C. When the encapsulation is vLan-ccc or extended-vlan-ccc, the configured VLAN tag is included in the control plane LDP advertisement

D. When the encapsulation is ethemet-ccc, tagged and untagged frames are both accepted in the data plane.

Answer DescriptionExplanation:

The customer interface in an LDP-signaled pseudowire is the interface on the PE router that connects to the CE device. An LDP-signaled pseudowire is a type of Layer 2 circuit that uses LDP to establish a point-to-point connection between two PE routers over an MPLS network. The customer interface can have different encapsulation types depending on the type of traffic that is carried over the pseudowire. The encapsulation types are ethernet-ccc, vlan-ccc, extended-vlan-ccc, atm-ccc, frame-relay-ccc, ppp-ccc, cisco-hdlc-ccc, and tcc-ccc. Depending on the encapsulation type, the customer interface can accept or reject tagged or untagged frames in the data plane, and include or exclude VLAN tags in the control plane LDP advertisement. The following table summarizes the behavior of different encapsulation types:

D. Configure the ignore-attached-bit parameter on all L1 routers

Answer DescriptionExplanation:

The attached bit is a flag in an IS-IS LSP that indicates whether a router is connected to another area or level (L2) of the network. By default, L2 routers set this bit when they advertise their LSPs to L1 routers, and L1 routers use this bit to select a default route to reach other areas or levels through L2 routers. However, this may result in suboptimal routing if there are multiple L2 routers with different paths to other areas or levels. To ensure that L1 routers have only the most specific routes available from L2 routers, you can configure the ignore-attached-bit parameter on all L1 routers. This makes L1 routers ignore the attached bit and install all interarea routes learned from L2 routers in their routing tables.

B. Bootstrap messages distribute RP information dynamically during an RP election.

D. Bootstrap messages are forwarded to all routers within a PIM sparse-mode domain.

Answer DescriptionExplanation:

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.

C. LSAs are acknowledged by the neighboring router.

Answer DescriptionExplanation:

OSPF Protocol Basics:

OSPF (Open Shortest Path First) is a link-state routing protocol.

Routers exchange LSAs (Link-State Advertisements) to share topology information.

LSA Acknowledgment Mechanism:

OSPF uses a reliable mechanism to ensure LSAs are received.

When a router sends an LSA to a neighbor, it expects an acknowledgment (ACK).

If an ACK is not received within a certain period, the router will retransmit the LSA.

Acknowledgment Process:

LSAs are sent over OSPF's reliable transport, which ensures delivery through acknowledgments.

This mechanism helps to maintain consistent and up-to-date topology databases across routers.

References:

OSPF RFC 2328

Understanding OSPF Operations

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.

Answer DescriptionExplanation:

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

• 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.
• 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.
• 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.
• 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:

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

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

A. LDP-signaled VPLS tunnels only support control bit 0.

C. BGP-signaled VPLS tunnels can use either RSVP or LDP between the PE routers.

Answer DescriptionExplanation:

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

B. Behavior aggregate classifiers

D. Fixed classifiers

E. Multifield Classifiers

Answer DescriptionExplanation:

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.

A. PSNPs are used to acknowledge a received LSP.

D. PSNPs are used to request a missing LSP.

Answer DescriptionExplanation:

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.