Nokia NRSII 4A0-C04 Set1 [001-050]

Question 1

Question: 1

An LSP traverses the path R1–R2–R3. With one-to-one fast reroute enabled, which router becomes a DMP for the detour tunnels?

A. Router R1

B. Router R2

C. Router R3

D. Router R4

E. Router R5

Answer 1

B. Router R2

Answer Explanation:
In one-to-one fast reroute (detour mode), the DMP (Detour Merge Point) is the router immediately downstream of the PLR (Point of Local Repair), typically the next hop along the LSP.
Here, if the LSP is R1 → R2 → R3:

R1 is the PLR, which protects the link to R2.

R2 is the next hop — therefore, it becomes the DMP.

The detour tunnel is built from R1 (PLR) to R2 (DMP), ready to activate if the primary path fails.

Thus, R2 is the DMP where the detour rejoins the primary path.

Question 2

Question: 2

Which of the following is NOT a characteristic of MPLS?

A. It provides the ability to establish connection-oriented paths over a connectionless IP network.

B. It provides a mechanism to engineer network traffic patterns independently of IP routing tables.

C. It will work over most physical layer protocols.

D. It can use GRE tunnels to transport data from many different protocols over an IP network.

Answer 2

D. It can use GRE tunnels to transport data from many different protocols over an IP network.

Answer Explanation:
MPLS (Multiprotocol Label Switching) does not rely on GRE (Generic Routing Encapsulation) for label switching or transport. Instead, MPLS uses label stacking and its own label-switched paths (LSPs) to forward traffic efficiently.
Option A is true: MPLS creates connection-oriented LSPs over a connectionless IP or Layer 2 network.

Option B is true: MPLS enables traffic engineering (TE) by directing traffic independently of the IGP’s shortest-path logic.

Option C is true: MPLS is agnostic to Layer 2, working over Ethernet, Frame Relay, ATM, etc.

Option D is not true: GRE is a separate tunneling mechanism, and while MPLS can be encapsulated in GRE (e.g., MPLS over GRE for VPNs), MPLS itself does not inherently use GRE to transport payloads.

Therefore, option D is not a characteristic of MPLS.

Question 3

Question: 3

Which of the following regarding per-platform label space is TRUE?

A. A separate label is used for each interface on which the FEC is advertised.

B. A single label is assigned to a FEC for all interfaces on the same router.

C. It is typically used when the device has ATM or Frame Relay interfaces.

D. It uses more label resources than a per-interface label space.

Answer 3

B. A single label is assigned to a FEC for all interfaces on the same router.

Answer Explanation:
MPLS supports two types of label spaces:
Per-platform label space:

A single label is used for a given FEC (Forwarding Equivalence Class) across all interfaces of the router.

This is the most common configuration in IP/MPLS networks.

It simplifies label management because the router maintains one label-to-FEC mapping globally.

Per-interface label space:

A separate label is assigned per logical or physical interface.

Used in specific technologies like ATM or Frame Relay, where label values (VCIs/VPNs) must be unique per port.

Therefore:
A is false: that describes per-interface label space.

B is true: this defines per-platform label space.

C is misleading: ATM/Frame Relay typically use per-interface, not per-platform.

D is false: per-interface consumes more label resources than per-platform.

Question 4

Question: 4

Which of the following is TRUE when the explicit null is implemented?

A. The penultimate router will forward packets to the eLER, based on the IP header.

B. The eLER will receive packets with a top label value of 0.

C. The eLER will receive packets with a top label value of 3.

D. The penultimate router will pop the top label from the packets.

Answer 4

B. The eLER will receive packets with a top label value of 0.

Answer Explanation:
In MPLS, explicit null (label 0 for IPv4, label 2 for IPv6) is used to signal the penultimate router (P router) to retain the MPLS header, but replace the original label with the explicit null label.

This behavior allows:

The eLER (egress Label Edge Router) to still process the MPLS label (especially important for QoS or ECMP).

The penultimate router does not pop the label as it would in regular PHP (Penultimate Hop Popping).

Breakdown of options:

A. False – that’s normal IP forwarding, not with explicit null.

B. True – label 0 is the explicit null, and it is received by the eLER.

C. False – label 3 is implicit null, which is not transmitted.

D. False – the penultimate router retains the label (it does not pop) when explicit null is used.

Question 5

Question: 5

If a Nokia 7750 SR is an iLER operating in pipe mode, which of the following regarding the TC field (EXP bits) is TRUE?

A. The TC field is set based on the value of the DSCP field inside the customer packet.

B. The TC field is set to a specific value via explicit administrative configuration.

C. The TC field is set to a system generated random number.

D. The TC field is set by the eLER.

Answer 5

B. The TC field is set to a specific value via explicit administrative configuration.

Question 6

Question: 6

Which MPLS label mode propagates a label mapping only for the FEC for which a router has a label mapping for the FEC’s next-hop?

