Implementing Cisco Service Provider Advanced Routing Solutions — Free Practice Questions
10 free sample questions from a bank of 253, with the correct answers and explanations. No signup required — start practising right now.
1What is a restriction of 6PE?
It cannot be implemented on VRFs.
It is implemented only over iBGP peers.
It adds a value of ::FFFE: on the IPv4 next hop address.
It is implemented only over eBGP peers.
Answer: A
The short version
A — 6PE cannot be implemented on VRFs. 6PE transports global IPv6 over an IPv4 MPLS core; per-VRF IPv6 VPN service requires 6VPE instead.
Key concepts in this question
6PE: IPv6 provider edge over IPv4 MPLS using labeled BGP, global table only.
6VPE: the VRF-aware variant that keeps customer IPv6 prefixes separate.
VRF restriction: 6PE has no VRF table to attach IPv6 VPN routes to.
Why A is correct
6PE is defined for internet or global IPv6 reachability across an IPv4-only core, with a single IPv6 routing context. Because it lacks VRF separation for IPv6, any design needing isolated customer VRFs must use 6VPE, making the VRF limitation the key 6PE restriction.
Why the others are wrong
B. 6PE is not limited to iBGP only; its restriction is about VRF support, not peering type.
C. The ::FFFF:0:0/96-style mapped next hop is a 6PE encoding detail, not a restriction on where it can run.
D. 6PE is not eBGP-only either; PE-P route exchange behavior does not define its VRF limit.
300-510 exam tip
6PE equals global IPv6 over IPv4 core, 6VPE equals VRF IPv6; if the stem says VRF, 6PE is the wrong tool.
2For which reason can two devices fail to establish an OSPF neighbor relationship?
The two devices have different process IDs
The two devices have different network types
The two devices have different router IDs
The two devices have the same area ID
Answer: B
The short version
B — Mismatched OSPF network types block adjacency. Hello, DR, and timing expectations differ by network type, so neighbors stall before ExStart.
Key concepts in this question
Network type: broadcast, nonbroadcast, point-to-point, point-to-multipoint, and loopback behaviors.
Adjacency requirements: area, subnet, timers, MTU, and network-type compatibility.
Non-requirements: process IDs are locally significant and router IDs must be unique, not equal.
Why B is correct
Two interfaces with different OSPF network types disagree on DR election and hello handling, commonly hanging in Init or ExStart. Aligning both sides to the same type lets the neighbor state machine proceed to Full, which is why this mismatch is a classic failure reason.
Why the others are wrong
A. Different process IDs are fine; the ID is local and never compared in hellos.
C. Different router IDs are required; identical IDs, not different ones, break adjacency.
D. Having the same area ID is required on the link; different areas, not the same area, prevent adjacency.
300-510 exam tip
Same subnet, same area, same timers, same network type, unique router IDs — spot which one the stem breaks.
3A network engineer is troubleshooting OSPF multiarea.Which Cisco IOS XR feature should the engineer use in order to streamline OSPF issue?
hierarchical CLI
routing process enabled by default on all interfaces
DR support for topology management
show lp ospf topology command
Answer: A
The short version
A — Use IOS XR hierarchical CLI for multiarea OSPF triage. Its mode-based structure scopes show and configuration commands per process and area.
Key concepts in this question
Hierarchical CLI: router ospf, area, and interface submodes in IOS XR.
Multiarea troubleshooting: isolate one area, interface, or neighbor at a time.
XR operational model: commit-based, structured configuration with matching show hierarchy.
Why A is correct
Multiarea OSPF faults hide in the wrong area or interface context. IOS XR hierarchical CLI lets the engineer enter the OSPF process, then the specific area and interface, and run focused checks without wading through the full global config, which streamlines the issue described.
Why the others are wrong
B. OSPF is not enabled on all interfaces by default; interfaces must still be placed in areas explicitly.
C. DR support is standard OSPF behavior for broadcast segments, not an XR troubleshooting feature.
D. The show syntax as worded is not the XR multiarea triage feature; hierarchy, not one magic command, is the point.
300-510 exam tip
IOS XR plus streamline or structure equals hierarchical CLI; DR and defaults are protocol constants, not XR tools.
4Which two BGP mechanisms are used to prevent routing loops when using a design with redundant route reflectors? (Choose two.)
Cluster-list
AS-Path
Originator ID
Community
Origin
Answer: A, C
The short version
A and C — Cluster-list and Originator ID stop reflector loops. Together they let redundant route reflectors recognize and discard updates they already handled.
Key concepts in this question
Originator ID: carries the originator's router ID inside the cluster.
Cluster-list: records every cluster a route has traversed.
Redundant reflectors: two reflectors serving the same clients can otherwise bounce updates.
Why A and C are correct
With redundant reflectors, a client update can be reflected by both servers and loop back. Originator ID tells a router to ignore its own originated route when it returns, and cluster-list tells a reflector to ignore a route that already passed through its cluster. The pair is the iBGP loop-prevention mechanism for reflector designs.
