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

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

From the provided IS-IS adjacency outputs:

R1 is configured to participate in both Level 1 and Level 2 (A): This is indicated by the adjacency states for both Level 1 and Level 2 on the R1 interfaces.

R2 is configured to participate in Level 2 only (D): This is shown by the adjacency state for Level 2 only on the R2 interfaces.

References:

The IS-IS adjacency outputs indicate the state and levels of participation for each router.

Configuration and command references from "Example configs for VMRCAXP01W.txt" and other documents provide context for understanding IS-IS states and levels​​​​​​.

In OSPF, the ExStart state indicates that the routers are attempting to establish a relationship and exchange information about their MTU settings. If the MTU settings do not match between the two routers on the link, it can prevent the adjacency from progressing past the ExStart state.

References:

From the image provided, you can see that the OSPF adjacency on the interface ge-0/0/2.0 is stuck in the ExStart state.

This state often suggests that there is a mismatch in the MTU settings between the routers on that interface.

To resolve this, ensure that both interfaces have the same MTU setting. You can check and set the MTU on Juniper routers using the following commands:

# Check current MTU settings

show interfaces ge-0/0/2

# Set MTU to a specific value (e.g., 1500)

set interfaces ge-0/0/2 mtu 1500

# Commit the configuration

commit

Understanding the Configuration:

The provided configuration and output snippets show how traffic is classified and assigned to different forwarding classes based on the IP precedence values.

The inet-precedence classifier maps specific IP precedence values to forwarding classes with associated loss priorities.

Review of Classifiers:

IP Precedence Value 100:

The IP precedence value 100 in binary is represented as 100 (binary for 4).

Matching with Classifiers:

According to the configuration shown in the exhibit:

classifiers {

inet-precedence cos;

}

The classifier cos maps the following:

forwarding-class expedited-forwarding;

loss-priority low code-points 100;

Conclusion:

The IP precedence value 100 matches the expedited-forwarding forwarding class with low loss-priority as per the configuration.

In the given scenario, the connection between DC1 and DC2 is routed through a Layer 3 network. This indicates that the devices connecting the two data centers must be capable of performing Layer 3 routing to ensure that traffic can be properly forwarded across the network. Additionally, the use of VXLAN suggests that Integrated Routing and Bridging (IRB) functionality is required to enable communication between Layer 2 networks over the Layer 3 infrastructure.

The border devices (QFX10002) must handle Layer 3 routing to manage IP traffic between the data centers.

IRB functionality is necessary for routing between VLANs, allowing VXLAN to carry Layer 2 traffic across the Layer 3 network.

References:

The diagrams indicate the use of VXLAN for Layer 2 extension over a Layer 3 network.

The need for IRB is suggested by the presence of routed interfaces (IRB1 and IRB2) in the data center diagrams.

The "Tech Ops Managed Router Juniper Install Guide" provides insights into the Layer 3 routing capabilities and configurations necessary for such setups​​​​.

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:

shell

Copy code

set protocols igmp interface ge-0/0/1.0

MLD:

shell

Copy code

set protocols mld interface ge-0/0/1.0

References:

Juniper IGMP Configuration Guide

Juniper MLD Configuration Guide

Understanding the Problem:

The ports between the access switches and the distribution switch are shutting down when the L2PT configuration is applied. This typically happens due to a mismatch in port configurations or protocol incompatibilities.

Examining the Configurations:

L2PT (Layer 2 Protocol Tunneling) allows tunneling of Layer 2 traffic, which includes protocols like STP (Spanning Tree Protocol), CDP (Cisco Discovery Protocol), VTP (VLAN Trunking Protocol), etc. over a Layer 2 network.

If the L2PT is applied on access ports, it may lead to conflicts or shut down the ports as access ports are typically not configured to handle Layer 2 protocol traffic beyond their designated VLAN.

Solution: Configure Trunk Ports:

By configuring the links between the access switches and the distribution switch as trunk ports, you allow multiple VLANs to be carried over a single physical link. Trunk ports can carry tagged traffic for multiple VLANs, which includes the tunneled Layer 2 protocols.

