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Nokia VPRN practice questions

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Question 1IP routing, switching and aggregation

In a Nokia VPRN deployment, which routing protocol is most commonly used to distribute customer routes between PE routers across the provider core?

  1. RIPv2 with split horizon
  2. IS-IS level 1 only
  3. MP-BGP with the VPN-IPv4 address family Correct answer.
  4. OSPFv2 within a single area

Explanation

VPRN customer routes are carried as VPN-IPv4 (or VPN-IPv6) reachability information by MP-BGP between PE routers, with each route tagged by a route distinguisher and route target. Interior gateway protocols such as OSPF or IS-IS are typically used to carry the provider's own infrastructure addresses and next-hop reachability, not the per-VRF customer prefixes.

Question 2IP routing, switching and aggregation

What is the primary function of a route distinguisher in a Nokia VPRN service?

  1. It makes customer prefixes unique across VRFs by prepending an identifier to form VPN-IPv4 routes Correct answer.
  2. It sets the QoS forwarding class for customer traffic
  3. It defines the encapsulation used on the access port
  4. It selects which IGP area the customer routes are advertised into

Explanation

The route distinguisher is an 8-byte value that is prepended to an IPv4 prefix to create a unique VPN-IPv4 route, allowing overlapping customer address space to coexist in BGP. It is locally significant and does not itself control which PEs import the route.

Question 3IP routing, switching and aggregation

A PE router receives a VPN-IPv4 route with route target 65000:100. Which VPRN will import this route?

  1. The VPRN whose vrf-import policy accepts route target 65000:100 Correct answer.
  2. The VPRN with the lowest service ID on the router
  3. The VPRN whose route distinguisher equals 65000:100
  4. The VPRN configured with the same SAP port identifier

Explanation

Import decisions are driven by the vrf-import policy, which matches on route target extended communities attached to the route. The route distinguisher only makes the prefix unique and plays no role in import matching.

Question 4IP routing, switching and aggregation

Which Nokia SR OS construct is used to bind a VPRN instance to the MP-BGP process so that its routes are exported?

  1. The mirror service with a destination SAP
  2. The base router interface with a loopback address
  3. The IES service with a spoke SDP
  4. The vprn context with an autonomous-system and router-id configured under the service Correct answer.

Explanation

A VPRN service requires its own vprn context containing a route distinguisher, route targets, and a BGP or other routing instance so that routes can be exported and imported. The base router provides transport reachability but does not itself carry the VRF's routing state.

Question 5IP routing, switching and aggregation

In Nokia SR OS, which command displays the routes installed in a specific VPRN routing instance?

  1. show service id <id> sap
  2. show router <instance> route-table Correct answer.
  3. show router bgp summary
  4. show port detail

Explanation

The per-instance routing table is inspected with show router <instance-name-or-id> route-table, which lists the active routes in that VRF. The command must specify the router instance to see VRF-specific routes rather than the base routing table.

Question 6IP routing, switching and aggregation

Which encapsulation type is used for an Ethernet VPRN access SAP on a Nokia SR OS platform?

  1. dot1q or null on an Ethernet port Correct answer.
  2. Frame Relay DLCI
  3. ATM VPI/VCI
  4. PPP over a synchronous serial interface

Explanation

Ethernet VPRN access uses dot1q (VLAN-tagged) or null (untagged) encapsulation on an Ethernet port or LAG. The other encapsulations belong to legacy WAN technologies not used for Ethernet SAPs.

Question 7IP routing, switching and aggregation

What does an MP-BGP next hop of 0.0.0.0 on a VPN-IPv4 route indicate in a Nokia VPRN?

  1. The route must be discarded because the next hop is unreachable
  2. The route should be imported into the base router table
  3. The route is a summary generated by the route reflector
  4. The route is locally originated and should be resolved to the originating PE's loopback Correct answer.

Explanation

When a PE originates a VPN-IPv4 route from a local VRF, it advertises a next hop of 0.0.0.0; the receiving PE resolves it to the originating PE's BGP next hop, typically the loopback address. This mechanism ensures traffic is sent to the correct PE rather than being dropped.

