Question 1

In a Carrier Supporting Carrier (CSC) VPRN, which of the following is NOT a benefit to the network provider?

Accepted Answer

D

Explanation: The Carrier Supporting Carrier (CSC) VPRN model is designed to scale by isolating the backbone provider from the routing and service complexity of its customer carriers. The backbone provider is shielded from the explosion in the number of end-customer routes and VPNs, as these are managed entirely by the customer carrier. However, the backbone provider must create a separate VPRN instance (a VRF) for each customer carrier it services. Therefore, as the number of customer carriers increases, the number of VRFs and associated BGP sessions on the backbone PE routers (CSC-PEs) grows linearly. This directly consumes resources and adds configuration overhead, making it a scaling consideration rather than an inherent scaling benefit of the architecture.

Question 2

Which of the following about BGP loops in a VPRN environment is TRUE?

Accepted Answer

B

Explanation: The standard BGP loop prevention mechanism relies on the ASPATH attribute; a BGP router rejects any route update where it sees its own Autonomous System (AS) number in the path. In a VPRN environment, it is common for a customer to use the same private AS number across multiple geographically separate sites. When a route from one customer site is advertised across the service provider's MP-BGP network to another of the customer's sites, the receiving Customer Edge (CE) router will see its own AS number in the ASPATH. Consequently, the CE router will drop the update, detecting a loop. This is the primary BGP loop challenge specific to VPRN architectures.

Question 3

https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_99_img_1.jpg To enable full spoke-to-spoke connectivity for the CE hub and spoke VPRN, on which router(s) should the displayed static-route be configured?

Accepted Answer

C

Explanation: In a hub-and-spoke VPRN topology, direct spoke-to-spoke communication is prevented. All traffic between spoke sites must transit through the central hub site. To enforce this traffic pattern, the spoke PEs (PE2 and PE3) are configured with a static route within the VPRN instance. The displayed static route (static-route 10.1.0.0/16 next-hop 10.1.1.1) directs traffic destined for the VPRN address space towards the hub CE's IP address (10.1.1.1). The spoke PEs resolve this next-hop via the MP-BGP route to the hub PE (PE1), ensuring that packets from one spoke are sent to the hub for routing to the destination spoke.

Question 4

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_49_img_2.jpg A Carrier Supporting Carrier (CSC) VPRN is configured for a customer carrier who is an Internet Service Provider (ISP). Which route is NOT present in PE1's global routing table?

Accepted Answer

C

Explanation: In a CSC deployment the service-provider (SP) PE keeps only the information it needs to reach (a) its own backbone, and (b) the directly-attached customer-carrier (CC) device. • The CE-facing subnet 10.10.10.6/30 is created as a connected route and therefore lives in the PE’s global routing table. • 192.50.1.1 is the SP loop-back carried by the SP IGP, so it is also in the global table. • 192.60.100.0/24 is a customer prefix that has been leaked into the global table so that next-hop resolution can be performed when the PE imposes transport labels. The remote CC-PE loop-back 10.10.10.3, however, is exchanged as a labeled IPv4 route inside the CSC VPRN only; it is not exported to the PE’s global RIB. Hence 10.10.10.3 is absent.

Question 5

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_67_img_1.jpg A Carrier Supporting Carrier (CSC) VPRN is configured for a customer carrier who is a BGP/MPLS service provider. If CE1 sends an IP packet to 192.168.200.1, which of the following is FALSE?

Accepted Answer

C

Explanation: In a CSC VPRN the super-carrier (CSC-PE1/PE2) treats the label that arrives from the customer carrier (the BGP-LU label) as the service label and leaves it untouched; it only adds (pushes) its own transport label for carriage across its backbone. Therefore CSC-PE1 never removes (“pops”) the BGP label nor alters (“swaps”) the VPN label. Options A, B and D accurately describe the standard push/swap/pop sequence at the ingress customer PE, the customer border (CSC-CE1) and the egress CSC-PE2 respectively, but statement C contradicts the defined data-plane behaviour and is false.

Question 6

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_80_img_1.jpg Routers RR1 and RR2 are configured as route reflectors. For the inter-AS model C VPRN, which of the following about the BGP sessions established between the routers is TRUE?

Accepted Answer

B

Explanation: In an inter-AS model C VPRN deployment that uses dedicated route-reflectors (RRs), each PE forms an MP-iBGP session only to the RR in its own AS. The ASBR in each AS forms an MP-iBGP session to its local RR so that VPN-IPv4/6 prefixes received over the inter-AS MP-eBGP link can be reflected to the PEs. The two RRs then create a multi-hop MP-eBGP session between themselves to exchange the labeled VPN routes across the AS boundary. Consequently, RR1 must maintain: 1) an MP-iBGP session with its client PE1, 2) an MP-iBGP session with the local ASBR1, and 3) a multi-hop MP-eBGP session with the remote RR2. Total = 3 sessions, making option B correct.

Question 7

Which of the following about the configuration of an inter-AS model C VPRN is FALSE?

Accepted Answer

B

Explanation: Inter-AS model C (RFC 4364 option C) only requires that each autonomous system have a transport MPLS tunnel of some sort (LDP, RSVP-TE, or SR). LDP itself is therefore optional. What is mandatory is: • inside each AS, VPN-IPv4/-IPv6 routes are carried by MP-iBGP (normally PE–RR or PE–PE); • between ASBRs the labeled VPN routes are exchanged with MP-eBGP; • on Nokia SR OS routers that act as ASBRs the command enable-inter-as-vpn must be configured to permit advertisement of VPN‐labeled NLRI across an external BGP session. Thus, only statement B, which makes LDP compulsory, is false.

