350-501 Practice Test 23 — 15 Questions

Question 1

An engineer is deploying MPLS-TE with FRR using the 1:1 detour method. Which statement about link protection in this scenario is true?

Accepted Answer

The detour LSP merges back with the main LSP after the protected link.. 1:1 detour creates a one-to-one backup LSP for each protected LSP. The detour LSP is pre-signaled and protects against link failure by re-routing traffic around the failed link.

Answer

The detour LSP is created dynamically after a failure is detected.

Answer

Link protection requires node protection to be configured.

Answer

A single bypass tunnel protects multiple LSPs over the same link.

Question 2

In MPLS, which operation is performed when a packet arrives at a transit router and the top label matches the router's own label assigned for the FEC?

Accepted Answer

Pop the top label.. When the top label is the router's own label (often an implicit null or explicit null), the router pops the label and forwards the packet based on the next label or IP header.

Answer

Push a new label onto the stack.

Answer

Drop the packet.

Answer

Swap the top label with a new label.

Question 3

In MPLS, what is the term for the operation where the top label is removed and replaced with a new label?

Accepted Answer

Swap. Swap is the operation where the incoming label is replaced with a new outgoing label, as determined by the LFIB.

Answer

Push

Answer

Pop

Answer

Replace

Question 4

In SR-MPLS, what is the purpose of the SRGB (Segment Routing Global Block)?

Accepted Answer

To provide a global label space for prefix SIDs. SRGB is a reserved label range used for globally significant prefix SIDs. All routers in the domain use the same SRGB to ensure consistent label mapping.

Answer

To define the range of labels used for LDP

Answer

To reserve labels for MPLS-TE tunnels

Answer

To allocate labels for adjacency SIDs

Question 5

An engineer is configuring MPLS LDP on a Cisco router. The router uses downstream unsolicited mode with liberal label retention. Which behavior describes the label distribution and retention on this router?

Accepted Answer

The router sends label bindings to all neighbors without receiving requests and retains all received label bindings.. Downstream unsolicited means the downstream router sends label bindings to all neighbors without being asked. Liberal label retention means the router keeps all received label bindings, even if the next hop is not reachable.

Answer

The router requests labels from neighbors and retains only labels for the best path.

Answer

The router sends label bindings only for directly connected routes and discards labels from non-reachable next hops.

Answer

The router sends label bindings only in response to requests from upstream neighbors and retains only labels for directly connected next hops.

Question 6

Which label distribution mode does LDP use by default in Cisco IOS?

Accepted Answer

Downstream unsolicited. LDP uses downstream unsolicited mode by default, where a router advertises labels to all neighbors without being asked.

Answer

Downstream on-demand

Answer

Upstream unsolicited

Answer

Upstream on-demand

Question 7

In MPLS-TE, what is the purpose of the Explicit Route Object (ERO) in the RSVP PATH message?

Accepted Answer

To specify the desired path as a list of nodes or links.. ERO specifies the strict or loose hops that the TE LSP must traverse. It allows the headend to enforce a specific path through the network.

Answer

To label the path with a tunnel ID.

Answer

To reserve bandwidth along the path.

Answer

To record the actual path taken by the LSP.

Question 8

In SR-MPLS, which THREE statements correctly describe the properties of Adjacency SIDs? (Choose three.)

Accepted Answer

Adjacency SIDs can be used in segment lists for SR-TE policies.. Adjacency SIDs are local to a router and represent a specific link. They are not global and are used for strict path control. They are allocated from a local label range (not SRGB).

Answer

Adjacency SIDs are allocated from the SRGB.

Answer

Adjacency SIDs are global and must be unique across the SR domain.

Question 9

In SRv6, what is the function of the 'End.DT4' behavior?

Accepted Answer

Decapsulation and IPv4 lookup in a VRF table. End.DT4 is a SRv6 endpoint behavior that decapsulates an IPv6 packet with an SRH and performs a lookup in the IPv4 VRF table for L3VPN.

Answer

Decapsulation and IPv6 lookup in a VRF table

Answer

Decapsulation and Ethernet switching

Answer

Encapsulation and forwarding to an IPv6 destination

Question 10

Which RSVP message is used to tear down an MPLS-TE LSP by being sent from the ingress toward the egress?

Accepted Answer

PATH Tear. RSVP-TE uses PATH messages to establish state and RESV to reserve. To tear down, a PathTear message is sent from the ingress to the egress, or a ResvTear from egress to ingress.

Answer

PATH Error

Answer

RESV Confirm

Answer

RESV Tear

Question 11

An engineer configures an SRv6 SID with the behavior End.DT6. What is the primary function of this SID?

Accepted Answer

Perform IPv6 decapsulation and forward using a VPN IPv6 routing table.. End.DT6 (Endpoint with Decapsulation and IPv6 table lookup) is used for L3VPN over SRv6. It decapsulates the outer IPv6 header and forwards based on the inner IPv6 destination using a specific VRF table.

Answer

Perform IPv4 decapsulation and forward using a VPN IPv4 table.

Answer

Perform IPv6 encapsulation and forward.

Answer

Perform IPv6 decapsulation and forward using the global IPv6 routing table.

Question 12

Which label is used for an Adjacency SID in SR-MPLS?

Accepted Answer

A label from the dynamic label range. The Adjacency SID is local to the router and represents a specific link; it is typically allocated from the dynamic label range, not the SRGB.

Answer

A label from RSVP-TE reserved range

Answer

A label from the static label range

Answer

A label from the SRGB (Segment Routing Global Block)

Question 13

In MPLS-TE Fast Reroute (FRR), what is a 'detour'?

Accepted Answer

A backup LSP that protects a single primary LSP. A detour is a 1:1 protection mechanism where a backup LSP is created for each protected LSP, often pre-signaled.

Answer

A secondary path for load balancing

Answer

A bypass tunnel that protects multiple LSPs

Answer

A mechanism to reroute traffic after failure detection

Question 14

In SR-TE, a headend router is configured with an SR Policy that includes an explicit candidate path with segment list [16001, 16003, 16005]. What does this segment list represent?

Accepted Answer

A list of node SIDs representing the path through routers with those SIDs. Each SID in the list is a node SID (Prefix-SID) of intermediate routers, forming a strict hop-by-hop path.

Answer

A list of labels for an RSVP-TE LSP

Answer

A list of adjacency SIDs for each link

Answer

A list of anycast SIDs for redundancy

Question 15

In MPLS, which operation occurs when a router receives a labeled packet and replaces the top label with a new label before forwarding?

Accepted Answer

Swap. In MPLS, the swap operation replaces the incoming top label with a new outgoing label as per the LFIB entry.

Answer

Lookup

Answer

Pop

Answer

Push