Question 1

Refer to the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_116_img_1.jpg Click the Exhibit hutton. You are configuring an interprovider Option C Layer 3 VPN to connect two customer sites. Referring to the exhibit, which three statements are correct? (Choose three.)

Accepted Answer

A, B, C

Explanation: In an Interprovider VPN Option C (also known as BGP Labeled Unicast), the roles and routing information of the network devices are distinct. PE Routers: Establish a direct, multi-hop BGP session with PEs in the remote AS to exchange L3VPN routes. To achieve this, they must learn the loopback addresses of the remote PEs, which are advertised by the ASBRs. They also run an IGP for internal reachability. ASBR Routers: Exchange the loopback addresses of their internal PE routers with the peer ASBR in the other AS using BGP with the labeled-unicast address family. They do not carry the customer L3VPN routes. P Routers: Function solely as label-switching routers within their own AS. They only need to maintain internal IGP routes to build LSPs towards the PEs and ASBRs in their AS. They have no visibility into external routes or L3VPN routes.

Question 2

You are configuring a BGP signaled Layer 2 VPN across your MPLS enabled core network. In this scenario, which statement is correct?

Accepted Answer

A

Explanation: In a BGP-signaled Layer 2 VPN (also known as a Kompella L2VPN), each customer site connected to a PE router must be assigned a site identifier. This identifier must be unique for each site within a particular Layer 2 VPN routing instance. The site identifier, along with the route distinguisher and label block, is used to create a unique Layer 2 VPN Network Layer Reachability Information (NLRI) prefix that BGP advertises to other PE routers. This mechanism allows the remote PE routers to identify the specific customer attachment circuit for which the pseudowire is being established.

Question 3

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_15_img_1.jpg Which two statements are true about the OSPF adjacency displayed in the exhibit? (Choose two.)

Accepted Answer

A, B

Explanation: The exhibit displays an OSPF neighbor in the Init state. This state signifies that the local router is receiving Hello packets from its neighbor, but bidirectional communication has not been established. This occurs because the neighbor's Hello packets do not contain the local router's ID, implying the neighbor is not processing the Hellos it receives. For an OSPF adjacency to form, several parameters must match between neighbors on a common network segment. Among these are the Hello interval and the Dead interval. If either of these timers is mismatched, the receiving router will discard the Hello packet, preventing the establishment of two-way communication and causing the neighbor relationship to be stuck in the Init state.

Question 4

Which statement is correct about IS-IS when it performs the Dijkstra algorithm?

Accepted Answer

B

Explanation: The IS-IS Shortest Path First (SPF) or Dijkstra algorithm calculates the shortest path from the local router to all other destinations. The algorithm maintains a 'tree' database for nodes with a confirmed shortest path and a 'candidate' database for nodes whose paths are being evaluated. The process iteratively selects the lowest-cost node from the candidate database and moves it to the tree database. Subsequently, it examines the neighbors of this newly added node (using the Link-State Database or LSDB) and adds them to the candidate database for future evaluation. Option B, despite its slightly imprecise wording, correctly describes this core iterative step of adding a neighbor of a node in the tree to the candidate list.

Question 5

Which two statements about IS-IS are correct? (Choose two.)

Accepted Answer

A, C

Explanation: In IS-IS, the Designated Intermediate System (DIS) on a broadcast multi-access network (like Ethernet) periodically sends Complete Sequence Number PDUs (CSNPs) to maintain Link-State Database (LSDB) synchronization among all routers on the segment. This makes statement A correct. Partial Sequence Number PDUs (PSNPs) are used to explicitly request a missing Link-State PDU (LSP) or to acknowledge the receipt of an LSP. The PSNP itself does not contain the full LSP but rather a summary or description of it, typically including the LSP ID, sequence number, and checksum. This makes statement C correct.

Question 6

Exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_2_img_1.jpg Referring to the exhibit; the 10.0.0.0/24 EBGP route is received on R5; however, the route is being hidden. What are two solutions that will solve this problem? (Choose two.)