Question 8IP routing, switching and aggregation

Which statement describes the purpose of a route target in a VPRN?

  1. It is a numeric identifier that makes the customer prefix globally unique
  2. It is the metric used for best-path selection within the VRF
  3. It is an extended community that controls which VRFs import and export a route Correct answer.
  4. It is the label used for the service transport tunnel

Explanation

Route targets are extended BGP communities attached to VPN routes; export targets are attached on advertisement and import policies match them to decide VRF installation. They are distinct from the route distinguisher, which provides prefix uniqueness.

Question 9IP routing, switching and aggregation

A customer VPRN has two CE connections on the same PE, one via a SAP and one via a spoke SDP. Which mechanism prevents routing loops between these attachments?

  1. Increasing the administrative distance on the SAP
  2. Split horizon groups configured on the VPRN interfaces Correct answer.
  3. BGP route reflection within the VRF
  4. Enabling VRRP on both interfaces

Explanation

Split horizon groups prevent routes learned from one member interface from being re-advertised out another member interface in the same group, which avoids Layer 3 loops in multi-homed VPRN designs. This is configured per VRF interface in SR OS.

Question 10IP routing, switching and aggregation

In a Nokia VPRN, which configuration is required so that a VRF learns routes from a customer CE running OSPF?

  1. An OSPF instance in the base router with a sham link
  2. An OSPF instance bound to the VRF interface with export of routes into MP-BGP Correct answer.
  3. A static default route in the base router
  4. An IS-IS instance on the access port

Explanation

The PE runs an OSPF instance inside the VRF toward the CE and redistributes those routes into MP-BGP for transport across the core. The base router OSPF is separate and carries provider infrastructure addresses only.

Question 11IP routing, switching and aggregation

Which BGP attribute is used to identify the originating PE for a VPN-IPv4 route so that route reflectors do not cause loops?

  1. Communities of type 0x0302
  2. Originator ID and cluster list Correct answer.
  3. Multi-exit discriminator
  4. Atomic aggregate

Explanation

Route reflectors add the ORIGINATOR_ID and CLUSTER_LIST attributes to reflected routes to prevent routing loops among clients. These attributes are used in the standard BGP loop-prevention mechanism for route reflection.

Question 12IP routing, switching and aggregation

A PE receives a VPN-IPv4 route for a prefix already present in the VRF from a local CE. Which attribute typically determines which path is preferred?

  1. The BGP local preference, then the MED, then the AS path length Correct answer.
  2. The route distinguisher value
  3. The VPRN service ID
  4. The SAP encapsulation type

Explanation

BGP best-path selection compares attributes in a defined order, with local preference, then locally originated, then AS path length, origin, MED, and so on. Local administrative values such as the route distinguisher or service ID do not participate in the selection.

Question 13IP routing, switching and aggregation

Which Nokia SR OS feature allows a VPRN to use a single MP-BGP session to carry multiple VPN address families?

  1. A separate BGP peer per VRF
  2. The base router BGP with an export policy
  3. An IES with a spoke SDP per VRF
  4. The family vpn-ipv4 and vpn-ipv6 negotiated within one BGP neighbor Correct answer.

Explanation

MP-BGP multiplexes multiple address families over a single TCP session; enabling the vpn-ipv4 and vpn-ipv6 families on one neighbor carries all VRF routes through that session. Using separate peers per VRF scales poorly and is not required.

Question 14IP routing, switching and aggregation

A customer requires that traffic from two VPRN sites use the same anycast IP address for a service. Which Nokia SR OS feature supports this in a VPRN?

  1. DHCP relay with option 82
  2. VRRP with a virtual MAC on the base router
  3. Proxy ARP on the access SAP
  4. Anycast or duplicate IP addressing with per-VRF host routes Correct answer.

Explanation

SR OS permits the same IP address to be configured on interfaces in different VRFs or with anycast semantics, because each VRF has its own independent routing and forwarding context. This isolation is what makes overlapping customer addressing viable.

