350-501 Networking Practice Test 13 — 15 Questions

Question 1

Which BGP attribute is used to influence inbound traffic to a multi-homed AS by indicating the preferred entry point?

Accepted Answer

MED. MED (Multi-Exit Discriminator) is used to influence inbound traffic from neighboring ASes by suggesting the preferred path into the AS.

Answer

AS_PATH

Answer

COMMUNITY

Answer

LOCAL_PREF

Question 2

A service provider is designing an OSPF network with multiple areas. Which TWO area types allow external routes (Type 5 LSAs) to be injected into the area? (Choose two.)

Accepted Answer

Standard area. Standard areas and the backbone area (Area 0) allow Type 5 LSAs. Stub, totally stubby, and NSSA do not accept Type 5 LSAs (NSSA converts Type 7 to Type 5 at ABR, but internally uses Type 7).

Answer

NSSA

Answer

Stub area

Answer

Totally stubby area

Question 3

Which TWO of the following are valid BGP extended community attributes? (Choose two.)

Accepted Answer

Site of Origin (SoO). Site of Origin (SoO) and Route Target (RT) are well-known BGP extended communities. Route Origin (RO) is a standard community, not an extended community. Standard and Large communities are also not extended communities. Thus, only SoO and RT are correct among the options, but the question asks for three; note that Color or Bandwidth are other valid extended communities not listed here.

Answer

Route Origin (RO)

Answer

Standard community

Answer

Large community

Question 4

An engineer is configuring BGP route reflectors to scale iBGP. Which TWO attributes are used to prevent routing loops in a route reflector cluster? (Choose two.)

Accepted Answer

ORIGINATOR_ID. CLUSTER_LIST and ORIGINATOR_ID are used to prevent loops. CLUSTER_LIST is a sequence of cluster IDs; ORIGINATOR_ID identifies the originator.

Answer

NEXT_HOP

Answer

LOCAL_PREF

Answer

AS_PATH

Question 5

Which IS-IS router type maintains a full Layer 2 routing table of all areas and can act as a gateway between areas?

Accepted Answer

Level 2. In IS-IS, Level 2 routers route between areas and maintain a complete L2 database. Level 1 routers route within an area, and Level 1/2 routers act as both, but the question asks for the type that maintains a full L2 routing table of all areas. Level 2 routers specifically perform inter-area routing.

Answer

Level 0

Answer

Level 1/2

Answer

Level 1

Question 6

An SP engineer is designing an OSPF network with several remote sites that should not receive external routes but need to reach external destinations via a default route. Which OSPF area type best meets this requirement while also preventing Type 5 LSAs from entering?

Accepted Answer

Totally stubby area. A totally stubby area blocks Type 5 and Type 3 LSAs (except a default route). A stub area blocks Type 5 but allows Type 3 (inter-area routes). An NSSA allows Type 7 LSAs for external routes from the area. A totally stubby area is the correct choice because it blocks both Type 5 and Type 3 (except default), meeting the requirement.

Answer

NSSA

Answer

Backbone area 0

Answer

Stub area

Question 7

In BGP, an SP router receives multiple routes to the same prefix. The first route has a weight of 100, LOCAL_PREF of 200, AS_PATH length 3, and is learned via eBGP. The second route has weight 50, LOCAL_PREF 150, AS_PATH length 2, and is learned via iBGP. According to BGP route selection, which route will be preferred?

Accepted Answer

The first route (weight 100). BGP selection order: highest weight first. Route 1 has weight 100, Route 2 has weight 50, so Route 1 is preferred regardless of other attributes.

Answer

The second route (AS_PATH length 2)

Answer

The first route (eBGP learned)

Answer

The second route (LOCAL_PREF 150)

Question 8

Which IS-IS TLV is used to carry Traffic Engineering (TE) information such as link bandwidth and TE metric in modern SP networks?

Accepted Answer

TLV 22 (extended IS reachability). IS-IS TE extensions use sub-TLVs within the extended IS reachability TLV (type 22). Specifically, TLV 135 (extended IP reachability) carries wide metrics, but TE information is carried in the extended IS reachability TLV (type 22) with sub-TLVs. The question asks for the TLV that carries TE info; the correct answer is the extended IS reachability TLV (type 22).