Accepted Answer

B, D

Explanation: The BGP route is hidden on R5 because the BGP next-hop address (192.168.1.1, the IP of R1) is not reachable from R5's perspective. By default, when R4 advertises an EBGP-learned route to an IBGP peer (R5), it does not change the next-hop attribute. There are two standard solutions to this problem: 1. Modify the next-hop attribute on R4 before advertising to R5. R4 can change the next-hop to its own IP address, a feature known as "next-hop-self". This makes the next-hop directly reachable for R5. 2. Ensure the original next-hop is reachable. This is done by advertising the external link prefix (192.168.1.0/30) into the Interior Gateway Protocol (IGP), allowing R5 to learn a route to 192.168.1.1.

Question 7

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_59_img_1.jpg You have MAC addresses moving in your EVPN environment Referring to the exhibit, which two statements are correct about the sequence number? (Choose two)

Accepted Answer

B, C

Explanation: In an EVPN environment, the MAC mobility feature uses a sequence number to handle host moves. When a PE device learns a MAC address locally that was previously associated with a remote PE, it advertises the MAC in a Type 2 route with an incremented sequence number. Receiving PEs compare the sequence number of the new advertisement with any existing entry for that MAC. The advertisement with the higher sequence number is considered the most recent, or latest, update. This mechanism allows the network to correctly identify the new location of the MAC address, thereby resolving the conflicting information from the old and new PEs about the MAC's ownership.

Question 8

Which two statements are correct about a sham link? (Choose two.)

Accepted Answer

A, C

Explanation: A sham link is a logical, unnumbered point-to-point link configured between two Provider Edge (PE) routers within a specific VRF instance. Its primary purpose in an MPLS L3VPN environment is to make the path over the MPLS backbone appear as an OSPF intra-area link. This is necessary when a customer has a direct "backdoor" link between two sites that are also connected via the VPN. By creating an OSPF adjacency over the sham link, the backbone path is advertised using Type 1 LSAs, which OSPF prefers over the inter-area path (Type 3 LSAs) that would otherwise be advertised. This ensures traffic correctly favors the MPLS backbone over the backdoor link.

Question 9

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_55_img_1.jpg Referring to the exhibit, which statement is correct?

Accepted Answer

A

Explanation: The vrf-target is a BGP extended community attribute that controls the import and export policies for routes within a VRF. In the provided configuration, both vrf-a and vrf-b share the same vrf-target value of target:100:1. When a single target is configured this way, it is used for both import and export policies. Consequently, routes learned from CE-1 in vrf-a are exported with target:100:1, and vrf-b is configured to import routes with this same target. This reciprocal relationship allows routes to be shared between the two VRFs, enabling communication between CE-1 and CE-2.

Question 10

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_27_img_1.jpg Referring to the exhibit, which three statements are correct about route 10 0 0.0/16 when using the default BGP advertisement rules'? (Choose three.)

Accepted Answer

A, B, C

Explanation: This question evaluates the understanding of default BGP next-hop advertisement rules. 1. (C) When R1 advertises the route to its external BGP (eBGP) peer R2, it sets the NEXTHOP attribute to its own IP address on the peering link, which is 192.168.1.1. 2. (B) When R2 advertises this eBGP-learned route to its internal BGP (iBGP) peer R3, the default behavior is to not change the NEXTHOP attribute. Therefore, R3 receives the route with the original next-hop of 192.168.1.1. 3. (A) When R2 advertises the route to its other eBGP peer R4, it again updates the NEXTHOP to its own IP address on that specific link, which is 172.16.1.1. These three options correctly describe the default next-hop behavior for both iBGP and eBGP sessions.