Question 15IP routing, switching and aggregation

Which configuration enables a VPRN to advertise its connected routes into MP-BGP automatically?

  1. A route reflector configured in the base router
  2. An import policy that matches all route targets
  3. A static route to the CE with a low preference
  4. An export policy applied under the VPRN BGP instance that matches the VRF's connected routes Correct answer.

Explanation

Connected and other VRF routes are exported into MP-BGP only when an export policy under the VRF's BGP instance selects them. Import policies control what enters the VRF, not what leaves it.

Question 16IP routing, switching and aggregation

A VPRN uses a spoke SDP to connect two PEs. Which statement about the service label is correct?

  1. The service label is the same for all services on the PE
  2. The service label is assigned by the CE router
  3. The service label replaces the transport label in the packet
  4. The service label is signaled per service and identifies the VRF at the egress PE Correct answer.

Explanation

In an SDP-based VPRN, the egress PE allocates a service label per service instance and signals it to the ingress PE, which pushes it beneath the transport label. The label identifies the destination VRF so the egress PE can forward the packet correctly.

Question 17IP routing, switching and aggregation

Which Nokia SR OS command verifies that a VPRN has imported the expected VPN-IPv4 routes from a remote PE?

  1. show router <instance> bgp routes vpn-ipv4 Correct answer.
  2. show service id <id> base
  3. show system resource-utilization
  4. show port statistics

Explanation

The per-instance BGP route table for the VPN-IPv4 family shows received VPN routes, their route targets, and their import status. The other commands report port, service, or system resource information rather than VPN route details.

Question 18IP routing, switching and aggregation

A customer VPRN must support IPv6 prefixes between sites. Which address family must be enabled on the MP-BGP session between the PEs?

  1. ipv6
  2. ipv4
  3. l2-vpn
  4. vpn-ipv6 Correct answer.

Explanation

IPv6 customer prefixes in a VPRN are carried as VPN-IPv6 routes, which requires the vpn-ipv6 address family on the MP-BGP session. The plain ipv6 family carries global IPv6 routes, not per-VRF VPN routes.

Question 19IP routing, switching and aggregation

In a Nokia VPRN, which mechanism ensures that a CE with a lower OSPF priority becomes the designated router on a multi-access segment?

  1. OSPF DR election based on interface priority and router ID Correct answer.
  2. BGP local preference
  3. VRRP priority
  4. LACP system priority

Explanation

OSPF elects a designated router on multi-access segments based on the highest interface priority, with router ID as a tiebreaker. BGP, VRRP, and LACP priorities govern different functions and do not influence OSPF DR election.

Question 20IP routing, switching and aggregation

A VPRN must be reachable from a remote site through a GRE tunnel between PEs. Which Nokia SR OS feature provides the tunnel transport?

  1. An IES with a loopback interface
  2. A VPLS with a mesh SDP
  3. A tunnel interface configured with GRE transport and bound to the VPRN Correct answer.
  4. A spoke SDP with an MPLS transport

Explanation

SR OS supports GRE tunnels as an alternative transport for VPN services, with the tunnel interface bound to the VRF or used as the SDP transport. MPLS-based SDPs are a separate transport option and do not use GRE encapsulation.

Question 21IP routing, switching and aggregation

Which statement best describes the difference between a VPRN and an IES in Nokia SR OS?

  1. A VPRN cannot use route targets, while an IES can
  2. A VPRN uses only static routes, while an IES uses dynamic routing
  3. A VPRN is a Layer 2 service, while an IES is a Layer 3 service
  4. A VPRN uses MP-BGP to extend the VRF across the provider core, while an IES is confined to interfaces on a single router Correct answer.

Explanation

A VPRN is a distributed Layer 3 VPN whose VRF is extended between PEs using MP-BGP and route targets. An IES provides Layer 3 connectivity only among interfaces local to a single router.

Question 22IP routing, switching and aggregation

A PE has two VPRNs with overlapping customer address space. Which configuration element guarantees the routes remain distinct in MP-BGP?

