300-410 Practice Test 26 — 15 Questions

Question 1

An engineer configures BFD for EIGRP and also applies an offset-list to increase the metric of a route. The BFD session is up, but the route with the offset-list is not being installed in the routing table. The engineer verifies that the offset-list is correctly configured. What is the most likely explanation?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The offset-list increased the feasible distance beyond the advertised distance, making the route no longer feasible.. EIGRP offset-lists can increase the metric of a route, but they affect the feasible distance (FD), not the advertised distance (AD). If the offset-list increases the FD such that the route is no longer feasible (i.e., the FD exceeds the AD of the successor), the route may be removed from the topology table. BFD does not interact with offset-lists.

Answer

The offset-list is applied to the wrong interface, so it does not affect the route.

Answer

The BFD session is flapping, causing EIGRP to remove the route.

Answer

The offset-list is using a metric that exceeds the maximum hop count for EIGRP.

Question 2

A network engineer is troubleshooting an MPLS L3VPN where CE1 cannot reach CE2. The PE routers are running OSPF as the IGP and LDP for label distribution. On PE1, the engineer sees that the VRF route for CE2's subnet is present, but the corresponding MPLS label is missing in the LFIB. The show mpls ldp neighbor command shows LDP neighbors are up. What is the most likely cause of the missing label?

Accepted Answer

LDP is not enabled on the interface facing the next-hop router.. The missing label in the LFIB despite the VRF route being present indicates that LDP is not binding a label to the BGP next-hop of the VPN route. Since the IGP route to the BGP next-hop is present but LDP has not assigned a label for it, the issue is likely that LDP is not enabled on the interface facing the next-hop router.

Answer

The VRF route is not redistributed into BGP on the remote PE.

Answer

MTU mismatch on the link between PE1 and P causes label imposition failure.

Answer

The mpls label protocol ldp command is missing under the VRF.

Question 3

A network engineer is troubleshooting an MPLS L3VPN where CE1 can ping the PE1 interface but cannot ping CE2. On PE1, show ip route vrf CUSTOMER shows the route to CE2's subnet, but show bgp vpnv4 unicast all neighbors 10.0.0.2 advertised-routes does not show the route. The BGP session between PE1 and PE2 is established. What is the most likely cause?

Accepted Answer

A route-map applied to the VRF export is filtering the route.. The route is present in the VRF but not advertised to the remote PE, indicating a BGP policy issue. Since the BGP session is up, the most likely cause is that the route is not being redistributed into BGP or is being filtered by a route-map or prefix-list on the VRF export.

Answer

The VRF export route-target does not match the import route-target on the remote PE.

Answer

The BGP session is not using the correct update-source.

Answer

The next-hop-self command is missing under the VRF address-family.

Question 4

What is the default export interval for NetFlow data when using the 'flow exporter' with UDP as the transport protocol?

Accepted Answer

Exports are triggered by flow aging or cache fullness, not a fixed interval.. The default export interval is based on flow cache timeout; there is no fixed interval—exports occur when flows age out or cache is full.

Answer

Every 60 seconds

Answer

Every 30 seconds

Answer

Every 10 seconds

Question 5

Which of the following is a mandatory field in a Flexible NetFlow flow record for IPv4 traffic?

Accepted Answer

Source IP address. The source IP address is a mandatory field in any IPv4 flow record; other fields like destination port are optional.

Answer

Destination port

Answer

Protocol type

Answer

TCP flags

Question 6

A network engineer is troubleshooting MPLS L3VPN where traffic from CE1 to CE2 is being dropped. On PE1, show mpls forwarding-table shows that the label for the BGP next-hop is 'Pop tag' (implicit null). The engineer checks the remote PE and sees that it is advertising implicit null for the BGP next-hop. What is the most likely reason for the traffic drop?

Accepted Answer

The remote PE does not have the CE route in its VRF.. Implicit null (pop tag) means the penultimate hop pops the label and forwards the IP packet. If the traffic is dropped, the issue is likely that the remote PE does not have a route to the CE in its VRF, so it drops the IP packet after label pop.

Answer

The penultimate hop is not popping the label correctly.

Answer

The MTU on the link between P and PE2 is too small.

Answer

The remote PE is configured with explicit null for the BGP next-hop.

Question 7

Drag and drop the steps to configure Flexible NetFlow with a custom flow record into the correct order, from first to last.

Accepted Answer

Define flow record with match ipv4 source address. The correct order follows Cisco IOS-XE configuration logic: first define the flow record with match fields, then define the flow exporter with destination and source, then define the flow monitor binding record and exporter, then apply the monitor to an interface in the ingress direction, and finally verify with 'show flow monitor'.

Question 8

Examine this MPLS configuration on a router:

ip cef
!
interface GigabitEthernet0/0
 ip address 172.16.1.1 255.255.255.252
 mpls ip
!
interface GigabitEthernet0/1
 ip address 172.16.2.1 255.255.255.252
!
router eigrp 100
 network 172.16.0.0
!
mpls ldp router-id Loopback0 force

What is the problem with this configuration?

