JN0-664 Service Provider Professional (JNCIP-SP) Questions and Answers

To allow Site 1 to access three VLANs that are located in Site 2 and Site 3, you need to configure three L2VPN routing instances on PE-1, one for each VLAN. Each L2VPN routing instance will have a different VLAN ID and a different VNI for VXLAN encapsulation. Each L2VPN routing instance will also have a different vrf-target export value to identify which VPN routes belong to which VLAN. This way, PE-1 can forward traffic from Site 1 to Site 2 and Site 3 based on the VLAN tags and VNIs.

The provided configuration is for a routing instance named VPN-A on a Juniper PE (Provider Edge) router. Let’s break it down:

Instance Type: VRF

The instance-type vrf; statement indicates that this is a Layer 3 VPN (L3VPN) using MPLS VPNs (RFC 4364 – BGP/MPLS IP VPNs).

This confirms that Option D (A Layer 3 VPN is configured) is correct ✅.

VRF Target and Interface Association

The vrf-target target:64512:1234; defines the route target (RT) for importing and exporting VPN routes.

The interface ge-0/0/1.0; binds this interface to the VRF.

BGP Configuration for CE (Customer Edge) Peering

The group CE section configures external BGP (EBGP) (type external;).

The neighbor 10.0.0.1 is in AS 64512 (peer-as 64512;).

The as-override; statement is used.

Evaluating the Answer Choices

✅ Option B: "This VPN connects customer sites that use the same AS number."

The as-override; command allows multiple customer sites that use the same AS number (64512) to communicate over the service provider’s MPLS network.

Normally, BGP prevents routes with the same AS in the AS_PATH from being accepted. The as-override feature replaces the customer's AS number with the provider’s AS, ensuring proper route advertisement.

✅ This statement is correct.

❌ Option A: "This VPN connects customer sites that use different AS numbers."

If the customer sites had different AS numbers, there would be no need for as-override.

The as-override feature is specifically used when all customer sites share the same AS number, ensuring that BGP routes are accepted.

❌ This statement is incorrect.

❌ Option C: "A Layer 2 VPN is configured."

A Layer 2 VPN (L2VPN) configuration would typically use instance-type l2vpn; or EVPN/VPLS-related parameters (e.g., protocols l2vpn or protocols vpls).

Since this configuration uses instance-type vrf; and BGP with a VRF target, it is clearly a Layer 3 VPN (L3VPN).

❌ This statement is incorrect.

✅ Option D: "A Layer 3 VPN is configured."

The instance-type vrf; confirms this is an MPLS Layer 3 VPN (L3VPN).

VRFs, BGP, and route targets (vrf-target) are specific to Layer 3 VPNs.

✅ This statement is correct.

Final Answer:

✅ B. This VPN connects customer sites that use the same AS number.

✅ D. A Layer 3 VPN is configured.

Verification from Juniper Documentation:

Juniper BGP/MPLS Layer 3 VPNs Guide confirms that instance-type vrf is used for L3VPNs.

Juniper BGP Configuration Guide states that as-override is applied when customer sites use the same AS number.

RFC 4364 (BGP/MPLS IP VPNs) explains how route targets and VRFs are used in L3VPN deployments.

The `vrf-target` statement in a Layer 3 VPN configuration is used to control the import and export of VPN routes by attaching a target community to the routes. This helps in defining which VPN routes should be imported into or exported from a particular VRF (Virtual Routing and Forwarding) instance.

1. **Understanding VRF Target**:

- The `vrf-target` statement specifies the extended community attributes (route targets) that are used to control the import and export of routes in a VRF.

- These attributes help in identifying which routes should be shared between different VRFs, particularly across different PE (Provider Edge) devices.

2. **Statements Analysis**:

- **A. This value is used to identify BGP routes learned from the local CE device.**

- Incorrect. The `vrf-target` attribute is not used to identify routes learned from the local CE device. It is used to manage routes between PE devices and within the provider's MPLS network.

- **B. This value is used to identify BGP routes learned from the remote PE device.**

- Correct. The `vrf-target` value helps in identifying which routes from remote PE devices should be imported into the local VRF. It essentially acts as a filter for importing BGP routes with matching target communities.

- **C. This value is used to add a target community to BGP routes advertised to the local CE device.**

- Incorrect. Routes advertised to the local CE device do not use the `vrf-target` attribute. Instead, these routes are typically managed within the local VRF routing table.

