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Nokia NRS I practice questions

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Question 1IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia SR OS router, which routing table holds the best routes selected by the route preference (administrative distance) comparison before they are installed into the forwarding table?

  1. The QoS policy table
  2. The FIB (Forwarding Information Base)
  3. The ARP cache
  4. The RIB (Routing Information Base) Correct answer.

Explanation

The RIB is the control-plane routing table where candidate routes from all protocols are compared and the best route per prefix is selected. The FIB is derived from the RIB and is what the forwarding engine actually uses, so it is a downstream product rather than the comparison point.

Question 2IP routing fundamentals and Nokia IP network routing, switching and aggregation

Two routes to 10.0.0.0/24 exist: a static route with preference 5 and an OSPF route with preference 10. Which route becomes active in the Nokia SR OS RIB?

  1. Neither route, because the preferences conflict
  2. The static route, because the lower preference value wins Correct answer.
  3. The OSPF route, because dynamic protocols override static routes
  4. Both routes, and traffic is load-balanced across them

Explanation

In Nokia SR OS, lower route preference values are preferred, so a static route with preference 5 beats an OSPF route with preference 10 for the same prefix. Only one best route is selected per prefix unless equal-cost multipath is configured on routes with identical preference.

Question 3IP routing fundamentals and Nokia IP network routing, switching and aggregation

What is the primary purpose of an IP interface configured on a Nokia SR OS router?

  1. To bind a VLAN tag to a SAP for wholesale aggregation
  2. To enable MPLS label distribution on a port
  3. To assign a MAC address to a physical port for Layer 2 bridging
  4. To assign an IP address and associated subnet to a logical Layer 3 termination point Correct answer.

Explanation

An IP interface gives a logical Layer 3 termination point an address, mask, and associated parameters so the router can send and receive IP traffic on that subnet. Layer 2 constructs such as SAPs and VLAN tags are configured on ports, not on the IP interface itself.

Question 4IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which statement describes the behavior of a Nokia SR OS router receiving a packet whose destination does not match any more-specific route and for which only a default route (0.0.0.0/0) exists?

  1. The packet is forwarded according to the default route's next hop Correct answer.
  2. The packet is dropped because no specific prefix matches
  3. The packet is flooded to all interfaces in the subnet
  4. The packet is queued until a specific route is learned

Explanation

A default route is the least-specific match and is used whenever no longer prefix matches the destination. Longest-prefix match means more specific routes win, but when none exist the default route provides the forwarding next hop.

Question 5IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, what does a /30 IPv4 subnet provide when used on a point-to-point link between two routers?

  1. Four usable host addresses
  2. Two usable host addresses Correct answer.
  3. One usable host address
  4. Six usable host addresses

Explanation

A /30 leaves 2 host bits, giving 4 addresses total, of which the network and broadcast addresses are reserved, leaving 2 usable host addresses. This is the classic choice for point-to-point links between two routers.

Question 6IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS command displays the contents of the routing table, including route preference and next hop?

  1. show port detail
  2. show router route-table Correct answer.
  3. show system cpu
  4. show service sap-using

Explanation

The show router route-table command displays the active routes in the routing table with their preference, metric, and next hop. The other commands report port, service SAP, and system resource information rather than routing entries.

Question 7IP routing fundamentals and Nokia IP network routing, switching and aggregation

What is the function of ARP on a Nokia SR OS router forwarding IPv4 traffic to a next hop on a directly connected Ethernet subnet?

  1. Selecting the best route by preference
  2. Assigning a VLAN tag to the egress frame
  3. Resolving the next-hop IP address to a destination MAC address Correct answer.
  4. Mapping the destination IP to an outgoing MPLS label

Explanation

ARP resolves an IPv4 next-hop address to the corresponding MAC address so the frame can be encapsulated with the correct destination MAC. It operates on directly connected subnets where the router must build the Layer 2 header.