Accepted Answer

The 'mpls ldp router-id' command references Loopback0, but no loopback interface is configured, causing LDP to fail.. The LDP router-id is set to Loopback0, but Loopback0 is not configured. This will cause LDP to fail to establish a router ID, and LDP sessions will not form. Additionally, EIGRP is used but that is fine. The missing loopback interface is the key issue.

Answer

EIGRP is not supported with MPLS; OSPF or IS-IS must be used.

Answer

The 'mpls ip' command is missing on GigabitEthernet0/1, so MPLS will not work on that interface.

Answer

CEF must be enabled under each interface, not just globally.

Question 9

An engineer configures Flexible NetFlow with a user-defined flow record that includes 'match ipv4 source address' and 'collect counter bytes'. Which TWO additional statements about this configuration are true? (Choose TWO.)

Accepted Answer

The 'match ipv4 source address' command defines a key field that is used to uniquely identify flows.. In Flexible NetFlow, the 'match' fields define the flow key; flows are uniquely identified by the combination of all match fields. The 'collect' fields define non-key data that is aggregated per flow. The flow record must be referenced by a flow monitor, which is then applied to an interface. The default flow record is 'netflow-original', which includes many default keys. The 'match' fields cannot be omitted; at least one match field is required. The 'collect' fields are optional and can include counters, timestamps, etc.

Answer

The flow record must be applied directly to an interface using the 'ip flow record' command.

Answer

If no 'match' commands are configured, the router will use the default match fields from the 'netflow-original' record.

Answer

The flow record can be used by both IPv4 and IPv6 traffic simultaneously without additional configuration.

Question 10

Which THREE symptoms indicate a potential MPLS label switching issue on a Cisco router? (Choose THREE.)

Accepted Answer

The output of 'show mpls forwarding-table' shows 'no label' for a specific prefix.. MPLS issues often manifest as incorrect label operations. 'show mpls forwarding-table' showing 'no label' for a route indicates a missing label binding. 'show mpls ldp neighbor' showing 'state: OPERATIONAL' is normal, not a symptom. 'debug mpls ldp errors' showing 'Label bindings not received' indicates a problem. 'show mpls forwarding-table' showing 'Pop tag' for a non-egress router suggests a misconfiguration. 'show mpls interfaces' showing 'IP' only (not MPLS) indicates MPLS is not enabled on the interface.

Answer

The output of 'show mpls ldp neighbor' shows 'state: OPERATIONAL' for all neighbors.

Answer

The output of 'show mpls interfaces' shows 'IP' only for an interface configured for MPLS.

Question 11

In ERSPAN, what is the default encapsulation type used for transporting mirrored packets across an IP network?

Accepted Answer

GRE. ERSPAN uses GRE (Generic Routing Encapsulation) to encapsulate the original packets for transport over an IP network.

Answer

IPsec

Answer

MPLS

Answer

VXLAN

Question 12

A network engineer is troubleshooting a route redistribution issue between OSPF and EIGRP. Routers R1 (OSPF) and R2 (EIGRP) are redistributing routes. The engineer notices that some OSPF routes are appearing in the EIGRP topology table on R2, but traffic to those destinations is being dropped. The show ip route command on R2 shows the redistributed routes with a next-hop of the R1 interface, but the route is not installed in the routing table. What is the most likely cause?

Accepted Answer

The redistribute ospf command under EIGRP is missing the default-metric configuration.. When redistributing from OSPF into EIGRP, the redistributed routes may have a next-hop that is not reachable via EIGRP, causing the route to be not installed in the routing table. This is often due to the default-metric not being set, causing EIGRP to use an incorrect metric.

Answer

OSPF has a higher administrative distance than EIGRP.

Answer

The EIGRP process on R2 has a distribute-list blocking these routes.

Answer

The OSPF process on R1 has a route filter blocking these routes.

Question 13

Drag and drop the steps to troubleshoot route summarization adjacency or connectivity failures into the correct order, from first to last.

Accepted Answer

Verify the summarization router has a null0 route. Start by verifying that the summarization router has a route to the null0 interface to prevent loops. Then, confirm that the summary route is being advertised to neighbors using show ip route. Next, check that the neighbor router receives the summary in its routing table. After that, examine the neighbor's routing table for the specific summarized prefix. Finally, test end-to-end connectivity using ping or traceroute to ensure the summary works.

Question 14

What is the default LDP keepalive timer value on Cisco IOS-XE routers?

Accepted Answer

180 seconds. The default LDP keepalive timer is 180 seconds, which is used to maintain the LDP session if no other messages are exchanged.

Answer

120 seconds

Answer

60 seconds

Answer

300 seconds

Question 15

Which MPLS label value is reserved for the Explicit NULL label and what is its purpose?

Accepted Answer

Label 0; used for the Explicit NULL label to indicate that the penultimate hop should pop the label.. Label value 0 is the IPv4 Explicit NULL label, used to signal the penultimate hop to pop the label stack and forward the packet based on the IP header.

Answer

Label 1; used for the Router Alert label.

Answer

Label 2; used for the Implicit NULL label.

Answer

Label 3; used for the Implicit NULL label.