This setup prevents the ports from shutting down and enables the correct tunneling of Layer 2 protocols.

References:

Juniper Documentation on L2PT Configuration

Troubleshooting Layer 2 Protocol Tunneling Issues

To ensure that each host is placed on a separate VLAN when using an unmanaged switch between the hosts and the EX Series switch:

Configure an input firewall filter on interface ge-0/0/3 to match the source MAC or IP address of the hosts to assign the VLANs:

By configuring an input firewall filter, you can match the source MAC or IP address of incoming traffic and assign the appropriate VLAN based on these criteria.

This method ensures that even though the switch between hosts and EX Series is unmanaged, VLAN assignments are still properly enforced at the EX Series switch.

Configuration Example:

set firewall family ethernet-switching filter VLAN-assignment term VLAN100 from source-mac-address xx:xx:xx:xx:xx:xx

set firewall family ethernet-switching filter VLAN-assignment term VLAN100 then vlan-assignment vlan 100

set firewall family ethernet-switching filter VLAN-assignment term VLAN200 from source-mac-address yy:yy:yy:yy:yy:yy

set firewall family ethernet-switching filter VLAN-assignment term VLAN200 then vlan-assignment vlan 200

set firewall family ethernet-switching filter VLAN-assignment term VLAN300 from source-mac-address zz:zz:zz:zz:zz:zz

set firewall family ethernet-switching filter VLAN-assignment term VLAN300 then vlan-assignment vlan 300

set interfaces ge-0/0/3 unit 0 family ethernet-switching filter input VLAN-assignment

References:

The command references from "Useful Juniper Commands.txt" and network configuration guides provide details on firewall filters and VLAN assignments​​.

When video packets are being dropped, and the network is configured to use the expedited-forwarding forwarding class, it typically indicates that the scheduler assigned to this class does not have sufficient bandwidth to handle the traffic. Adjusting the scheduler to allocate more bandwidth to the expedited-forwarding class will ensure that video packets are transmitted without being dropped.

Steps:

Identify the scheduler map: First, identify the scheduler map that is applied to the interfaces. This can be done using the following command:

shell

Copy code

show configuration class-of-service scheduler-maps

Adjust the scheduler: Modify the scheduler for the expedited-forwarding forwarding class to support a higher transmit rate. You can edit the scheduler configuration to increase the bandwidth allocated.

Example:

shell

Copy code

set class-of-service schedulers expedited-forwarding transmit-rate percent 30

Apply the configuration: Apply the modified scheduler to the interfaces using the following commands:

shell

Copy code

set class-of-service interfaces ge-0/0/0 scheduler-map

set class-of-service interfaces ge-0/0/1 scheduler-map

commit

References:

Useful Juniper Commands.txt

Tech Ops Managed Router Juniper Install Guide

The address range 232.0.0.0/8 is reserved for Source-Specific Multicast (SSM). This range is specifically allocated for SSM where data is sent from a specific source to the receivers.

References:

Source-Specific Multicast (SSM) Overview, RFC 4607

- Configure the local routing device so that it appears to be overloaded. You might do this when you want the routing device to participate in OSPF routing, but do not want it to be used for transit traffic. - Traffic destined to directly attached interfaces continues to reach the routing device. - When configured, the transit interface metrics are set to the maximum value of 65535. https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/ref/statement/overload-edit-protocols-ospf.html

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospf-route-control.html#id-understanding-ospf-overload-function

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:

plaintext

Copy code

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

Understanding IEEE 802.3af Standard:

IEEE 802.3af, also known as PoE (Power over Ethernet), specifies the standard for delivering power over Ethernet cables.

This standard allows devices like IP phones to receive power along with data over the same cable.

Maximum Power Allocation:

According to the IEEE 802.3af standard, the maximum power that can be delivered to a powered device is 15.4 watts.

This power is delivered over Category 5 (Cat 5) cables or higher.

EX Series Switches Compliance:

Juniper EX Series switches with PoE support adhere to the IEEE 802.3af standard.

Thus, each PoE port on these switches can allocate up to 15.4 watts to connected devices.

References:

IEEE 802.3af standard specifications

Juniper EX Series switch documentation