Question 8IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which protocol provides loop-free Layer 2 topology by electing a root bridge and blocking redundant paths in a Nokia IP aggregation network?

  1. OSPF
  2. BGP
  3. Spanning Tree Protocol Correct answer.
  4. LDP

Explanation

Spanning Tree Protocol elects a root bridge and places redundant ports in a blocking state to produce a loop-free Layer 2 topology. OSPF, BGP, and LDP are Layer 3 and label distribution protocols and do not block Layer 2 ports.

Question 9IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router has two OSPF routes to 192.168.5.0/24 with equal preference but different metrics of 20 and 30. How does the RIB treat these routes?

  1. The routes are discarded because metrics differ
  2. Both routes are installed and traffic is load-balanced
  3. The route with metric 20 is selected as best Correct answer.
  4. The route with metric 30 is selected as best

Explanation

When preference is equal, the lower metric wins, so the route with metric 20 is selected as the best route. Equal-cost multipath requires equal metrics, so differing metrics prevent load balancing across these two.

Question 10IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS construct is used to group physical ports into a logical bundle that provides increased bandwidth and link redundancy for IP routing?

  1. A LAG (Link Aggregation Group) Correct answer.
  2. A VPRN service
  3. A static route
  4. An IP interface

Explanation

A Link Aggregation Group bundles multiple physical links into one logical link, providing aggregated bandwidth and resilience if a member fails. IP interfaces, VPRN services, and static routes are Layer 3 constructs that do not bundle physical ports.

Question 11IP routing fundamentals and Nokia IP network routing, switching and aggregation

What is the effect of configuring an IPv4 address with a /31 mask on a point-to-point interface in Nokia SR OS?

  1. Both addresses are usable for the two endpoints without a broadcast address Correct answer.
  2. The subnet is invalid and cannot be configured
  3. Four addresses are usable for hosts
  4. Only one address is usable because one is reserved for broadcast

Explanation

RFC 3021 allows /31 on point-to-point links, using both addresses as host addresses and eliminating the network and broadcast reservations. This conserves address space on router-to-router links.

Question 12IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which statement correctly describes the relationship between the Nokia SR OS routing table and the forwarding table for a given prefix?

  1. Both tables are populated independently by routing protocols
  2. The best route in the routing table is programmed into the forwarding table used by the line cards Correct answer.
  3. The forwarding table is programmed first and then copied into the routing table
  4. The forwarding table contains all candidate routes for a prefix

Explanation

Route selection happens in the control plane RIB, and only the selected best route is programmed into the forwarding table used by the forwarding engine. Candidate routes that lose the preference and metric comparison are not installed.

Question 13IP routing fundamentals and Nokia IP network routing, switching and aggregation

A network engineer wants OSPF routes to be preferred over ISIS routes for the same prefix on a Nokia SR OS router. Which change accomplishes this?

  1. Enable equal-cost multipath for both protocols
  2. Configure an OSPF metric lower than the ISIS metric
  3. Increase the OSPF reference bandwidth
  4. Configure an OSPF preference lower than the ISIS preference Correct answer.

Explanation

Preference is compared before metric across protocols, so lowering OSPF preference below ISIS preference makes OSPF routes win. Metric is only compared within the same protocol or when preference is equal.

Question 14IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS feature allows a router to forward traffic for a prefix using multiple next hops of equal cost simultaneously?

  1. Policy-based routing
  2. Route preference
  3. ECMP (Equal-Cost Multipath) Correct answer.
  4. VRRP

Explanation

ECMP installs multiple equal-cost next hops for a prefix so traffic is distributed across them, improving utilization and resilience. VRRP provides gateway redundancy, preference selects a single best route, and policy-based routing overrides normal destination-based forwarding.

Question 15IP routing fundamentals and Nokia IP network routing, switching and aggregation

What role does a VRRP virtual router play in a Nokia IP aggregation network providing first-hop redundancy?

