350-501 Practice Test 6 — 10 Questions

Question 1

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 2

An engineer is designing an MPLS L3VPN solution and must ensure that the provider edge (PE) routers can handle routing updates for multiple customers without interfering with each other. Which mechanism should be used on the PE routers?

Accepted Answer

VRF-Lite. VRF-Lite (Virtual Routing and Forwarding) is the correct mechanism because it allows a single PE router to maintain multiple separate routing tables (VRFs), each dedicated to a different customer. This ensures that routing updates for one customer are isolated from another, preventing interference. VRF-Lite achieves this without MPLS, using only IP forwarding and per-VRF routing instances.

Answer

Route distinguishers

Answer

Route reflectors

Answer

MPLS-TE

Question 3

A network operator wants to prefer a specific BGP route from a peer for a prefix. After applying a route-map to set local preference to 200, the route is still not preferred over a route from another peer with local preference 150. What could be the issue?

Accepted Answer

The prefix was received with a higher weight.. BGP uses multiple attributes in a specific order of precedence when selecting the best path. Weight (Cisco-proprietary) is checked first, before local preference. If the peer's route has a higher weight (e.g., 32768 for locally injected routes or a manually set value), it will be preferred over a route with a local preference of 200, even if the other route's local preference is only 150.

Answer

The neighbor address-family is not correct.

Answer

The route-map was applied on the wrong BGP neighbor direction.

Answer

The route is received via an IBGP session.

Question 4

Which THREE of the following L3VPN services require the use of a dedicated control plane per VPN instance?

Accepted Answer

6VPE. 6VPE (IPv6 VPN Provider Edge) requires a dedicated control plane per VPN instance because it uses separate per-VPN routing tables and a distinct BGP session (typically MP-BGP with the IPv6 address family) to exchange IPv6 VPN routes. This ensures that each customer's IPv6 routing information is isolated and processed independently, which is a core requirement for L3VPN services that maintain per-VPN forwarding and control plane separation.

Answer

VPLS

Answer

MDT VPN

Question 5

An SP network is implementing BGP PIC (Prefix Independent Convergence) for fast failover. What is the primary mechanism used by BGP PIC to achieve sub-second convergence?

Accepted Answer

It pre-computes and installs a backup path in the FIB for each prefix. BGP PIC uses a backup path (often a pre-computed alternate path) that is installed in the FIB along with the primary path. Upon failure of the primary path, traffic is switched to the backup path without waiting for BGP convergence.

Answer

It uses route summarization to reduce the number of prefixes

Answer

It implements BGP multipath to load balance traffic

Answer

It relies on BFD to detect failures quickly

Question 6

A network engineer is designing a Layer 2 VPN using EVPN with MPLS data plane. The customer requires all-hub multipoint connectivity with optimal multicast replication. Which EVPN route type is used to advertise multicast group membership?

Accepted Answer

Route Type 6 (Selective Multicast Ethernet Tag). Route Type 6 (Selective Multicast Ethernet Tag) is used in EVPN to advertise multicast group membership for selective multicast replication. This allows the provider edge (PE) routers to build optimal multicast trees for specific groups, enabling efficient all-hub multipoint connectivity with EVPN-MPLS data plane.

Answer

Route Type 3 (Inclusive Multicast Ethernet Tag)

Answer

Route Type 2 (MAC/IP Advertisement)

Answer

Route Type 4 (Ethernet Segment)

Question 7

In SRv6, which SID behavior is used to achieve L3VPN IPv6 VPN forwarding, where the SID points to a VPN instance and performs decapsulation and IPv6 lookup?

Accepted Answer

End.DT6. End.DT6 is the SRv6 endpoint behavior for L3VPN over IPv6, performing decapsulation and lookup in the appropriate VPN routing table.

Answer

End.X

Answer

End.DT2U

Answer

End.DT4

Question 8

A service provider is deploying Segment Routing in the MPLS core using IS-IS. Which extension is required in IS-IS to advertise the prefix-SID?

Accepted Answer

Sub-TLV 3 (Prefix-SID). In IS-IS, the Prefix-SID is advertised using Sub-TLV 3, which is carried within TLV 135 (Extended IP Reachability). This sub-TLV contains the SID value and flags, enabling Segment Routing in the MPLS core. Without Sub-TLV 3, the prefix-SID cannot be signaled, making it the required extension.

Answer

TLV 22 (Extended IS Reachability)

Answer

TLV 242 (Router Capability)

Answer

TLV 135 (Extended IP Reachability)

Question 9

A large service provider operates a national MPLS backbone with over 200 P routers and 500 PE routers. They use IS-IS as the IGP with segment routing and have deployed TI-LFA for link and node protection. Recently, a core router (P1) suffered a complete failure, and during the failure, traffic for some prefixes was dropped for over 200ms. After the failure, the network recovered within seconds. The engineer suspects that TI-LFA did not provide the expected sub-50ms protection for some destinations. Further analysis reveals that the affected prefixes have their BGP next-hop on a router that is multiple hops away, and the P1 failure impacted both the primary path and the backup path computed by TI-LFA. The engineer reviews the TI-LFA configuration and finds that 'fast-reroute per-prefix ti-lfa' is enabled under router isis. The engineer also notes that P1 was not a protecting node for those prefixes. Which action should the engineer take to improve convergence time for these prefixes?

Accepted Answer

Add the 'sr-protect' option under the fast-reroute configuration to enable node protection. For TI-LFA to provide node protection, the 'sr-protect' option should be configured, which forces the node to attempt to provide protection even for traffic that transits through the node. Option A is wrong because interface-level TI-LFA would not help; the issue is node-level. Option C is wrong because increasing IGP timers may cause slower convergence. Option D is wrong because there is no need for an additional LDP backup.

Answer

Configure TI-LFA on all interfaces using 'fast-reroute per-prefix ti-lfa interface'

Answer

Reduce the IGP timers and enable incremental SPF to accelerate convergence

Answer

Deploy LDP as a fallback label distribution protocol to provide additional backup paths

Question 10

In a service provider network, the access layer connects end customers. Which technology is commonly used for fibre-based access in GPON deployments?

Accepted Answer

GPON. GPON (Gigabit Passive Optical Network) is a fibre-based access technology standardized by ITU-T.

Answer

DSL

Answer

MPLS

Answer

Metro Ethernet