A. Independent control mode

B. Ordered control mode

C. Liberal label retention mode

D. Conservative label retention mode

E. Downstream on demand label distribution mode

Answer 6

B. Ordered control mode

Answer Explanation:
There are two MPLS label distribution control modes:
Independent Control Mode

Each router can advertise a label for a FEC as soon as it learns about the FEC, regardless of whether it has received a label from the next hop.

Ordered Control Mode

A router waits to advertise a label for a FEC until it has:

A label mapping from the next-hop router, or

It is the egress for the FEC.

So, ordered mode is more conservative and ensures a more synchronized label propagation along the LSP.
Breakdown of other options:
A. Independent control mode – propagates labels independently, even if the next-hop does not have one.

C. Liberal label retention mode – controls how unused labels are stored, not when they’re advertised.

D. Conservative label retention mode – only keeps labels from valid next-hops.

E. Downstream on demand – relates to when a router requests a label, not how labels are propagated.

Question 7

Question: 7

Which of the following best describes downstream on demand label distribution?

A. An LSR answers requests for label mappings immediately, without waiting for a label mapping from the next-hop.

B. An LSR advertises label mappings to all peers for which it might be a next-hop for a given FEC.

C. An LSR distributes a label mapping for a FEC when it has been requested to do so.

D. An LSR propagates a label mapping downstream for a FEC, only if it has a label mapping for the FEC’s next-hop.

Answer 7

C. An LSR distributes a label mapping for a FEC when it has been requested to do so.

Answer Explanation:
There are two main label distribution methods in MPLS:

Downstream Unsolicited

A Label Switch Router (LSR) automatically advertises label mappings for known FECs to all appropriate peers.

Downstream on Demand

An LSR only sends a label mapping when a peer explicitly requests it.

This is useful in constrained or traffic-engineered environments where control over label distribution is needed.

Option Review:

A. Incorrect – that describes independent control mode, not label distribution method.

B. Incorrect – that’s downstream unsolicited.

C. ✅ Correct – describes downstream on demand precisely.

D. Incorrect – that’s related to ordered control mode, not label distribution.

Question 8

Question: 8

Which of the following regarding MPLS label value assignment is FALSE?

A. Label values may be dynamically assigned by LDP.

B. Label values may be dynamically assigned by RSVP-TE.

C. Label values may be reserved for special uses.

D. Label values may be dynamically assigned by IGP.

Answer 8

D. Label values may be dynamically assigned by IGP.

Answer Explanation:
MPLS labels can be dynamically assigned by label distribution protocols, but not by IGPs.

Here’s the breakdown:

A. True – LDP (Label Distribution Protocol) dynamically assigns and advertises labels for FECs.

B. True – RSVP-TE (Resource Reservation Protocol - Traffic Engineering) also dynamically assigns labels during LSP setup.

C. True – Certain label values are reserved, e.g.:

0: IPv4 Explicit Null

1: Router Alert

3: Implicit Null (used for PHP)

D. False – IGPs (like OSPF, IS-IS) do not assign MPLS labels. They only provide routing information (topology, next-hops) that LDP or RSVP-TE may use to assign labels.

Question 9

Question: 9

Which of the following is a characteristic of LDP Hello messages?

A. They are multicast to the All Hosts address.

B. They are broadcast to the subnet broadcast address.

C. They are multicast to the All Routers address.

D. They are broadcast or multicast, depending on the physical media.

Answer 9

C. They are multicast to the All Routers address.

Answer Explanation:

LDP (Label Distribution Protocol) uses Hello messages to discover and maintain adjacency with LDP peers on directly connected links.

These messages are sent via UDP port 646.

They are multicast to the “All Routers” group address:

For IPv4, this is 224.0.0.2.

For IPv6, it would be FF02::2.

This allows all routers on the subnet to receive the message and respond if they support LDP.

Option Analysis:

A. ❌ Incorrect – 224.0.0.1 is the All Hosts address, not used by LDP.

B. ❌ Incorrect – LDP does not use subnet-wide broadcasts.

C. ✅ Correct – LDP Hello messages are multicast to 224.0.0.2 (All Routers).

D. ❌ Incorrect – LDP always uses multicast, not broadcast, regardless of media.

Question 10

Question: 10

What is the purpose of a T-LDP session?

A. It allows link LDP to be configured on the edge devices only.

B. It is used to signal the transport labels in the provider core.

C. It allows selective control over which devices are configured for LDP.

D. It is used to signal the service labels in the provider core.

Answer 10

D. It is used to signal the service labels in the provider core.

Answer Explanation:

T-LDP (Targeted Label Distribution Protocol) is a variation of LDP used to establish non-directly connected LDP sessions. It is commonly used in MPLS VPNs and pseudowire services.

The primary use of T-LDP is to signal service labels (e.g., for Layer 2 VPNs, pseudowires, or VPLS).

These service labels are switched end-to-end across the provider’s MPLS core.

Option Breakdown:

A. False – T-LDP is not about limiting LDP to edge devices.

B. False – Transport labels are typically signaled by standard LDP or RSVP-TE, not T-LDP.

C. False – While T-LDP is manually configured between peers, the statement is vague and misleading.

D. ✅ Correct – T-LDP is used to signal service labels (e.g., VC labels for pseudowires) across the MPLS network.

Question 11

Question: 11

Which of the following about LDP sessions is TRUE?

