MPLS Operations practice questions

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?

Trap 1: The VRF route is not redistributed into BGP on the remote PE.

Incorrect because the VRF route is present on PE1, indicating redistribution is working; the issue is label binding, not route advertisement.

Trap 2: MTU mismatch on the link between PE1 and P causes label imposition…

Incorrect because an MTU mismatch would cause packet drops, not a missing label in the LFIB; LDP would still assign a label.

Trap 3: The mpls label protocol ldp command is missing under the VRF.

Incorrect because LDP is configured globally or per interface, not under a VRF; VRF configuration does not affect LDP label assignment.

A
LDP is not enabled on the interface facing the next-hop router.
Correct because LDP must be enabled on the interface that connects to the next-hop router to assign a label for the IGP route, which is used to resolve the BGP next-hop in MPLS VPN.
B
The VRF route is not redistributed into BGP on the remote PE.
Why wrong: Incorrect because the VRF route is present on PE1, indicating redistribution is working; the issue is label binding, not route advertisement.
C
MTU mismatch on the link between PE1 and P causes label imposition failure.
Why wrong: Incorrect because an MTU mismatch would cause packet drops, not a missing label in the LFIB; LDP would still assign a label.
D
The mpls label protocol ldp command is missing under the VRF.
Why wrong: Incorrect because LDP is configured globally or per interface, not under a VRF; VRF configuration does not affect LDP label assignment.

Question 2hardmultiple choice

A network engineer is troubleshooting MPLS traffic engineering (TE) tunnels. A TE tunnel from Router A to Router B is configured but remains down. The engineer runs show mpls traffic-eng tunnels and sees that the tunnel is in 'down' state with the error 'Path computation failed'. The IGP is OSPF with MPLS TE enabled, and the network is fully meshed. What is the most likely root cause?

Trap 1: The tunnel destination is not reachable via the IGP.

Incorrect because the tunnel destination is a TE tunnel headend; reachability is not required for TE path computation, only the TED.

Trap 2: RSVP is not configured on the tunnel interface.

Incorrect because RSVP is used for signaling, but the path computation fails before signaling; RSVP configuration is not the cause of computation failure.

Trap 3: The tunnel bandwidth is set too high, exceeding available bandwidth.

Incorrect because while bandwidth constraints can cause path computation failure, the error message 'Path computation failed' without specific bandwidth details suggests a more fundamental issue like missing TE configuration.

A
MPLS TE is not enabled on all interfaces along the path.
Correct because MPLS TE must be enabled on each interface to advertise link attributes into the TED; otherwise, the headend cannot compute a constraint-based path.
B
The tunnel destination is not reachable via the IGP.
Why wrong: Incorrect because the tunnel destination is a TE tunnel headend; reachability is not required for TE path computation, only the TED.
C
RSVP is not configured on the tunnel interface.
Why wrong: Incorrect because RSVP is used for signaling, but the path computation fails before signaling; RSVP configuration is not the cause of computation failure.
D
The tunnel bandwidth is set too high, exceeding available bandwidth.
Why wrong: Incorrect because while bandwidth constraints can cause path computation failure, the error message 'Path computation failed' without specific bandwidth details suggests a more fundamental issue like missing TE configuration.

Question 3mediummultiple choice

A network engineer is troubleshooting an MPLS L2VPN (VPWS) where the pseudowire between two PE routers is down. The show mpls l2transport vc command displays state 'down' and the VC ID is correct on both ends. The engineer checks the MPLS LDP session and sees it is up, but the targeted LDP session for the pseudowire is not established. What is the most likely cause?

Trap 1: The VC ID does not match on both ends.

Incorrect because the stem states the VC ID is correct on both ends; a mismatch would cause a different symptom.

Trap 2: The IGP is not converging, causing reachability issues.

Incorrect because the LDP session is up, indicating IGP reachability is fine; the targeted session is a separate issue.

Trap 3: The mpls label protocol ldp command is missing globally.

Incorrect because LDP is already operational (session up), so the global protocol is configured; the targeted session requires additional configuration.