  1. A unique route target per VPRN
  2. A unique SAP port per VPRN
  3. A unique service ID per VPRN
  4. A unique route distinguisher per VPRN Correct answer.

Explanation

The route distinguisher prepends an 8-byte value to the IPv4 prefix, so identical customer prefixes in different VRFs become distinct VPN-IPv4 routes. Route targets control import and export but do not create uniqueness.

Question 23IP routing, switching and aggregation

In a VPRN using BGP between PE and CE, which configuration prevents the CE from becoming a transit path between two PE sites?

  1. A static default route toward the CE
  2. A higher local preference on all CE routes
  3. An AS path or community-based export policy that blocks re-advertisement of routes learned from the other site Correct answer.
  4. Disabling split horizon on the VRF interfaces

Explanation

Controlling re-advertisement with export policies based on AS path or communities prevents the CE from learning routes from one site and advertising them back to another. Local preference and default routes do not prevent transit behavior.

Question 24IP routing, switching and aggregation

A network engineer observes that a VPRN route is present in the VRF table but traffic is dropped at the egress PE. Which is the most likely cause?

  1. The egress PE has no matching route target import or the service label is not programmed Correct answer.
  2. The BGP session is using the ipv4 family
  3. The ingress PE has an incorrect route distinguisher
  4. The CE router has an incorrect default gateway

Explanation

If the route is installed but forwarding fails, the egress PE may lack a matching import policy or its forwarding plane may not have the service label programmed. These are data-plane and import-policy issues, not a missing control-plane route.

Question 25IP routing, switching and aggregation

Which design consideration applies when a VPRN uses a sham link between two PEs for OSPF?

  1. The sham link replaces the need for route targets
  2. The sham link eliminates the need for a route distinguisher
  3. The sham link creates a point-to-point OSPF adjacency over MP-BGP to keep intra-area paths preferred Correct answer.
  4. The sham link is used only for IPv6 address families

Explanation

A sham link is a point-to-point OSPF adjacency carried over the MPLS core between PEs, making the VPN appear as a single OSPF area so intra-area routes are preferred over backdoor paths. It does not replace route targets or route distinguishers.

Question 26IP routing, switching and aggregation

In Nokia SR OS, which VPRN service object holds the customer-facing IP interface that connects to a CE router?

  1. The SAP on a customer port
  2. The VRF context interface Correct answer.
  3. The network interface toward the PE
  4. The loopback system interface

Explanation

A VPRN is built as a virtual router instance, and the customer-facing IP interface is created inside the VRF context, where addresses and protocols such as OSPF or BGP are configured. SAPs and SDPs are layer-2 attachments that bind the service to ports or tunnels, not the IP interface itself.

Question 27IP routing, switching and aggregation

Which Nokia SR OS construct binds a VPRN service to a remote PE over an MPLS transport tunnel without a physical port at the far end?

  1. A QinQ SAP
  2. A mesh SDP
  3. An IES interface
  4. A spoke SDP Correct answer.

Explanation

A spoke SDP is a point-to-point pseudowire that connects the local service to a remote PE, carrying traffic over the transport tunnel such as LDP or RSVP-TE LSP. Mesh SDPs are used for multipoint VPLS connectivity rather than point-to-point VPRN attachment.

Question 28IP routing, switching and aggregation

What is the purpose of the service ID when creating a VPRN in Nokia SR OS?

  1. It uniquely identifies the service instance on the router Correct answer.
  2. It sets the MPLS label used on the network
  3. It defines the route target community value
  4. It specifies the transport tunnel type

Explanation

The service ID is a locally significant number that identifies the service instance within the router configuration and is used in commands and show output. Labels and route targets are configured separately and are not derived from this identifier.

Question 29IP routing, switching and aggregation

A VPRN must exchange routes with a directly connected CE using OSPF. Which VPRN configuration step is required before OSPF adjacencies can form?