- **D. This value is used to add a target community to BGP routes advertised to the remote PE device.**

- Correct. When advertising routes from the local PE to remote PE devices, the `vrf-target` value is added to these routes. This target community ensures that the correct routes are shared across the VPN.

**Conclusion**:

The correct statements about the `vrf-target` configuration in a Layer 3 VPN scenario are:

**B. This value is used to identify BGP routes learned from the remote PE device.**

**D. This value is used to add a target community to BGP routes advertised to the remote PE device.**

**References**:

- Juniper Networks Documentation on VRF Target: [VRF Target Configuration](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/layer-3-vpns.html)

- MPLS and VPN Architectures by Ivan Pepelnjak and Jim Guichard

https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/load-balancing-bgp-session.html

Prefer the route with the lower origin code. Routes learned from an IGP have a lower origin code than those learned from an exterior gateway protocol (EGP), and both have lower origin codes than incomplete routes (routes whose origin is unknown). https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/bgp/topics/concept/routing-protocols-address-representation.html

Class of Service (CoS) in networking is used to manage traffic by classifying, scheduling, and sometimes modifying packets to ensure network performance and Quality of Service (QoS). Different CoS components are used to achieve these goals. Let's analyze each option to determine which CoS component allows you to alter class-of-service values on the outbound interface of an edge router.

1. **Output Policer**:

- Policing is used to control the rate of traffic sent to or from a network interface. It can drop or remark traffic that exceeds a certain rate.

- Policing is not typically used to alter CoS values but to enforce traffic limits.

2. **Scheduler**:

- A scheduler is responsible for managing the order in which packets are transmitted out of an interface based on their CoS markings. It can allocate bandwidth and prioritize traffic.

- The scheduler manages how packets are queued and sent but does not alter the CoS values of packets.

3. **Rewrite Rules**:

- Rewrite rules are used to modify the CoS values of packets, such as DSCP (Differentiated Services Code Point) or 802.1p bits, as they exit an interface.

- Rewrite rules can alter the class-of-service values in the packet headers to match the desired policies of the outbound interface.

- Therefore, rewrite rules are the correct component for altering CoS values on an outbound interface.

4. **Forwarding Classes**:

- Forwarding classes are used to categorize packets into different traffic classes within a router for QoS handling.

- They help in defining how packets should be treated by the scheduler but do not directly modify the CoS values.

**Conclusion**:

To alter class-of-service values in packets on the outbound interface of an edge router, the correct CoS component to use is:

**C. rewrite rules**

**References**:

- Juniper Networks Documentation on CoS: [Class of Service Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/class-of-service-overview.html)

- Junos OS CoS Configuration Guide: [Rewrite Rules](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/class-of-service-rewrite-rules.html)

Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol used to move information efficiently within a computer network. It uses a series of Protocol Data Units (PDUs) to manage the network's topology and ensure consistency across all routers in the network. Specifically, Link State PDUs (LSPs), Complete Sequence Number PDUs (CSNPs), and Partial Sequence Number PDUs (PSNPs) play crucial roles in this process.

1. **PSNPs (Partial Sequence Number PDUs)**:

- **Acknowledge a received LSP**: PSNPs are used to acknowledge the receipt of LSPs. When a router receives an LSP, it sends a PSNP back to the sender to confirm that the LSP has been received.

- **Request a missing LSP**: PSNPs are also used to request missing LSPs. If a router identifies a missing LSP based on sequence numbers, it can send a PSNP to request the specific LSP from its neighbors.

2. **CSNPs (Complete Sequence Number PDUs)**:

- **Summarize LSPs**: CSNPs are used to summarize all the LSPs known to a router. They are typically sent at regular intervals to provide a complete list of LSPs in a database. They are not used to acknowledge or request specific LSPs but provide an overview of all LSPs for database synchronization.

Based on this understanding, let's evaluate the statements:

- **A. PSNPs are used to acknowledge a received LSP.**

- Correct. PSNPs serve the purpose of acknowledging LSPs received from other routers.

- **B. CSNPs are used to acknowledge a received LSP.**

- Incorrect. CSNPs are not used for acknowledging LSPs; they are used to provide a summary of all LSPs.

- **C. CSNPs are used to request a missing LSP.**

- Incorrect. CSNPs are not used to request missing LSPs; this is the role of PSNPs.

- **D. PSNPs are used to request a missing LSP.**

- Correct. PSNPs are used to request specific missing LSPs when a router detects that it is missing information.