A
The mpls ldp neighbor command is missing on one or both PEs.
Correct because targeted LDP sessions require explicit configuration using the mpls ldp neighbor command to initiate the session for pseudowire signaling.
B
The VC ID does not match on both ends.
Why wrong: Incorrect because the stem states the VC ID is correct on both ends; a mismatch would cause a different symptom.
C
The IGP is not converging, causing reachability issues.
Why wrong: Incorrect because the LDP session is up, indicating IGP reachability is fine; the targeted session is a separate issue.
D
The mpls label protocol ldp command is missing globally.
Why wrong: Incorrect because LDP is already operational (session up), so the global protocol is configured; the targeted session requires additional configuration.

Question 4mediummultiple choice

A network engineer is troubleshooting MPLS traffic where packets are being dropped at a P router. The engineer runs show mpls forwarding-table and sees that the outgoing label for a specific FEC is 'Untagged' instead of a valid label. The IGP is running correctly, and LDP neighbors are established. What is the most likely cause?

Trap 1: The IGP metric is too high, causing LDP to prefer a different path.

Incorrect because LDP uses IGP next-hop; if the IGP metric is high, LDP still assigns a label, but the path may be suboptimal.

Trap 2: The mpls label range is exhausted.

Incorrect because label exhaustion would cause LDP to fail to allocate labels, but the symptom would be 'No label' or 'Label allocation failed', not 'Untagged'.

Trap 3: The router is configured with mpls ldp advertise-labels for host…

Incorrect because this command controls which prefixes are advertised, not whether LDP is enabled on an interface; the FEC would not be advertised at all, not show as 'Untagged'.

A
LDP is not enabled on the outgoing interface.
Correct because LDP must be enabled on each interface to assign a label for the FEC; without it, the label remains 'Untagged' and packets are dropped.
B
The IGP metric is too high, causing LDP to prefer a different path.
Why wrong: Incorrect because LDP uses IGP next-hop; if the IGP metric is high, LDP still assigns a label, but the path may be suboptimal.
C
The mpls label range is exhausted.
Why wrong: Incorrect because label exhaustion would cause LDP to fail to allocate labels, but the symptom would be 'No label' or 'Label allocation failed', not 'Untagged'.
D
The router is configured with mpls ldp advertise-labels for host routes only.
Why wrong: Incorrect because this command controls which prefixes are advertised, not whether LDP is enabled on an interface; the FEC would not be advertised at all, not show as 'Untagged'.

Open the full BGP breakdown →

Question 5hardmultiple choice

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?

Trap 1: The VRF export route-target does not match the import route-target…

Incorrect because route-target mismatch would affect import on the remote PE, not advertisement from the local PE; the route would still be advertised.

Trap 2: The BGP session is not using the correct update-source.

Incorrect because the BGP session is established, so the update-source is correct; the issue is with route advertisement, not session establishment.

Trap 3: The next-hop-self command is missing under the VRF address-family.

Incorrect because next-hop-self affects the next-hop attribute, not whether the route is advertised; the route would still be sent.

A
The VRF export route-target does not match the import route-target on the remote PE.
Why wrong: Incorrect because route-target mismatch would affect import on the remote PE, not advertisement from the local PE; the route would still be advertised.
B
A route-map applied to the VRF export is filtering the route.
Correct because a route-map on VRF export can filter routes before they are advertised to BGP, preventing the route from being sent to the remote PE.
C
The BGP session is not using the correct update-source.
Why wrong: Incorrect because the BGP session is established, so the update-source is correct; the issue is with route advertisement, not session establishment.
D
The next-hop-self command is missing under the VRF address-family.
Why wrong: Incorrect because next-hop-self affects the next-hop attribute, not whether the route is advertised; the route would still be sent.

Question 6mediummultiple choice

A network engineer is troubleshooting MPLS LDP where the LDP session between two directly connected routers is not forming. The engineer runs show mpls ldp discovery and sees that LDP hellos are being sent and received on the link. However, show mpls ldp neighbor shows no neighbors. What is the most likely cause?

Trap 1: The mpls label protocol ldp command is missing globally.