A. Frame mode requires multiple sessions between peers.

B. The lower transport address initiates the session.

C. Established LDP sessions run over a TCP connection.

D. An LDP session is established immediately after Init messages are exchanged between peers.

Answer 11

C. Established LDP sessions run over a TCP connection.

Answer Explanation:
LDP (Label Distribution Protocol) establishes and maintains sessions between peers using a TCP connection over port 646.
Here’s the correct context for each option:

A. False – Frame mode LDP refers to how labels are applied to frames (e.g., Ethernet), not about session count.

B. False – The LDP session initiator is based on the higher transport address (usually loopback IP), not the lower one.

C. ✅ True – LDP sessions are established over TCP (port 646) once Hello and Init messages succeed.

D. False – LDP session is established after successful exchange of Init and KeepAlive messages — not just Init alone.

Question 12

Question: 12

After the lsp-ping command is executed, which of the following best describes the router’s action?

Exhibit CLI Output Summary:
The router runs oam lsp-ping prefix 192.10.1.2/32 and receives a reply from 10.10.10.2.
The output confirms a successful MPLS echo request with a return code of 3 (Egress Router), indicating the label-switched path terminates at the destination.

A. MPLS Echo Request packets are sent unlabeled to the prefix 192.10.1.2.

B. MPLS Echo Request packets are sent within the LDP tunnel that are signaled for 192.10.1.2.

C. MPLS Echo Request packets are sent within the RSVP-TE tunnel that are signaled for 192.10.1.2.

D. MPLS Echo Request packets are sent over TCP.

Answer 12

C. MPLS Echo Request packets are sent within the RSVP-TE tunnel that are signaled for 192.10.1.2.

The use of lsp-ping and return code “rc=3 (EgressRtr)” indicates the packet was labeled and traversed an RSVP-TE tunnel to the egress router.

Question 13

Question: 13

When router R1 forwards a PATH message to router R2, which of the following about the PATH message’s IP header is TRUE?

A. The options field is set to router alert.

B. The source address is R1’s egress interface address.

C. The destination address is R2’s ingress interface address.

D. The HOP object includes R2’s system address.

Answer 13

A. The options field is set to router alert.

The Router Alert option in the IP header is used so intermediate routers process the RSVP PATH message instead of forwarding it blindly.

Question 14

Question: 14

This LSP terminates on a system IP address. What is the system address of the destination node?

A. 10.32.1.2

B. 10.1.4.78

C. 10.48.1.1

D. 10.1.2.2

Answer 14

B. 10.1.4.78

Answer Explanation:

The system IP address the LSP is configured to terminate on is explicitly defined in the command:

lsp “LSP-to-PE2”
to 10.1.4.78

This means the destination of the LSP is the router with the system IP address 10.1.4.78.

Option Breakdown:
A. 10.32.1.2 ❌
This is just one of the intermediate hops (hop 4) in the strict path to reach the destination. It’s not the final system address.

B. 10.1.4.78 ✅
This is the target of the LSP. It is explicitly listed in the to field of the LSP configuration, which represents the system IP of the destination.

C. 10.48.1.1 ❌
This is hop 1 in the strict path. Like the others, it’s just a transit router.

D. 10.1.2.2 ❌
This is hop 3, another transit router in the LSP path.

Question 15

Question: 15

What are the default settings for RSVP-TE on the Nokia 7750 SR?

A. Per-interface label space, liberal retention mode

B. Per-platform label space, liberal retention mode

C. Per-interface label space, conservative retention mode

D. Per-platform label space, conservative retention mode

Answer 15

B. Per-platform label space, liberal retention mode

(This is the default behavior for RSVP-TE on Nokia 7750 SR platforms.)

Question 16

Question: 16

Which of the following is FALSE?

A. The lsp-ping tool is used to perform a unidirectional LSP test.

B. The router 10.10.10.2 is the egress router of the LSP.

C. The router can reach the far-end of the LSP through an RSVP-TE tunnel.

D. The router can reach the far-end of the LSP through an LDP tunnel.

Answer 16

D. The router can reach the far-end of the LSP through an LDP tunnel.

(The presence of rc=3 (EgressRtr) confirms this is an RSVP-TE LSP, not LDP.)

Question 17

Question: 17

What labels are encapsulated in the tunnels used by a 6PE deployment?

A. The inner label is the IPv4 Explicit Null. The outer label is the MPLS transport label.

B. The inner label is an MPLS transport label. The outer label is the IPv4 Explicit Null.

C. The inner label is the IPv6 Explicit Null. The outer label is an MPLS transport label.

D. The inner label is an MPLS transport label. The outer label is the IPv6 Explicit Null.

Answer 17

C. The inner label is the IPv6 Explicit Null. The outer label is an MPLS transport label.

(In 6PE, the inner label identifies the IPv6 route and may be the IPv6 Explicit Null [label 2] for QoS, while the outer is the MPLS LSP label.)

