350-501 MPLS and Segment Routing Practice Test 12 — 15 Questions

Question 1

An engineer is configuring MPLS on a Cisco router. Which label operation is performed on the ingress LSR when a packet enters the MPLS domain?

Accepted Answer

Push a new label. The ingress LSR pushes a new label onto the stack, encapsulating the original IP packet with an MPLS header.

Answer

Pop the top label

Answer

No label operation

Answer

Swap the top label

Question 2

In an MPLS network using LDP, which LDP mode allocates a label for every prefix in the routing table and advertises it to all LDP neighbors, regardless of whether the neighbor requests it?

Accepted Answer

Downstream unsolicited with liberal label retention. Downstream unsolicited (DU) mode means a router advertises labels for all its prefixes to all neighbors without waiting for a request.

Answer

Downstream on demand with liberal label retention

Answer

Downstream unsolicited with conservative label retention

Answer

Downstream on demand with conservative label retention

Question 3

An MPLS TE tunnel is configured with an explicit path. Which RSVP message is used by the headend to signal the path and carry the Explicit Route Object (ERO) listing the hops?

Accepted Answer

PATH. The PATH message is sent downstream from the headend and contains the ERO that specifies the explicit route.

Answer

RESV

Answer

PATH_TEAR

Answer

RESV_CONFIRM

Question 4

In RSVP-TE, which filter spec style allows multiple senders to share the same reserved resources on a link, as long as their flows do not exceed the reservation?

Accepted Answer

Shared Explicit (SE). Shared Explicit (SE) style allows multiple senders to share a single reservation, with explicit sender list.

Answer

Distinct Explicit (DE)

Answer

Fixed Filter (FF)

Answer

Wildcard Filter (WF)

Question 5

Which MPLS TE mechanism provides link protection by pre-establishing a backup LSP that bypasses a specific link, activated when the link fails?

Accepted Answer

Bypass tunnel. RSVP-TE Fast Reroute uses bypass tunnels to protect links, providing local repair upon failure.

Answer

LDP FRR

Answer

Detour tunnel

Answer

TE backup path

Question 6

An engineer is configuring SR-MPLS in an IS-IS network. Which IS-IS TLV is used to advertise the Segment Routing Global Block (SRGB) and Node-SID assignments?

Accepted Answer

TLV 242. The IS-IS SR-Capabilities sub-TLV (TLV 242) advertises the SRGB range, while the SR-Algorithm sub-TLV (TLV 242) and Prefix-SID sub-TLV (TLV 135) advertise Node-SIDs.

Answer

TLV 135

Answer

TLV 229

Answer

TLV 22

Question 7

In SRv6, which endpoint behavior is used for decapsulation and forwarding to a Layer 3 VPN IPv4 destination, removing the outer IPv6 header?

Accepted Answer

End.DT4. End.DT4 is the SRv6 endpoint behavior for decapsulation and table lookup in the VPN IPv4 table.

Answer

End.X

Answer

End.DT6

Answer

End.DT2U

Question 8

In SRv6 micro-SID (uSID) compression, which part of the SID is used to carry a compressed instruction set, enabling efficient forwarding with a shorter SID list?

Accepted Answer

Function. The micro-SID block consists of a locator followed by compressed function and argument, reducing the SID list size.

Answer

Block

Answer

Locator

Answer

Argument

Question 9

Which component in EVPN is used to uniquely identify an Ethernet segment across multiple PE devices in a multi-homing scenario?

Accepted Answer

ESI. The Ethernet Segment Identifier (ESI) is a 10-byte value that identifies a specific multihomed site.

Answer

RT-2

Answer

MAC-VRF

Answer

EVI

Question 10

In EVPN multi-homing with all-active mode, which mechanism is used to elect a designated forwarder (DF) for broadcast, unknown unicast, and multicast (BUM) traffic on a given Ethernet segment?

Accepted Answer

DF election via ESI label and route type 4. The DF election is performed using a deterministic algorithm based on the ESI and the list of PEs, with the lowest IP address becoming DF.

Answer

Load balancing via MLAG

Answer

ES-IS protocol

Answer

MSTP

Question 11

An SR-TE policy is configured with a candidate path containing multiple segment lists. Which selection criteria is used to choose the active segment list among the candidate paths?

Accepted Answer

Preference value. The preference value (or priority) is used to select the best candidate path; higher preference wins.

Answer

Color

Answer

Metric type (IGP or TE)

Answer

Hop count

Question 12

Which TWO statements about MPLS label operations are correct? (Choose two.)

Accepted Answer

Label swapping is performed at every transit LSR.. Penultimate Hop Popping (PHP) removes the label before the final hop, and the ingress LSR pushes the initial label.

Answer

The ingress LSR performs a swap operation.

Answer

The egress LSR always performs a pop operation.

Answer

Label popping always happens at the penultimate hop.

Question 13

Which THREE are valid SRv6 endpoint behaviors for VPN services? (Choose three.)

Accepted Answer

End.DT2U. End.DT4 for IPv4 L3VPN, End.DT6 for IPv6 L3VPN, and End.DT2U for L2VPN are defined SRv6 behaviors.

Answer

End.B6

Answer

End.X

Question 14

Which THREE are mechanisms used in EVPN to support multi-homing and load balancing? (Choose three.)

Accepted Answer

Aliasing. ESI identifies the segment, DF election avoids duplicates, and aliasing allows traffic to be forwarded to any PE in the multi-homing group.

Answer

Spanning Tree Protocol (STP)

Answer

Virtual Router Redundancy Protocol (VRRP)

Question 15

In an MPLS network using LDP, which statement correctly describes the label distribution behavior for a given FEC?

Accepted Answer

Labels are advertised unsolicited to all neighbors, and all labels are retained even if not used (liberal label retention).. LDP uses downstream unsolicited mode by default, where each LSR advertises labels for all FECs to all neighbors without being asked, and liberal label retention stores all received labels even if not currently used.

Answer

Labels are advertised only in response to a request from an upstream neighbor (downstream on demand).

Answer

Labels are advertised unsolicited but only the best label for each FEC is retained (conservative label retention).

Answer

Labels are advertised only when the LSR has an outgoing label for the FEC (ordered label distribution).