350-501 Services Practice Test 4 — 15 Questions

Question 1

A service provider is configuring VRF-lite between two CE routers connected to the same PE. The CE routers are in different VRFs. Which command allows the PE router to forward traffic between the VRFs?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

ip route vrf RED 0.0.0.0 0.0.0.0 vrf BLUE. The command `ip route vrf RED 0.0.0.0 0.0.0.0 vrf BLUE` creates a static inter-VRF route on the PE router, allowing traffic from VRF RED to be forwarded to VRF BLUE without requiring MPLS or BGP. This is the standard method for VRF-lite inter-VRF communication on the same PE, using a static route that points to the next-hop VRF instead of an IP address.

Answer

vrf forward RED

Answer

route-target export RED:100 import BLUE:100

Answer

ip route vrf RED 0.0.0.0 0.0.0.0 10.1.1.1 global

Question 2

A service provider is deploying MPLS L3VPN and wants to ensure that routes from a specific customer VRF are only advertised to a specific remote PE. Which mechanism should be used?

Accepted Answer

Applying a route-map to the VRF export statement. A route-map applied to the VRF export statement allows granular control over which routes are advertised to specific BGP VPNv4 neighbors. By matching on route targets or other attributes, the route-map can filter outbound routes per neighbor, ensuring that routes from a specific customer VRF are only sent to a designated remote PE.

Answer

Configuring a separate VPNv4 address-family for that PE

Answer

Using a unique route-distinguisher per VRF

Answer

Setting the next-hop-self on the PE

Question 3

In a Segment Routing network with TI-LFA enabled, which mechanism prevents micro-loops during a link failure?

Accepted Answer

Explicit path with segment list and delay timer. In Segment Routing with TI-LFA, micro-loops are prevented by using an explicit path with a segment list and a delay timer. When a link fails, the protecting router installs a backup path with a segment list that steers traffic around the failure, and a delay timer ensures that the backup path is not activated until the network has converged, preventing transient loops.

Answer

Constraint Shortest Path First computation

Answer

Loop-Free Alternate precomputed backup paths

Answer

Prefix Independent Convergence with fast reroute

Question 4

A service provider is implementing QoS on a PE router for customer traffic. Which tool should be used to classify traffic based on application layer information?

Accepted Answer

MQC with NBAR. NBAR (Network-Based Application Recognition) is a deep packet inspection (DPI) engine within the Modular QoS CLI (MQC) that can identify applications by inspecting payloads up to Layer 7. This allows classification of traffic based on application-layer information such as HTTP, DNS, or proprietary protocols, which is exactly what the question requires.

Answer

Access-list

Answer

Shaping

Answer

Policy-map with police

Question 5

Which multicast RP model is recommended for large-scale networks to provide redundancy and load sharing?

Accepted Answer

Anycast-RP. Anycast-RP is recommended for large-scale networks because it allows multiple RPs to share the same IP address, providing redundancy and load sharing without requiring dynamic RP discovery protocols. This model uses MSDP (Multicast Source Discovery Protocol) or PIM (Protocol Independent Multicast) to synchronize multicast state between RPs, ensuring that sources and receivers can register with the nearest RP for optimal path selection.

Answer

Auto-RP

Answer

BSR

Answer

Static RP

Question 6

A service provider is migrating from LDP to Segment Routing. What is the correct order of operations to ensure uninterrupted MPLS forwarding?

Accepted Answer

Enable SR on each router one by one while LDP remains active, then remove LDP after SR is stable.. It follows the recommended migration strategy of running LDP and Segment Routing (SR) in parallel. By enabling SR on each router one by one while LDP remains active, MPLS forwarding continues uninterrupted via LDP until SR is fully deployed and stable. Once SR is verified on all routers, LDP can be safely removed without causing any forwarding black holes.

Answer

Enable SR on all routers simultaneously.

Answer

Configure IS-IS SR extensions on all routers, then disable LDP.

Answer

Disable LDP first to free labels, then enable SR.

Question 7

In EVPN multihoming with all-active mode, what is the purpose of the aliasing capability?

Accepted Answer

It enables one PE to advertise MAC addresses for another PE in the same ES.. In EVPN all-active multihoming, the aliasing capability allows a PE that has learned a MAC address via local attachment to the Ethernet Segment (ES) to advertise that MAC address on behalf of other PEs in the same ES. This enables remote PEs to load-balance traffic destined to that MAC across all multihomed PEs, even if only one PE actually learned the MAC locally. Without aliasing, traffic would be forced to the specific PE that learned the MAC, defeating the purpose of all-active redundancy.

Answer

It permits the use of a single ESI label across all PEs in the ES.

Answer

It reduces the number of BGP updates by aggregating MAC routes.

Answer

It allows load balancing of traffic across all PEs.

Question 8

A service provider is using LISP to provide host mobility. Which LISP component is responsible for storing the mapping of EID to RLOC?

Accepted Answer

Map-Server. In LISP (RFC 6830), the Map-Server (MS) is the central repository that stores the mapping of Endpoint Identifiers (EIDs) to Routing Locators (RLOCs). When an Ingress Tunnel Router (ITR) needs to forward traffic to a destination EID, it queries the Map-Resolver, which in turn contacts the Map-Server to retrieve the authoritative mapping. The Map-Server also accepts registration from Egress Tunnel Routers (ETRs) on behalf of their EID prefixes, making it the definitive source for EID-to-RLOC bindings.

Answer

Altitude

Answer

Tunnel Router

Answer

Map-Resolver

Question 9

Refer to the exhibit. A PE router has this BGP configuration. The CE router is advertising a default route via eBGP. However, the PE is not installing the route in the VRF table. What is the most likely cause?