**Conclusion**:

The correct statements about IS-IS are:

**A. PSNPs are used to acknowledge a received LSP.**

**D. PSNPs are used to request a missing LSP.**

**References**:

- Juniper Networks Documentation on IS-IS: [IS-IS Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/is-is-routing-overview.html)

- RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and Dual Environments: [RFC 1195](https://tools.ietf.org/html/rfc1195) which details the operation and use of IS-IS, including the roles of PSNPs and CSNPs.

The issue arises because R3’s group-range (224.1.1.0/28) is more specific than R2’s group-range (224.1.1.0/24). In PIM bootstrap (BSR), the RP with the longest prefix (most specific group-range) is preferred, regardless of priority. Even though R3 has a higher bootstrap priority (210 vs. R2’s 200), its more specific /28 group-range takes precedence for groups within 224.1.1.0/28.

Why Option D is Correct:

To force R4 to use R2 for all joins, R2’s group-range must be more specific than R3’s. For example:

If R2’s group-range is changed to 224.1.1.0/28 (same as R3) but with a higher priority, R2 would win (priority is compared only when group-ranges are equal).

If R2’s group-range is changed to 224.1.1.0/29 (more specific than /28), it will override R3’s /28 for groups in the /29 range.

The key is prefix specificity, which overrides priority in BSR elections.

Why Other Options Are Incorrect:

A. Change bootstrap priority on R2 to be higher than R3:

Priority is evaluated only when group-ranges are identical. Since R3’s group-range (/28) is more specific than R2’s (/24), R3 will still win for groups in 224.1.1.0/28, even if R2’s priority is higher.

B. Change the default route in inet.2 on R4:

RPF routes (inet.2) determine how traffic reaches the RP, but they do not influence RP election logic (BSR priority/group-range).

C. Change R2’s local address to be higher than R3’s:

The RP address is a tiebreaker only if priorities and group-ranges are equal. Since R3’s group-range is more specific, this change has no impact.

Key Takeaways:

BSR RP Election Order:

Longest group prefix (most specific).

Highest priority (if prefixes are equal).

Highest RP address (if prefixes and priorities are equal).

To override R3, R2 must advertise a more specific group-range (e.g., /28 or smaller) to ensure it is selected for the desired multicast groups.

Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol that supports Level 1 (L1), Level 2 (L2), or both (L1/L2) operations. The way IS-IS sends Hello (IIH) packets depends on whether the interface is point-to-point (P2P) or broadcast (LAN).

Evaluating the Answer Choices

✅ Option A: "If a point-to-point interface is in both L1 and L2, separate hello messages are sent for each level."

Incorrect!

On point-to-point (P2P) interfaces, only one combined Hello message is sent for both L1 and L2.

IS-IS P2P Hellos include both Level 1 and Level 2 TLVs in the same message.

Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It operates in two levels, Level 1 (L1) and Level 2 (L2), and supports hierarchical routing within a multi-area network.

Let's analyze each statement to determine its correctness in the context of IS-IS multi-area networks.

1. **Statement A: Internal L1 PDUs are flooded to the local area's L2 routers.**

- This statement is correct. L1 PDUs (Protocol Data Units) are flooded within the L1 area and also to the L2 routers that are present in the same area. These L2 routers act as the boundary routers that connect the local L1 area to other L1 areas via L2.

2. **Statement B: External L2 PDUs are flooded to all L2 routers in other areas.**

- This statement is correct. L2 PDUs are flooded throughout the entire L2 backbone, which includes all L2 routers in different areas. This ensures that inter-area routing information is shared across the network.

3. **Statement C: Internal L1 PDUs are flooded to all L1 routers in other areas.**

- This statement is incorrect. Internal L1 PDUs are only flooded within the local L1 area. They do not cross L1 area boundaries; inter-area communication is handled by L2 routers.

4. **Statement D: Internal L1 PDUs are only flooded to the local area's L1 routers.**

- This statement is correct. Internal L1 PDUs are indeed only flooded within their local L1 area, and do not go beyond it.

5. **Statement E: External L2 PDUs are only flooded to the local area's L2 routers.**

- This statement is incorrect. External L2 PDUs are flooded to all L2 routers throughout the IS-IS network, not just to those in the local area. This allows L2 routers to maintain a complete map of the network's topology.