  1. Bind the interface to a mesh SDP
  2. Enable an export policy for VPN-IPv4
  3. Add the CE-facing interface to an OSPF area Correct answer.
  4. Create a route target for the OSPF process

Explanation

OSPF runs as a routing protocol inside the VRF context, and each participating interface must be assigned to an OSPF area before adjacencies can form. Export policies and route targets affect MP-BGP distribution of the resulting routes, not OSPF neighbor formation.

Question 30IP routing, switching and aggregation

Which address family must be negotiated on the MP-BGP session between PEs to carry IPv4 VPRN routes?

  1. vpn-ipv4 Correct answer.
  2. l2-vpn
  3. ipv4 unicast
  4. ipv6 unicast

Explanation

VPRN routes are advertised as VPN-IPv4 routes, so the MP-BGP session must negotiate the vpn-ipv4 address family. Plain ipv4 unicast carries global table routes and cannot convey the route distinguisher and route target information needed for VPN separation.

Question 31IP routing, switching and aggregation

Which protocol is commonly used to distribute transport labels between PE routers so that VPRN traffic can traverse the MPLS core?

  1. LDP Correct answer.
  2. IS-IS
  3. RIPv2
  4. BFD

Explanation

Label Distribution Protocol advertises label bindings for core prefixes so that packets can be label-switched across the MPLS transport. IS-IS distributes IP reachability but does not itself allocate the transport labels used for forwarding.

Question 32IP routing, switching and aggregation

Which Nokia SR OS classic CLI command displays the routes installed in a specific VPRN routing table?

  1. show port detail
  2. show router bgp summary
  3. show router <vprn-service-id> route-table Correct answer.
  4. show router route-table

Explanation

In the classic CLI, show router <vprn-service-id> route-table selects the VPRN by its service ID and displays that instance's routing table. Without the VPRN selector, show router route-table displays the base router's routing table.

Question 33IP routing, switching and aggregation

Which statement describes how a route distinguisher is used for a VPRN?

  1. It sets the metric used for path selection
  2. It defines the transport tunnel between PEs
  3. It selects which remote PEs may import the routes
  4. It makes otherwise identical customer prefixes unique in MP-BGP Correct answer.

Explanation

The route distinguisher is prepended to customer prefixes to create unique VPN-IPv4 NLRI, allowing overlapping customer address space to coexist in BGP. Import control is performed by route targets, not by the route distinguisher.

Question 34IP routing, switching and aggregation

A PE receives a VPN-IPv4 route whose route target matches the VRF import policy but whose next hop resolves to an unreachable address. What is the result for that route in the VRF?

  1. It is converted to a static route
  2. It is rejected and never stored
  3. It is kept but not used for forwarding Correct answer.
  4. It is installed as a valid route

Explanation

BGP can retain a route whose next hop does not resolve, but the route is not eligible for installation in the forwarding table until a valid tunnel to the next hop exists. Once the tunnel becomes available, the route can be promoted to active.

Question 35IP routing, switching and aggregation

Two VPRN sites connected to the same PE need to exchange traffic locally without traversing the core. Which Nokia SR OS feature provides this local forwarding?

  1. Auto-bind LDP
  2. Sham link
  3. Route reflection
  4. Local VPRN route lookup Correct answer.

Explanation

When two sites of the same VPRN terminate on one PE, the router resolves traffic through its own VRF route lookup and forwards it locally rather than sending it across the core. This local switching avoids tromboning traffic through a remote PE.

Question 36IP routing, switching and aggregation

Which BGP community value is carried as an extended community to control VPRN route import on the receiving PE?

  1. The originator ID
  2. The cluster list
  3. The local preference
  4. The route target Correct answer.

Explanation

Route targets are BGP extended communities attached to VPN-IPv4 routes and matched against VRF import and export policies. Originator ID, cluster list, and local preference are standard attributes used for loop prevention and path selection.

Question 37IP routing, switching and aggregation

A VPRN is configured with an export policy that rejects all routes. What is the effect on MP-BGP advertisement of that VRF's connected prefixes?