Incorrect because LDP hellos are being sent, indicating LDP is enabled globally; the issue is with session establishment.

Trap 2: The interface is configured with mpls ldp igp sync.

Incorrect because LDP-IGP synchronization affects label advertisement and IGP metric, not LDP session formation.

Trap 3: The LDP session is using a non-default transport address.

Incorrect because if the transport address is non-default, it must be reachable; the issue is reachability, not the address itself.

A
The LDP router-id is not reachable via the IGP.
Correct because LDP uses TCP to establish the session, and the router-id must be reachable; if the IGP does not have a route to the peer's LDP router-id, the TCP connection fails.
B
The mpls label protocol ldp command is missing globally.
Why wrong: Incorrect because LDP hellos are being sent, indicating LDP is enabled globally; the issue is with session establishment.
C
The interface is configured with mpls ldp igp sync.
Why wrong: Incorrect because LDP-IGP synchronization affects label advertisement and IGP metric, not LDP session formation.
D
The LDP session is using a non-default transport address.
Why wrong: Incorrect because if the transport address is non-default, it must be reachable; the issue is reachability, not the address itself.

Question 7hardmultiple choice

A network engineer is troubleshooting MPLS traffic where packets are being forwarded without a label (IP forwarding) instead of being label-switched. The engineer runs show mpls forwarding-table and sees that the FEC for the destination prefix has a valid label. However, show ip cef shows that the outgoing interface is not MPLS-enabled. What is the most likely cause?

Trap 1: The CEF is disabled globally.

Incorrect because CEF must be enabled for MPLS; if CEF were disabled, show ip cef would not work, and the symptom would be different.

Trap 2: The mpls label protocol ldp command is missing on the interface.

Incorrect because LDP is already assigning labels; the mpls label protocol command only affects label distribution, not forwarding.

Trap 3: The interface is a loopback interface.

Incorrect because loopback interfaces are not typically used for MPLS forwarding; the issue is with a physical or subinterface.

A
The outgoing interface is missing the mpls ip command.
Correct because mpls ip on the interface enables MPLS forwarding; without it, CEF will not impose a label and will forward the packet as IP.
B
The CEF is disabled globally.
Why wrong: Incorrect because CEF must be enabled for MPLS; if CEF were disabled, show ip cef would not work, and the symptom would be different.
C
The mpls label protocol ldp command is missing on the interface.
Why wrong: Incorrect because LDP is already assigning labels; the mpls label protocol command only affects label distribution, not forwarding.
D
The interface is a loopback interface.
Why wrong: Incorrect because loopback interfaces are not typically used for MPLS forwarding; the issue is with a physical or subinterface.

Question 8hardmultiple choice

A network engineer is troubleshooting MPLS TE where a tunnel is configured with explicit path but the tunnel remains down. The show mpls traffic-eng tunnels command shows 'Path computation failed' and the show mpls traffic-eng topology command shows that the explicit path includes a router that is not in the TED. What is the most likely cause?

Trap 1: The explicit path is configured with a loose next-hop.

Incorrect because loose next-hops are allowed in explicit paths; the issue is that the router is not in the TED at all.

Trap 2: The tunnel destination is not reachable via the IGP.

Incorrect because TE tunnels do not require IGP reachability to the destination; they use the TED for path computation.

Trap 3: The mpls traffic-eng tunnels command is missing on the headend.

Incorrect because the tunnel is configured and the headend is attempting path computation; the command is present.

A
The router in the explicit path does not have MPLS TE enabled.
Correct because for a router to appear in the TED, MPLS TE must be enabled globally and on its interfaces; otherwise, the headend cannot include it in the path.
B
The explicit path is configured with a loose next-hop.
Why wrong: Incorrect because loose next-hops are allowed in explicit paths; the issue is that the router is not in the TED at all.
C
The tunnel destination is not reachable via the IGP.
Why wrong: Incorrect because TE tunnels do not require IGP reachability to the destination; they use the TED for path computation.
D
The mpls traffic-eng tunnels command is missing on the headend.
Why wrong: Incorrect because the tunnel is configured and the headend is attempting path computation; the command is present.

