https://www.juniper.net/documentation/us/en/software/nce/feature-guide-virtual-private-lan-service/topics/task/vpls-ldp-signaling-solutions.html

https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/topics/concept/vpns-configuring-vpls-routing-instances.html#id-11510150__id-11568648

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.

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.

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

Option A (Correct):

In IS-IS, the Designated Intermediate System (DIS) is elected based on the highest configured priority (as defined in Junos OS).

If priorities are equal, the router with the highest MAC address becomes the DIS.

A priority value of 10 will always override a lower priority (e.g., 1).

To transport IPv6 traffic over an IPv4-based MPLS network using BGP, you need to configure two address families: family inet6 labeled-unicast and family inet6 unicast. The former is used to exchange IPv6 routes with MPLS labels between PE routers, and the latter is used to exchange IPv6 routes without labels between PE and CE routers. The mpis ipv6-tunneling command enables the PE routers to encapsulate the IPv6 packets with an MPLS label stack and an IPv4 header before sending them over the MPLS network.

IS-IS is an interior gateway protocol that uses link-state routing to exchange routing information among routers within a single autonomous system. IS-IS uses two types of addresses to identify routers and areas: system ID and area address. The system ID is a unique identifier for each router in an IS-IS domain. The system ID is 6 octets long and can be derived from the MAC address or manually configured. The area address is a variable-length identifier for each area in an IS-IS domain. The area address can be 1 to 13 octets long and is composed of high-order octets of the address. An IS-IS instance may be assigned multiple area addresses, which are considered synonymous. Multiple synonymous area addresses are useful when merging or splitting areas in the domain1. In this question, we have a network based on IS-IS with four routers (R1_1, R1_2, R2_1, and R2_2) belonging to area 0001. The area address for area 0001 is 49.0001. The NSEL byte for area 0001 is the last octet of the address, which is 01. The NSEL byte stands for Network Service Access Point Selector (NSAP Selector) and indicates the type of service requested from the network layer2. Therefore, the correct statement in this scenario is that the NSEL byte for area 0001 is 01.

Junos platforms use different mechanisms to evaluate incoming traffic for CoS purposes, such as:

Behavior aggregate classifiers: These classifiers use a single field in a packet header to classify traffic into different forwarding classes and loss priorities based on predefined or user-defined values.

Fixed classifiers: These classifiers use a fixed field in a packet header to classify traffic into different forwarding classes and loss priorities based on predefined values.

Multifield classifiers: These classifiers use multiple fields in a packet header to classify traffic into different forwarding classes and loss priorities based on user-defined values and filters.

Rewrite rules and traffic shapers are not used to evaluate incoming traffic for CoS purposes, but rather to modify or shape outgoing traffic based on CoS policies.

EVPN is a technology that connects L2 network segments separated by an L3 network using a virtual Layer 2 network overlay over the Layer 3 network. EVPN uses BGP as its control protocol to exchange different types of routes for different purposes. Type 2 routes are used to advertise MAC address and IP address pairs learned using ARP snooping from the local CE devices. Type 3 routes are used to join a multicast tree to flood traffic such as broadcast, unknown unicast, and multicast (BUM) traffic.

In the exhibit, we see two VRF (Virtual Routing and Forwarding) instances, CE-1 and CE-2, configured on a Juniper router. Each VRF is associated with a route-distinguisher (RD) and a vrf-target value.

Understanding the Role of vrf-target

The vrf-target is used to define Route Targets (RT), which control the import and export of VPN routes in MPLS Layer 3 VPNs (L3VPNs).

If two VRFs share the same RT, they will import each other's routes, allowing communication between them.

In this case, both VRFs have the same vrf-target:

vrf-target target:65512:100;

Since both CE-1 and CE-2 have the same RT (65512:100), they will import and export each other’s routes, enabling route sharing between them.

Understanding route-distinguisher (RD)

The RD (Route Distinguisher) only ensures uniqueness of overlapping IP prefixes within the MPLS network.

It does not control route sharing between VRFs.

In the exhibit, both VRFs have the same RD (65512:1), but this does not influence whether they share routes.

Correct Answer Selection

A (Correct): The vrf-target configuration enables route sharing between CE-1 and CE-2 since they have the same RT (65512:100).

B (Incorrect): The vrf-target does the opposite—it allows sharing, not blocking.

C (Incorrect): The route-distinguisher only provides unique route identification, but does not affect route sharing.

D (Incorrect): Again, route-distinguisher has no impact on route sharing.

Reference from Juniper Official Documentation

✅ Juniper Documentation - Junos MPLS VPNs Configuration Guide:

"Route targets (vrf-target) are used to control the import and export of VPN routes between different VRFs. VRFs with the same route target can import and export routes to each other, enabling inter-VRF communication."

Thus, the correct answer is:

✅ A. The vrf-target configuration will allow routes to be shared between CE-1 and CE-2.

