350-501 Practice Test 14 — 15 Questions

Question 1

A service provider wants to influence inbound traffic from a customer AS. The customer AS is multi-homed to two provider ASes. Which BGP community is most effective to make the customer prefer a specific entry point?

Accepted Answer

Set community 'local-preference 200' on routes from the desired entry point.. The provider can set the 'prepend' community (e.g., 100:1) to request the customer to prepend AS path, but that is outbound. To influence inbound, the provider should use communities that affect the customer's BGP decision process, like local preference. However, the most effective is to set a higher local preference on routes advertised to the customer from the desired entry point. This is typically done via the 'local-preference' community (e.g., 2:100).

Answer

Set community 'no-export' on routes from the undesired entry point.

Answer

Set community 'prepend 3' on routes from the desired entry point.

Answer

Set community 'no-advertise' on routes from the undesired entry point.

Question 2

Which THREE BGP path attributes are considered during the best path selection process after local preference? (Choose three.)

Accepted Answer

Multi-exit discriminator (MED). After local preference, BGP considers: AS path length, origin type, MED (multi-exit discriminator). Next-hop is considered earlier? Actually order: weight, local pref, local (originate), AS path, origin, MED, etc. So correct: AS path, origin, MED.

Answer

Next-hop IP address

Answer

Router ID

Question 3

Which TWO statements correctly describe differences between PIM dense mode and PIM sparse mode? (Choose two.)

Accepted Answer

PIM-DM assumes all downstream routers want to receive multicast traffic, so it initially floods traffic.. PIM-DM floods everywhere and prunes; PIM-SM uses RPs and explicit join. Dense mode uses flood-and-prune; sparse mode uses pull model.

Answer

PIM-DM supports the use of a bootstrap router (BSR) for RP discovery.

Answer

PIM-SM is more bandwidth efficient for high density groups.

Answer

PIM-DM uses explicit join messages, while PIM-SM uses flood and prune.

Question 4

A network engineer applies the above configuration on a PE router. The PE receives route 172.16.1.0/24 from eBGP peer 10.1.1.1. Which communities will be attached to this route?

Accepted Answer

65000:100 and 65000:200. The route-map SET_COMM matches prefix 172.16.1.0/24 (permitted by prefix-list CUSTOMER). It sets two communities: 65000:100 and 65000:200. Standard community list includes both.

Answer

65000:100 only

Answer

No communities are attached because the route-map does not specify additive.

Answer

65000:200 only

Question 5

Based on the exhibit, which statement about label allocation for prefix 10.1.1.0/24 is true?

Accepted Answer

The local router allocated label 161 for the prefix. The remote binding from 192.168.2.2 shows 'imp-null', meaning that router is advertising an implicit null label (POP). This indicates that the next-hop is directly connected or the router is the egress for that prefix.

Answer

Router 192.168.2.2 is the penultimate hop for this prefix.

Answer

The local router will use PHP for this prefix.

Answer

Router 192.168.1.1 is the egress LSR for this prefix.

Question 6

An engineer is troubleshooting MPLS forwarding. On a router, the 'show mpls forwarding-table' command displays that for a specific FEC, the outgoing label is 'Untagged'. What does this indicate?

Accepted Answer

The router is the penultimate hop, performing PHP.. Option A is correct because 'Untagged' indicates that the router is performing Penultimate Hop Popping (PHP), meaning it will remove the MPLS label before forwarding to the egress router. Option B is incorrect because the egress LSR would typically show 'Pop Label' or the label itself. Option C is plausible but not standard; 'Untagged' does not indicate lack of MPLS support on the next-hop. Option D is incorrect because explicit null would show 'ExpNull'.

Answer

The label has been explicitly null.

Answer

The router is the egress LSR.

Answer

The next-hop router does not support MPLS.

Question 7

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.. Option D is correct because BGP path selection checks weight first. If the other route has a higher weight (Cisco proprietary), it will be preferred regardless of local preference. Option A is incorrect because even if applied incorrectly, local preference would still take effect from internal peers. Option B is plausible but less likely; address-family mismatch would prevent route exchange entirely. Option C is incorrect because local preference is compared among all received routes.

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 8

An engineer is deploying Segment Routing in an MPLS network. To ensure that routers can forward packets based on SR-MPLS labels without requiring LDP, which requirement must be met?

Accepted Answer

IS-IS or OSPF must have the SR extension enabled.. Option C is correct because for SR-MPLS forwarding, the IGP (IS-IS or OSPF) must have the Segment Routing extension enabled to distribute prefix-SIDs. Option A is incorrect; BGP-LU is not required for SR-MPLS. Option B is incorrect; LDP is not needed if SR is used. Option D is incorrect; the overload bit is unrelated.

