350-501 MPLS and Segment Routing Practice Test 5 — 15 Questions

Question 1

An engineer is configuring MPLS LDP on a Cisco router. The router is using downstream unsolicited mode and liberal label retention. Which statement correctly describes the label advertisement behavior?

Accepted Answer

Labels are advertised to all LDP peers for all known prefixes without a request.. In downstream unsolicited mode, the router advertises labels for all known prefixes to all neighbors, even if the neighbor did not request them. Liberal label retention keeps all received labels, even if not currently used.

Answer

Labels are retained only for directly connected neighbors.

Answer

Label advertisements are sent only for prefixes learned via BGP.

Answer

Labels are advertised only when explicitly requested by a neighbor.

Question 2

In an MPLS-TE tunnel configuration, which RSVP message carries the Explicit Route Object (ERO) that specifies the explicit path the tunnel must follow?

Accepted Answer

PATH message. In RSVP-TE, the PATH message includes the ERO to define the explicit route the traffic should take. The RESV message is sent back to confirm the reservation.

Answer

RSVP_TEAR message

Answer

RSVP_ERR message

Answer

RESV message

Question 3

A network operator is implementing segment routing (SR-MPLS) using OSPF as the IGP. Which OSPF TLV is used to advertise the Node SID (Prefix SID) for a router's loopback address?

Accepted Answer

Extended Prefix TLV. In OSPF, the Extended Prefix TLV (type 1) carries the Prefix SID sub-TLV for segment routing. The Adjacency SID is carried in the Extended Link TLV.

Answer

Router Information TLV

Answer

Traffic Engineering TLV

Answer

Extended Link TLV

Question 4

Which label operation is performed on a router when an MPLS packet arrives with a top label that matches a local label assigned to a directly connected prefix?

Accepted Answer

Pop. If the top label corresponds to a directly connected prefix, the router will pop the label (penultimate hop popping or explicit null) and forward the packet based on the inner header.

Answer

No operation, label is ignored

Answer

Push

Answer

Swap

Question 5

An engineer is configuring RSVP-TE fast reroute for link protection. Which protection method uses a pre-configured bypass tunnel that protects multiple LSPs on the same link?

Accepted Answer

Facility backup. In RSVP-TE FRR, facility backup uses a bypass tunnel that can protect multiple LSPs on the same link. In contrast, 1:1 detour creates a separate detour LSP for each protected LSP.

Answer

Local Path Protection

Answer

Global Repair

Answer

1:1 detour

Question 6

In SRv6, which behavior is used for L3VPN decapsulation (removing the outer IPv6 header and SRH, and forwarding the inner IPv4 packet based on the VPN routing table)?

Accepted Answer

End.DT4. End.DT4 is the SRv6 endpoint behavior for decapsulation and table lookup for IPv4 L3VPN. End.DT6 is for IPv6 L3VPN, End.DT2U is for L2VPN.

Answer

End.DT2U

Answer

End.DT6

Answer

End

Question 7

What is the purpose of the SRGB (Segment Routing Global Block) in SR-MPLS?

Accepted Answer

It defines a contiguous block of labels used for global SIDs such as Node SIDs.. The SRGB defines a range of labels reserved for global segment routing SIDs (e.g., Node SIDs). It ensures that the same label value represents the same prefix across the domain, avoiding label conflicts.

Answer

It defines the range of labels for Adjacency SIDs.

Answer

It is used to reserve labels for RSVP-TE tunnels.

Answer

It is the set of labels allowed for MPLS VPNs.

Question 8

In an EVPN-VPWS (Virtual Private Wire Service) deployment, which identifier is used to uniquely identify an Ethernet Segment for multi-homing?

Accepted Answer

Ethernet Segment Identifier (ESI). In EVPN-VPWS, the Ethernet Segment Identifier (ESI) uniquely identifies an Ethernet Segment across all multi-homed Provider Edge (PE) nodes. This 10-byte value is used in Designated Forwarder (DF) election and split-horizon filtering to prevent loops when a Customer Edge (CE) is multi-homed to multiple PEs. The ESI is carried in EVPN routes (Type 1 and Type 4) to signal multi-homing membership.