  1. It presents a shared virtual IP and MAC address used as the default gateway by hosts Correct answer.
  2. It blocks redundant Layer 2 ports
  3. It distributes routing updates between aggregation switches
  4. It assigns MPLS labels to aggregated traffic

Explanation

VRRP presents a virtual IP and MAC address shared by a master and backup router, so hosts use a resilient default gateway that survives a router failure. Routing update distribution, label assignment, and port blocking are handled by other protocols.

Question 16IP routing fundamentals and Nokia IP network routing, switching and aggregation

A static route is configured in Nokia SR OS with a next hop that is not directly connected and no resolve option. What is the likely result?

  1. The route is installed and traffic is dropped at egress
  2. The route is automatically resolved through any available interface
  3. The route remains inactive until the next hop is resolvable Correct answer.
  4. The route replaces the default route

Explanation

A static route with an indirect next hop needs resolution to a directly connected address before it can be installed; without resolution it stays inactive. Nokia SR OS provides resolution options to allow recursive lookup, but absent that the route is not usable.

Question 17IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which address type is used by a router as the source when generating protocol traffic such as OSPF hello packets on an interface?

  1. The MAC address of the port
  2. The broadcast address of the subnet
  3. The system loopback address only
  4. The interface's primary IPv4 address Correct answer.

Explanation

Protocol packets originated on an interface typically use that interface's primary IP address as the source, which is why correct interface addressing matters for adjacency formation. The system address is used for router-id and certain loopback-originated traffic, not for interface-local hellos.

Question 18IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS address resolution behavior occurs when a router forwards to a next hop on a directly connected subnet but has no ARP entry for it?

  1. The router uses the broadcast MAC address as the destination
  2. The router forwards the packet to the default gateway instead
  3. The router floods the packet on all ports of the subnet
  4. The router sends an ARP request and queues or drops the packet until resolution completes Correct answer.

Explanation

When no ARP entry exists, the router issues an ARP request for the next-hop address and holds or drops the triggering packet until the reply arrives. Forwarding cannot proceed without the destination MAC address for the frame.

Question 19IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS service type provides a Layer 3 IP VPN with per-service routing tables for connecting customer sites over an MPLS network?

  1. VPLS
  2. VPRN Correct answer.
  3. IES
  4. EPIPE

Explanation

A VPRN is a virtual private routed network service that maintains a separate Layer 3 routing table per service instance. VPLS and EPIPE are Layer 2 services, and IES provides Layer 3 connectivity to a single service without MPLS-based VPN routing.

Question 20IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router has an OSPF route and a BGP route to the same prefix with identical preference values. Which additional attribute is used to break the tie in the RIB?

  1. The route metric, with the lower value preferred Correct answer.
  2. The egress port number
  3. The protocol's administrative age
  4. The next-hop MAC address

Explanation

When preference is identical, the metric is compared and the lower metric wins. If both preference and metric are equal, ECMP may install both, but the tie-break attribute before that is metric.

Question 21IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia IP aggregation design, what is the main benefit of using a Layer 3 routed access model instead of a Layer 2 spanning-tree access model?

  1. It uses all links actively and avoids blocked ports and large failure domains Correct answer.
  2. It guarantees zero packet loss during convergence
  3. It eliminates the need for IP addressing on access switches
  4. It removes the requirement for routing protocols

Explanation

A Layer 3 routed access model forwards over all links using routing protocols, avoiding spanning-tree blocked ports and confining failure domains. Access switches still need IP addressing and a routing protocol, and convergence is fast but not loss-free.

Question 22IP routing fundamentals and Nokia IP network routing, switching and aggregation

A static route in Nokia SR OS is configured with preference 5 and another static route to the same prefix with preference 10, both with valid next hops. What is the outcome?

  1. Both routes are active and load-balanced
  2. Only the preference 5 route is active in the forwarding table Correct answer.
  3. The preference 10 route is active
  4. Both routes are inactive until a protocol route appears

Explanation

Static routes follow the same preference comparison as other routes, so the lower preference value wins and only that route is installed. Load balancing would require equal preference and equal cost.