Why the others are wrong
B. AS-Path prevents eBGP loops between autonomous systems, not iBGP loops inside a reflector cluster.
D. Community tags policy and filtering; it does not detect reflector reflection loops.
E. Origin describes how a route entered BGP (IGP, EGP, incomplete) and plays no loop-prevention role here.
300-510 exam tip
Reflector plus redundant equals Originator ID and cluster-list; AS-Path is the eBGP answer, not the iBGP one.
5In Cisco IOS-XR, the maximum-prefix command, to control the number of prefixes that can be installed from a BGP neighbor, is configured under which configuration mode?
RP/0/RSP0/CPU0:P2(config-bgp)#
RP/0/RSP0/CPU0:P2(config-bgp-nbr)#
RP/0/RSP0/CPU0:P2(config-bgp-nbr-af)#
RP/0/RSP0/CPU0:P2(config-bgp-af)#
Answer: C
The short version
C — Maximum-prefix lives under the neighbor address family in XR. The config-bgp-nbr-af mode scopes the prefix limit to one neighbor and one family.
Key concepts in this question
Maximum-prefix: caps accepted prefixes to protect memory and stability.
XR BGP hierarchy: instance, neighbor, then neighbor address family.
Per-family scope: IPv4 unicast and IPv6 unicast limits are set independently.
Why C is correct
In IOS XR the limit must apply per address family for a specific peer, so the command is entered at RP/0/RSP0/CPU0:P2(config-bgp-nbr-af)#. That context binds the threshold to the neighbor's IPv4 or IPv6 unicast session rather than to the whole BGP process.
Why the others are wrong
A.config-bgp is the global BGP process level, too broad for a per-neighbor prefix cap.
B.config-bgp-nbr configures the neighbor session itself but not the per-family prefix policy.
D.config-bgp-af is the global address-family level, not tied to the specific neighbor being limited.
300-510 exam tip
Per-neighbor per-family BGP policy in XR means nbr-af; process or global-af levels are too high in the hierarchy.
6An engineer with an employee ID: 4535:15:507 must implement PIM-SSM in the network to support a new multicast messaging service. All the routers in the network run a distance vector routing protocol. Unicast routing is established on the network and is working normally. What must the engineer enable to continue the implementation process?
PIM RP feature on the network
IGMPv3 on all interfaces that participate in multicast
PIM dense mode and IGMPv2 on all interfaces that participate in multicast
PIM dense mode on all devices on the network
Answer: B
The short version
B — PIM-SSM needs IGMPv3 on the participating interfaces. Only version 3 lets hosts request a specific source with each group join.
Key concepts in this question
PIM-SSM: source-specific trees built directly toward (S,G) with no shared tree.
IGMPv3: adds source include and exclude signaling from receivers.
RP independence: SSM needs no rendezvous point because the source is explicit.
Why B is correct
SSM forwarding depends on the receiver naming both source and group. IGMPv3 is the only IGMP version that carries (S,G) include requests, so every multicast-facing interface must run it before SSM joins can build source trees over the working unicast routing.
Why the others are wrong
A. A PIM RP belongs to sparse-mode shared trees; SSM explicitly avoids any RP.
C. Dense mode plus IGMPv2 floods then prunes and cannot signal source-specific joins.
D. Dense mode alone on all devices still lacks source-specific receiver signaling and wastes bandwidth.
300-510 exam tip
SSM in the stem means IGMPv3 and no RP; any RP or dense-mode answer is the ASM distractor.
7Refer to the exhibit. Dedicated MPLS Layer 3 services for VRF customer A are configured on the MPLS network for FTP access. OSPF with area 0 configuration is used as the interior routing protocol between the routers, and LDP is up and running on the MPLS network. After recent maintenance work on the MPLS network, IP address 172.16.100.1 cannot access the FTP server with IP address 172.16.192.21. All loopbacks are reachable on the network. Which configuration must the engineer apply to correct the problem?
Configure passive-interface under the Gi0/2 interface on R22.
Configure ip ospf network point-to-point under the Lo0 interface on R33.
Configure network 33.33.10.1 0.0.0.255 area 0 under the OSPF configuration on R33.
Configure ip cef under the global configuration on R22.
Answer: D
The short version
D — Re-enable CEF on R22 so MPLS label switching works. Loopbacks prove control-plane reachability, but VRF data-plane forwarding still needs a CEF-built LFIB.
Key concepts in this question
CEF: builds FIB and LFIB entries used for IP and MPLS forwarding.
LDP plus OSPF: control plane can be up while the data plane is broken.
VRF FTP flow: customer packets must be label-imposed and disposed per VRF path.
Why D is correct
All loopbacks reachable with OSPF area 0 and LDP up points away from routing to forwarding: without ip cef, R22 cannot program label imposition and disposition for VRF customer A. Configuring CEF globally restores the label path between 172.16.100.1 and the FTP server at 172.16.192.21 after maintenance disabled it.
Why the others are wrong
A. Passive-interface on Gi0/2 would suppress OSPF hellos and worsen reachability, not repair label forwarding.
B. Point-to-point under Lo0 changes loopback network-type handling and is unrelated to a missing CEF data plane.
C. Adding another OSPF network statement is unnecessary when loopbacks are already reachable via area 0.
300-510 exam tip
Control plane up but MPLS VPN traffic blackholed after maintenance means check CEF first.
