JN0-649 Enterprise Routing and Switching Professional (JNCIP-ENT) Questions and Answers

To troubleshoot why ISP peers are not receiving any routes in a multihomed BGP setup, the following steps are essential:

Verify Active BGP Routes: Ensure that the BGP routes are active in the routing table. Only active routes can be advertised to BGP peers.

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show route protocol bgp

Verify Export Policies: Check the export policies configured on your router. The export policies determine which routes are advertised to BGP peers. If these policies are incorrectly configured or missing, routes will not be advertised.

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show configuration policy-options policy-statement

show configuration protocols bgp group export

References:

Useful Juniper Commands.txt

Tech Ops Managed Router Juniper Install Guide

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

Step 1: Identify the problem.

Devices do not support VPN NLRI, and you must prevent these devices from receiving BGP VPN routes.

Step 2: Analyze the possible solutions.

Option A: Configure an import policy on the remote peer to reject the routes when they are received.

This approach would require configuration on the remote peer, which might not always be practical or possible.

Option B: Configure an export policy on the local BGP peer to reject the VPN routes being sent to the remote peer.

This ensures the local BGP peer does not send the VPN routes to the remote peer, directly addressing the problem.

Option C: Configure a route reflector for the VPN NLRI.

This does not solve the issue of preventing the advertisement of VPN routes to non-supporting peers.

Option D: Configure the apply-vpn-export feature on the local BGP peer.

This feature ensures that the VPN export policies are applied, preventing the advertisement of VPN routes to peers that do not support VPN NLRI.

Step 3: Verify the configurations.

Option B and Option D directly address the requirement without needing configurations on the remote peer.

References:

Juniper BGP configuration guide on export policies​​​​​​.

Commands for applying export policies:

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set policy-options policy-statement term from protocol bgp-vpn

set policy-options policy-statement term then reject

set protocols bgp group export

set protocols bgp apply-vpn-export

For devices like printers that do not support 802.1X authentication, you can configure static MAC bypass. This allows traffic from devices with specific MAC addresses to bypass 802.1X authentication and gain network access directly.

References:

From the Juniper documentation, you can implement static MAC bypass for devices that do not support 802.1X by configuring their MAC addresses to be statically permitted on the network.

Useful Juniper Commands.txt

Tech Ops Managed Router Juniper Install Guide

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# Example configuration for static MAC bypass

set protocols dot1x authenticator interface ge-0/0/1.0 mac-radius static-mac 00:11:22:33:44:55

commit

These configurations and explanations should address the questions accurately based on the provided information and referenced documents.

Reviewing MST Configuration:

The configuration shown in the exhibit indicates MST (Multiple Spanning Tree) configuration for DS-1 and DS-2 switches.

For DS-1:

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mstp {

configuration-name Region-1;

revision-level 1;

interface ge-0/0/8;

interface ge-0/0/9;

interface ge-0/0/10;

interface ge-0/0/12;

msti 1 {

bridge-priority 4k;

vlan 10-19;

}

msti 2 {

bridge-priority 8k;

vlan 20-29;

}

}

For DS-2:

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mstp {

configuration-name Region-1;

revision-level 1;

interface ge-0/0/8;

interface ge-0/0/9;

interface ge-0/0/10;

interface ge-0/0/12;

msti 1 {

bridge-priority 8k;

vlan 10-19;

}

}

Understanding Bridge Priority:

In MSTP, the switch with the lowest bridge priority becomes the root bridge for the respective MST instance.

For MSTI 1:

DS-1 bridge-priority is 4k (4096)

DS-2 bridge-priority is 8k (8192)

Thus, DS-1 will be the root bridge for MSTI 1.

For MSTI 2:

DS-1 bridge-priority is 8k (8192)

DS-2 does not participate in MSTI 2.

Thus, DS-1 will be the root bridge for MSTI 2.

Analyzing VLAN Assignments:

DS-1 MSTI 1: VLANs 10-19, priority 4k

DS-1 MSTI 2: VLANs 20-29, priority 8k

DS-2 MSTI 1: VLANs 10-19, priority 8k

DS-2 does not have MSTI 2 configuration.

Conclusion:

DS-1 is the root bridge for MSTI 1 (C)

DS-2 does not participate in MSTI 2 (eliminates A)

DS-1 is the root bridge for MSTI 2 (D)

DS-2 is not the root bridge for MSTI 1 (eliminates B)

References:

Configuration snippets

Understanding of MSTP priorities and root bridge election

Understanding Multicast Listener Registration Protocols:

Multicast listener registration protocols are used to manage multicast group memberships on a network.