Open the full BGP breakdown →

Question 9mediummultiple choice

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?

Trap 1: The penultimate hop is not popping the label correctly.

Incorrect because the label is being popped as per implicit null; the issue is after the pop.

Trap 2: The MTU on the link between P and PE2 is too small.

Incorrect because MTU issues would cause fragmentation or drops regardless of label pop; the symptom is specific to missing VRF route.

Trap 3: The remote PE is configured with explicit null for the BGP next-hop.

Incorrect because the stem states implicit null is advertised; explicit null would be a different label value.

A
The remote PE does not have the CE route in its VRF.
Correct because after label pop, the packet is forwarded as IP; if the remote PE lacks the VRF route, it drops the packet.
B
The penultimate hop is not popping the label correctly.
Why wrong: Incorrect because the label is being popped as per implicit null; the issue is after the pop.
C
The MTU on the link between P and PE2 is too small.
Why wrong: Incorrect because MTU issues would cause fragmentation or drops regardless of label pop; the symptom is specific to missing VRF route.
D
The remote PE is configured with explicit null for the BGP next-hop.
Why wrong: Incorrect because the stem states implicit null is advertised; explicit null would be a different label value.

Question 10mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show mpls ldp neighbor

Peer LDP Ident: 10.0.0.2:0; Local LDP Ident 10.0.0.1:0 TCP connection: 10.0.0.2.646 - 10.0.0.1.52868 State: Oper; Msgs sent/rcvd: 123/120; Downstream Up time: 02:15:30 LDP discovery sources: GigabitEthernet0/0, Src IP addr: 192.168.1.2 Addresses bound to peer LDP Ident:

10.0.0.2        192.168.1.2

Based on this output, which statement is correct?

Trap 1: The LDP session is down because the state is 'Oper'.

'Oper' means operational, not down.

Trap 2: The LDP neighbor is using upstream label distribution.

The output shows 'Downstream', not upstream.

Trap 3: The LDP session is using TCP port 179.

LDP uses TCP port 646, not 179.

A
The LDP session is down because the state is 'Oper'.
Why wrong: 'Oper' means operational, not down.
B
The LDP session is established and operational.
'State: Oper' indicates the session is operational.
C
The LDP neighbor is using upstream label distribution.
Why wrong: The output shows 'Downstream', not upstream.
D
The LDP session is using TCP port 179.
Why wrong: LDP uses TCP port 646, not 179.

Question 11hardmultiple choice

A network engineer runs the following command on Router R1:

R1# show mpls forwarding-table

Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 16 Pop Label 10.1.1.0/24 0 Gi0/0 192.168.1.2 17 21 10.2.2.0/24 1500 Gi0/0 192.168.1.2 18 Untagged 10.3.3.0/24 0 Gi0/1 192.168.2.2

Based on this output, what is the problem with the label entry for 10.3.3.0/24?

Trap 1: The label 18 is being swapped correctly.

The outgoing label is 'Untagged', not swapped.

Trap 2: The prefix 10.3.3.0/24 is being forwarded with MPLS label 18.

The outgoing label is 'Untagged', so no label is used.

Trap 3: The label 18 is being popped by the next-hop router.

Pop Label is used for penultimate hop popping, not 'Untagged'.

A
The label 18 is being swapped correctly.
Why wrong: The outgoing label is 'Untagged', not swapped.
B
The prefix 10.3.3.0/24 is being forwarded with MPLS label 18.
Why wrong: The outgoing label is 'Untagged', so no label is used.
C
The next-hop router 192.168.2.2 is not an LDP neighbor for this prefix.
'Untagged' indicates the next hop did not provide a label.
D
The label 18 is being popped by the next-hop router.
Why wrong: Pop Label is used for penultimate hop popping, not 'Untagged'.

Question 12mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show mpls l2transport vc 100 detail

Local interface: Gi0/0/0 up, line protocol up Destination: 10.0.0.2, VC ID: 100, VC status: down Last error: No remote LDP session

Based on this output, what is the most likely cause of the VC being down?

Trap 1: The local interface Gi0/0/0 is administratively down.

