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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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?

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

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

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

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

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

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

Which TWO configuration steps are required to enable MPLS on a Cisco IOS-XE router using LDP? (Choose TWO.)

Which THREE statements about MPLS label operations (push, swap, pop) are true? (Choose THREE.)

In an MPLS network, Router R1 is a provider edge (PE) router that redistributes BGP routes into OSPF. The network experiences intermittent loss of reachability to a specific prefix 10.10.10.0/24. R1 configuration includes: 'router ospf 1 redistribute bgp 65000 subnets metric-type 1' and 'router bgp 65000 neighbor 10.0.0.2 route-map SET-METRIC in' with a route-map that sets metric 100. R2, a P router, shows 'show ip route 10.10.10.0' output: 'O E1 10.10.10.0/24 [110/20] via 10.0.0.1, 00:00:15' but traffic fails. What is the root cause?

A DMVPN network with EIGRP as the routing protocol experiences spoke-to-spoke tunnel failures. Hub router R1 has configuration: 'interface Tunnel0 ip nhrp network-id 1 ip nhrp map multicast dynamic ip nhrp redirect' and 'router eigrp 100 network 10.0.0.0'. Spoke router R2 shows 'show ip nhrp brief' output: '10.0.0.1/32 via 192.168.1.1, Tunnel0 created 00:10:00, dynamic' but 'show ip eigrp neighbors' shows only the hub. What is the root cause?

In an MPLS LDP network, routers R1 and R2 are directly connected via GigabitEthernet0/0. R1 shows 'show mpls ldp neighbor' output: 'Peer LDP Ident: 10.0.0.2:0, Local LDP Ident: 10.0.0.1:0, TCP connection: 10.0.0.2.646 - 10.0.0.1.646, State: OPERATIONAL' but 'show mpls forwarding-table' for prefix 192.168.1.0/24 shows 'No label'. R2 has the same prefix in its routing table. What is the root cause?

A VRF route leaking configuration causes unexpected reachability. Router R1 has VRF RED and VRF BLUE. Configuration: 'ip vrf RED rd 100:1 route-target export 100:1 route-target import 100:2' and 'ip vrf BLUE rd 100:2 route-target export 100:2 route-target import 100:1'. Router R2 is a route reflector with 'address-family ipv4 vrf RED' and 'address-family ipv4 vrf BLUE'. A host in VRF RED can ping a host in VRF BLUE, but not vice versa. What is the root cause?

In an MPLS network, OSPF network type mismatch causes routing issues. Router R1 and R2 are connected via a multi-access Ethernet link. R1 has 'interface GigabitEthernet0/0 ip ospf network point-to-point', while R2 has default OSPF network type broadcast. R1 shows 'show ip ospf neighbor' output: 'Neighbor 10.0.0.2, interface address 10.0.0.2, state FULL' but 'show ip route' does not include routes from R2. What is the root cause?

EIGRP stuck-in-active (SIA) occurs in a large network. Router R1 shows 'show ip eigrp topology 10.0.0.0/24' output: 'P 10.0.0.0/24, 1 successors, FD is 128000, Q is 0, SIA is 00:01:00' and 'show ip eigrp neighbors' shows neighbor R2 in state 'Active'. R1 configuration includes 'router eigrp 100 network 10.0.0.0 passive-interface default'. What is the root cause?

BGP attribute manipulation causes unexpected path selection. Router R1 and R2 are eBGP peers. R1 receives prefix 172.16.0.0/16 from R2 with MED 50 and from another peer R3 with MED 100. R1 has configuration: 'route-map SET-MED permit 10 set metric 200' applied to neighbor R2 inbound. R1 shows 'show ip bgp 172.16.0.0' output: 'BGP routing table entry for 172.16.0.0/16, version 2, Paths: (2 available, best #2) Path #1: from R2 with MED 200, Path #2: from R3 with MED 100'. The best path is via R3, but the network expects R2 to be preferred. What is the root cause?

CoPP (Control Plane Policing) rate-limit impacts legitimate traffic. Router R1 has CoPP policy applied: 'class-map match-all BGP class-map match-all SSH match protocol bgp match protocol ssh policy-map COPP class BGP police 10000 conform-action transmit exceed-action drop'. Network engineers cannot SSH to R1, but BGP sessions are stable. 'show policy-map control-plane' output shows 'BGP class: 0 packets, 0 bytes' and 'SSH class: 0 packets, 0 bytes'. What is the root cause?