Question 23IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which consideration explains why a /24 subnet on a point-to-point link between two routers is wasteful compared with a /30?

  1. The /24 requires a larger MTU than a /30
  2. The /24 cannot be assigned to an IP interface in SR OS
  3. The /24 reserves 254 addresses that the two-endpoint link cannot use Correct answer.
  4. The /24 cannot be advertised by a routing protocol

Explanation

A /24 contains 256 addresses, of which only two are needed on a point-to-point link, wasting 254 addresses that could be used elsewhere. A /30 or /31 conserves address space for links with exactly two endpoints.

Question 24IP routing fundamentals and Nokia IP network routing, switching and aggregation

An engineer observes that a prefix has multiple candidate routes but only one appears in the forwarding table. Which explanation is most consistent with Nokia SR OS behavior?

  1. Routing protocols withdraw losing routes before installation
  2. The FIB only stores routes with preference 0
  3. The forwarding table is full and dropped the other routes
  4. The RIB selected the best route by preference and metric and programmed only that route into the FIB Correct answer.

Explanation

The RIB compares preference first and then metric, selecting a single best route per prefix unless ECMP is configured, and only the selected route is programmed into the FIB. Losing candidates remain in the RIB as less-preferred but are not forwarded.

Question 25IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which mechanism allows a router to forward traffic based on criteria other than the destination address, such as source address or DSCP, overriding the normal route lookup?

  1. VRRP
  2. Route preference
  3. Policy-based routing Correct answer.
  4. ECMP

Explanation

Policy-based routing matches configured criteria such as source address or DSCP and forwards the traffic to a specified next hop, bypassing normal destination-based lookup. ECMP, VRRP, and route preference all operate within the standard destination-based decision.

Question 26IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which interface type is used to carry a single customer VLAN over an Ethernet port when the port is configured in network mode for IP routing?

  1. A network interface with dot1q encapsulation referencing a specific VLAN tag Correct answer.
  2. A VPLS service bound to the SAP
  3. A regular port configured with an IP address and a null encapsulation
  4. An IES service with a loopback interface

Explanation

In network mode, a port carries a single VLAN-tagged interface via dot1q encapsulation, and the interface is bound to a specific VLAN tag on that port. The port itself does not hold an IP address; the logical IP interface does. This is the standard way to build routed VLAN links in SR OS.

Question 27IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS command displays the operational state and configuration summary of a specific router interface, including its IP address and associated port?

  1. show router interface Correct answer.
  2. show router route-table
  3. show service id
  4. show port statistics

Explanation

The show router interface command lists router interfaces with their IP addresses, operational state, and the port they are bound to. It is the standard way to verify that a logical IP interface is up and correctly addressed. The other commands address ports, routes, or services rather than router interfaces.

Question 28IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, what does the preference value of a route control?

  1. The order in which routes from different sources are compared when selecting the active route Correct answer.
  2. The cost applied to a static route's next hop
  3. The metric advertised to OSPF neighbors
  4. The administrative distance used only by BGP

Explanation

Preference in SR OS ranks routes learned from different sources, such as static, OSPF, IS-IS, and BGP, so the routing table can select one active route per prefix. Lower preference values are preferred. Preference is distinct from the metric, which compares routes from the same source.

Question 29IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS entity is the logical interface that holds an IPv4 address and is used as the source for routing protocol sessions on a router?

  1. A loopback interface Correct answer.
  2. A physical port in hybrid mode
  3. A SAP on an IES service
  4. A VPLS spoke SDP

Explanation

A loopback interface is a logical, always-up interface that holds an IP address and is commonly used as the router ID and source for routing protocol sessions. Because it does not depend on a single physical link, it provides stable reachability. SAPs, ports, and SDPs do not serve this purpose.

Question 30IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS command is used to display the ARP cache entries for a router interface?