Question 18

Question: 18

Which of the following about an ERO in an RSVP PATH message is FALSE?

A. ERO is used by downstream routers to determine the next-hop for the LSP.

B. ERO contains label information used to signal an LSP path.

C. ERO is not always present in the PATH message.

D. Each downstream router updates information inside the ERO.

Answer 18

B. ERO contains label information used to signal an LSP path.

(Explanation: The ERO [Explicit Route Object] contains the intended path or hop sequence for the LSP but does not contain label information. Labels are exchanged via RESV messages.)

Question 19

Question: 19

Which of the following about Type 10 opaque LSAs is TRUE?

A. Type 10 opaque LSAs are supported by IS-IS.

B. Type 10 opaque LSAs are flooded to all areas of the routing domain.

C. Type 10 opaque LSAs are stored in an LSDB.

D. Type 10 opaque LSAs are used for traffic engineering support.

Answer 19

C. Type 10 opaque LSAs are stored in an LSDB.

(Explanation: Type 10 opaque LSAs are area-scoped OSPF LSAs used to carry additional information like traffic engineering data and are stored in the OSPF LSDB.)

Question 20

Question: 20

Which of the following about MPLS shortcuts for IGP on a Nokia 7750 SR is FALSE?

A. An IGP route takes priority over a transport tunnel.

B. Both LDP and RSVP-TE based tunnels can be used.

C. MPLS tunnels can be used to resolve the prefixes learned via IGP.

D. Multiple MPLS tunnels can be installed in the FIB.

Answer 20

A. An IGP route takes priority over a transport tunnel.

(This is false because MPLS shortcuts allow the IGP to resolve next hops via MPLS tunnels instead of preferring the IGP route directly.)

Question 21

Question: 21

Initially, all ports on a Nokia 7750 SR have 10Gbps bandwidth. RSVP configuration limits reservable bandwidth to 30 percent on all interfaces. An LSP is signaled reserving 1 Gbps bandwidth. How much unreserved bandwidth is left on the interface?

A. 10 Gbps

B. 7 Gbps

C. 3 Gbps

D. 2 Gbps

Answer 21

D. 2 Gbps

Calculation:

Total port bandwidth = 10 Gbps

Reservable bandwidth = 30% of 10 Gbps = 3 Gbps

LSP reservation = 1 Gbps

Remaining unreserved bandwidth = 3 Gbps - 1 Gbps = 2 Gbps

Correct Answer: D. 2 Gbps ✅

Question 22

Question: 22

How does a DMP inform the downstream routers that it has merged detour tunnels?

A. The DMP sends the DMP_Object in each detour’s PATH messages.

B. The DMP summarizes PATH messages, giving each detour its own MSGJD.

C. The DMP identifies itself as the previous hop in each detour’s PATH message.

D. The DMP sends a single PATH message containing the merged DETOUR_Objects.

Answer 22

A. The DMP sends the DMP_Object in each detour’s PATH messages.

(DMP stands for Detour Merge Point. To notify downstream routers of merged detours, it includes the DMP_Object in the PATH messages for each detour LSP.)

Question 23

Question: 23

Two LSPs traverse the path R1–R2–R3. Both LSPs are configured with facility fast reroute and link protection. When router R1 is the PLR (Point of Local Repair), which router becomes the Merge Point (MP) for this LSP?

A. Router R1

B. Router R2

C. Router R3

D. Router R4

E. Router R5

Answer 23

B. Router R2

Answer Explanation:

In RSVP-TE Facility Fast Reroute (FRR) with link protection:
The PLR (Point of Local Repair) is the router upstream of the protected link.

The MP (Merge Point) is the router downstream of the protected link – typically, the next-hop router.

In this scenario:

R1 is the PLR, protecting the link R1–R2.

Therefore, the MP is R2, as it is the next-hop router where the detour tunnel rejoins the main LSP.

This aligns with link protection behavior, where a bypass tunnel from PLR (R1) reroutes around the protected link and terminates at the next-hop (R2), the MP.

Question 24

Question 24:

The path of a fast reroute protected LSP is R1–R2–R3.
Which of the following about the protected LSP path is TRUE?

A. All routers along the path, R1, R2, and R3 can be PLRs.

B. If the R1–R2 link fails, router R4 becomes an MP.

C. If the R2–R3 link fails, router R3 becomes a PLR.

D. Router R1 is the LSP head-end and can be a PLR.

Answer 24

D. Router R1 is the LSP head-end and can be a PLR.

Explanation:
PLR (Point of Local Repair): The router upstream of a protected link that initiates a detour.

MP (Merge Point): The router where the detour rejoins the primary LSP.

R1–R2–R3 is the primary path.

R1 is the LSP head-end and sits upstream of the R1–R2 link, so it can act as a PLR.

Option A is incorrect: R3 is the tail-end and cannot be a PLR.

Option B is incorrect: R4 is not along the primary path and is not the merge point.