Question 11

In IS-IS, which two statements are correct about the designated intermediate system (DIS) on a multi-access network segment? (Choose two)

Accepted Answer

A, C

Explanation: In IS-IS, the Designated Intermediate System (DIS) is elected on a multi-access (broadcast) network. The election is based on the interface priority, with the highest priority value winning the election. The default priority is 64. If two or more routers share the highest priority, the router with the highest MAC address (or system ID) becomes the DIS. Unlike OSPF's Designated Router (DR), the IS-IS DIS does not act as a central point for adjacencies. On an IS-IS multi-access segment, all routers form a full mesh of adjacencies with every other router on that same segment. The primary role of the DIS is to create and flood a pseudonode Link-State PDU (LSP) that represents the multi-access network itself.

Question 12

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_19_img_1.jpg Referring to the exhibit, a working L3VPN exists that connects VPN-A sites CoS is configured correctly to match on the MPLS EXP bits of the LSP, but when traffic is sent from Site-1 to Site-2, PE-2 is not classifying the traffic correctly What should you do to solve the problem?

Accepted Answer

B

Explanation: The exhibit shows that the egress router, PE-2, is advertising label 3 (Implicit Null) to the penultimate hop router (P). This instructs the P router to perform Penultimate Hop Popping (PHP), removing the outer MPLS label before forwarding the packet to PE-2. When the outer label is removed, the associated MPLS EXP bits, which carry the Class of Service (CoS) information, are also lost. Consequently, PE-2 receives a plain IP packet (with the inner VPN label) and cannot classify it based on the outer label's EXP bits. To resolve this, the explicit-null option must be configured on the egress router, PE-2. This causes PE-2 to advertise the Explicit Null label (label 0), preventing PHP and ensuring the MPLS header with the EXP bits is preserved until it reaches PE-2 for proper CoS classification.

Question 13

Exhibit https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Juniper_JN0-664/page_46_img_1.jpg Referring to the exhibit, you are receiving the 192.168 0 0/16 route on both R3 and R4 from your EBGP neighbor You must ensure that R1 and R2 receive both BGP routes from the route reflector In this scenario, which BGP feature should you configure to accomplish this behavior?

Accepted Answer

A

Explanation: By default, a BGP route reflector selects a single best path for a prefix and advertises only that path to its clients. The BGP add-path feature is designed to overcome this limitation by allowing a BGP speaker to advertise multiple paths for the same prefix. By configuring add-path on the route reflector, it can send more than just its calculated best path to clients R1 and R2. This ensures that R1 and R2 receive both available routes for the 192.168.0.0/16 prefix, one via R3 and the other via R4, providing path diversity and enabling faster failover or load balancing at the client level.

Question 14

You are asked to protect your company's customers from amplification attacks. In this scenario, what is Juniper's recommended protection method?

Accepted Answer

B

Explanation: BGP Flow Specification (FlowSpec) is Juniper's recommended method for mitigating distributed denial-of-service (DDoS) attacks, including amplification attacks. FlowSpec enables the distribution of traffic filtering rules (flow routes) via BGP to network edge routers. This allows an operator to create highly specific rules that match the attack traffic's characteristics (e.g., source/destination ports, protocol) and apply an action, such as 'discard'. This surgically removes the malicious traffic at the network edge before it can consume the customer's bandwidth, while allowing legitimate traffic to the same destination to pass, thus protecting the customer with minimal service impact.

Question 15

You are responding to an RFP for a new MPLS VPN implementation. The solution must use LDP for
signaling and support Layer 2 connectivity without using BGP The solution must be scalable and
support multiple VPN connections over a single MPLS LSP The customer wants to maintain all routing
for their Private network
In this scenario, which solution do you propose?

Accepted Answer

C

Explanation: The scenario requires a Layer 2 VPN solution that uses LDP for signaling and explicitly excludes BGP. An LDP Layer 2 circuit, also known as a Martini-style pseudowire, meets these requirements perfectly. It establishes point-to-point Layer 2 connections across an MPLS core using a targeted LDP session between the Provider Edge (PE) routers to signal the virtual circuit (VC) labels. This allows multiple Layer 2 circuits to be multiplexed over a single transport LSP, providing scalability. Because it is a Layer 2 service, the customer retains full control over their private network routing, fulfilling all conditions specified in the RFP.

Free Juniper JN0-664 Actual Exam Questions