**Conclusion**:

Given the analysis, the correct answers are:

**A. Internal L1 PDUs are flooded to the local area's L2 routers.**

**B. External L2 PDUs are flooded to all L2 routers in other areas.**

**D. Internal L1 PDUs are only flooded to the local area's L1 routers.**

**References**:

- Juniper Networks Documentation on IS-IS: [IS-IS Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/is-is-routing-overview.html)

- RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and Dual Environments: [RFC 1195](https://tools.ietf.org/html/rfc1195) which details the operation of IS-IS in multi-area networks.

Analyzing the Exhibit

The diagram represents BGP peering between:

AS 65512 (Enterprise Network)

AS 65511 (ISP-A)

R3 and R4 are peering with ISP-A using EBGP.

R1, R2, R3, and R4 are peering within AS 65512 using IBGP.

Understanding BGP Route Behavior

Option A: "By default, the next-hop value for these routes is not changed by ISP-A before being sent to R3." ❌

Incorrect!

EBGP behavior: When a BGP route is advertised via EBGP, the next-hop IP is changed to the router's own IP by default.

Since ISP-A is advertising routes via EBGP to R3, the next-hop is changed to ISP-A’s IP.

Thus, this statement is incorrect.

Option B: "The BGP local-preference value that is used by ISP-A is not advertised to R3." ✅

Correct!

BGP Local Preference (LOCAL_PREF) is an IBGP-only attribute.

Local Preference is NOT shared over EBGP because it is used within an AS to influence route selection.

ISP-A will not send LOCAL_PREF to R3, as R3 is in a different AS.

Thus, this statement is correct.

Option C: "All BGP attribute values must be removed before receiving the routes." ❌

Incorrect!

BGP does not remove all attributes when advertising routes. Some attributes are modified (e.g., next-hop, AS-PATH), but others (like MED, community) may be preserved.

Thus, this statement is incorrect.

Option D: "The next-hop value for these routes is changed by ISP-A before being sent to R3." ✅

Correct!

As per default EBGP behavior, the next-hop is changed when a route is advertised to an EBGP peer.

This means ISP-A changes the next-hop to its own IP before sending it to R3.

Thus, this statement is correct.

Final Answer:

✅ B. The BGP local-preference value that is used by ISP-A is not advertised to R3.

✅ D. The next-hop value for these routes is changed by ISP-A before being sent to R3.

Verification from Juniper Documentation:

Juniper BGP Configuration Guide confirms that LOCAL_PREF is not advertised over EBGP.

RFC 4271 (BGP-4) specifies that next-hop is changed by default when advertising routes via EBGP.

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/show-route-advertising-protocol.html

In the exhibit, we see an internal BGP (iBGP) setup within AS 65512, and an external BGP (eBGP) connection between R3 and ISP-A (AS 65511). The questions focus on the behavior of BGP routes advertised from R3 to R1 within the same AS.

1. **BGP Next-Hop Attribute (Option A and D)**:

- In iBGP, the next-hop attribute is **not** changed when a route is advertised to another iBGP peer. This means that when R3 advertises a route to R1, it retains the original next-hop value as learned from the eBGP peer (ISP-A).

- Therefore, Option D is correct: "By default, the next-hop value for these routes is not changed by R3 before being sent to R1."

2. **BGP Attributes (Option B and C)**:

- BGP attributes such as local preference, AS-path, and others are crucial for BGP route selection. The local preference attribute is used within an AS to indicate the preferred path for outbound traffic.

- When R3 advertises BGP routes to R1, it includes the local preference value assigned to those routes. This value is not removed and is propagated within the iBGP mesh.

- Therefore, Option C is correct: "By default, the BGP local-preference value that is assigned on R3 is advertised to R1."

**References**:

- Juniper Networks documentation on BGP behavior provides detailed insights into the propagation of BGP attributes within iBGP and eBGP contexts. Specifically, the Junos OS documentation covers the default behavior of next-hop and local preference attributes in BGP configurations.

- Junos OS BGP Configuration Guide: [Junos OS BGP Configuration Guide](https://www.juniper.net/documentation/en_US/junos/topics/concept/bgp-overview.html)

- For a deeper understanding of BGP attributes and their default behaviors, the "Juniper Networks Day One: Exploring BGP" book is an excellent resource.

To create a summary route for IS-IS, you need to configure a policy statement that matches the prefixes to be summarized and sets the next-hop to discard. You also need to configure a summary-address statement under the IS-IS protocol hierarchy that references the policy statement. In this case, the policy statement leak-v6 is trying to match the prefix 2001:db9:a:fa00::/61 exactly, but this prefix is not advertised by any router in the network. Therefore, no summary route is created. To fix this, you need to delete the longer keyword from the route-filter term and change the prefix length to /61 exact. This will match any prefix that falls within the /61 range. You also need to delete the export statement under protocols isis, because this will export all routes that match the policy statement to other IS-IS routers, which is not desired for a summary route.