Option C is incorrect: R3 is the egress (tail-end), and only upstream routers can be PLRs.

Question 25

Question 25 If the primary path fails, which backup LSP path will the head-end router pick first? A. The Standby with the highest next-hop IP. B. The first Standby in the list. C. The Standby with the longest uptime. D. The Standby with the lowest next-hop IP.

Answer 25

B. The first Standby in the list. Answer Explanation: When a primary RSVP-TE path fails, the head-end router (LER) selects the first operational Standby path in the configured list order. The order listed in the CLI output (from top to bottom) reflects the configured path preference. Among the Standby options: tor6-2 appears first → it is Up and eligible. tor6-1 is also Up, but it is second in order. Since both are administratively and operationally Up, the router picks the first Standby path that is operational — which is tor6-2. Why the other answers are incorrect: A. ❌ Highest IP is not the selection criteria. C. ❌ Uptime is not relevant for standby selection. D. ❌ Lowest next-hop IP is not used unless configured with specific metrics or preferences.

Question 26

Question 26: Which of the following about Fast Reroute link protection tunnels is FALSE? A. Link protection tunnels are established if a router is unable to establish node protection tunnels. B. Link protection tunnels are only requested for a primary LSP path. C. Link protection tunnels can be created for both one-to-one or facility Fast Reroute. D. Link protection tunnels detour around a failed next downstream router.

Answer 26

D. Link protection tunnels detour around a failed next downstream router. This statement is false because link protection tunnels protect against link failures, not node (router) failures. Detouring around a failed downstream router refers to node protection, not link protection.

Question 27

Question 27: An LSP is configured with one-to-one FRR and node protection on a Nokia 7750 SR. Which of the following is FALSE? A. Each PLR signals a protection tunnel that avoids the downstream node. B. A single protection tunnel can protect all LSPs that go through the same hop. C. A link protection tunnel is signaled if a node protection tunnel cannot be established. D. Protection tunnels used in this LSP are also detour tunnels.

Answer 27

B. A single protection tunnel can protect all LSPs that go through the same hop. This is false in the context of one-to-one (detour) FRR, where each LSP gets a unique detour tunnel. Shared protection is only possible in facility FRR (one-to-many), where a bypass tunnel can be reused across multiple LSPs for the same protected element.

Question 28

Question: 28 A fully loose LSP "toR6" is configured. All links have the same cost and all routers are Nokia 7750 SRs. The LSP currently traverses the path R1-R2-R7-R8-R4-R6 and the resignal timer is enabled. Which of the following about this LSP is FALSE? A: The LSP will switchover to another path if a failure occurs. B: The LSP will switchover to a better path as soon as it is available. C: CSPF must be enabled for this LSP to attempt to find a better path. D: The LSP will switchover to a better path in a MBB fashion.

Answer 28

B: The LSP will switchover to a better path as soon as it is available. Answer Explanation: A fully loose RSVP-TE LSP: Does not define explicit hops (it's computed dynamically by CSPF). Resignal timers control when the head-end router attempts to re-establish the LSP using a better path if one becomes available. Let’s break down the statements: A: True – If a link in the current path fails, RSVP-TE can trigger reroute to another valid path. B: ❌ False – Even with CSPF and better path available, the LSP does not switch immediately. It waits for the resignal timer to expire, then attempts to reestablish using the better path. C: True – CSPF (Constrained Shortest Path First) is required for computing better paths. D: True – When it does switchover (e.g., after resignal), it uses MBB (Make-Before-Break) to avoid traffic loss.

Question 29

Question 29: An LDP tunnel is established on router R1 towards router R6. The link between routers R2 and R4 goes down. What will happen to the MPLS data traffic to router R6 IMMEDIATELY after the link goes down? A: MPLS data traffic will be discarded until the IGP finds a new next-hop to router R3. B: MPLS data traffic will be discarded unless the LDP tunnel has a standby secondary path. C: MPLS data traffic will not be discarded because router R1 received labels from both next-hops, routers R2 and R3. D: MPLS data traffic will not be discarded because of fast reroute capability on router R2.

Answer 29

C: MPLS data traffic will not be discarded because router R1 received labels from both next-hops, routers R2 and R3. Answer Explanation: In an LDP-based MPLS network, each router uses IGP (like OSPF or IS-IS) to determine the best path and then uses LDP to exchange labels for those IGP next-hops. Here’s what happens in this topology: R1 has an LDP tunnel to R6. Both R2 and R3 are valid IGP next-hops for reaching R6. R1 receives label bindings from both R2 and R3, and installs one as primary (R2) and the other as backup (R3). When the R2–R4 link fails, IGP quickly converges and selects the alternate path via R3. Since R1 already has a label binding from R3, it can immediately switch to forwarding MPLS traffic through R3 without discarding packets. Option Analysis: A. False – Traffic is not discarded if alternate labels are available. B. False – LDP doesn’t use RSVP-like standby secondary paths; label redundancy is based on IGP and label bindings. C. ✅ Correct – R1 already had labels from R2 and R3, so it can reroute traffic immediately. D. False – LDP does not support Fast Reroute (FRR) natively like RSVP-TE.

