link-State Protocol Data Units (LSPs). In such environments, features that limit unnecessary LSP flooding while maintaining correct routing behavior and loop-free operation are essential. The two most relevant features in this context are mesh-groups and incremental SPF.
Option B is correct. Mesh-group functionality in IS-IS allows a router to suppress flooding of LSPs on certain interfaces, typically broadcast or multi-access networks where many adjacencies exist. Within a mesh-group, routers only flood LSPs to one neighbor (usually a designated intermediate node), reducing redundant flooding and thereby saving bandwidth and CPU cycles. The “mesh-group blocked” setting ensures that flooding is suppressed in the designated direction, reducing overall LSP propagation without creating black holes, as LSPs are still delivered through other paths.
Option D is also correct. Partial-SPF or incremental SPF is a performance optimization that allows IS-IS routers to compute SPF only for parts of the network graph that have changed, rather than recalculating the entire topology upon every LSP change. This reduces CPU utilization and speeds up convergence in large IS-IS domains. It does not affect LSP flooding directly but enhances scalability by reducing processing requirements on intermediate routers.
Option A, tuning the LSP-refresh-interval, does not significantly reduce flooding. LSPs still need to be flooded when there are topology changes. While increasing the interval (default: 900 seconds) to something like 90 seconds reduces periodic refreshes, it does not mitigate flooding during actual topology changes or LSP updates.
Option C, setting the overload bit with ignore-lsp-errors, is used in failure or maintenance situations. The overload bit signals that the router should not be used for transit traffic, and ignore-lsp-errors prevents such routers from being removed from the SPF calculation due to malformed LSPs. While useful in some scenarios, it is not a general solution for flooding reduction and can unintentionally remove paths if misused.
Option E, route leaking between level 1 and level 2, applies to multi-level IS-IS domains, not single-area topologies. Since the question specifies a single-area IS-IS deployment (likely Level 2 only), route leaking is not applicable.
Thus, the correct answers that reduce flooding while maintaining loop-free connectivity are B and D.
Question 8
During an MPLS Layer-3 VPN deployment, the customer reports that routes are received but traffic is black-holed. PE routers use iBGP IPv4 unicast sessions over the service provider core (no next-hop-self).
Which two configurations resolve the issue without adding static routes? (Choose 2.)
A. Activate VPNv4 address-family and enable next-hop-self on all MP-BGP sessions
B. Configure LDP-IGP synchronization on every core interface toward the remote PE
C. Enable Directed-LDP between the two PE routers to exchange targeted LDP bindings
D. Deploy BGP Label Unicast (LU) SAFI for IPv4 so that VPN prefixes carry transport labels
E. Configure loopback interfaces as the update-source for MP-BGP and advertise them via IGP
Answer: D, E
Explanation:
In an MPLS Layer 3 VPN environment, black-holing of traffic is commonly caused when the PE router advertises a route to a remote site, but the core routers lack a label-switched path (LSP) to the next-hop of that route. Since BGP by default advertises routes with the loopback of the PE router as the next-hop, the MPLS core must be able to resolve that next-hop via LDP or another label distribution mechanism. If LDP does not have a label binding for the BGP next-hop, packets cannot be forwarded via MPLS and are dropped.
Option D is correct. BGP Label Unicast (LU)—also known as SAFI 4 (IPv4 + Label)—enables BGP to carry both the IPv4 route and an associated label, eliminating the reliance on LDP to resolve the next-hop. When LU is deployed between PEs (and optionally P routers), each router learns both the VPN route and a label for reaching the next-hop, thus supporting end-to-end MPLS forwarding without depending on LDP. This is especially helpful in modern deployments or inter-AS MPLS VPNs.
Option E is also correct. Configuring loopback interfaces as the update-source for MP-BGP sessions ensures consistent next-hop reachability. Advertising these loopbacks into the IGP allows LDP (or RSVP-TE, or segment routing) to establish proper label-switched paths to the PE routers. Without the loopback being known to the IGP, label bindings won't be created, and traffic forwarding will fail.
Option A is incorrect in this context because enabling next-hop-self changes the next-hop to the local PE's address, which solves the black-hole issue but contradicts the question’s condition: no next-hop-self is to be used.
Option B, enabling LDP-IGP synchronization, prevents IGP from installing routes until LDP has advertised a label. This helps during convergence but does not fix black-holing due to missing labels.
Option C, Directed-LDP, is typically used for targeted LDP sessions across non-directly connected peers. It's more relevant in inter-provider LDP setups or specific LDP scenarios, not for general intra-domain MPLS VPN deployment.
Therefore, the configurations that resolve the issue without adding static routes are D and E.
Question 9
An engineer must enforce inbound traffic engineering using BGP communities on an eBGP multihomed edge. Upstream ISPs honor RFC 1998.
