350-501 Services — Timed 10 Questions

Question 1

A service provider is deploying EVPN-VPWS to replace legacy pseudowire connections for point-to-point Layer 2 services. They notice that MAC addresses learned from a CE device are not properly advertised to the remote PE. Which EVPN route type is responsible for advertising MAC address reachability information in a VPWS scenario?

10 minute time limit — choose an answer to begin.

Accepted Answer

Route Type 2 (MAC/IP Advertisement). In EVPN-VPWS, when MAC learning is enabled on the point-to-point service, MAC address reachability is advertised using Route Type 2 (MAC/IP Advertisement). Route Type 1 (Ethernet Auto-Discovery) is used for service discovery and label allocation, but it does not carry MAC addresses. Therefore, Route Type 2 is responsible for advertising MAC address reachability in this scenario.

Answer

Route Type 1 (Ethernet Auto-Discovery)

Answer

Route Type 5 (IP Prefix)

Answer

Route Type 3 (Inclusive Multicast)

Question 2

A customer is connected to a service provider MPLS L3VPN network using BGP. The CE advertises a prefix 10.1.1.0/24 to the PE. On the PE, the customer's VRF route table shows the route with the next-hop set to the CE. When the PE receives a packet destined to 10.1.1.1, what label stack will the PE apply before forwarding the packet across the MPLS core?

Accepted Answer

Both the transport label and the VPN label. When the ingress PE receives a packet destined to 10.1.1.1, it performs a VRF lookup and finds the route 10.1.1.0/24 with a VPN label assigned by the egress PE. The ingress PE must push two labels: the VPN label (inner) and the transport label (outer) to reach the egress PE across the MPLS core. The transport label (e.g., LDP or RSVP) is used to forward the packet through the core, and the VPN label is used by the egress PE to identify the correct VRF after PHP removes the transport label. Thus, the label stack applied by the ingress PE includes both labels.

Answer

Only the transport label (LDP or RSVP) for the egress PE

Answer

Only the MPLS VPN label assigned to the route by the egress PE

Answer

No label, because the CE is directly connected

Question 3

A service provider is deploying MPLS Layer 3 VPN and needs to ensure that BGP next-hop resolution works correctly for VPNv4 prefixes learned from a route reflector. The PE routers are directly connected to the RR via iBGP, and there is an IGP running within the MPLS core. Which condition must be met for the PE to install the VPNv4 prefix into its routing table?

Accepted Answer

The next-hop must be reachable via the IGP with an MPLS label.. For a PE router to install a VPNv4 prefix learned from a route reflector into its routing table, the BGP next-hop (typically the remote PE) must be reachable via the IGP with an associated MPLS label. This ensures that the transport LSP exists to forward traffic toward the next-hop, which is required for MPLS L3VPN operation. Without an MPLS label in the IGP for the next-hop, the PE cannot build the necessary label stack and will not install the VPNv4 route.

Answer

The next-hop must be a directly connected interface.

Answer

The PE must have a VPN label for the next-hop.

Answer

The IGP must be IS-IS, not OSPF.

Question 4

A service provider is designing a multicast solution for a Layer 3 VPN. They want to use MVPN with BGP signaling (draft-rosen). The PE routers are configured with VRF and multicast routing enabled. Which BGP address family must be enabled between PE routers to carry multicast routing information?

Accepted Answer

MCAST-VPN address family. In a draft-rosen MVPN (Multicast VPN) implementation, BGP is used to signal multicast routing information between PE routers. The MCAST-VPN address family (AFI 25, SAFI 5) is specifically defined to carry multicast VPN routes, including Intra-AS I-PMSI A-D routes and S-PMSI A-D routes, enabling the exchange of multicast state and tunnel information across the MPLS/VPN backbone.

Answer

MVPN does not use BGP; it uses PIM.

Answer

VPNv4 address family

Answer

IPv4 multicast address family

Question 5

A network engineer is troubleshooting an MPLS TE tunnel that is not coming up. The tunnel is configured with a strict explicit path, and the path includes an interface that is currently down. Which action should the engineer take to allow the tunnel to use an alternative path?