Route summarization blocks specific routes in an MPLS network. Router R1 is a PE router that summarizes routes from a VRF into BGP. Configuration: 'router bgp 65000 address-family ipv4 vrf CUSTOMER network 10.0.0.0 255.255.252.0' and 'aggregate-address 10.0.0.0 255.255.252.0 summary-only'. A specific prefix 10.0.3.0/24 is not reachable from the MPLS core. 'show ip bgp vpnv4 vrf CUSTOMER 10.0.3.0/24' output: 'Not in table'. What is the root cause?

A network engineer runs the following command to troubleshoot an MPLS Operations issue: R1# debug mpls ldp transport 10.1.1.1 Output: *Mar 1 00:01:23.456: LDP: Sent hello to 10.1.1.1 (UDP 646) on GigabitEthernet0/0 *Mar 1 00:01:23.789: LDP: Received hello from 10.1.1.1 (UDP 646) on GigabitEthernet0/0 *Mar 1 00:01:24.012: LDP: Opened TCP connection to 10.1.1.1:646 *Mar 1 00:01:24.345: LDP: Initialization msg sent to 10.1.1.1 *Mar 1 00:01:24.678: LDP: Initialization msg received from 10.1.1.1 *Mar 1 00:01:25.001: LDP: Session with 10.1.1.1:0 (0x1234) is UP What does this output indicate?

A network engineer runs the following command to verify MPLS LDP label bindings: R1# show mpls ldp bindings 192.168.1.0 255.255.255.0 Output: lib entry: 192.168.1.0/24, rev 8 local binding: label: 101 remote binding: lsr: 10.0.0.2:0, label: 201 remote binding: lsr: 10.0.0.3:0, label: 301 What does this output indicate?

A network engineer runs the following command to examine MPLS LDP neighbor details: R1# show mpls ldp neighbor detail Output: Peer LDP Ident: 10.0.0.2:0; Local LDP Ident 10.0.0.1:0 TCP connection: 10.0.0.2.646 - 10.0.0.1.55432 State: Oper; Msgs sent/rcvd: 123/456; Downstream on demand Up time: 1w2d LDP discovery sources: GigabitEthernet0/0, hello interval: 5 s, targeted: no Addresses bound to peer LDP Ident: 10.0.0.2 10.0.1.2 192.168.1.1 What does this output indicate?

A network engineer runs the following command to debug MPLS LDP label advertisements: R1# debug mpls ldp labels Output: *Mar 1 00:01:23.456: LDP: Sent label mapping for 192.168.1.0/24, label 101 *Mar 1 00:01:23.789: LDP: Received label mapping for 192.168.2.0/24, label 201 *Mar 1 00:01:24.012: LDP: Sent label mapping for 10.0.0.0/8, label 102 *Mar 1 00:01:24.345: LDP: Received label mapping for 10.0.0.0/8, label 202 What does this output indicate?

A network engineer runs the following command to verify MPLS forwarding: R1# show mpls forwarding-table 192.168.1.0 255.255.255.0 detail Output: Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 101 201 192.168.1.0/24 0 Gi0/0 10.0.0.2 MAC/Encaps: 14/18, MTU: 1500, Label Stack {201} No output feature configured What does this output indicate?

A network engineer runs the following command to debug MPLS LDP session establishment: R1# debug mpls ldp session Output: *Mar 1 00:01:23.456: LDP: Session with 10.0.0.2:0 (0x1234) is UP *Mar 1 00:01:24.567: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN *Mar 1 00:01:25.678: LDP: Session with 10.0.0.2:0 (0x1234) is UP *Mar 1 00:01:26.789: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN What does this output indicate?

A network engineer runs the following command to verify MPLS LDP discovery sources: R1# show mpls ldp discovery detail Output: Local LDP Identifier: 10.0.0.1:0 Discovery Sources: Interfaces: GigabitEthernet0/0 (hello interval 5 s, targeted hello interval 10 s) LDP Id: 10.0.0.2:0, transport address: 10.0.0.2 Hold time: 15 s (local: 15, peer: 15) GigabitEthernet0/1 (hello interval 5 s, targeted hello interval 10 s) LDP Id: 10.0.0.3:0, transport address: 10.0.0.3 Hold time: 15 s (local: 15, peer: 15) What does this output indicate?