BGP route reflectors are BGP routers that are allowed to ignore the IBGP loop avoidance rule and advertise IBGP learned routes to other IBGP peers under specific conditions. BGP route reflectors can reduce the number of IBGP sessions and updates in a network by eliminating the need for a full mesh of IBGP peers. BGP route reflectors can have three types of peerings:

EBGP neighbor: A BGP router that belongs to a different autonomous system (AS) than the route reflector.

IBGP client neighbor: An IBGP router that receives reflected routes from the route reflector. A client does not need to peer with other clients or non-clients.

IBGP non-client neighbor: An IBGP router that does not receive reflected routes from the route reflector. A non-client needs to peer with other non-clients and the route reflector.

In the exhibit, we can see that RR1 and RR2 are route reflectors in the same AS with reachability redundancy. They have two types of peerings: EBGP neighbors (R1 and R4) and IBGP client neighbors (Client1, Client2, and Client3). RR1 and RR2 are also peered with each other as IBGP non-client neighbors.

Layer 2 VPNs don’t support fragmentation in the provider network. It is critical that the provider network supports the largest frame that the CE devices can generate after the MPLS and virtual routing and forwarding (VRF) labels are added by the PE devices. This example leaves the CE devices at the default 1500-byte maximum transmission unit (MTU) while configuring the provider core to support a 4000 byte MTU. This configuration avoids discards by ensuring the CE devices cannot exceed the MTU in the provider’s network.

Interprovider Option C for Layer 3 VPNs involves the use of Autonomous System Boundary Routers (ASBRs) to exchange labeled VPN-IPv4 routes between different Autonomous Systems (AS). This option requires BGP sessions between ASBRs, and the VPN routes are carried end-to-end using MPLS labels. Here’s a detailed analysis of the roles of different routers in this scenario:

1. **ASBR Routers**:

- ASBRs are responsible for exchanging VPN-IPv4 routes between different ASes.

- **A. ASBR routers maintain the internal routes from its own AS and the loopback addresses from the other AS PEs.**

- Correct. ASBRs maintain routes to internal destinations within their own AS, and they also need to know the loopback addresses of PEs in the other AS to set up the BGP sessions and MPLS tunnels.

2. **PE Routers**:

- PE routers are responsible for maintaining VPN routes and label information to forward VPN traffic correctly.

- **B. PE routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

- Correct. PE routers need to maintain:

- Internal routes within their AS for routing.

- Loopback addresses of other AS PEs for establishing MPLS LSPs.

- L3VPN routes to provide end-to-end VPN connectivity.

3. **P Routers**:

- P routers are the core routers that do not participate in BGP VPN routing but forward labeled packets based on MPLS labels.

- **C. P routers only maintain the internal routes from their own AS.**

- Correct. P routers maintain the internal routing information to forward packets within the AS and use MPLS labels for forwarding VPN packets. They do not maintain VPN routes or routes from other ASes.

4. **Incorrect Statements**:

- **D. P routers maintain the internal routes from its own AS and the loopback address from the other AS PEs.**

- Incorrect. P routers do not need to maintain the loopback addresses of other AS PEs. They only maintain internal routing and MPLS label information.

- **E. ASBR routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

- Incorrect. ASBR routers do not maintain L3VPN routes. They exchange labeled VPN-IPv4 routes with other ASBRs and forward them to PE routers.

**Conclusion**:

The correct answers are:

**A. ASBR routers maintain the internal routes from its own AS and the loopback addresses from the other AS PEs.**

**B. PE routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

**C. P routers only maintain the internal routes from their own AS.**

**References**:

- Juniper Networks Documentation on Interprovider VPNs: [Interprovider VPN Configuration](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/mpls-vpn-interprovider.html)

- MPLS and VPN Architectures, CCIP Edition by Ivan Pepelnjak and Jim Guichard

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospfv2-sham-links.html

The vrf-target statement is used in routing-instances to define route-target communities for VPN route import and export policies.

vrf-target export → Controls which route targets (RTs) are added to advertised routes (used when sending routes to remote PEs).

vrf-target import → Controls which VPN routes are accepted into the VRF (used when receiving routes from remote PEs).