Question 8

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_64_img_1.jpg For the Inter-AS model B VPRN, which of the following about the inter-as-label output on ASBR1 is TRUE?

Accepted Answer

B

Explanation: In Inter-AS Option B, each ASBR replaces the VPN label learned from its internal PE with a new label before advertising the route to the external ASBR. On SR OS the CLI field inter-as-label shows exactly the label that will be carried in the MP-eBGP update sent to the peer. From the exhibit, inter-as-label = 131068; therefore ASBR1 advertises label 131068 to ASBR2. The original service label 131069 (displayed only as “label”) is kept for traffic arriving from the internal side and is not exported across the AS boundary.

Question 9

What is wrong with the VPRN configuration applied on this Nokia 7750 SR? https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_90_img_1.jpg

Accepted Answer

C

Explanation: The router-id command configured within a VPRN service context is specifically used by routing protocols, such as BGP or OSPF, that are running within that VPRN instance (typically for PE-CE routing). The provided configuration snippet does not show any routing protocols being configured within the VPRN. Therefore, the router-id 10.10.10.1 command is superfluous and has no operational effect. In the absence of a specific need, a VPRN should inherit the main router's system-level router ID. Including unnecessary commands is considered incorrect configuration practice.

Question 10

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_56_img_1.jpg AS-override is configured on PE1 to eliminate the BGP loops. What is the expected AS-Path in the VPN-IPv4 route 64496:10:192.168.2.0/27 received by PE1?

Accepted Answer

C

Explanation: The route 192.168.2.0/27 originates from CE2, which is in Autonomous System (AS) 64497. When CE2 advertises this route to PE2 via eBGP, it prepends its own AS number, making the AS-Path 64497. PE2 then advertises this route to PE1 as a VPN-IPv4 route using Multiprotocol iBGP (MP-iBGP). A fundamental rule of iBGP is that the AS-Path attribute is not modified when advertising routes to an internal peer. Therefore, PE1 receives the VPN-IPv4 route from PE2 with the AS-Path unchanged: 64497. The as-override command configured on PE1 is only relevant for routes being advertised from PE1 to CE1; it does not affect routes received by PE1.

Question 11

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_67_img_2.jpg A Carrier Supporting Carrier (CSC) VPRN is configured for a customer carrier who is an Internet Service Provider (ISP). If CE1 sends an IP packet to 192.60.100.1, which of the following is FALSE?

Accepted Answer

C

Question 12

For the data packets in a VPRN, how is the inner label in an MPLS packet signaled?

Accepted Answer

C

Explanation: In a Virtual Private Routed Network (VPRN), a two-label stack is used to forward customer traffic across the provider's MPLS core. The inner label, often called the VPN or service label, is crucial for the egress PE router to identify which specific VPRN instance (and its corresponding Virtual Routing and Forwarding table, or VRF) the incoming packet belongs to. This inner label is allocated by the egress PE and advertised to other PE routers along with the customer's VPN-IPv4 prefixes. The signaling protocol used for this exchange of routing information and labels between PE routers is Multi-Protocol BGP (MP-BGP).

Question 13

For a Carrier Supporting Carrier (CSC) VPRN where the customer carrier is a BGP/MPLS VPN Service Provider (SP), which of the following is FALSE?

Accepted Answer

A

Explanation: The question's premise explicitly states that the customer carrier is a "BGP/MPLS VPN Service Provider". By definition, such a provider utilizes an MPLS-enabled core to establish Label Switched Paths (LSPs) for traffic transport and uses Multiprotocol BGP (MP-BGP) to exchange VPN routing information. This architecture is fundamentally different from a "pure IP network," which would rely solely on IP routing protocols like OSPF or IS-IS for reachability without an underlying MPLS transport for VPN services. Therefore, the statement that a BGP/MPLS VPN SP "can be a pure IP network" is a direct contradiction of the established premise, making it the false statement.

Question 14

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_74_img_1.jpg Routers RR1 and RR2 are configured as route reflectors. For the inter-AS model C VPRN, which of the following about the VPN-IPv4 route advertisement is FALSE?

Accepted Answer

D

Explanation: In a standard BGP route-reflector (RR) topology, a client (PE1) establishes an iBGP session exclusively with its designated route reflector (RR1). PE1 advertises its learned VPN-IPv4 prefixes, such as 192.1.1.0/27, only to RR1. The route reflector is then responsible for propagating this route to its other iBGP peers, including other clients (like ASBR1) and non-clients. PE1 would not have a direct iBGP peering with ASBR1, as this would contradict the purpose of using a route reflector to simplify the iBGP mesh. Therefore, the statement that PE1 advertises the route to both RR1 and ASBR1 is false.

Question 15

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-106/page_77_img_1.jpg Internet access is provided to the Red VPRN (ID 10) via an Internet VRF (ID 500). For this configuration, which communities must be imported on the Red and Internet VRFs?

Accepted Answer

B

Explanation: This configuration represents a hub-and-spoke VPRN topology, where the Internet VRF (hub) provides a shared service to the Red VPRN (spoke). For the Red VPRN to function, it must import two sets of routes: 1. Routes from its own sites, which are tagged with the "Red-Only" community (its native route target). This ensures intra-VPRN connectivity. 2. The default route from the Internet VRF, which is tagged with the "Internet" community. This provides the path to the internet. The Internet VRF only needs to learn the routes from the Red VPRN to provide a return path for traffic. Therefore, it only needs to import the "Red-Only" community.

Free Nokia 4A0-106 Actual Exam Questions