8What is determined by running the same hash algorithm on all PIMv2 routers?
The SPT from the last hop router to the multicast source
Which RP to use from a set of candidate RPs in the RP set
Which BSR to use for a particular multicast group
Auto RP election
The SPT from the RP to the multicast source
Answer: B
The short version
B — The shared hash picks one RP from the candidate set. Every PIMv2 router runs the same algorithm so all agree on the RP for each group.
Key concepts in this question
BSR and RP-set: bootstrap router floods the candidate-RP list domain-wide.
Deterministic hash: function of group address and candidate-RP address.
Consistency goal: all routers must select the same RP without extra signaling.
Why B is correct
When several candidate RPs cover the same group range, each router hashes the group with each candidate and chooses the highest value. Because the inputs and algorithm are identical everywhere, the whole domain converges on one RP per group, which is exactly what running the same hash guarantees.
Why the others are wrong
A. The shortest-path tree to the source is built from unicast routing and joins, not from the RP hash.
C. BSR election uses priority and address comparison, not the RP-selection hash.
D. Auto-RP uses Cisco announce and discovery messages, not the BSR hash function.
E. The RP-to-source tree is standard PIM registration and SPT logic, unrelated to choosing among candidate RPs.
300-510 exam tip
Same hash on all PIMv2 routers equals same RP choice; BSR election and SPT building are separate mechanisms.
9Refer to the exhibit. An engineer is comparing these RPL and route map configurations. Which two conclusions will the engineer reach? (Choose two.)
RPL is applying local preference 50 and community (2:666) for all prefixes, but the route map is applying only local preference 50 for all prefixes.
RPL and the route map are applying only local preference 50 for prefix 172.22.0.0/16.
RPL is applying local preference 50 and community (2:666) for prefix 172.22.0.0/16, but the route map is applying only local preference 50 for the same prefix.
RPL is applying local preference 100 and community (2:100) for multiple prefixes, but the route map is applying default local preference for multiple prefixes.
RPL is applying policy only on BGP IPv6 address families, but the route map is applying policy on BGP IPv4 and IPv6 address families.
Answer: C, D
The short version
C and D — RPL sets community plus local preference where the map sets only preference, then falls through differently. The exhibit shows matching behavior on 172.22.0.0/16 but divergent defaults afterward.
Key concepts in this question
RPL: IOS XR route-policy language with explicit pass, drop, and community sets.
Route map: IOS route-map clauses with match and set actions.
Default handling: unmatched prefixes get RPL else-branch versus route-map default local preference.
Why C and D are correct
For 172.22.0.0/16 both tools match, but RPL applies local preference 50 together with community (2:666) while the route map applies only local preference 50. For the remaining prefixes RPL applies local preference 100 with community (2:100), whereas the route map leaves them at default local preference, giving the two stated conclusions.
Why the others are wrong
A. RPL does not stamp every prefix with 50 and (2:666); the community plus 50 applies to the matched prefix in the exhibit.
B. The two are not identical on 172.22.0.0/16 because only RPL adds community (2:666) there.
E. The difference shown is attribute handling on IPv4 prefixes, not an IPv6-only versus dual-family split.
300-510 exam tip
RPL versus route-map exhibits hinge on communities and else-branch defaults; check who sets community and who leaves default preference.
10Refer to the exhibit. After recent configuration changes to a customer's network, a network engineer notices that R2 cannot communicate with R3. Both FastEthernet interfaces on R2 and R3 are up and configured with the correct IP addresses. MD5 password configured on R2 and R3 match with no issues. What is the minimum change the engineer must make to enable R2 and R3 to communicate and fix the problem?
Configure virtual links between R1 and R3.
Configure a loopback interface on R2 and assign it to area 0.
Configure interface F0/0 on R1 and R2 to be in area 0.
Define area 2 as a NSSA on R2 and R3.
Answer: B
The short version
B — Give R2 an area 0 loopback to restore backbone continuity. Both Ethernets are up with matching MD5, so the failure is area design, and a local area 0 interface makes R2 touch the backbone.
Key concepts in this question
Backbone rule: all OSPF areas must attach to area 0, directly or via virtual link.
Loopback in area 0: counts as a backbone attachment for the local router.
Minimal change: one loopback avoids re-addressing physical links or building virtual links.
Why B is correct
Up interfaces, correct IPs, and matching MD5 rule out Layer 1 through authentication. The remaining classic cause is a partitioned or non-backbone-only R2 that cannot exchange inter-area routes with R3. Adding a loopback in area 0 gives R2 a backbone interface, satisfying contiguity with the least disruption.
Why the others are wrong
A. Virtual links between R1 and R3 fix a different discontiguity and add complexity instead of the minimal local fix.
C. Moving F0/0 on R1 and R2 into area 0 renumbers the area design on live links, which is more invasive.
D. Making area 2 an NSSA changes LSA flooding and stub behavior but does not create the missing backbone attachment.
300-510 exam tip
Up plus correct IP plus matching auth but no OSPF communication means check backbone attachment before touching areas or passwords.