Bootstrap messages are PIM messages that are used to distribute rendezvous point (RP) information dynamically during an RP election. Bootstrap messages are sent by bootstrap routers (BSRs), which are routers that are elected to perform the RP discovery function for a PIM sparse-mode domain. Bootstrap messages contain information about candidate RPs and their multicast groups, as well as BSR priority and hash mask length. Bootstrap messages are forwarded to all routers within a PIM sparse-mode domain using hop-by-hop flooding.

In the exhibit, the PE-to-CE protocol used is OSPF, and there is an OSPF neighborship between CE-1 and CE-2 within the same Area 0. Let's analyze the default OSPF routing behavior in this setup to determine the correct statement.

1. **OSPF Neighborship**:

- CE-1 and CE-2 have an OSPF neighborship directly within Area 0.

- OSPF prefers intra-area routes over inter-area and external routes.

2. **Default Routing Behavior**:

- Since CE-1 and CE-2 are directly connected through an OSPF link within the same area, OSPF will prefer this direct intra-area path over any other paths learned via the PE routers and the L3VPN.

- This is because intra-area routes have a lower metric compared to inter-area or external routes.

3. **Metric Considerations**:

- By default, OSPF will route traffic between Site-1 and Site-2 through the direct link between CE-1 and CE-2, unless the link's metric is artificially increased to make it less preferable.

- There is no need to adjust metrics for the CE-1 to PE-1 link to prefer the CE-1 to CE-2 path, as OSPF already prefers direct intra-area paths.

**Conclusion**:

Given the default behavior of OSPF and the topology shown in the exhibit, the correct statement is:

**B. Hosts at Site-1 will reach hosts at Site-2 through the CE-1 and CE-2 link by default.**

**References**:

- OSPF Design Guide: [Juniper Networks OSPF Design Guide](https://www.juniper.net/documentation/en_US/junos/topics/concept/ospf-design-overview.html)

- Juniper Networks Technical Documentation on OSPF: [Junos OS OSPF Configuration Guide](https://www.juniper.net/documentation/en_US/junos/topics/concept/ospf-routing-overview.html)

This is an EVPN Type-2 route, also called a MAC/IP advertisement route, that is used to advertise host IP and MAC address information to other VTEPs in an EVPN network. The route type field in the EVPN NLRI has a value of 2, indicating a Type-2 route. The device advertising this route into EVPN is 192.168.101.5, which is the IP address of the VTEP that learned the host information from the local CE device. This IP address is carried in the MPLS label field of the route as part of the VXLAN encapsulation.

In the provided exhibit, the configuration involves using a RIB (Routing Information Base) group to facilitate internet access for VPN-A Site 1 through PE-1. The goal is to provide VRF Internet access over a single connection.

1. **Understanding RIB Groups**:

- RIB groups allow for the import and export of routes between different routing tables.

- In this scenario, we have two RIBs: `inet.0` (the main routing table) and `VPN-A.inet.0` (the VRF-specific routing table).

2. **Statement Analysis**:

- **A. You must use the RIB group to move a default route, which is learned through BGP, from the inet.0 table to the VPN-A.inet.0 table.**

- Correct. To provide Internet access to VPN-A, the default route (0.0.0.0/0) learned via BGP in the `inet.0` table must be made available in the `VPN-A.inet.0` table. This is done using the RIB group to import the default route.

- **B. You do not need to use the RIB group to move interface routes from the inet.0 table to the VPN-A.inet.0 table.**

- Correct. Interface routes (connected routes) are typically directly added to both the global and the VRF routing tables without needing a RIB group. These routes are known to the VRF because the interfaces are part of the VRF configuration.

- **C. You do not need to use the RIB group default route, which is learned through BGP, from the inet.0 table to the VPN-A.inet.0 table.**

- Incorrect. As discussed, the default route needs to be imported into the VRF's routing table using a RIB group to enable Internet access for the VRF.

- **D. You must use the RIB group to move interface routes from the inet.0 table to the VPN-A.inet.0 table.**

- Incorrect. Interface routes are directly associated with the VRF interfaces and are automatically known to the VRF routing table. There is no need to use a RIB group for these routes.

**Conclusion**:

The correct answers are:

**A. You must use the RIB group to move a default route, which is learned through BGP, from the inet.0 table to the VPN-A.inet.0 table.**

**B. You do not need to use the RIB group to move interface routes from the inet.0 table to the VPN-A.inet.0 table.**

**References**:

- Juniper Networks Documentation on RIB Groups: [RIB Groups Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/rib-groups-overview.html)

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

https://www.juniper.net/documentation/us/en/software/junos/cos/topics/concept/packet-flow-cos-process-cos-config-guide.html

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.

BGP route target filtering can be configured on PE devices or on route reflectors (RRs). Configuring BGP route target filtering on RRs is more efficient and scalable, as it reduces the number of BGP sessions and updates between PE devices. To configure BGP route target filtering on RRs, the following steps are required:

Configure the family route-target statement under the BGP group or neighbor configuration on the RRs. This enables the exchange of the route-target address family between the RRs and their clients (PE devices). Configure the resolution rib bgp.l3vpn.0 resolution-ribs inet.0 statement under the routing-options configuration on the RRs. This enables the RRs to resolve next hops for VPN routes using the inet.0 routing table.

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)