They allow devices to join or leave multicast groups dynamically.

Protocols Supported by Junos:

MLD (Multicast Listener Discovery):

Used for IPv6 multicast group management. It is the IPv6 equivalent of IGMP.

MLD allows routers to discover multicast listeners on a network.

IGMP (Internet Group Management Protocol):

Used for IPv4 multicast group management.

IGMP enables hosts to join and leave multicast groups and allows routers to manage multicast group memberships.

Verification and Configuration in Junos:

MLD and IGMP are supported on Juniper devices running the Junos operating system.

Configuration examples:

IGMP:

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set protocols igmp interface ge-0/0/1.0

MLD:

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set protocols mld interface ge-0/0/1.0

References:

Juniper IGMP Configuration Guide

Juniper MLD Configuration Guide

Enabling LLDP-MED:

LLDP-MED (Link Layer Discovery Protocol - Media Endpoint Discovery) is an extension of LLDP specifically for VoIP devices.

It allows network devices to advertise and receive configuration information, such as VLAN IDs, from the network switch.

Voice VLAN Feature:

The voice VLAN feature on switches is designed to simplify the deployment of VoIP by automatically placing voice traffic on a designated VLAN.

Configuring the appropriate access interfaces and VLAN ID for voice traffic ensures that voice packets are prioritized and properly segmented from other types of traffic.

Configuration Steps:

Enable LLDP-MED on the appropriate access interfaces:

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set protocols lldp-med interface ge-0/0/0

Enable the voice VLAN feature and specify the VLAN ID:

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set ethernet-switching-options voip interface ge-0/0/0 vlan voice

set ethernet-switching-options voip interface ge-0/0/0 forwarding-class assured-forwarding

References:

Juniper documentation on LLDP-MED

Juniper EX Series switch configuration guide for voice VLAN

 Captive Portal Functionality:

Captive portals are used to enforce user authentication by redirecting web browser requests to a login page until authentication is successful.

 Operation:

When a user connects to the network, their HTTP requests are intercepted and redirected to the captive portal login page. This process continues until the user provides valid credentials.

 Implementation:

Juniper Configuration:

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set security authentication-web redirect-url "http:// "

set security zones security-zone interfaces host-inbound-traffic system-services http

set security zones security-zone interfaces host-inbound-traffic system-services https

set access profile captive-portal

This configuration ensures that all HTTP/HTTPS traffic is redirected to the specified captive portal for authentication.

 References:

Detailed configuration and operation are documented in "Tech Ops Managed Router Juniper Install Guide" and related documents​​​​.

Multitenancy with Routing Instances:

In a multitenant network, different tenants are isolated using routing instances.

Each routing instance can have its own routing table and policies.

BGP and Load Balancing:

BGP (Border Gateway Protocol) is often used for interconnecting different autonomous systems or for internal routing.

Load balancing in BGP can be achieved using the multipath feature, which allows the installation of multiple paths to the same destination in the routing table.

Additionally, configuring per-packet load balancing ensures that traffic is distributed across multiple paths more granularly.

Configuring Multipath in BGP:

Hierarchy Considerations: The multipath option must be configured at appropriate hierarchies to ensure it applies to the correct scope (either globally or within a specific routing instance).

Detailed Configuration:

Statement C: Configure a load-balance per-packet policy and apply it at the [edit routing-options forwarding-table] hierarchy.

Correct: Configuring a load-balance per-packet policy ensures that packets are distributed evenly across multiple paths. This is crucial for achieving effective load balancing.

Configuration Example:

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set routing-options forwarding-table export load-balance-per-packet

Policy Definition Example:

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set policy-options policy-statement load-balance-per-packet term 1 then load-balance per-packet

Statement D: Configure the multipath option at the [edit routing-instances routing-options] hierarchy.

Correct: Configuring multipath within a routing instance ensures that the load balancing feature is applied specifically to that instance, which is crucial in a multitenant environment.

Configuration Example:

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set routing-instances routing-options multipath

References:

Useful Juniper Commands

Juniper Routing Instances and Multipath Configuration

These configurations ensure that load balancing is achieved within each routing instance, leveraging both per-packet load balancing and the multipath feature in Junos OS for BGP. By configuring at the forwarding-table and routing-instance levels, you ensure the load balancing behavior is correctly applied to achieve the desired network performance and redundancy.

Reviewing POE Interface Information:

The exhibit shows the output of show poe interface and show poe controller commands.