Accepted Answer

The neighbor 10.1.1.1 is not configured under the address-family ipv4 vrf CUSTOMER. The BGP configuration shows that the neighbor 10.1.1.1 is configured under the BGP IPv4 unicast address-family, but not under the address-family ipv4 vrf CUSTOMER. For a VRF to install a route learned via eBGP from a CE router, the neighbor must be explicitly activated under the VRF address-family. Without this, the PE will receive the default route but will not place it into the VRF routing table.

Answer

The redistribute connected command under the VRF is overwriting the default route

Answer

The next-hop-self under the VRF address-family is not set

Answer

The default-information originate command is missing

Question 10

A service provider is configuring BGP community propagation in an MPLS VPN network. Which two actions are necessary to ensure that communities are passed from CE to remote PE?

Accepted Answer

Configure send-community on the CE-to-PE BGP session. B is correct because the `send-community` command must be configured on the CE-to-PE BGP session to allow standard BGP communities (e.g., NO_EXPORT) to be propagated from the CE router into the MPLS VPN network. Without this, the PE router will strip communities from incoming BGP updates, preventing them from reaching the remote PE.

Answer

Configure no bgp default community-mode

Answer

Configure vrf forwarding with route-target both

Answer

Configure route-map to filter communities

Question 11

Which two of the following are characteristics of MPLS Traffic Engineering that differentiate it from pure MPLS forwarding?

Accepted Answer

Allows bandwidth reservation. MPLS Traffic Engineering (MPLS-TE) explicitly supports bandwidth reservation, which allows an operator to guarantee a certain amount of bandwidth for a traffic-engineered LSP. This is a key differentiator from pure MPLS forwarding, where LSPs are created without any bandwidth awareness and simply forward packets based on the label-swapping mechanism.

Answer

Requires LDP for LSP creation

Answer

Provides optimal load balancing based on topology

Answer

Uses RSVP for label distribution

Question 12

Which three of the following are valid methods for protecting a pseudowire in an MPLS network?

Accepted Answer

Multi-segment PW with backup. Multi-segment PW (MS-PW) with backup is a valid protection method because it allows a pseudowire to be established across multiple MPLS segments, with a backup PW path that can take over if the primary MS-PW fails. This provides end-to-end pseudowire redundancy by using a secondary switched path, ensuring service continuity in multi-domain or multi-area MPLS networks.

Answer

Ethernet OAM CFM

Answer

LSP ping for fault detection

Question 13

A service provider operates a Layer 2 MPLS VPN using VPLS. Recently, two new CE routers were added to the VPLS domain, but they cannot ping each other. The existing CEs can communicate. The network uses BGP autodiscovery and signaling. The new CEs are connected to different PEs. The 'show vfi status' command on the new PEs indicates the VFI is up but the pseudowire to the remote PE is down. The BGP session between the PEs is established and the L2VPN address family routes are exchanged. What is the most probable cause?

Accepted Answer

The route-target on the new PEs does not match the existing VPLS context. B is correct because BGP autodiscovery for VPLS relies on route-target (RT) matching to import remote VPLS endpoints into the local VFI. If the RT configured on the new PEs does not match the RT used by the existing VPLS context, the remote pseudowire will not be created even though BGP sessions are up and L2VPN routes are exchanged. The 'show vfi status' showing VFI up but pseudowire down is a classic symptom of RT mismatch, as the local PE cannot associate the received BGP routes with the correct VPLS instance.

Answer

The BGP neighbor is not activated under the VPLS address-family

Answer

The MTU mismatch between PEs

Answer

The VFI name is not consistent across PEs

Question 14

A customer's MPLS L3VPN has two CE routers connected to two different PEs, but the PEs are not receiving the customer's routes from each other. The PE-CE routing protocol is OSPF. The PEs have the VRF configured with OSPF process, and the routes from CE are in the VRF routing table. The MP-BGP session between PEs is up and the VPNv4 address family is working. On the source PE, the routes show as not advertised to BGP. What is the likely issue?

Accepted Answer

The OSPF process on the PE is not redistributed into BGP VPNv4 under the VRF. In an MPLS L3VPN with OSPF as the PE-CE protocol, the VRF OSPF process must be explicitly redistributed into the MP-BGP VPNv4 address family using the `redistribute ospf <process-id> match internal external` command under the VRF address-family IPv4. Without this redistribution, the OSPF routes learned from the CE remain in the VRF routing table but are never injected into BGP, so they are not advertised to the remote PE, even though the MP-BGP session is up and the VPNv4 address family is working.

Answer

The route-target export on the source PE does not match the import on the remote PE

Answer

The OSPF network type is not set to broadcast

Answer

The next-hop-self is not configured under the VRF OSPF process

Question 15

A service provider is deploying IGMPv3 snooping on an MVPN network to optimize multicast forwarding. After configuration, multicast traffic is not reaching receivers. The source is sending to group 239.1.1.1. The PE router has received the IGMP report from the receiver, and the MDT is established. What is the most likely reason?

Accepted Answer

The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report. IGMPv3 snooping on the PE router processes the receiver's IGMPv3 report. If the SSM range (232.0.0.0/8) is applied to group 239.1.1.1, the receiver must send an IGMPv3 (S,G) report to join a specific source. However, if the receiver sends a (*,G) report (which is allowed only in ASM mode), the IGMP snooping will not install the forwarding entry, causing multicast traffic to be dropped even though the MDT is established.

Answer

The RP for the group is not configured

Answer

The IGMP snooping is filtering the multicast traffic because of wrong VLAN configuration

Answer

The multicast routing is not enabled globally