Question 30

Question 30: Fill in the blanks: A ___ device has all interfaces inside the provider domain, and a ___ device has at least one interface outside the provider domain. A: PE, P B: P, PE C: PE, CE D: CE, PE E: CE, P

Answer 30

B: P, PE

Question 31

Question 31: Consider a device that uses per-platform label space; which of the following fields is NOT contained in the LFIB? A: Incoming label B: Outgoing label C: Incoming interface D: Outgoing interface

Answer 31

C: Incoming interface Explanation: The Label Forwarding Information Base (LFIB) on an MPLS router typically contains: Incoming label Outgoing label Outgoing interface It does not need the incoming interface when using per-platform label space, because the label is unique across all interfaces on the platform.

Question 32

Question 32: Which of the following regarding MPLS encapsulation for VPRN services is TRUE? A: The customer's Layer 3 header is removed at the iLER. B: The customer's Layer 2 header is removed at the iLER. C: The customer's Layer 3 header is removed at the eLER. D: The customer's Layer 2 header is removed at the eLER.

Answer 32

B: The customer's Layer 2 header is removed at the iLER. In MPLS VPRN services: The ingress Label Edge Router (iLER) receives the customer Ethernet frame. It removes the Layer 2 header (Ethernet) and retains the Layer 3 payload (IP). It then encapsulates the packet with MPLS labels (one for transport and another for VPN).

Question 33

Question 33: Which of the following about the Link LDP discovery process on the Nokia 7750 SR is FALSE? A: LDP Hello messages are sent over TCP. B: LDP Hello messages are sent to the All Routers address 224.0.0.2. C: LDP Hello messages are exchanged between all directly connected LDP enabled routers. D: Each LDP enabled router must have its own unique system IP address.

Answer 33

A: LDP Hello messages are sent over TCP. This is false because LDP Hello messages are actually sent over UDP port 646, not TCP. TCP is used after discovery, during session establishment for LDP.

Question 34

Question 34: Which of the following devices assumes the active role during the establishment of an LDP session? A: The peer with the higher physical address. B: The peer with the higher transport address. C: The peer with the lower physical address. D: The peer with the lower transport address. E: The peer that generated the first Hello message.

Answer 34

B: The peer with the higher transport address. In LDP session establishment, both peers exchange Hello messages, and then initiate a TCP connection for session setup. The peer with the higher transport address (typically the system IP address) assumes the active role (initiates the TCP connection).

Question 35

Question 35: Which of the following messages is NOT used in T-LDP operation? A: Hello message B: Init message C: Keepalive message D: Label Mapping message E: ACK message

Answer 35

E: ACK message T-LDP (Targeted Label Distribution Protocol) uses the same message types as standard LDP for session establishment and label exchange: Hello (for discovery) Init (to initiate a session) Keepalive (to maintain session) Label Mapping (to advertise labels) There is no ACK message type in the LDP specification; LDP is a reliable protocol running over TCP, so acknowledgments are handled inherently by TCP, not by a separate ACK message.

Question 36

Question 36: Which of the following is FALSE? A: The router can reach prefix 192.10.1.2/32 through a RSVP-TE tunnel. B: The router can reach prefix 192.10.1.2/32 through an LDP tunnel. C: The router 10.10.10.2 is the egress router of the prefix 192.10.1.2/32. D: The lsp-ping tool is used to perform a unidirectional LSP test.

Answer 36

B: The router can reach prefix 192.10.1.2/32 through an LDP tunnel. Explanation: The use of lsp-ping with a prefix is specific to RSVP-TE LSPs — not LDP. The presence of the return code rc=3 (EgressRtr) confirms that this is an RSVP-TE LSP test. Therefore, statement B is FALSE — the router is not using LDP to reach that prefix.

Question 37

Question 37: Which of the following about LSP path configuration on a Nokia 7750 SR is TRUE? A: The path must include at least one hop. B: The path may be used for multiple LSPs. C: The path may be used multiple times in a single LSP. D: The path must define a tunnel destination IP address.

Answer 37

B: The path may be used for multiple LSPs. Explanation: On the Nokia 7750 SR, a path object (e.g., named “to-PE2”) defines a list of strict or loose hops and can be reused across multiple LSPs, which enhances configuration efficiency. A is incorrect — a valid path can contain zero hops (i.e., dynamically resolved). C is incorrect — a path can be referenced once per LSP; you can't reuse the same path multiple times in a single LSP. D is incorrect — the LSP defines the tunnel destination IP, not the path object.

Question 38

Question 38: What action should be taken when the LSP from R1 to R6 fails along the R3–R6 segment? A: Send a PATH Tear message toward router R6. B: Send a PATH Tear message toward router R1. C: Send a PATH Error message toward router R6. D: Send a PATH Error message toward router R1.