The interface is up and line protocol up.

Trap 2: The remote router 10.0.0.2 is not reachable via IP.

The error is specifically about LDP session, not IP reachability.

Trap 3: The VC ID 100 is mismatched on the remote router.

VC ID mismatch would show a different error, like 'VC ID mismatch'.

A
The local interface Gi0/0/0 is administratively down.
Why wrong: The interface is up and line protocol up.
B
The remote router 10.0.0.2 is not reachable via IP.
Why wrong: The error is specifically about LDP session, not IP reachability.
C
The LDP session between the routers is not established.
The last error confirms 'No remote LDP session'.
D
The VC ID 100 is mismatched on the remote router.
Why wrong: VC ID mismatch would show a different error, like 'VC ID mismatch'.

Open the full BGP breakdown →

Question 13mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show bgp ipv4 unicast summary

BGP router identifier 10.0.0.1, local AS number 65001 BGP table version is 10, main routing table version 10

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.0.2        4        65002     123      120       10    0    0 02:15:30        5
10.0.0.3        4        65003      50       45       10    0    0 00:00:12 Idle (PfxRcd: 0)

Based on this output, what is the problem with neighbor 10.0.0.3?

Trap 1: The neighbor 10.0.0.3 is operational and exchanging prefixes.

The state is 'Idle', not 'Established'.

Trap 2: The neighbor 10.0.0.3 has sent 5 prefixes.

PfxRcd is 0, meaning no prefixes received.

Trap 3: The BGP table version is mismatched.

The table version is 10 for both neighbors, so no mismatch.

A
The neighbor 10.0.0.3 is operational and exchanging prefixes.
Why wrong: The state is 'Idle', not 'Established'.
B
The BGP session to 10.0.0.3 is flapping.
The state 'Idle' with a short uptime indicates the session is down and trying to re-establish.
C
The neighbor 10.0.0.3 has sent 5 prefixes.
Why wrong: PfxRcd is 0, meaning no prefixes received.
D
The BGP table version is mismatched.
Why wrong: The table version is 10 for both neighbors, so no mismatch.

Question 14easymultiple choice

A network engineer runs the following command on Router R1:

R1# show ip route ospf

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP a - application route + - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
O        10.1.1.0/24 [110/20] via 192.168.1.2, 00:15:30, GigabitEthernet0/0
O        10.2.2.0/24 [110/30] via 192.168.1.2, 00:15:30, GigabitEthernet0/0

Based on this output, which statement is correct?

Trap 1: The router has a default route via OSPF.

The output says 'Gateway of last resort is not set'.

Trap 2: The OSPF neighbor is down.

Routes are present, so the neighbor is up.

Trap 3: The metric for 10.2.2.0/24 is 20.

The metric is 30, not 20.

A
The router has a default route via OSPF.
Why wrong: The output says 'Gateway of last resort is not set'.
B
The router has two OSPF routes to different subnets.
Two OSPF routes are listed: 10.1.1.0/24 and 10.2.2.0/24.
C
The OSPF neighbor is down.
Why wrong: Routes are present, so the neighbor is up.
D
The metric for 10.2.2.0/24 is 20.
Why wrong: The metric is 30, not 20.

Question 15easymultiple choice

A network engineer runs the following command on Router R1:

R1# show dmvpn

Legend: Attrb -> S: Static, D: Dynamic, I: Incomplete N: NATed, L: Local, X: No Socket

# Ent -> Number of NHRP entries with same NBMA peer

NHS Status: E => Expecting Replies, R => Responding, W => Waiting UpDn Time -> Up or Down Time for a Tunnel ==========================================================================

Interface: Tunnel0, IPv4 NHRP Details

Type:Hub, NHRP Peers:2,

# Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb

----- --------------- --------------- ----- -------- ----- 1 192.168.1.2 10.0.0.2 UP 00:15:30 D 1 192.168.1.3 10.0.0.3 UP 00:10:20 D

Based on this output, what is the role of Router R1?

Trap 1: Router R1 is a DMVPN spoke.

The type is 'Hub', not 'Spoke'.

