350-501 Networking Practice Test 6 — 15 Questions

Question 1

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, the BGP best path selection process evaluates the AS path length. A shorter AS path is preferred because it indicates a less complex path to the destination network. This attribute is directly compared next, making option C correct.

Answer

Next-hop IP address

Answer

Router ID

Question 2

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 operates on the assumption that every downstream router wants to receive multicast traffic for a given group. It initially floods multicast traffic out all PIM-enabled interfaces, then prunes back branches that do not have interested receivers. This flood-and-prune behavior is fundamental to PIM-DM's design for dense multicast environments.

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 3

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_COMMUNITY' is applied to the eBGP neighbor 10.1.1.1 via the `neighbor 10.1.1.1 route-map SET_COMMUNITY in` command. The route-map first matches all routes with `match ip address prefix-list ANY` (which permits 0.0.0.0/0 le 32), then executes the `set community 65000:100 65000:200` action. Since the `additive` keyword is not used, the set command replaces any existing communities with the two listed communities (65000:100 and 65000:200). Therefore, both communities are attached to the route 172.16.1.0/24.

Answer

65000:100 only

Answer

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

Answer

65000:200 only

Question 4

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 exhibit shows that the local router (192.168.1.2) has allocated label 161 for prefix 10.1.1.0/24, as indicated in the output of the 'show mpls forwarding-table' command. This label is assigned by the local router as the ingress LSR to forward traffic toward the egress LSR (192.168.1.1). The correct statement is that the local router allocated label 161 for this 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 5

Based on the exhibit, which OSPF network type is configured on this interface?

Accepted Answer

Point-to-Point. The OSPF network type is determined by the interface configuration. The 'ip ospf network point-to-point' command explicitly sets the interface to point-to-point mode, which eliminates the need for DR/BDR election and uses multicast hello packets (224.0.0.5) to neighbors. This is the correct answer because the exhibit shows this exact configuration.

Answer

Non-Broadcast

Answer

Broadcast

Answer

Point-to-Multipoint

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.. When the 'show mpls forwarding-table' command shows 'Untagged' for a specific FEC, it indicates that the router is performing Penultimate Hop Popping (PHP). In PHP, the penultimate router (the router before the egress LSR) pops the MPLS label and forwards the packet as an IP packet (untagged) to the egress LSR. This is standard behavior to avoid the egress LSR having to perform a double lookup.

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.. 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 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.. Segment Routing (SR) can operate without LDP by encoding the forwarding path as a list of MPLS labels derived from the IGP. For routers to allocate and advertise these SR-MPLS labels, the IGP (IS-IS or OSPF) must have the Segment Routing extension enabled. This allows the IGP to distribute prefix-SIDs (labels) that routers use to forward packets, eliminating the need for LDP.

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

In a Layer 3 MPLS VPN, a customer site that is part of VRF RED is unable to communicate with another site that is also in VRF RED. The 'show ip bgp vpnv4 vrf RED' command shows the routes, but the router does not install them in the routing table. Which configuration element is most likely missing?

Accepted Answer

The route-target import on the receiving PE.. In a Layer 3 MPLS VPN, VRF RED routes are learned via MP-BGP between PEs. The 'show ip bgp vpnv4 vrf RED' command confirms the routes are present in the BGP table, but they are not installed in the routing table because the receiving PE lacks the correct route-target import configuration. The route-target import statement on the VRF determines which VPNv4 routes are accepted and installed into the VRF's RIB; without it, the routes remain in BGP but are not added to the routing table.

Answer

A BGP session between PEs.

Answer

The route-target export on the receiving PE.

Answer

An MPLS LDP session between PEs.

Question 10

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.. The 'set-overload-bit' command causes the IS-IS router to set the overload bit in its Link State PDUs (LSPs). This signals to other routers that the advertising router should not be used for transit traffic, but it still participates in SPF calculations and can be reached as a leaf or end node. Therefore, the router retains its routes and adjacency, but other routers will not forward traffic through it.

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 11

An engineer configures MPLS TE tunnels. After configuration, the tunnel remains down. The 'show mpls traffic-eng tunnels' output shows 'Tunnel is down - path computation failed'. What is the most likely cause?

Accepted Answer

IGP TE extensions are not enabled on the head-end router.. The 'path computation failed' error indicates that the head-end router cannot find a valid path for the MPLS TE tunnel. IGP TE extensions (OSPF TE or IS-IS TE) must be enabled on the head-end router to flood link attributes (bandwidth, TE metrics) and build the TED (Traffic Engineering Database). Without the TED, CSPF (Constrained Shortest Path First) cannot compute a path, leaving the tunnel down.

Answer

RSVP is not enabled on the head-end router.

Answer

MPLS LDP is not enabled on the head-end router.

Answer

There is an MTU mismatch along the path.

Question 12

A router is receiving a BGP prefix with community 100:100. The operator wants to modify the local preference to 200 for this prefix. Which configuration will achieve this?

Accepted Answer

route-map SET_LP permit 10, match community 100, set local-preference 200. The route-map uses `match community 100` to identify the BGP community value 100:100 (in Cisco's default format, the community is matched without the colon), and `set local-preference 200` modifies the local preference for that prefix to 200. This is the standard method to influence inbound BGP path selection by adjusting local preference based on community matching.

Answer

route-map SET_LP permit 10, match ip address prefix-list, set weight 200

Answer

ip bgp-community new-format, route-map SET_LP permit 10, match community 100, set community 200

Answer

route-map SET_LP permit 10, match community 100, set metric 200

Question 13

An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?

Accepted Answer

The LSA refresh interval has expired.. In OSPF, LSAs have a default refresh interval of 30 minutes (1800 seconds). When this timer expires, the router that originated the LSA re-floods it to maintain database synchronization, even if no topology changes have occurred. This is normal OSPF behavior defined in RFC 2328, and it explains why LSAs are flooded every 30 minutes.

Answer

The routers are using LSU packets incorrectly.

Answer

There is a flapping interface on the network.

Answer

The dead timer is set too low.

Question 14

An engineer is troubleshooting BGP convergence. The router has multiple paths for a prefix, but it selects a path with a lower local preference over a path with a higher local preference. The higher local preference path is from an EBGP peer. What could cause this?

Accepted Answer

The path with lower local preference has a higher weight.. B is correct because BGP selects the path with the highest weight first, before considering local preference. Weight is a Cisco-proprietary attribute that is local to the router and takes precedence over all other BGP attributes. Therefore, a path with a lower local preference but a higher weight will be preferred over a path with a higher local preference but a lower weight, even if the higher local preference path comes from an EBGP peer.

Answer

The router is configured with 'bgp deterministic-med'.

Answer

The path with lower local preference has a higher router ID.

Answer

The path with lower local preference has a lower MED.

Question 15

Which TWO conditions must be met for a BGP route to be considered valid and used for forwarding?

Accepted Answer

The route must be the best path selected by BGP.. BGP only installs the best path into the routing table for forwarding. BGP selects a single best path from all available paths for a given prefix based on its path selection algorithm (e.g., highest weight, local preference, shortest AS path). Only this best path is considered valid for forwarding, even if multiple paths exist in the BGP table.

Answer

The BGP synchronization must be enabled.

Answer

The AS path must not contain the router's own AS.

Answer

The prefix must be in the BGP table.