A network engineer runs the following command to debug MPLS LDP errors: R1# debug mpls ldp errors Output: *Mar 1 00:01:23.456: LDP: Received malformed hello from 10.0.0.2 *Mar 1 00:01:23.789: LDP: Received malformed initialization from 10.0.0.2 *Mar 1 00:01:24.012: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN What does this output indicate?

A network engineer runs the following command to verify MPLS LDP label bindings for a specific prefix: R1# show mpls ldp bindings 10.0.0.0 255.0.0.0 Output: lib entry: 10.0.0.0/8, rev 10 local binding: label: imp-null remote binding: lsr: 10.0.0.2:0, label: imp-null remote binding: lsr: 10.0.0.3:0, label: 302 What does this output indicate?

What is the default hello interval for the Label Distribution Protocol (LDP) on a Cisco IOS-XE router?

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

In MPLS, what is the default behavior of a Cisco IOS-XE router regarding the 'auto-summary' command for BGP routes?

Which LDP message type is used to request label bindings from a neighbor?

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

In MPLS, what is the default label distribution control mode for LDP on Cisco IOS-XE?

What is the default maximum number of labels that can be imposed in the MPLS label stack on a Cisco IOS-XE router?

Which MPLS label is used for the Router Alert function, and what is its purpose?

In MPLS LDP, what is the default label retention mode on Cisco IOS-XE routers?

Drag and drop the steps for MPLS LDP label discovery and distribution into the correct order, from first to last.

Drag and drop the steps for troubleshooting MPLS operations adjacency or connectivity failures into the correct order, from first to last.

Drag and drop the steps for verifying and validating MPLS operations operational state into the correct order, from first to last.

Which TWO statements correctly describe the behavior of TTL propagation in MPLS networks? (Choose TWO.)

Which TWO statements about MPLS label imposition, disposition, and swapping are true? (Choose TWO.)

An engineer is troubleshooting an MPLS LDP session that fails to establish between two directly connected routers. Which TWO commands can be used to verify LDP operation? (Choose TWO.)

Which TWO statements about MPLS label stack operations in a Layer 3 VPN (L3VPN) are true? (Choose TWO.)

Which TWO statements about MPLS Traffic Engineering (MPLS-TE) are true? (Choose TWO.)

An engineer configures MPLS on a router with OSPF as the IGP. The OSPF neighbor is stuck in EXSTART state. The engineer verifies that both routers have matching MTU values on the connecting interfaces. What is the most likely cause of this issue?

An engineer configures EIGRP named mode on a router. The neighbor adjacency forms, but the router does not install any routes from the neighbor. The engineer checks and confirms that the neighbor is not configured as a stub. What is the most likely explanation?

An engineer configures BGP between two iBGP peers in the same AS. The engineer sets 'next-hop-self' on the neighbor statement. However, the routes received from the iBGP peer still show the original next-hop as unreachable. What is the most likely explanation?

An engineer configures mutual redistribution between OSPF and EIGRP on a router. After the configuration, a routing loop occurs for a specific prefix. The engineer checks and confirms that route tagging is not used. What is the most likely explanation?

An engineer configures a DMVPN Phase 2 network. Spoke-to-spoke tunnels are established, but traffic between spokes is not being forwarded directly; it is still going through the hub. The engineer verifies that NHRP is working and spoke-to-spoke registrations are successful. What is the most likely explanation?

An engineer configures IPsec site-to-site VPN between two routers. The tunnel is established, but no traffic is encrypted. The engineer checks the crypto map and access-list and confirms they match the interesting traffic. What is the most likely explanation?

An engineer configures Control Plane Policing (CoPP) on a router to protect the control plane. After applying the policy, the router becomes unreachable via SSH and SNMP. The engineer checks the policy and confirms that the class-map for SSH and SNMP traffic is set to 'permit'. What is the most likely explanation?

An engineer configures unicast Reverse Path Forwarding (uRPF) in strict mode on an interface. After the configuration, legitimate traffic from a customer network is being dropped. The engineer confirms that the route for the customer subnet exists in the routing table and points to the correct interface. What is the most likely explanation?

An engineer configures MPLS forwarding on a router. The MPLS LDP neighbors are established, but some prefixes are not being assigned labels. The engineer checks the 'show mpls ldp bindings' and sees that the prefixes are missing. What is the most likely explanation?