  1. The prefixes are advertised but marked as best
  2. The prefixes are advertised only to route reflectors
  3. The prefixes are advertised with a null route target
  4. The prefixes are not advertised to remote PEs Correct answer.

Explanation

The VPRN export policy filters which routes from the VRF are placed into MP-BGP, so a reject-all policy prevents any of those prefixes from being advertised. Local forwarding inside the VRF is unaffected because the routes remain in the VRF table.

Question 38IP routing, switching and aggregation

A design requires that a VPRN site use a backup path over a second PE when the primary PE fails. Which mechanism provides fast convergence for the VPN routes?

  1. Increasing the OSPF hello interval
  2. BGP add-paths with a higher local preference backup
  3. BFD-triggered IGP convergence plus BGP next-hop tracking Correct answer.
  4. Static route redistribution into the VRF

Explanation

Fast failover relies on rapid detection of transport failure, typically BFD driving IGP convergence, combined with BGP next-hop tracking so VPN routes are invalidated promptly. Backup paths then become eligible once the primary next hop no longer resolves.

Question 39IP routing, switching and aggregation

Which Nokia SR OS configuration element determines the MPLS label a PE uses to receive traffic for a VPRN from remote PEs?

  1. The route distinguisher value
  2. The service label allocated for the VPRN Correct answer.
  3. The VRF interface address
  4. The route target community

Explanation

Each VPRN is assigned a service label that remote PEs use as the inner label when sending traffic into that VRF. The label is advertised with the VPN route so the ingress PE knows which label to push.

Question 40IP routing, switching and aggregation

A customer VPRN must carry both IPv4 and IPv6 prefixes between sites. Which MP-BGP configuration supports this requirement?

  1. Enable the l2-vpn family
  2. Enable both vpn-ipv4 and vpn-ipv6 families Correct answer.
  3. Enable only the vpn-ipv4 family
  4. Enable only the ipv6 unicast family

Explanation

IPv4 VPN routes are carried in vpn-ipv4 and IPv6 VPN routes in vpn-ipv6, so both families must be negotiated on the PE-to-PE session. The VRF must also have IPv6 interfaces and protocols configured for the IPv6 prefixes to exist.

Question 41IP routing, switching and aggregation

Which statement explains why a route reflector is commonly deployed in a large VPRN MP-BGP design?

  1. It encrypts VPN-IPv4 updates
  2. It reduces the number of required iBGP sessions between PEs Correct answer.
  3. It resolves the next hop for VPN routes
  4. It allocates service labels for each VRF

Explanation

A route reflector reflects VPN-IPv4 updates among clients so full-mesh iBGP sessions are not required between every PE pair. It does not perform label allocation, next-hop resolution, or encryption.

Question 42IP routing, switching and aggregation

A VPRN uses a sham link between two PEs to connect OSPF areas. What is the primary purpose of the sham link?

  1. To provide encryption for OSPF updates
  2. To carry customer traffic over the core as a backup path
  3. To make the OSPF backbone appear contiguous across the VPN Correct answer.
  4. To replace the need for route targets

Explanation

A sham link creates an intra-area OSPF adjacency over the MPLS core so that the VPN appears as a single contiguous OSPF area, avoiding inter-area or intra-area design problems. It is a control-plane mechanism for OSPF, not a general traffic backup or encryption feature.

Question 43IP routing, switching and aggregation

Which Nokia SR OS feature allows a VPRN to advertise its routes into MP-BGP without manually creating an export policy for each prefix?

  1. Route redistribution of connected routes Correct answer.
  2. BGP next-hop-self
  3. Auto-export of VRF routes
  4. Anycast service addresses

Explanation

Connected and protocol-learned routes are injected into the VRF's BGP process through redistribution configuration, which then exports them as VPN-IPv4 routes. This avoids creating per-prefix policies for each connected subnet.

Question 44IP routing, switching and aggregation

A VPRN route is present and active in the VRF table on the egress PE, but customer traffic is dropped. Which area should be checked first?

