MPLS Operations

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?

Question 3hardmultiple 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?

Question 4mediummultiple 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?

Question 5mediummultiple 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?

Question 6hardmultiple 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?

Question 7mediummultiple 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?

Question 8hardmultiple 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?

Question 9hardmultiple 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?

Question 10mediummultiple 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?

Question 11mediummultiple 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?

Question 12hardmultiple 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?

Question 13mediummultiple 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?

Question 14mediummultiple 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?

Question 15easymultiple choice

Read the full VPN explanation →

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?

Question 16easymultiple 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?

Question 17mediummultiple choice

Study the full ACL explanation →

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?

Question 18mediummultiple 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?

Question 19easymultiple 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?

Question 20mediummultiple 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?

Question 21mediummultiple 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?

Question 22mediummultiple choice

Study the full EIGRP explanation →

Given the following partial configuration:

ip cef

interface Loopback0
 ip address 10.0.0.1 255.255.255.255

interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.1 0.0.0.0 area 0
 network 10.1.1.0 0.0.0.3 area 0

! mpls ldp router-id Loopback0 force

What is missing from this configuration to ensure proper MPLS LDP operation?

Question 23mediummultiple choice

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?

Question 24mediummultiple choice

Consider the following configuration snippet:

ip cef

interface GigabitEthernet0/0
 ip address 10.0.0.1 255.255.255.252

mpls ip !

interface GigabitEthernet0/1
 ip address 10.0.1.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.0 0.0.0.3 area 0
 network 10.0.1.0 0.0.0.3 area 0

! mpls ldp router-id Loopback0 force !

interface Loopback0
 ip address 192.168.0.1 255.255.255.255

What will happen when this router attempts to establish an LDP session with a neighbor on GigabitEthernet0/0?

Question 25mediummultiple choice

Given the following configuration:

ip cef

interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252

mpls ip !

interface GigabitEthernet0/1
 ip address 10.2.2.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.0 0.255.255.255 area 0

! mpls ldp router-id Loopback0 force !

interface Loopback0
 ip address 192.168.0.1 255.255.255.255

A network engineer notices that LDP sessions are not establishing. What is the most likely cause?

Question 26easymultiple choice

What is the default behavior of LDP when establishing a session between two directly connected routers?

Question 27mediummultiple choice

In MPLS, what is the purpose of the TTL propagation feature?

Question 28mediummultiple choice

Which of the following statements about MPLS label imposition and disposition is true?

Question 29mediummulti select

Which TWO commands would a network engineer use to verify the MPLS label forwarding table on a Cisco IOS-XE router? (Choose TWO.)

Question 30mediummulti select

Which TWO statements about MPLS label imposition (push) are true? (Choose TWO.)

Question 31hardmulti select

Full Practice Test →All Objectives

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

More MPLS Operations questions available in the full practice test.

Continue Practising →

All 300-410 Objectives

Objective 201.0

MPLS Operations

300-410 Practice Questions

300-410 MPLS Operations — Practice Questions

30 questions from this objective

Question 2mediummultiple choice

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?

Question 3hardmultiple 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?

Question 4mediummultiple 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?

Question 5mediummultiple 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?

Question 6hardmultiple 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?

Question 7mediummultiple 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?

Question 8hardmultiple 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?

Question 9hardmultiple 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?

Question 10mediummultiple 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?

Question 11mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show mpls ldp neighbor

10.0.0.2        192.168.1.2

Based on this output, which statement is correct?

Question 12hardmultiple choice

A network engineer runs the following command on Router R1:

R1# show mpls forwarding-table

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

Question 13mediummultiple 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?

Question 14mediummultiple 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?

Question 15easymultiple choice

Read the full VPN explanation →

A network engineer runs the following command on Router R1:

R1# show ip route ospf

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?

Question 16easymultiple 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?

Question 17mediummultiple choice

Study the full ACL explanation →

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?

Question 18mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show policy-map control-plane

Control Plane

Service-policy input: CoPP

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

Question 19easymultiple choice

A network engineer runs the following command on Router R1:

R1# show ip sla statistics 1

Based on this output, which statement is correct?

Question 20mediummultiple 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?

Question 21mediummultiple 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?

Question 22mediummultiple choice

Study the full EIGRP explanation →

Given the following partial configuration:

ip cef

interface Loopback0
 ip address 10.0.0.1 255.255.255.255

interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.1 0.0.0.0 area 0
 network 10.1.1.0 0.0.0.3 area 0

! mpls ldp router-id Loopback0 force

What is missing from this configuration to ensure proper MPLS LDP operation?

Question 23mediummultiple choice

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?

Question 24mediummultiple choice

Consider the following configuration snippet:

ip cef

interface GigabitEthernet0/0
 ip address 10.0.0.1 255.255.255.252

mpls ip !

interface GigabitEthernet0/1
 ip address 10.0.1.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.0 0.0.0.3 area 0
 network 10.0.1.0 0.0.0.3 area 0

! mpls ldp router-id Loopback0 force !

interface Loopback0
 ip address 192.168.0.1 255.255.255.255

What will happen when this router attempts to establish an LDP session with a neighbor on GigabitEthernet0/0?

Question 25mediummultiple choice

Given the following configuration:

ip cef

interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252

mpls ip !

interface GigabitEthernet0/1
 ip address 10.2.2.1 255.255.255.252

mpls ip !

router ospf 1
 network 10.0.0.0 0.255.255.255 area 0

! mpls ldp router-id Loopback0 force !

interface Loopback0
 ip address 192.168.0.1 255.255.255.255

A network engineer notices that LDP sessions are not establishing. What is the most likely cause?

Question 26easymultiple choice

What is the default behavior of LDP when establishing a session between two directly connected routers?

Question 27mediummultiple choice

In MPLS, what is the purpose of the TTL propagation feature?

Question 28mediummultiple choice

Which of the following statements about MPLS label imposition and disposition is true?

Question 29mediummulti select

Which TWO commands would a network engineer use to verify the MPLS label forwarding table on a Cisco IOS-XE router? (Choose TWO.)

Question 30mediummulti select

Which TWO statements about MPLS label imposition (push) are true? (Choose TWO.)

Question 31hardmulti select