350-501 Practice Test 2 — 10 Questions

Question 1

A service provider is deploying MPLS L3VPN and notices that BGP next-hop resolution for VPNv4 routes fails on the PE routers. The PE routers are running OSPF as the IGP and have loopback interfaces used for LDP and BGP peering. Which configuration change should the engineer implement to ensure that the BGP next-hop is reachable?

Accepted Answer

Configure 'neighbor x.x.x.x update-source loopback0' under the BGP router configuration.. The BGP next-hop for VPNv4 routes is typically the loopback interface of the remote PE router. For BGP to consider the next-hop reachable, the local PE must have an IGP route to that loopback address. The 'neighbor x.x.x.x update-source loopback0' command ensures that BGP uses the loopback interface as the source IP for the TCP session, which aligns the BGP peering address with the IGP-advertised loopback, making the next-hop reachable via OSPF.

Answer

Configure 'neighbor x.x.x.x allowas-in 1' under the BGP VRF configuration.

Answer

Apply the 'neighbor x.x.x.x next-hop-self' command under the BGP VRF configuration.

Answer

Increase the 'maximum-paths' value under the BGP address-family VPNv4.

Question 2

Which TWO are benefits of using Segment Routing (SR) over traditional LDP-based MPLS?

Accepted Answer

Eliminates the need for LDP and RSVP-TE protocols.. Option A is correct because Segment Routing (SR) eliminates the need for the Label Distribution Protocol (LDP) and Resource Reservation Protocol with Traffic Engineering (RSVP-TE) by encoding MPLS labels directly into the Interior Gateway Protocol (IGP), such as OSPF or IS-IS. This simplifies the control plane by removing these protocols entirely, reducing operational complexity and resource overhead.

Answer

Requires only OSPF as the IGP.

Answer

Reduces label imposition at the ingress PE.

Answer

Faster convergence due to BGP PIC.

Question 3

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?

Accepted Answer

ip route vrf RED 0.0.0.0 0.0.0.0 vrf BLUE. Option D is correct because 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 4

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. Option B is correct because a route-map on the VRF export can filter which routes are advertised into VPNv4. Option A is incorrect as RD does not filter advertisements. Option C is incorrect because VPNv4 address-family is shared among PEs. Option D is incorrect as next-hop-self does not control route advertisement.

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 5

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.. Option A is correct because 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 6

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 7

Refer to the exhibit. A service provider is receiving BGP prefixes from a customer (AS 64512). The provider wants to tag all routes from that customer that match prefix 10.1.0.0/16 or more specific with community 65000:100, while not modifying other routes. After applying the configuration, which statement is true?

Accepted Answer

Only routes matching 10.1.0.0/16 or more specific will have the community added; other routes remain unchanged.. The configuration uses a route-map applied to the neighbor with a match clause referencing a prefix-list that permits 10.1.0.0/16 le 32. This matches the exact prefix and any more specific prefix (up to /32). The set community 65000:100 action adds the community without using the additive keyword, but because the route-map does not contain a deny clause for non-matching routes, all routes are still accepted; only matching routes have the community added. Thus, only routes matching 10.1.0.0/16 or more specific will have community 65000:100 added, and other routes remain unchanged.

Answer

Routes with a mask longer than /24 will be rejected by the prefix-list.

Answer

All routes from the customer will have their communities replaced with 65000:100.

Answer

Routes not matching the prefix-list will be denied and not installed.

Question 8

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 9

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 10

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.