  1. show router arp Correct answer.
  2. show port detail
  3. show router neighbor
  4. show router bgp summary

Explanation

The show router arp command displays IPv4 ARP entries, mapping IP addresses to MAC addresses for directly connected next hops. It is useful for verifying that resolution has succeeded. The other commands show neighbor relationships, BGP status, or port details.

Question 31IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia SR OS VPRN, which construct provides the per-service routing instance that isolates customer routes from the global routing table?

  1. The IES service's subscriber interface
  2. The VPRN service's own routing context Correct answer.
  3. The VPLS service's MAC table
  4. The base router instance

Explanation

A VPRN is a Layer 3 VPN service with its own routing context, so customer routes are kept separate from the base router table. Interfaces and protocols are configured within that service context. The base router instance is the global table, not an isolated customer instance.

Question 32IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS protocol is a link-state Interior Gateway Protocol that uses a designated router election on broadcast multi-access networks?

  1. OSPF Correct answer.
  2. RIP
  3. VRRP
  4. BGP

Explanation

OSPF is a link-state IGP that elects a designated router and backup designated router on broadcast multi-access segments to reduce adjacency count. BGP is a path-vector inter-domain protocol, RIP is distance-vector, and VRRP provides first-hop redundancy.

Question 33IP routing fundamentals and Nokia IP network routing, switching and aggregation

What is the primary purpose of a Layer 3 routed access design in a Nokia IP aggregation network?

  1. To extend a single broadcast domain to all access switches
  2. To terminate user subnets on the access switch and route between them, limiting Layer 2 failure domains Correct answer.
  3. To centralize all default gateways on a single core router
  4. To replace all routing with transparent bridging

Explanation

In a Layer 3 routed access design, access switches terminate subnets and route traffic toward the aggregation layer, so broadcast domains stay small and Spanning Tree dependencies are reduced. This improves convergence and stability. Extending broadcast domains or centralizing gateways describes Layer 2 designs instead.

Question 34IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router learns a prefix from both OSPF and IS-IS with default preferences. Which route becomes active in the routing table?

  1. The OSPF route, because OSPF has a lower default preference than IS-IS Correct answer.
  2. Both routes are installed and used equally
  3. Neither route is installed until a static route is added
  4. The IS-IS route, because IS-IS has a lower default preference than OSPF

Explanation

In SR OS, OSPF has a lower default preference value than IS-IS, so the OSPF route is preferred when both protocols offer the same prefix. Lower preference means higher priority. The IS-IS route remains as a candidate but is not active.

Question 35IP routing fundamentals and Nokia IP network routing, switching and aggregation

An engineer configures an IPv4 interface with a /30 mask on a point-to-point link between two Nokia SR OS routers. How many usable host addresses does this subnet provide?

  1. Six
  2. Two Correct answer.
  3. One
  4. Four

Explanation

A /30 leaves 2 host bits, giving 4 addresses, of which the network and broadcast addresses are reserved, so 2 usable addresses remain. That is exactly enough for the two router endpoints. A /31 would also work on point-to-point links but is a different design choice.

Question 36IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which statement describes how an ECMP group forwards traffic for a prefix with multiple equal-cost next hops?

  1. It distributes flows across the next hops using a hashing algorithm Correct answer.
  2. It sends all traffic to the first next hop and uses others only on failure
  3. It load-balances every packet independently regardless of flow
  4. It requires BGP multipath to be enabled for any ECMP

Explanation

SR OS ECMP installs multiple equal-cost next hops for a prefix and distributes traffic across them using a hash, typically based on flow identifiers such as source and destination addresses. Hashing keeps packets of a flow on the same path, preserving order. ECMP is not limited to BGP.

Question 37IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router has a static route to 10.10.0.0/16 with next hop 192.0.2.1 and no resolve option, and 192.0.2.1 is not on a directly connected subnet. What is the result?