Answer 38

D: Send a PATH Error message toward router R1. When a failure is detected in RSVP-TE along a path (e.g., link R3–R6 goes down), the downstream router (R3) sends a PATH Error message upstream toward the head-end LSR (R1) to inform it of the failure. This triggers rerouting or protection switching. PATH Tear is used when the LSP is intentionally torn down (e.g., deprovisioned), not for failures. PATH Error toward R1 is the standard RSVP-TE mechanism in response to a link failure.

Question 39

Question 39: Which of the following about CSPF is TRUE? A: The tail-end router performs the CSPF calculation for an LSP. B: CSPF calculations are always performed on RSVP-TE based LSPs. C: The head-end router performs the CSPF calculation for an LSP. D: Each downstream router performs its own CSPF calculation for an LSP.

Answer 39

C: The head-end router performs the CSPF calculation for an LSP. Explanation: CSPF (Constrained Shortest Path First) is an enhanced version of SPF that considers constraints such as bandwidth, admin group, etc. In RSVP-TE, the head-end (ingress) router computes the path using CSPF before signaling the LSP using RSVP PATH messages. The tail-end router does not compute the path; it simply receives it. Downstream routers do not perform CSPF; they forward the RSVP PATH message and reserve resources. CSPF is typically only used for explicit path selection in TE tunnels, not always required for every RSVP-TE tunnel (so B is not always true).

Question 40

Question 40: Which of the following describes 6PE? A: P routers run IPv4 only. PE routers run IPv4 only and exchange IPv6 routes using MP-BGP. B: P routers run IPv4 only. PE routers run both IPv4 and IPv6 and exchange IPv6 routes using MP-BGP. C: P routers run IPv6 only. PE routers run both IPv4 and IPv6 and exchange IPv4 routes using MP-BGP. D: P routers run IPv6 only. PE routers run IPv6 only and exchange IPv4 routes using MP-BGP.

Answer 40

B: P routers run IPv4 only. PE routers run both IPv4 and IPv6 and exchange IPv6 routes using MP-BGP. Explanation: 6PE (IPv6 Provider Edge) enables IPv6 over an IPv4 MPLS core without upgrading the core routers to IPv6. P routers (provider core) do not need to support IPv6; they only switch labels (IPv4-based MPLS). PE routers (provider edge) are dual-stack (IPv4 + IPv6) and use MP-BGP to exchange IPv6 routes (AFI/SAFI 2/1). These IPv6 routes are carried over MPLS tunnels (RSVP or LDP) using label stack encapsulation.

Question 41

Question 41: To enable the LDP-over-RSVP feature, which of the following configurations is NOT required on a Nokia 7750 SR? A: Enable the ldp-over-rsvp feature on all PEs and ABRs along the LSP tunnel. B: Configure Link-LDP sessions between each PE-ABR and ABR-ABR pair. C: Configure RSVP-TE LSPs in each area between each PE-ABR and ABR-ABR pair. D: Configure T-LDP sessions with the tunneling option.

Answer 41

D: Configure T-LDP sessions with the tunneling option. Explanation: To enable LDP-over-RSVP (also known as LDP tunneling) on a Nokia 7750 SR: You must enable the ldp-over-rsvp feature on the PE and ABR routers (Choice A). Link-LDP is used to signal the LDP label bindings (Choice B). RSVP-TE LSPs must exist between ABR and PE nodes to act as the transport (Choice C). However, T-LDP is not required for LDP-over-RSVP. T-LDP is typically used for targeted sessions (e.g., loopback-to-loopback) in VPN contexts, not basic LDP-over-RSVP transport.

Question 42

Question 42: Which of the following is NOT required when configuring an LSP with an admin group constraint on a Nokia 7750 SR? A: Enable traffic engineering on all routers along the LSP path. B: Enable CSPF on the head-end router. C: Configure a path definition on all routers along the LSP path. D: Enable MPLS and RSVP on all routers along the LSP path.

Answer 42

C: Configure a path definition on all routers along the LSP path. When using admin group constraints, the Constrained Shortest Path First (CSPF) algorithm automatically calculates paths that satisfy those constraints. Required configurations include: Enabling RSVP and MPLS (Label Distribution and Signaling). Enabling Traffic Engineering on the routers. Enabling CSPF on the head-end so the LSP respects the admin group. But: You do NOT need to manually configure a path on every router. That's only necessary in explicit path configurations. CSPF dynamically computes the LSP based on admin groups.

Question 43

Question 43 An LSP path is established on router R1 toward router R6. If there is a problem on router R4, but the link between R2 and R4 remains up, which of the following will affect the failure detection time? A. The time router R2 takes to receive a PATH Error message from router R4. B. The time router R2 takes to find out a number of RSVP Hello messages have been missed. C. The time router R2 takes to send a PATH Tear message to the head-end router. D. The time router R2 takes to receive a PATH message from router R4 after a PATH refresh interval.

Answer 43

B. The time router R2 takes to find out a number of RSVP Hello messages have been missed. This is because RSVP Hello messages are used for rapid failure detection between adjacent RSVP neighbors. If R4 becomes unresponsive but the physical link remains up, R2 will detect the failure only after missing a number of Hello messages.