Which two community pairs achieve AS-prepend of three occurrences on ISP A and one occurrence on ISP B? (Choose 2.)
A. xxx:70 applied on routes sent to ISP A
B. xxx:90 applied on routes sent to ISP A
C. xxx:120 applied on routes sent to ISP B
D. xxx:110 applied on routes sent to ISP B
E. xxx:80 applied on routes sent to ISP A
Answer: B, D
Explanation:
Inbound traffic engineering is the practice of influencing how other autonomous systems (ASes) send traffic toward your AS. One widely accepted method for this is AS-path prepending, where the path to your AS is artificially lengthened to make it less preferable in BGP route selection. RFC 1998 defines a standard for using BGP well-known communities that an ISP can honor to automatically prepend its own AS number multiple times when advertising customer routes.
The format of these communities is typically ASN:value, where the value specifies the desired prepend count in a vendor- or provider-specific way. Common values used by ISPs that support RFC 1998 (e.g., many Tier 1 providers) include:
ASN:70 – no prepending
ASN:80 – prepend once
ASN:90 – prepend twice
ASN:110 – prepend once
ASN:120 – prepend two times
These values may vary slightly by provider, but typically, they follow this pattern, and most Tier 1 ISPs document this.
In this scenario, the goal is to apply:
Three prepends on ISP A
One prepend on ISP B
To achieve three prepends on ISP A, you typically need to apply a community such as xxx:90 or xxx:100, depending on the provider. The value xxx:90 usually translates to the ISP adding its own AS number three times, which matches the requirement for ISP A.
To get one prepend on ISP B, use a community like xxx:110, which typically results in the ISP adding its AS number once to the path.
Let’s evaluate each option:
A. xxx:70 = Usually indicates no prepending → Incorrect for ISP A.
B. xxx:90 = Usually triggers three prepends → Correct for ISP A.
C. xxx:120 = Usually causes two prepends → Too much for ISP B.
D. xxx:110 = Typically means one prepend → Correct for ISP B.
E. xxx:80 = Typically means one prepend → Too few for ISP A.
Therefore, the correct pair of communities to meet the requirement is B (three prepends on ISP A) and D (one prepend on ISP B).
Question 10
When configuring MPLS-TE fast reroute (FRR) local protection, which two RSVP objects must be signaled for a Point-to-Point TE-tunnel to guarantee node-protect capability? (Choose 2.)
A. RESOURCE-PREEMPTION object with priority 0
B. FAST-REROUTE object with the One-to-One backup flag
C. SESSION-ATTRIBUTE object with the LOCAL-PROTECTION-DESIRED bit set
D. EXCLUDE-ANY / INCLUDE-ALL affinity constraints matching backup path
E. LABEL-RESTRICTION object specifying merge-point-protection
Answer: B, C
Explanation:
MPLS Traffic Engineering (TE) Fast Reroute (FRR) provides local protection to quickly reroute traffic around failed links or nodes. FRR allows traffic carried over a primary Label Switched Path (LSP) to be rapidly redirected onto a precomputed backup LSP, called a detour or bypass tunnel, in the event of failure. Two types of protection are supported:
Link-protect: Protects only the interface/link.
Node-protect: Protects the entire next-hop node, ensuring that both link and node failures are handled.
To enable node protection, the head-end and midpoints must signal the right RSVP-TE attributes.
Option B is correct. The FAST-REROUTE object with the One-to-One backup flag signals the intent to establish a detour LSP for each protected LSP hop (rather than a shared bypass tunnel). While facility backup (many-to-one) is often used in practice, this flag is relevant for per-LSP protection and supports node protection capabilities when appropriately configured.
Option C is also correct. The SESSION-ATTRIBUTE object with the LOCAL-PROTECTION-DESIRED bit set tells the RSVP process that local protection should be used for this LSP. It signals to the router that FRR (fast reroute) capability is required for this tunnel, prompting the creation of backup LSPs. Without this flag, routers do not compute local detours or bypass tunnels for FRR.
Option A, specifying a priority 0 in the RESOURCE-PREEMPTION object, is unrelated to protection type. That object defines setup and hold priorities, which control resource reservation and preemption behavior. It does not signal the desire for node or link protection.
Option D, using affinity constraints, is for path selection and policy enforcement (e.g., choosing LSPs that meet certain color/tag requirements). It may influence backup path selection but is not a required signal for FRR or node-protect capability.
Option E, the LABEL-RESTRICTION object, is a theoretical object not widely used in this context. It is not part of the core RSVP-TE signaling needed to guarantee node protection in MPLS-TE.
Thus, the correct objects required to enable node-protection for MPLS-TE FRR are B and C.