  1. The static route remains inactive until a route to 192.0.2.1 is resolved or resolve is enabled Correct answer.
  2. The static route becomes active and forwards traffic directly to 192.0.2.1
  3. The static route is converted into an OSPF external route
  4. The router automatically creates a connected route to 192.0.2.0/24

Explanation

Without the resolve option, a static next hop must be directly reachable for the route to become active. If the next hop is not on a connected subnet, the route stays inactive until a route to the next hop exists or resolve is configured. SR OS does not create connected routes automatically.

Question 38IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS command displays the content of the forwarding table (FIB) rather than the routing table (RIB)?

  1. show router fib Correct answer.
  2. show router interface
  3. show router ospf neighbor
  4. show router route-table

Explanation

The show router fib command displays the forwarding table entries actually used for packet forwarding, including next-hop and label information. The route-table command shows the routing table, which may contain candidate routes not installed in the FIB. The other commands show interfaces or protocol adjacencies.

Question 39IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia SR OS VPRN, which parameter must be configured so that the service can exchange routes with the base router or other services?

  1. A SAP with null encapsulation
  2. A VRRP virtual router ID
  3. A route distinguisher and route target plus a protocol such as BGP within the service Correct answer.
  4. A VPLS MAC learning policy

Explanation

A VPRN uses a route distinguisher to make its prefixes unique and route targets to control import and export of routes, along with a routing protocol such as MP-BGP inside the service. These parameters allow route exchange with the base router or other VPRNs. MAC policies, null SAPs, and VRRP IDs do not serve this role.

Question 40IP routing fundamentals and Nokia IP network routing, switching and aggregation

An engineer wants to verify which next hop a Nokia SR OS router uses for a specific prefix in the active forwarding table. Which command output should be examined?

  1. The output of show router route-table with the prefix specified Correct answer.
  2. The output of show service id
  3. The output of show port statistics
  4. The output of show router arp only

Explanation

Specifying the prefix with show router route-table shows the route entries, including the next hop selected for the active route. This confirms the forwarding decision for that prefix. Port statistics, service details, and ARP alone do not show the chosen route.

Question 41IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, what is the effect of configuring a VRRP virtual router with a higher priority on one router than another in the same VRID group?

  1. Both routers become masters simultaneously
  2. The higher-priority router becomes the master and owns the virtual MAC forwarding Correct answer.
  3. Priority has no effect unless preempt is disabled
  4. The lower-priority router becomes the master to balance load

Explanation

VRRP elects the router with the highest priority as master, and the master answers ARP for the virtual IP and forwards traffic for the virtual MAC. The other routers stay in backup state. Priority is the primary election criterion, independent of preempt.

Question 42IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS mechanism allows a router to forward packets based on criteria such as source address or protocol in addition to the destination address?

  1. ECMP hashing
  2. BGP route reflection
  3. Policy-based routing Correct answer.
  4. MAC learning

Explanation

Policy-based routing in SR OS uses configured policies to match packet fields such as source address or protocol and direct matching traffic to a specified next hop. This overrides the normal destination-based lookup for matched traffic. ECMP hashing, route reflection, and MAC learning do not provide this capability.

Question 43IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which address type is used as the next-hop address for a directly connected IPv6 neighbor on an Ethernet link?

  1. The all-nodes multicast address
  2. The neighbor's multicast address
  3. The router's own global address
  4. The neighbor's link-local address Correct answer.

Explanation

IPv6 next hops on a directly connected link are typically link-local addresses, which are resolved through Neighbor Discovery. Link-local addresses are sufficient for on-link forwarding and remain valid even if global addressing changes. Multicast addresses identify groups, not individual neighbors.

Question 44IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router has two static routes to the same prefix, one with preference 5 and one with preference 10, both with valid next hops. Which route is installed in the forwarding table?

  1. Neither route is installed until OSPF confirms reachability
  2. Both routes are installed and used equally
  3. The route with preference 5, because lower values are preferred Correct answer.
  4. The route with preference 10, because higher values are preferred

Explanation

SR OS prefers lower preference values, so the static route with preference 5 is selected as the active route. The route with preference 10 stays as a candidate and is not installed in the forwarding table while the better route exists. Preference is local and does not require OSPF confirmation.