Trap 2: Router R1 is a DMVPN server.

DMVPN uses hub/spoke terminology, not server.

Trap 3: Router R1 is a DMVPN client.

The type is 'Hub', not client.

A
Router R1 is a DMVPN spoke.
Why wrong: The type is 'Hub', not 'Spoke'.
B
Router R1 is a DMVPN hub.
The output explicitly states 'Type:Hub'.
C
Router R1 is a DMVPN server.
Why wrong: DMVPN uses hub/spoke terminology, not server.
D
Router R1 is a DMVPN client.
Why wrong: The type is 'Hub', not client.

Question 16mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show ip nhrp
10.0.0.2/32 via 10.0.0.2, Tunnel0 created 00:15:30, expire 01:44:30

Type: dynamic, Flags: used NBMA address: 192.168.1.2

10.0.0.3/32 via 10.0.0.3, Tunnel0 created 00:10:20, expire 01:49:40

Type: dynamic, Flags: used NBMA address: 192.168.1.3

Based on this output, which statement is correct?

Trap 1: Both NHRP entries are static.

The type is 'dynamic', not static.

Trap 2: The NHRP entries have expired.

The expire times are in the future (01:44:30 and 01:49:40).

Trap 3: The NBMA addresses are IPv6 addresses.

The NBMA addresses are IPv4 (192.168.1.2 and 192.168.1.3).

A
Both NHRP entries are static.
Why wrong: The type is 'dynamic', not static.
B
Both NHRP entries are active and dynamically learned.
Type dynamic and flags used indicate active dynamic entries.
C
The NHRP entries have expired.
Why wrong: The expire times are in the future (01:44:30 and 01:49:40).
D
The NBMA addresses are IPv6 addresses.
Why wrong: The NBMA addresses are IPv4 (192.168.1.2 and 192.168.1.3).

Question 17mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show policy-map control-plane

Control Plane

Service-policy input: CoPP

class-map: MANAGEMENT (match-all) 5 packets, 500 bytes 5 minute offered rate 0 bps police: cir 8000 bps, bc 1500 bytes conformed 5 packets, 500 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop conformed 0 bps, exceed 0 bps

class-map: ATTACK (match-all) 100 packets, 10000 bytes 5 minute offered rate 0 bps police: cir 8000 bps, bc 1500 bytes conformed 0 packets, 0 bytes; actions: transmit exceeded 100 packets, 10000 bytes; actions: drop conformed 0 bps, exceed 0 bps

Based on this output, what is happening to traffic matching class ATTACK?

Trap 1: All traffic in class ATTACK is being transmitted.

Conformed packets are 0, so no packets are transmitted.

Trap 2: Traffic in class ATTACK is being rate-limited but not dropped.

The exceed action is drop, not transmit.

Trap 3: Traffic in class ATTACK is being marked down.

No marking action is shown; only transmit and drop.

A
All traffic in class ATTACK is being transmitted.
Why wrong: Conformed packets are 0, so no packets are transmitted.
B
All traffic in class ATTACK is being dropped.
Exceeded 100 packets, all dropped.
C
Traffic in class ATTACK is being rate-limited but not dropped.
Why wrong: The exceed action is drop, not transmit.
D
Traffic in class ATTACK is being marked down.
Why wrong: No marking action is shown; only transmit and drop.

Question 18easymultiple choice

A network engineer runs the following command on Router R1:

R1# show ip sla statistics 1

IPSLAs Latest Operation Statistics IPSLA operation id: 1 Type of operation: icmp-echo Latest RTT: 10 milliseconds Latest operation start time: 00:15:30 UTC Mon Mar 1 2021 Latest operation return code: OK Number of successes: 100 Number of failures: 0 Operation time to live: Forever

Based on this output, which statement is correct?

Trap 1: The IP SLA operation has failed 100 times.

Number of failures is 0.

Trap 2: The IP SLA operation type is udp-jitter.

The type is icmp-echo.

Trap 3: The IP SLA operation has expired.

Operation time to live is Forever.