Answer

TLV 128 (IP reachability)

Answer

TLV 135 (extended IP reachability)

Answer

TLV 1 (area addresses)

Question 9

A service provider is implementing 6PE to carry IPv6 traffic over an existing MPLS IPv4 core. Which BGP extension is required on the provider edge (PE) routers to exchange IPv6 prefixes with an IPv4 next-hop?

Accepted Answer

MP-BGP for the IPv6 address family with an IPv4 next-hop encoded in the MP_REACH_NLRI. 6PE uses BGP multiprotocol extensions (MP-BGP) with the IPv6 Address Family Identifier (AFI) and subsequent AFI (SAFI) to carry IPv6 prefixes. The next-hop is encoded as an IPv4 address using the 'next-hop' attribute with an IPv4 address. This is done via MP_REACH_NLRI for IPv6 with an IPv4 next-hop.

Answer

BGP IPv6 unicast address family with IPv6 next-hop

Answer

BGP IPv4 unicast address family with the IPv6 prefix as a label

Answer

BGP VPNv4 address family

Question 10

An SP network uses OSPF with RSVP-TE for traffic engineering. Which OSPF extension is required to advertise TE link parameters such as maximum reservable bandwidth?

Accepted Answer

OSPF Type 10 Opaque LSAs. OSPF TE extensions are defined in RFC 3630, which introduces the Opaque LSA (Type 9, 10, 11). Specifically, Type 10 Opaque LSAs carry TE information. The TE LSA is carried in an Opaque LSA of area scope (Type 10).

Answer

OSPF Type 7 LSAs

Answer

OSPF Type 11 Opaque LSAs

Answer

OSPF Type 5 LSAs

Question 11

In an IS-IS network, a service provider wants to achieve fast convergence using Partial Route Computation (PRC). Which of the following events triggers a PRC instead of a full SPF?

Accepted Answer

An IP prefix is withdrawn from a directly connected network. PRC is triggered when an IP prefix changes (addition, removal, or metric change) without a change in the IS-IS topology (i.e., no change in adjacency or reachable IS-IS neighbors). PRC only recalculates the affected prefixes, avoiding full SPF.

Answer

A router's system ID changes

Answer

An LSP with a new fragment arrives

Answer

A new adjacency is formed between two routers

Question 12

Which BGP attribute is used to indicate the preference of a route within an AS and is propagated to iBGP peers but not to eBGP peers by default?

Accepted Answer

LOCAL_PREF. LOCAL_PREF is a well-known discretionary attribute that indicates the degree of preference for a route within an AS. It is sent to iBGP peers but not to eBGP peers by default.

Answer

WEIGHT

Answer

MED

Answer

AS_PATH

Question 13

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 14

An SP is deploying NAT64 to allow IPv6-only clients to access IPv4 servers. Which address translation mechanism is used by NAT64 to map IPv6 addresses to IPv4 addresses?

Accepted Answer

Embedding IPv4 addresses in IPv6 addresses using a predefined prefix. NAT64 uses a well-known prefix (64:ff9b::/96) to embed IPv4 addresses into IPv6 addresses. The IPv4 address is appended to the prefix, creating an IPv6 address that represents the IPv4 destination.

Answer

IPv6-over-IPv4 tunneling

Answer

DNS64

Answer

Stateful translation of IPv6 to IPv4 using a pool of IPv4 addresses

Question 15

In BGP confederation, how does the AS_PATH attribute handle the confederation sub-AS numbers to prevent loops?

Accepted Answer

Confederation sub-AS numbers are carried in a separate confederation AS_PATH segment and are stripped when routes leave the confederation. In BGP confederation, confederation sub-AS numbers are carried in a separate confederation AS_PATH segment and are not visible to external BGP peers. The confederation AS_PATH is used for loop prevention within the confederation, while the regular AS_PATH remains unchanged when routes leave the confederation.

Answer

Confederation sub-AS numbers are added to the regular AS_PATH

Answer

Confederation sub-AS numbers are replaced by the confederation identifier

Answer

Confederation sub-AS numbers are ignored for loop detection