Question 44

Question 44: If the primary path goes down, which secondary LSP path will the head-end router select first? A. Secondary_Path-1 B. Secondary_Path-2 C. Secondary_Path-3 D. Secondary_Path-4

Answer 44

C. Secondary_Path-3 Answer Explanation: In Nokia SR OS RSVP-TE LSPs, the failover behavior works as follows: If the primary path fails, the head-end router evaluates standby secondary paths. Among the standby paths, it uses the one with the lowest path-preference value (i.e., most preferred). In this config: Secondary_Path-3 is standby with path-preference 10 ✅ Secondary_Path-4 is standby with path-preference 20 ❌ Secondary_Path-1 and Secondary_Path-2 are not standby paths and won't be used for automatic failover.

Question 45

Question 45: Facility fast reroute with node protection is enabled for an LSP. Which of the following is FALSE? A. Each PLR signals a bypass tunnel that avoids the next-hop downstream router. B. When a failure occurs, the PLR pushes an additional label onto the label stack. C. No bypass tunnel is established if the PLR cannot provide node protection. D. The head-end router sets the local protection desired flag in the session attribute object.

Answer 45

C. No bypass tunnel is established if the PLR cannot provide node protection. This statement is false because the PLR will still attempt to provide link protection even if node protection is not available. Facility FRR can fall back to link protection when node protection is not possible. Therefore, a bypass tunnel can still be established for link protection.

Question 46

Question 46: An LDP tunnel is established on R1–R2–R4–R6 because the link between routers R3 and R6 is down. With the LDP-IGP Sync feature enabled, what happens immediately after the link is restored? A. A new LDP session is established on R1–R3–R6 as soon as the FIB is updated. B. The LDP session remains unchanged until the existing path R1–R2–R4–R6 goes down. C. A new LDP session is established on R1–R3–R6 as soon as router R1 receives a new label for router R6. D. The LDP session remains unchanged until router R3 stops advertising the maximum metric for the link to router R6.

Answer 46

D. The LDP session remains unchanged until router R3 stops advertising the maximum metric for the link to router R6. With LDP-IGP Synchronization enabled, LDP waits until label bindings are exchanged before the IGP allows traffic to be forwarded over the restored link. Router R3 advertises a maximum metric for the R3–R6 link until LDP is ready. Once LDP is synchronized, the metric returns to normal, and traffic is shifted back. This avoids blackholing traffic during label setup.

Question 47

Question 47: An LSP traverses R1–R2–R4–R6 and one-to-one fast reroute with link protection is enabled. All links have the same cost. Which of the following about DMP and MP is TRUE? A. R3 and R5 become DMPs; R6 becomes MP. B. R3 and R5 become DMPs; R4 becomes MP. C. R3, R5, and R6 become DMPs; R4 becomes MP. D. R1, R3, and R5 become DMPs; R4 and R6 become MPs.

Answer 47

B. R3 and R5 become DMPs; R4 becomes MP. Answer Explanation: With one-to-one fast reroute and link protection enabled, the merge point (MP) is the router immediately downstream of the protected link—in this case, R4. The detour merge points (DMPs) are routers that could serve as alternate next-hops in the event of a failure—R3 and R5 in this topology.

Question 48

Question 48: Which of the following devices inspects the MPLS header in the received packet, and exchanges it for a new MPLS header? A. iLER B. LER C. LSR D. PE E. eLER

Answer 48

C. LSR Answer Explanation: An LSR (Label Switch Router) is responsible for inspecting the MPLS header, making forwarding decisions based on the label, and swapping it for a new label as the packet traverses the MPLS network. This operation is known as label swapping, which is the core function of an MPLS transit node (LSR). In contrast, iLER and eLER refer to ingress and egress LERs, which push or pop labels, not swap them.

Question 49

Question 49: Which of the following defines an FEC in traditional IP? A. A group of packets that will be forwarded by the router in the same manner, over the same path. B. A group of packets that arrive at the router on the same interface. C. A group of packets that leave the router on the same interface. D. A group of packets that arrive at the router on the same interface, from the same source.

Answer 49

A. A group of packets that will be forwarded by the router in the same manner, over the same path. Answer Explanation: In traditional IP forwarding, a Forwarding Equivalence Class (FEC) is defined as a group of packets that the network treats the same way when forwarding—this means they follow the same path and receive the same forwarding treatment (e.g., same QoS, next-hop). This is a foundational concept in MPLS, where a label is assigned to an entire FEC rather than individual packets.

Question 50

Question 50: Which MPLS mode saves only active label mappings received from peer LSRs? A. Conservative label retention B. Liberal label retention C. Downstream on demand D. Downstream unsolicited

Answer 50

A. Conservative label retention Answer Explanation: In MPLS, Conservative Label Retention Mode ensures that a router only stores label bindings (label mappings) that are actually being used in its forwarding path—those received from its active next-hop LSRs. This is more memory-efficient and is often used in Downstream-on-Demand distribution mode. In contrast, Liberal Label Retention Mode stores all received labels, even from non-active next hops.