Answer

MPLS LDP must be enabled on all interfaces.

Answer

All routers must run BGP-LU.

Answer

The IGP must have the overload bit set.

Question 9

A service provider is deploying MPLS in its core network. The core routers are all configured with LDP. Which label operation does an ingress PE perform on the first packet of a new flow?

Accepted Answer

Push a new label onto the packet. The ingress PE pushes a new label onto the packet. Option B is correct because LDP assigns labels for each FEC, and the ingress PE pushes an outer label. Option A is wrong because swapping is done at transit LSRs. Option C is wrong because PHP results in label removal at the penultimate hop. Option D is wrong because pop is the same as removal.

Answer

Remove the label stack entirely

Answer

Pop the label (PHP)

Answer

Swap the incoming label for an outgoing label

Question 10

Which THREE are requirements for deploying MPLS Traffic Engineering with RSVP-TE?

Accepted Answer

Links must have reservable bandwidth advertised. RSVP-TE signaling, CSPF computation, and reservable bandwidth are key. Options B, D, and E are correct. Option A is wrong because LDP is not required. Option C is wrong because OSPFv3 is for IPv6; RSVP-TE works with IS-IS or OSPFv2.

Answer

OSPFv3 must be the IGP

Answer

LDP must be enabled on all routers

Question 11

A network engineer is troubleshooting QoS in a service provider environment. Customer traffic is marked with DSCP AF31 (011010) at the CE. On the PE router, the policy maps trust DSCP and sets the CoS to 4. However, core routers remark the DSCP to 0. What is the most likely cause?

Accepted Answer

A policer on the core router is marking down out-of-contract traffic. The core routers likely have a policy that marks down packets exceeding their contracted rate. Option D is correct because a policer could mark down the DSCP. Option A is wrong because MPLS EXP is separate from DSCP. Option B is wrong because MPLS EXP is not involved. Option C is wrong because re-marking on core is not typical if configured correctly.

Answer

The core routers use LDP labels and ignore DSCP

Answer

The ingress PE did not set MPLS EXP bits

Answer

The MPLS EXP bits are not copied from DSCP

Question 12

Which TWO are functions of the MPLS data plane?

Accepted Answer

Label push at ingress LSR. Label push, swap, pop are data plane operations. Options A and C are correct. Option B is wrong because LDP is control plane. Option D is wrong because metric calculation is IGP. Option E is wrong because BGP is control plane.

Answer

Label distribution via LDP

Answer

Metric calculation for routing

Answer

Route exchange via BGP

Question 13

A service provider is deploying Segment Routing (SR) with TI-LFA for fast convergence. Which mechanism does TI-LFA use to repair a link failure in a node segment path?

Accepted Answer

Precomputes a backup path using a segment list (label stack) that avoids the failed link. TI-LFA uses a post-convergence path and pushes additional segment IDs (SIDs) for the repair path. Option A is correct because TI-LFA relies on MPLS label stacking to steer traffic around the failure. Option B is wrong because RSVP-TE is different. Option C is wrong because BFD only detects failure. Option D is wrong because LFA alone does not use segment routing.

Answer

Uses loop-free alternate (LFA) as defined in IPFRR

Answer

Uses RSVP-TE to signal a protected LSP

Answer

Relies on BFD to trigger a backup path in the forwarding table

Question 14

An engineer configures the 'set-overload-bit' command on an IS-IS router. What is the immediate effect on the network?

Accepted Answer

The router is not used as a transit path but still has routes.. Option C is correct because setting the overload bit in IS-IS LSPs tells other routers not to use this router for transit traffic, but it still advertises its own prefixes and can be a destination. Option A is incorrect; the router still participates in SPF. Option B is incorrect; LSPs are still advertised. Option D is incorrect; neighbors remain adjacent.

Answer

The router stops participating in SPF calculations.

Answer

The router's LSPs are no longer advertised.

Answer

The router's neighbors drop adjacency.

Question 15

In an MPLS VPN environment, which address family is used to exchange VPNv4 routes between PE routers?

Accepted Answer

VPNv4 unicast. BGP address family VPNv4 (AF 128) is used to carry IPv4 VPN routes between PEs. Option B is correct. Option A is wrong because IPv4 unicast is for global routes. Option C is wrong because VPNv6 is for IPv6. Option D is wrong because RT is a community attribute, not an address family.

Answer

Route-target (RT)

Answer

IPv4 unicast

Answer

VPNv6 unicast