A
The IP SLA operation has failed 100 times.
Why wrong: Number of failures is 0.
B
The IP SLA operation is successful and has a low RTT.
Return code OK, RTT 10 ms, 100 successes.
C
The IP SLA operation type is udp-jitter.
Why wrong: The type is icmp-echo.
D
The IP SLA operation has expired.
Why wrong: Operation time to live is Forever.

Question 19mediummultiple choice

Examine the following partial MPLS configuration on a Cisco IOS-XE router:

interface GigabitEthernet0/0
 ip address 10.0.1.1 255.255.255.252

mpls ip mpls label protocol ldp !

router ospf 1
 network 10.0.1.0 0.0.0.3 area 0

! mpls ldp router-id Loopback0 force

What is the effect of this configuration?

Trap 1: LDP will use the IP address of GigabitEthernet0/0 as the router ID…

The 'force' keyword is valid and overrides the default selection of the highest IP address. Without 'force', LDP might choose a different router ID if a higher IP appears later.

Trap 2: LDP sessions will fail because OSPF is not redistributed into LDP.

LDP does not require redistribution of routing protocols; it uses the IGP routing table to establish label bindings for FECs. OSPF is sufficient for reachability.

Trap 3: MPLS forwarding will not occur because 'mpls label protocol ldp' is…

The command is optional and does not cause conflict; it simply specifies the label distribution protocol. MPLS forwarding will work normally.

A
LDP will establish a session with the neighbor on GigabitEthernet0/0, using Loopback0 as the transport address.
The 'mpls ldp router-id Loopback0 force' command forces LDP to use Loopback0 as the router ID, which becomes the transport address for LDP sessions. The 'mpls ip' on the interface enables label switching and LDP hello messages.
B
LDP will use the IP address of GigabitEthernet0/0 as the router ID because 'force' is not valid.
Why wrong: The 'force' keyword is valid and overrides the default selection of the highest IP address. Without 'force', LDP might choose a different router ID if a higher IP appears later.
C
LDP sessions will fail because OSPF is not redistributed into LDP.
Why wrong: LDP does not require redistribution of routing protocols; it uses the IGP routing table to establish label bindings for FECs. OSPF is sufficient for reachability.
D
MPLS forwarding will not occur because 'mpls label protocol ldp' is redundant and causes a conflict.
Why wrong: The command is optional and does not cause conflict; it simply specifies the label distribution protocol. MPLS forwarding will work normally.

Question 20mediummultiple choice

Consider the following MPLS configuration on a Cisco router:

ip cef

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.252

mpls ip !

interface GigabitEthernet0/1
 ip address 192.168.2.1 255.255.255.252

mpls ip ! mpls ldp router-id GigabitEthernet0/0

What is the likely problem with this configuration?

Trap 1: Missing 'mpls label protocol ldp' under the interfaces will prevent…

The 'mpls ip' command enables LDP on the interface by default; explicit 'mpls label protocol ldp' is not required.

Trap 2: Cisco Express Forwarding (CEF) must be explicitly enabled globally;…

CEF is enabled by default on most IOS-XE images. The 'ip cef' command is shown, but even without it, MPLS requires CEF which is typically on.

Trap 3: The configuration is correct and will work without any issues.

While it might work initially, using a physical interface as the LDP router ID is a design flaw that can cause instability.

A
The router-id command is incorrectly referencing a physical interface; LDP may flap if GigabitEthernet0/0 goes down.
Using a physical interface as the LDP router ID is not recommended because if that interface fails, LDP sessions will reset. A loopback interface should be used for stability.
B
Missing 'mpls label protocol ldp' under the interfaces will prevent LDP from running.
Why wrong: The 'mpls ip' command enables LDP on the interface by default; explicit 'mpls label protocol ldp' is not required.
C
Cisco Express Forwarding (CEF) must be explicitly enabled globally; it is not enabled by default.
Why wrong: CEF is enabled by default on most IOS-XE images. The 'ip cef' command is shown, but even without it, MPLS requires CEF which is typically on.
D
The configuration is correct and will work without any issues.
Why wrong: While it might work initially, using a physical interface as the LDP router ID is a design flaw that can cause instability.