Question 45IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia IP aggregation design, why is a /31 mask often chosen for point-to-point links between routers instead of a /30?

  1. A /31 automatically creates a loopback interface
  2. A /31 provides two addresses usable by the two endpoints, conserving address space Correct answer.
  3. A /31 provides four usable addresses for future growth
  4. A /31 is required for OSPF to form adjacencies

Explanation

A /31 uses both addresses for the two endpoints, avoiding the reserved network and broadcast addresses of a /30 and conserving address space. SR OS supports /31 on point-to-point interfaces. OSPF does not require /31, and a /31 does not create loopback interfaces.

Question 46IP routing fundamentals and Nokia IP network routing, switching and aggregation

Which Nokia SR OS command displays OSPF neighbor adjacencies and their current state on a router?

  1. show router route-table
  2. show router interface
  3. show router ospf neighbor Correct answer.
  4. show router arp

Explanation

The show router ospf neighbor command lists OSPF neighbors with their state, such as Full, which confirms that adjacencies have formed. The route-table command shows routes, ARP shows address mappings, and interface shows interface addressing.

Question 47IP routing fundamentals and Nokia IP network routing, switching and aggregation

In Nokia SR OS, which protocol provides loop-free Layer 2 topology by electing a root bridge and blocking redundant paths?

  1. VRRP
  2. LDP
  3. OSPF
  4. STP Correct answer.

Explanation

Spanning Tree Protocol elects a root bridge and blocks redundant ports to create a loop-free Layer 2 topology. OSPF is a Layer 3 routing protocol, VRRP provides gateway redundancy, and LDP distributes labels for MPLS.

Question 48IP routing fundamentals and Nokia IP network routing, switching and aggregation

A Nokia SR OS router receives a packet for a destination prefix that has multiple candidate routes but only one active route in the routing table. Which statement explains this?

  1. The routing table selects one best route per prefix based on preference and metric, and only that route is installed for forwarding Correct answer.
  2. All candidate routes are installed and used simultaneously
  3. The router drops all packets until all candidate routes are removed
  4. The forwarding table ignores the routing table entirely

Explanation

The routing table selects a single best route per prefix using preference first and then metric, and that active route is installed for forwarding. Other candidate routes remain available as backups but are not used while the best route is active. ECMP is the exception when multiple equal-cost routes exist.

Question 49IP routing fundamentals and Nokia IP network routing, switching and aggregation

In a Nokia SR OS VPRN, a customer site is connected through a SAP on a PE router. Which function does the SAP perform?

  1. It provides the route distinguisher for the VPRN
  2. It elects the VRRP master for the customer subnet
  3. It carries MPLS labels between PE routers
  4. It terminates the customer VLAN on the PE and binds it to the service routing instance Correct answer.

Explanation

A SAP identifies the attachment point where customer traffic enters the service on the PE, terminating the VLAN and binding it to the VPRN routing instance. The route distinguisher is a separate VPRN parameter, VRRP election is unrelated, and MPLS labels are carried over network interfaces or SDPs.

Question 50IP routing fundamentals and Nokia IP network routing, switching and aggregation

An engineer needs to confirm that a Nokia SR OS router prefers an OSPF route over a BGP route for the same prefix. Which configuration change achieves this?

  1. Set the BGP preference to a higher value than the OSPF preference Correct answer.
  2. Disable the OSPF protocol on the router
  3. Set the OSPF preference to a higher value than the BGP preference
  4. Enable ECMP so both routes are used

Explanation

Because lower preference wins, raising the BGP preference above the OSPF preference makes the OSPF route active for the shared prefix. The reverse change would favor BGP. ECMP does not apply because the routes come from different sources with different preferences, and disabling OSPF removes the OSPF route entirely.