350-501 Practice Test 21 — 15 Questions

Question 1

An SP engineer configures IS-IS fast convergence mechanisms. Which three techniques help achieve sub-second convergence in IS-IS?

Accepted Answer

Incremental SPF (iSPF). BFD provides fast failure detection, PRC recalculates only affected routes, and SPF incremental (iSPF) reduces SPF computation. LFA provides fast reroute.

Answer

Full SPF recalculation

Answer

LDP label distribution

Question 2

In BGP confederation, which attribute is used to prevent loops between sub-ASes?

Accepted Answer

Confederation AS_PATH. The confederation AS_PATH (AS_CONFED_SEQUENCE and AS_CONFED_SET) is used to track the path within the confederation, and loop detection checks this attribute.

Answer

CLUSTER_LIST

Answer

AS_PATH

Answer

ORIGINATOR_ID

Question 3

In BGP, which attribute is used to prevent routing loops when route reflectors are deployed?

Accepted Answer

Originator ID. Originator ID is used by route reflectors to prevent loops. If a router receives a route with its own router ID as originator, it discards it.

Answer

Cluster ID

Answer

AS_PATH

Answer

NEXT_HOP

Question 4

In BGP route selection, if two routes have the same weight, local preference, and are both locally originated, which attribute is considered next?

Accepted Answer

AS_PATH length. After weight, local pref, and locally originated, BGP compares AS_PATH length (shorter is preferred).

Answer

ORIGIN code

Answer

NEXT_HOP metric

Answer

MED

Question 5

An ISP is implementing BGP PIC (Prefix Independent Convergence) for edge routers. Which BGP feature must be enabled to support PIC for core-facing failures?

Accepted Answer

BGP additional-paths install. BGP PIC relies on installing a backup path in the FIB. For core-facing failures, BGP Fast External Fallover and BGP PIC with backup paths are used; specifically, 'bgp additional-paths install' is needed to install backup paths.

Answer

BGP deterministic-med

Answer

BGP route refresh

Answer

BGP bestpath as-path multipath-relax

Question 6

A service provider deploys BGP route reflectors in the core. Which mechanism prevents routing loops within the route reflector cluster?

Accepted Answer

Originator-id attribute. The originator-id attribute is set by the route reflector to the router-id of the originating router, preventing loops by checking if the originator-id matches the local router-id.

Answer

Next-hop-self command

Answer

Cluster-list attribute and cluster-id

Answer

AS_PATH loop detection

Question 7

Which OSPF network type elects a Designated Router (DR) and Backup Designated Router (BDR) to reduce the number of adjacencies on a multi-access segment?

Accepted Answer

Broadcast. Broadcast network type uses DR/BDR election. Point-to-point and NBMA do not elect DR/BDR (NBMA does elect DR/BDR but is less common).

Answer

Point-to-point

Answer

Loopback

Answer

Point-to-multipoint

Question 8

In SR-TE PCE, which protocol does the PCE use to communicate with the PCC (Path Computation Client) to set up LSPs?

Accepted Answer

PCEP. In Segment Routing Traffic Engineering (SR-TE) with a Path Computation Element (PCE), the PCE communicates with the Path Computation Client (PCC) using the Path Computation Element Protocol (PCEP), as defined in RFC 5440 and extended for SR by RFC 8664. PCEP is specifically designed for path computation requests and responses, and for initiating and setting up LSPs via the PCE-initiated LSP stateful model (RFC 8281). The PCC sends path computation requests to the PCE, and the PCE responds with computed paths, which the PCC then uses to instantiate SR-TE LSPs.

Answer

RESTCONF

Answer

NETCONF

Answer

BGP-LS

Question 9

A service provider wants to provide IPv6 connectivity over an MPLS IPv4 core using 6PE. Which BGP extension is required on the provider edge routers?

Accepted Answer

IPv6 address family with next-hop encoded as an IPv4-mapped IPv6 address. 6PE uses MP-BGP with the IPv6 address family and an IPv4 next-hop (the PE's IPv4 address), encoded via the IPv4-mapped IPv6 address format.

Answer

Labeled unicast IPv4 address family

Answer

VPNv4 address family with route-target extended community

Answer

IPv6 address family with next-hop encoded as an IPv6 address

Question 10

An SP is deploying IPv6 using 6VPE. Which THREE components are required? (Choose three.)

Accepted Answer

Customer edge (CE) routers with IPv6 connectivity. 6VPE requires MPLS core, MP-BGP with VPNv6 address family, and CE routers running IPv6. LDP is used for label distribution in the core.

Answer

6rd tunneling

Answer

NAT64 translation

Question 11

An OSPF network is configured with RSVP-TE. Which OSPF extension is used to advertise TE link attributes such as bandwidth and administrative group?

Accepted Answer

OSPF Type 10 Opaque LSA. OSPF TE extensions use Opaque LSAs (Type 9, 10, 11) to carry TE information. Type 10 (area-local) is commonly used for TE.

Answer

OSPF Type 1 LSA

Answer

OSPF Type 5 LSA

Answer

OSPF Type 7 LSA

Question 12

A service provider is deploying OSPFv3 for IPv6 in its core. The network uses multiple areas. Which LSA type is used by OSPFv3 to advertise prefix information for inter-area routes?

Accepted Answer

Inter-Area Prefix LSA (Type 0x2003). In OSPFv3, Inter-Area Prefix LSAs (Type 0x2003) are used to advertise prefixes from other areas.

Answer

Network LSA (Type 0x2002)

Answer

Intra-Area Prefix LSA (Type 0x2009)

Answer

Router LSA (Type 0x2001)

Question 13

Which IS-IS metric type supports values up to 2^24-1 and is used for traffic engineering?

Accepted Answer

Wide metrics. IS-IS wide metrics use a 24-bit field, allowing values up to 16,777,215, and are required for TE.

Answer

Extended metrics

Answer

Narrow metrics

Answer

TE metrics

Question 14

In IS-IS, which type of router is responsible for exchanging routing information between different areas?

Accepted Answer

L2 router. L2 routers handle inter-area routing in IS-IS, while L1 routers handle intra-area routing. L1/L2 routers act as both.

Answer

L1/L2 router

Answer

L1 router

Answer

Attached router

Question 15

Which three BGP attributes are considered during the route selection process before comparing AS_PATH length? (Choose three.)

Accepted Answer

LOCAL_PREF. Weight, LOCAL_PREF, and locally originated routes are compared before AS_PATH length in the BGP best path selection algorithm.

Answer

NEXT_HOP

Answer

MED