The show poe interface command provides information about the PoE (Power over Ethernet) status on each interface.

Maximum Wattage Allocation:

The show poe controller output indicates that the maximum power available is 100 watts:

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Controller Maximum Power consumption Guard Management Status Lldp

index power band

0 100.00W 22.40W 10W Class AT_MODE Disabled

Thus, statement A is correct.

Power Consumption and Interface Priority:

The interface ge-0/0/11 has a high priority with a max power of 25.4W and current consumption of 11.4W:

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ge-0/0/11 Enabled ON 25.4W(L) High 11.4W 4

Given its high priority, ge-0/0/11 will continue to receive power even if the total power consumption exceeds 90 watts, as high-priority interfaces are less likely to be powered off when resources are low.

POE Status on Interfaces:

The ge-0/0/0 interface is shown as Enabled OFF, indicating PoE is not currently enabled.

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ge-0/0/0 Enabled OFF 15.4W Low 0.0W not-applicable

PoE+ Support:

The ge-0/0/10 interface has a power class of 4, which indicates support for PoE+.

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ge-0/0/10 Enabled ON 25.4W(L) Low 11.0W 4

References:

Exhibit output for show poe interface

Understanding PoE and PoE+ classes and priorities

Understanding the Problem:

The requirement is to provide Layer 2 connectivity between campus sites using Ethernet switches through a metro Ethernet service provider who is using Q-in-Q tagging.

Design Considerations:

VXLAN Implementation:

VXLAN (Virtual Extensible LAN) can be used to extend Layer 2 networks over Layer 3 networks. It is often used to provide scalability and flexibility in modern data center networks. In this case, VXLAN could be used to encapsulate Layer 2 frames within UDP packets, allowing them to be transported over the service provider’s network.

S-Tag Configuration:

Q-in-Q tagging, also known as 802.1ad, involves an outer tag (S-Tag) and an inner tag (C-Tag). The service provider network uses the S-Tag to identify and segregate customer traffic. Therefore, each campus switch must have the correct S-Tag (300 in this case) configured to ensure the service provider can correctly handle and route the traffic.

References:

Juniper Networks: Understanding VXLAN

Configuring Q-in-Q Tagging

Dynamic VLAN assignment using 802.1X authentication relies on vendor-specific attributes (VSAs) to assign VLANs dynamically based on the authentication results. The modes that support using VSAs for dynamic VLAN assignment are:

Single-Secure Supplicant Mode: This mode supports a single secure client on a port and can use VSAs to dynamically assign VLANs based on the authentication result.

Multiple Supplicant Mode: This mode supports multiple clients on a single port, each with its own authentication session, and can use VSAs to dynamically assign VLANs.

References:

The Juniper documentation and configuration guides discuss the capabilities of these modes in supporting dynamic VLAN assignment through VSAs. Specific configuration examples and guidelines can be found in the documents:

Useful Juniper Commands.txt

Tech Ops Managed Router Juniper Install Guide

# Example of enabling single-secure supplicant mode

set protocols dot1x authenticator interface ge-0/0/1.0 supplicant multiple

# Example of enabling multiple supplicant mode

set protocols dot1x authenticator interface ge-0/0/1.0 supplicant multiple

The correct sequence for BGP active route selection when BGP multipath or multihop are not configured is as follows:

Higher local preference: Routes with a higher local preference are preferred.

Shortest AS path: Routes with the shortest AS path are preferred.

Lower origin code: Routes with lower origin code (IGP < EGP < Incomplete) are preferred.

Lowest router ID: Routes with the lowest router ID are preferred.

Lowest peer address: Routes with the lowest peer address are preferred.

References:

Standard BGP route selection criteria as outlined in network routing protocols.

Documentation from "Useful Juniper Commands.txt" and "Juniper Commands.pdf" which include detailed BGP operational commands and preferences​​​​.

802.1X Authentication and Re-authentication:

802.1X is used for network access control, where clients (supplicants) authenticate through a RADIUS server.

If a client cannot re-authenticate, the network access behavior depends on the configured action.

Permit Access Configuration:

The permit action ensures that the client continues to have network access if re-authentication fails.

This is crucial in scenarios where continuous access is needed despite temporary authentication issues.

Configuration Syntax:

On the Juniper device, configure the permit action:

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set protocols dot1x authenticator authentication-profile re-authentication permit

References:

Juniper documentation on 802.1X configuration

Understanding 802.1X re-authentication and access control mechanisms