Answer

Ethernet Tag ID

Answer

MAC address of the CE

Answer

Route Distinguisher (RD)

Question 9

Which component of SRv6 SID format is used to identify the specific function (e.g., End, End.X) on the node?

Accepted Answer

Function. The SRv6 SID is structured as Locator:Function:Argument. The Function part identifies the specific behavior to be executed on the node, such as End or End.X.

Answer

Argument

Answer

Block

Answer

Locator

Question 10

In SR-TE, a headend router is configured with an SR Policy using an explicit candidate path that includes a segment list [100, 200, 300]. If all routers have the same SRGB starting at 10000, what is the actual outgoing label stack for the first segment?

Accepted Answer

10100, 10200, 10300. In SR-MPLS, the SID values in the segment list are relative to the SRGB. If the SRGB starts at 10000, a SID value of 100 corresponds to label 10100 (10000 + 100). So the first segment label is 10100.

Answer

100, 200, 300

Answer

10000, 20000, 30000

Answer

Labels depend on LDP allocation

Question 11

Which label distribution protocol is replaced by segment routing in SR-MPLS deployments?

Accepted Answer

LDP. In SR-MPLS deployments, segment routing replaces LDP as the label distribution protocol. LDP traditionally distributes labels for each prefix in the IGP, while segment routing uses the IGP itself to advertise prefix-SIDs and adjacency-SIDs, eliminating the need for a separate label distribution protocol. This simplifies the control plane and removes the dependency on LDP.

Answer

RSVP-TE

Answer

IGP itself

Answer

BGP

Question 12

When configuring an MPLS-TE tunnel with affinity/constraint-based routing, what is the effect of assigning a link attribute of 'red' and setting the tunnel's affinity to include 'red' with the 'include-all' keyword?

Accepted Answer

The tunnel must use only links that have the 'red' attribute.. The 'include-all' affinity means the tunnel path must include all links that have the specified color attribute. If a link does not have 'red' attribute, it is excluded from the CSPF computation.

Answer

The tunnel will prefer links with 'red' but may use others if necessary.

Answer

The tunnel will use a strict explicit path.

Answer

The tunnel will avoid links with 'red'.

Question 13

An engineer is designing an EVPN IRB (Integrated Routing and Bridging) solution. Which two statements about EVPN IRB are correct? (Choose two.)

Accepted Answer

EVPN IRB uses an anycast default gateway IP and MAC that is shared across all PEs.. EVPN IRB provides bridging at Layer 2 and routing at Layer 3 with an anycast default gateway. It uses asymmetric IRB (bridging locally, routing via VRF) and symmetric IRB (both directions route). The anycast gateway MAC is shared across all PEs.

Answer

EVPN IRB does not support multi-homing.

Answer

EVPN IRB only supports IPv6 traffic.

Answer

EVPN IRB requires a separate VRF for each MAC-VRF.

Question 14

Which three statements correctly describe the SRv6 micro-SID (uSID) concept? (Choose three.)

Accepted Answer

Micro-SID encodes multiple SIDs within a single 128-bit IPv6 address.. SRv6 micro-SID uses a compressed SID format where multiple SIDs are encoded in a single 128-bit IPv6 address. It reduces overhead by combining SIDs into a carrier SID. The uSID instruction is usually 16 bits, and the locator block is shared.

Answer

Micro-SID is incompatible with SR-MPLS.

Answer

Micro-SID requires a dedicated SRH extension header.

Question 15

In an MPLS network using RSVP-TE for traffic engineering, which two mechanisms can be used for fast reroute (FRR) protection? (Choose two.)

Accepted Answer

Facility backup using a bypass tunnel. RSVP-TE FRR offers two protection methods: facility backup (bypass tunnel) and 1:1 protection (detour LSP). Global Repair is not a standard term; Local Protection is used in segment routing.

Answer

Local Protection using segment routing adjacency SID

Answer

Global Repair using a secondary LSP from headend

Answer

Hot Standby Router Protocol (HSRP)