300-410 MPLS Operations Practice Test 4 — 15 Questions

Question 1

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?

Accepted Answer

Packets with label 101 will be swapped to label 201 and forwarded to 10.0.0.2. The output shows the MPLS forwarding table entry for prefix 192.168.1.0/24. The local label is 101, outgoing label is 201, next hop is 10.0.0.2 via GigabitEthernet0/0. The label stack contains only label 201.

Answer

Packets with label 101 will be popped and forwarded as IP packets

Answer

The prefix 192.168.1.0/24 is directly connected

Answer

The label stack has two labels

Question 2

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?

Accepted Answer

The LDP session with 10.0.0.2 is flapping. The debug output shows the LDP session with neighbor 10.0.0.2 is flapping (repeatedly going UP and DOWN). This indicates instability in the LDP session.

Answer

The LDP session with 10.0.0.2 is stable

Answer

The LDP session with 10.0.0.2 is using targeted hello

Answer

The LDP session with 10.0.0.2 is down permanently

Question 3

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?

Accepted Answer

R1 has discovered two LDP neighbors via link hellos on two different interfaces. The output shows LDP discovery sources. R1 has discovered two LDP neighbors via link hellos on interfaces GigabitEthernet0/0 and GigabitEthernet0/1. Both neighbors have a hold time of 15 seconds.

Answer

R1 is using targeted hellos only

Answer

R1 has no LDP neighbors

Answer

The LDP session with 10.0.0.2 is down

Question 4

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?

Accepted Answer

The LDP session with 10.0.0.2 failed due to malformed messages from the neighbor. The debug output shows LDP errors. R1 received malformed hello and initialization messages from neighbor 10.0.0.2, causing the LDP session to go down. This indicates a configuration mismatch or software bug on the neighbor.

Answer

The LDP session with 10.0.0.2 is up and stable

Answer

R1 is sending malformed messages to 10.0.0.2

Answer

The LDP session is using incorrect transport address

Question 5

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?

Accepted Answer

R1 will pop the label for 10.0.0.0/8 before forwarding to the next hop. The output shows label bindings for prefix 10.0.0.0/8. R1 has assigned implicit null label (label 3) locally, meaning it will pop the label before forwarding. Neighbor 10.0.0.2 also uses implicit null, while 10.0.0.3 uses label 302.

Answer

R1 will swap the label for 10.0.0.0/8

Answer

All neighbors are using implicit null for this prefix

Answer

The prefix 10.0.0.0/8 is not in the routing table

Question 6

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

Accepted Answer

5 seconds. LDP hello messages are sent every 5 seconds by default on Cisco IOS-XE routers to discover and maintain adjacencies.

Answer

10 seconds

Answer

15 seconds

Answer

3 seconds

Question 7

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.

Question 8

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

Accepted Answer

Auto-summary is disabled by default for BGP.. By default, auto-summary is disabled in Cisco IOS-XE for BGP, meaning that BGP will not automatically summarize subnets to their classful boundaries.

Answer

Auto-summary is enabled by default for BGP.

Answer

Auto-summary is enabled by default only for directly connected routes.

Answer

Auto-summary is disabled by default for BGP but enabled for OSPF.

Question 9

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

Accepted Answer

Label Request message. The Label Request message is sent by an LDP router to request a label binding for a specific FEC from its neighbor.

Answer

Label Mapping message

Answer

Label Withdraw message

Answer

Label Release message

Question 10

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 11

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

Accepted Answer

Ordered Label Distribution Control mode. The default label distribution control mode is Ordered, meaning that a router will only advertise a label for a FEC if it has a label from its next hop or if it is the egress router.

Answer

Independent Label Distribution Control mode

Answer

Liberal Label Retention mode

Answer

Conservative Label Retention mode

Question 12

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

Accepted Answer

6 labels. The default maximum label stack depth is 6 labels on Cisco IOS-XE routers, though this can be increased with the 'mpls label range' command.

Answer

3 labels

Answer

10 labels

Answer

Unlimited

Question 13

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

Accepted Answer

Label 1; used to alert the router to examine the packet in the control plane.. Label 1 is the Router Alert label, used to indicate that the packet should be examined by the router's control plane, typically for OAM or RSVP-TE messages.

Answer

Label 0; used to alert the router to examine the packet.

Answer

Label 2; used to alert the router to examine the packet.

Answer

Label 3; used to alert the router to examine the packet.

Question 14

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

Accepted Answer

Liberal Label Retention mode. The default label retention mode is Liberal, meaning that a router retains all label bindings received from neighbors, even if the neighbor is not the next hop for the FEC.

Answer

Conservative Label Retention mode

Answer

Ordered Label Retention mode

Answer

Independent Label Retention mode

Question 15

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

Accepted Answer

Establish TCP connection on port 646. LDP begins by establishing a TCP connection between peers, then sends Hello messages to discover neighbors, forms an adjacency, exchanges label mappings, and finally populates the LIB with learned labels.