  1. The service label and SDP or SAP binding on the egress PE Correct answer.
  2. The route distinguisher value on both PEs
  3. The MP-BGP session state on the ingress PE
  4. The OSPF hello interval on the CE

Explanation

If the control plane installed the route but forwarding fails, the data plane path is suspect, including the service label mapping and the SAP or SDP binding that should deliver traffic to the CE. Checking these bindings verifies that the label leads to a valid egress attachment.

Question 45IP routing, switching and aggregation

A PE has two VPRNs whose imported VPN-IPv4 routes overlap in prefix space. Which configuration element keeps the routes in separate VRF tables?

  1. A shared route distinguisher and shared route targets
  2. The same VRF interface address in both VPRNs
  3. A single service ID for both VPRNs
  4. A unique route distinguisher per VRF and matching route targets Correct answer.

Explanation

Each VRF uses its own route distinguisher to make its prefixes unique in MP-BGP, and route targets control which routes are imported into which VRF. Together these keep overlapping customer address space isolated.

Question 46IP routing, switching and aggregation

In a VPRN using BGP between the PE and a CE, which configuration prevents the CE from being used as a transit path between two PE sites?

  1. Enabling next-hop-self on the PE
  2. Applying an AS path filter to reject routes containing the PE AS Correct answer.
  3. Configuring a higher local preference on CE routes
  4. Setting the CE as a route reflector

Explanation

If a CE advertises routes learned from one PE site back toward another PE, the PE AS appears in the AS path. Filtering routes that contain the local AS prevents the CE from acting as transit between sites.

Question 47IP routing, switching and aggregation

A VPRN uses MP-BGP with route reflectors, and a PE receives a VPN-IPv4 route with its own originator ID. What does this indicate?

  1. The route was originated by a remote PE
  2. The route target is misconfigured
  3. A routing loop exists and the route should be discarded Correct answer.
  4. The next hop is unreachable

Explanation

The originator ID attribute records the router that first injected the route into BGP. If a router sees its own originator ID, a routing loop has formed, and the route is not accepted.

Question 48IP routing, switching and aggregation

Which protocol combination is typically required in the base router to support VPRN transport across an MPLS core?

  1. An IGP for loopback reachability plus LDP or RSVP-TE for labels Correct answer.
  2. RIP plus BFD, with no label distribution
  3. BGP only, with no IGP in the base router
  4. OSPF inside each VRF plus static routes in the base

Explanation

The base router needs an IGP to advertise PE loopback addresses and a label distribution protocol such as LDP or RSVP-TE to build transport LSPs between PEs. VRF protocols are independent of this base transport layer.

Question 49IP routing, switching and aggregation

What is the effect of configuring a VPRN network interface with a lower metric than an alternate path to the same remote prefix?

  1. It influences path selection so the lower-metric path is preferred Correct answer.
  2. It forces the prefix into the base routing table
  3. It changes the route target used for import
  4. It disables MP-BGP advertisement of the prefix

Explanation

The network interface metric contributes to the cost of the path and influences which route is selected when multiple paths exist. Route targets and MP-BGP advertisement are controlled by separate configuration.

Question 50IP routing, switching and aggregation

In a Nokia SR OS VPRN, which value is used to identify the label that the egress PE allocates for a VPN-IPv4 prefix and advertises with the route over MP-BGP, so that the ingress PE can build the label stack toward the remote site?

  1. The MPLS label carried in the NLRI of the VPN-IPv4 route as a label block offset
  2. The service ID configured under the VPRN service context, which is signaled as the VPN label
  3. The outer transport label distributed by LDP or RSVP-TE for the PE loopback
  4. The inner label assigned from the VPRN's label pool, advertised as the VPN label in the MP-BGP update Correct answer.

Explanation

A VPN-IPv4 route advertised over MP-BGP carries a label field in its NLRI; this is the VPN label allocated by the egress PE from that VPRN's label pool, and it identifies the VRF to which the packet must be delivered. The ingress PE pushes this label beneath the transport label, so the egress PE can pop the transport label and use the VPN label to select the correct VPRN instance. The service ID is a local identifier and is not signaled as the VPN label.