Accepted Answer

Change the explicit path to 'loose' for the down interface.. Changing the explicit path from 'strict' to 'loose' for the down interface allows the MPLS TE tunnel to use an alternative next-hop that is reachable, even if the specified interface is down. A strict explicit path requires every hop to be directly connected, so a down interface prevents the tunnel from coming up. By making the hop loose, the router can route around the failed link using the IGP's best path to the next specified node.

Answer

Increase the path-option preference value.

Answer

Disable path protection on the tunnel.

Answer

Configure an affinity constraint to exclude the down interface.

Question 6

Which TWO statements about BGP FlowSpec (RFC 8955) are correct?

Accepted Answer

FlowSpec can be deployed in BGP sessions between a route reflector and a client.. BGP FlowSpec (RFC 8955) can be deployed between a route reflector and its clients. The route reflector propagates FlowSpec NLRI (Network Layer Reachability Information) to its clients, allowing the clients to install traffic filtering rules without requiring a full BGP mesh. This is a common deployment model in service provider networks to distribute flow-spec routes efficiently.

Answer

FlowSpec uses a separate BGP session from the regular IPv4 unicast session.

Answer

FlowSpec is designed to replace ACLs on provider edge routers.

Answer

FlowSpec requires MPLS forwarding to operate.

Question 7

Which THREE characteristics apply to the BGP-LS (BGP Link State) protocol?

Accepted Answer

It uses a separate address family from VPNv4.. BGP-LS uses a separate address family (AFI 16388 / SAFI 71) from VPNv4 (AFI 1 / SAFI 128) to carry link-state information. This separation allows BGP-LS to operate independently from VPNv4 routes, enabling the collection and distribution of IGP topology data without interfering with MPLS VPN signaling.

Answer

It supports only IS-IS, not OSPF.

Answer

It carries traffic-engineering parameters in the NLRI.

Question 8

Refer to the exhibit. A service provider is applying this QoS policy on a PE-CE interface. The business customer complains that voice traffic (marked with DSCP EF) experiences drops during congestion. What is the likely cause?

Accepted Answer

The police rate under the REALTIME class is limiting voice traffic to 10% of bandwidth.. The REALTIME class uses the 'police' command to enforce a rate of 10% of the interface bandwidth. When voice traffic marked DSCP EF exceeds this policed rate, packets are dropped, even though the class is configured with priority queuing. The police rate is the bottleneck, not the priority queue itself.

Answer

The priority level is set too low; voice should be priority level 4.

Answer

The 'bandwidth remaining ratio' command under class-default is starving the priority queue.

Answer

The policy is applied in the output direction; it should be input.

Question 9

Refer to the exhibit. A network engineer is troubleshooting MPLS forwarding for prefix 10.10.10.0/24. The router shows two entries. What does the 'Pop tag' in the outgoing tag indicate?

Accepted Answer

The router will pop the MPLS label before forwarding the packet.. The 'Pop tag' in the outgoing tag indicates that the router is the penultimate hop in the MPLS LSP. According to Penultimate Hop Popping (PHP) behavior, the penultimate router removes (pops) the top label before forwarding the IP packet to the egress LSR, so the egress router receives a pure IP packet and does not need to perform a label lookup. This is standard MPLS behavior defined in RFC 3031.

Answer

The router will swap the label with the local label 16.

Answer

The router has received an error in label distribution.

Answer

The router will forward the packet without an MPLS label.

Question 10

A service provider is implementing L2VPN using EoMPLS. The CE devices are connected to two different PE routers, and the PE routers are configured with xconnect under the attachment circuit. Which command is required on the PE routers to establish the pseudowire?

Accepted Answer

mpls l2transport route 10.1.1.2 100. The `mpls l2transport route` command is used under the xconnect configuration on a PE router to specify the remote PE's IP address and the VC ID for the pseudowire. This command establishes the MPLS L2VPN circuit by creating a targeted LDP session for label exchange, which is required for EoMPLS pseudowire setup.

Answer

l2vpn xconnect context

Answer

neighbor 10.1.1.2 remote-as 100

Answer

pseudowire 10.1.1.2 100 encapsulation mpls